jsonpath scanner: reentrant scanner

[pgsql.git] / src / common / jsonapi.c

/*-------------------------------------------------------------------------
 *
 * jsonapi.c
 *              JSON parser and lexer interfaces
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/common/jsonapi.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include "common/jsonapi.h"
#include "mb/pg_wchar.h"
#include "port/pg_lfind.h"

#ifdef JSONAPI_USE_PQEXPBUFFER
#include "pqexpbuffer.h"
#else
#include "lib/stringinfo.h"
#include "miscadmin.h"
#endif

/*
 * By default, we will use palloc/pfree along with StringInfo.  In libpq,
 * use malloc and PQExpBuffer, and return JSON_OUT_OF_MEMORY on out-of-memory.
 */
#ifdef JSONAPI_USE_PQEXPBUFFER

#define STRDUP(s) strdup(s)
#define ALLOC(size) malloc(size)
#define ALLOC0(size) calloc(1, size)
#define REALLOC realloc
#define FREE(s) free(s)

#define jsonapi_appendStringInfo                        appendPQExpBuffer
#define jsonapi_appendBinaryStringInfo          appendBinaryPQExpBuffer
#define jsonapi_appendStringInfoChar            appendPQExpBufferChar
/* XXX should we add a macro version to PQExpBuffer? */
#define jsonapi_appendStringInfoCharMacro       appendPQExpBufferChar
#define jsonapi_makeStringInfo                          createPQExpBuffer
#define jsonapi_initStringInfo                          initPQExpBuffer
#define jsonapi_resetStringInfo                         resetPQExpBuffer
#define jsonapi_termStringInfo                          termPQExpBuffer
#define jsonapi_destroyStringInfo                       destroyPQExpBuffer

#else                                                   /* !JSONAPI_USE_PQEXPBUFFER */

#define STRDUP(s) pstrdup(s)
#define ALLOC(size) palloc(size)
#define ALLOC0(size) palloc0(size)
#define REALLOC repalloc

#ifdef FRONTEND
#define FREE pfree
#else
/*
 * Backend pfree() doesn't handle NULL pointers like the frontend's does; smooth
 * that over to reduce mental gymnastics. Avoid multiple evaluation of the macro
 * argument to avoid future hair-pulling.
 */
#define FREE(s) do {    \
        void *__v = (s);        \
        if (__v)                        \
                pfree(__v);             \
} while (0)
#endif

#define jsonapi_appendStringInfo                        appendStringInfo
#define jsonapi_appendBinaryStringInfo          appendBinaryStringInfo
#define jsonapi_appendStringInfoChar            appendStringInfoChar
#define jsonapi_appendStringInfoCharMacro       appendStringInfoCharMacro
#define jsonapi_makeStringInfo                          makeStringInfo
#define jsonapi_initStringInfo                          initStringInfo
#define jsonapi_resetStringInfo                         resetStringInfo
#define jsonapi_termStringInfo(s)                       pfree((s)->data)
#define jsonapi_destroyStringInfo                       destroyStringInfo

#endif                                                  /* JSONAPI_USE_PQEXPBUFFER */

/*
 * The context of the parser is maintained by the recursive descent
 * mechanism, but is passed explicitly to the error reporting routine
 * for better diagnostics.
 */
typedef enum                                    /* contexts of JSON parser */
{
        JSON_PARSE_VALUE,                       /* expecting a value */
        JSON_PARSE_STRING,                      /* expecting a string (for a field name) */
        JSON_PARSE_ARRAY_START,         /* saw '[', expecting value or ']' */
        JSON_PARSE_ARRAY_NEXT,          /* saw array element, expecting ',' or ']' */
        JSON_PARSE_OBJECT_START,        /* saw '{', expecting label or '}' */
        JSON_PARSE_OBJECT_LABEL,        /* saw object label, expecting ':' */
        JSON_PARSE_OBJECT_NEXT,         /* saw object value, expecting ',' or '}' */
        JSON_PARSE_OBJECT_COMMA,        /* saw object ',', expecting next label */
        JSON_PARSE_END,                         /* saw the end of a document, expect nothing */
} JsonParseContext;

/*
 * Setup for table-driven parser.
 * These enums need to be separate from the JsonTokenType and from each other
 * so we can have all of them on the prediction stack, which consists of
 * tokens, non-terminals, and semantic action markers.
 */

enum JsonNonTerminal
{
        JSON_NT_JSON = 32,
        JSON_NT_ARRAY_ELEMENTS,
        JSON_NT_MORE_ARRAY_ELEMENTS,
        JSON_NT_KEY_PAIRS,
        JSON_NT_MORE_KEY_PAIRS,
};

enum JsonParserSem
{
        JSON_SEM_OSTART = 64,
        JSON_SEM_OEND,
        JSON_SEM_ASTART,
        JSON_SEM_AEND,
        JSON_SEM_OFIELD_INIT,
        JSON_SEM_OFIELD_START,
        JSON_SEM_OFIELD_END,
        JSON_SEM_AELEM_START,
        JSON_SEM_AELEM_END,
        JSON_SEM_SCALAR_INIT,
        JSON_SEM_SCALAR_CALL,
};

/*
 * struct containing the 3 stacks used in non-recursive parsing,
 * and the token and value for scalars that need to be preserved
 * across calls.
 *
 * typedef appears in jsonapi.h
 */
struct JsonParserStack
{
        int                     stack_size;
        char       *prediction;
        size_t          pred_index;
        /* these two are indexed by lex_level */
        char      **fnames;
        bool       *fnull;
        JsonTokenType scalar_tok;
        char       *scalar_val;
};

/*
 * struct containing state used when there is a possible partial token at the
 * end of a json chunk when we are doing incremental parsing.
 *
 * typedef appears in jsonapi.h
 */
struct JsonIncrementalState
{
        bool            started;
        bool            is_last_chunk;
        bool            partial_completed;
        jsonapi_StrValType partial_token;
};

/*
 * constants and macros used in the nonrecursive parser
 */
#define JSON_NUM_TERMINALS 13
#define JSON_NUM_NONTERMINALS 5
#define JSON_NT_OFFSET JSON_NT_JSON
/* for indexing the table */
#define OFS(NT) (NT) - JSON_NT_OFFSET
/* classify items we get off the stack */
#define IS_SEM(x) ((x) & 0x40)
#define IS_NT(x)  ((x) & 0x20)

/*
 * These productions are stored in reverse order right to left so that when
 * they are pushed on the stack what we expect next is at the top of the stack.
 */
static char JSON_PROD_EPSILON[] = {0};  /* epsilon - an empty production */

/* JSON -> string */
static char JSON_PROD_SCALAR_STRING[] = {JSON_SEM_SCALAR_CALL, JSON_TOKEN_STRING, JSON_SEM_SCALAR_INIT, 0};

/* JSON -> number */
static char JSON_PROD_SCALAR_NUMBER[] = {JSON_SEM_SCALAR_CALL, JSON_TOKEN_NUMBER, JSON_SEM_SCALAR_INIT, 0};

/* JSON -> 'true' */
static char JSON_PROD_SCALAR_TRUE[] = {JSON_SEM_SCALAR_CALL, JSON_TOKEN_TRUE, JSON_SEM_SCALAR_INIT, 0};

/* JSON -> 'false' */
static char JSON_PROD_SCALAR_FALSE[] = {JSON_SEM_SCALAR_CALL, JSON_TOKEN_FALSE, JSON_SEM_SCALAR_INIT, 0};

/* JSON -> 'null' */
static char JSON_PROD_SCALAR_NULL[] = {JSON_SEM_SCALAR_CALL, JSON_TOKEN_NULL, JSON_SEM_SCALAR_INIT, 0};

/* JSON -> '{' KEY_PAIRS '}' */
static char JSON_PROD_OBJECT[] = {JSON_SEM_OEND, JSON_TOKEN_OBJECT_END, JSON_NT_KEY_PAIRS, JSON_TOKEN_OBJECT_START, JSON_SEM_OSTART, 0};

/* JSON -> '[' ARRAY_ELEMENTS ']' */
static char JSON_PROD_ARRAY[] = {JSON_SEM_AEND, JSON_TOKEN_ARRAY_END, JSON_NT_ARRAY_ELEMENTS, JSON_TOKEN_ARRAY_START, JSON_SEM_ASTART, 0};

/* ARRAY_ELEMENTS -> JSON MORE_ARRAY_ELEMENTS */
static char JSON_PROD_ARRAY_ELEMENTS[] = {JSON_NT_MORE_ARRAY_ELEMENTS, JSON_SEM_AELEM_END, JSON_NT_JSON, JSON_SEM_AELEM_START, 0};

/* MORE_ARRAY_ELEMENTS -> ',' JSON MORE_ARRAY_ELEMENTS */
static char JSON_PROD_MORE_ARRAY_ELEMENTS[] = {JSON_NT_MORE_ARRAY_ELEMENTS, JSON_SEM_AELEM_END, JSON_NT_JSON, JSON_SEM_AELEM_START, JSON_TOKEN_COMMA, 0};

/* KEY_PAIRS -> string ':' JSON MORE_KEY_PAIRS */
static char JSON_PROD_KEY_PAIRS[] = {JSON_NT_MORE_KEY_PAIRS, JSON_SEM_OFIELD_END, JSON_NT_JSON, JSON_SEM_OFIELD_START, JSON_TOKEN_COLON, JSON_TOKEN_STRING, JSON_SEM_OFIELD_INIT, 0};

/* MORE_KEY_PAIRS -> ',' string ':'  JSON MORE_KEY_PAIRS */
static char JSON_PROD_MORE_KEY_PAIRS[] = {JSON_NT_MORE_KEY_PAIRS, JSON_SEM_OFIELD_END, JSON_NT_JSON, JSON_SEM_OFIELD_START, JSON_TOKEN_COLON, JSON_TOKEN_STRING, JSON_SEM_OFIELD_INIT, JSON_TOKEN_COMMA, 0};

/*
 * Note: there are also epsilon productions for ARRAY_ELEMENTS,
 * MORE_ARRAY_ELEMENTS, KEY_PAIRS and MORE_KEY_PAIRS
 * They are all the same as none require any semantic actions.
 */

/*
 * Table connecting the productions with their director sets of
 * terminal symbols.
 * Any combination not specified here represents an error.
 */

typedef struct
{
        size_t          len;
        char       *prod;
} td_entry;

#define TD_ENTRY(PROD) { sizeof(PROD) - 1, (PROD) }

static td_entry td_parser_table[JSON_NUM_NONTERMINALS][JSON_NUM_TERMINALS] =
{
        /* JSON */
        [OFS(JSON_NT_JSON)][JSON_TOKEN_STRING] = TD_ENTRY(JSON_PROD_SCALAR_STRING),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_NUMBER] = TD_ENTRY(JSON_PROD_SCALAR_NUMBER),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_TRUE] = TD_ENTRY(JSON_PROD_SCALAR_TRUE),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_FALSE] = TD_ENTRY(JSON_PROD_SCALAR_FALSE),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_NULL] = TD_ENTRY(JSON_PROD_SCALAR_NULL),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_ARRAY_START] = TD_ENTRY(JSON_PROD_ARRAY),
        [OFS(JSON_NT_JSON)][JSON_TOKEN_OBJECT_START] = TD_ENTRY(JSON_PROD_OBJECT),
        /* ARRAY_ELEMENTS */
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_ARRAY_START] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_OBJECT_START] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_STRING] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_NUMBER] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_TRUE] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_FALSE] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_NULL] = TD_ENTRY(JSON_PROD_ARRAY_ELEMENTS),
        [OFS(JSON_NT_ARRAY_ELEMENTS)][JSON_TOKEN_ARRAY_END] = TD_ENTRY(JSON_PROD_EPSILON),
        /* MORE_ARRAY_ELEMENTS */
        [OFS(JSON_NT_MORE_ARRAY_ELEMENTS)][JSON_TOKEN_COMMA] = TD_ENTRY(JSON_PROD_MORE_ARRAY_ELEMENTS),
        [OFS(JSON_NT_MORE_ARRAY_ELEMENTS)][JSON_TOKEN_ARRAY_END] = TD_ENTRY(JSON_PROD_EPSILON),
        /* KEY_PAIRS */
        [OFS(JSON_NT_KEY_PAIRS)][JSON_TOKEN_STRING] = TD_ENTRY(JSON_PROD_KEY_PAIRS),
        [OFS(JSON_NT_KEY_PAIRS)][JSON_TOKEN_OBJECT_END] = TD_ENTRY(JSON_PROD_EPSILON),
        /* MORE_KEY_PAIRS */
        [OFS(JSON_NT_MORE_KEY_PAIRS)][JSON_TOKEN_COMMA] = TD_ENTRY(JSON_PROD_MORE_KEY_PAIRS),
        [OFS(JSON_NT_MORE_KEY_PAIRS)][JSON_TOKEN_OBJECT_END] = TD_ENTRY(JSON_PROD_EPSILON),
};

/* the GOAL production. Not stored in the table, but will be the initial contents of the prediction stack */
static char JSON_PROD_GOAL[] = {JSON_TOKEN_END, JSON_NT_JSON, 0};

static inline JsonParseErrorType json_lex_string(JsonLexContext *lex);
static inline JsonParseErrorType json_lex_number(JsonLexContext *lex, const char *s,
                                                                                                 bool *num_err, size_t *total_len);
static inline JsonParseErrorType parse_scalar(JsonLexContext *lex, const JsonSemAction *sem);
static JsonParseErrorType parse_object_field(JsonLexContext *lex, const JsonSemAction *sem);
static JsonParseErrorType parse_object(JsonLexContext *lex, const JsonSemAction *sem);
static JsonParseErrorType parse_array_element(JsonLexContext *lex, const JsonSemAction *sem);
static JsonParseErrorType parse_array(JsonLexContext *lex, const JsonSemAction *sem);
static JsonParseErrorType report_parse_error(JsonParseContext ctx, JsonLexContext *lex);
static bool allocate_incremental_state(JsonLexContext *lex);
static inline void set_fname(JsonLexContext *lex, char *fname);

/* the null action object used for pure validation */
const JsonSemAction nullSemAction =
{
        NULL, NULL, NULL, NULL, NULL,
        NULL, NULL, NULL, NULL, NULL
};

/* sentinels used for out-of-memory conditions */
static JsonLexContext failed_oom;
static JsonIncrementalState failed_inc_oom;

/* Parser support routines */

/*
 * lex_peek
 *
 * what is the current look_ahead token?
*/
static inline JsonTokenType
lex_peek(JsonLexContext *lex)
{
        return lex->token_type;
}

/*
 * lex_expect
 *
 * move the lexer to the next token if the current look_ahead token matches
 * the parameter token. Otherwise, report an error.
 */
static inline JsonParseErrorType
lex_expect(JsonParseContext ctx, JsonLexContext *lex, JsonTokenType token)
{
        if (lex_peek(lex) == token)
                return json_lex(lex);
        else
                return report_parse_error(ctx, lex);
}

/* chars to consider as part of an alphanumeric token */
#define JSON_ALPHANUMERIC_CHAR(c)  \
        (((c) >= 'a' && (c) <= 'z') || \
         ((c) >= 'A' && (c) <= 'Z') || \
         ((c) >= '0' && (c) <= '9') || \
         (c) == '_' || \
         IS_HIGHBIT_SET(c))

/*
 * Utility function to check if a string is a valid JSON number.
 *
 * str is of length len, and need not be null-terminated.
 */
bool
IsValidJsonNumber(const char *str, size_t len)
{
        bool            numeric_error;
        size_t          total_len;
        JsonLexContext dummy_lex = {0};

        if (len <= 0)
                return false;

        /*
         * json_lex_number expects a leading  '-' to have been eaten already.
         *
         * having to cast away the constness of str is ugly, but there's not much
         * easy alternative.
         */
        if (*str == '-')
        {
                dummy_lex.input = str + 1;
                dummy_lex.input_length = len - 1;
        }
        else
        {
                dummy_lex.input = str;
                dummy_lex.input_length = len;
        }

        dummy_lex.token_start = dummy_lex.input;

        json_lex_number(&dummy_lex, dummy_lex.input, &numeric_error, &total_len);

        return (!numeric_error) && (total_len == dummy_lex.input_length);
}

/*
 * makeJsonLexContextCstringLen
 *              Initialize the given JsonLexContext object, or create one
 *
 * If a valid 'lex' pointer is given, it is initialized.  This can
 * be used for stack-allocated structs, saving overhead.  If NULL is
 * given, a new struct is allocated.
 *
 * If need_escapes is true, ->strval stores the unescaped lexemes.
 * Unescaping is expensive, so only request it when necessary.
 *
 * If need_escapes is true or lex was given as NULL, then caller is
 * responsible for freeing the returned struct, either by calling
 * freeJsonLexContext() or (in backend environment) via memory context
 * cleanup.
 *
 * In shlib code, any out-of-memory failures will be deferred to time
 * of use; this function is guaranteed to return a valid JsonLexContext.
 */
JsonLexContext *
makeJsonLexContextCstringLen(JsonLexContext *lex, const char *json,
                                                         size_t len, int encoding, bool need_escapes)
{
        if (lex == NULL)
        {
                lex = ALLOC0(sizeof(JsonLexContext));
                if (!lex)
                        return &failed_oom;
                lex->flags |= JSONLEX_FREE_STRUCT;
        }
        else
                memset(lex, 0, sizeof(JsonLexContext));

        lex->errormsg = NULL;
        lex->input = lex->token_terminator = lex->line_start = json;
        lex->line_number = 1;
        lex->input_length = len;
        lex->input_encoding = encoding;
        lex->need_escapes = need_escapes;
        if (need_escapes)
        {
                /*
                 * This call can fail in shlib code. We defer error handling to time
                 * of use (json_lex_string()) since we might not need to parse any
                 * strings anyway.
                 */
                lex->strval = jsonapi_makeStringInfo();
                lex->flags |= JSONLEX_FREE_STRVAL;
        }

        return lex;
}

/*
 * Allocates the internal bookkeeping structures for incremental parsing. This
 * can only fail in-band with shlib code.
 */
#define JS_STACK_CHUNK_SIZE 64
#define JS_MAX_PROD_LEN 10              /* more than we need */
#define JSON_TD_MAX_STACK 6400  /* hard coded for now - this is a REALLY high
                                                                 * number */
static bool
allocate_incremental_state(JsonLexContext *lex)
{
        void       *pstack,
                           *prediction,
                           *fnames,
                           *fnull;

        lex->inc_state = ALLOC0(sizeof(JsonIncrementalState));
        pstack = ALLOC0(sizeof(JsonParserStack));
        prediction = ALLOC(JS_STACK_CHUNK_SIZE * JS_MAX_PROD_LEN);
        fnames = ALLOC(JS_STACK_CHUNK_SIZE * sizeof(char *));
        fnull = ALLOC(JS_STACK_CHUNK_SIZE * sizeof(bool));

#ifdef JSONAPI_USE_PQEXPBUFFER
        if (!lex->inc_state
                || !pstack
                || !prediction
                || !fnames
                || !fnull)
        {
                FREE(lex->inc_state);
                FREE(pstack);
                FREE(prediction);
                FREE(fnames);
                FREE(fnull);

                lex->inc_state = &failed_inc_oom;
                return false;
        }
#endif

        jsonapi_initStringInfo(&(lex->inc_state->partial_token));
        lex->pstack = pstack;
        lex->pstack->stack_size = JS_STACK_CHUNK_SIZE;
        lex->pstack->prediction = prediction;
        lex->pstack->fnames = fnames;
        lex->pstack->fnull = fnull;

        /*
         * fnames between 0 and lex_level must always be defined so that
         * freeJsonLexContext() can handle them safely. inc/dec_lex_level() handle
         * the rest.
         */
        Assert(lex->lex_level == 0);
        lex->pstack->fnames[0] = NULL;

        lex->incremental = true;
        return true;
}


/*
 * makeJsonLexContextIncremental
 *
 * Similar to above but set up for use in incremental parsing. That means we
 * need explicit stacks for predictions, field names and null indicators, but
 * we don't need the input, that will be handed in bit by bit to the
 * parse routine. We also need an accumulator for partial tokens in case
 * the boundary between chunks happens to fall in the middle of a token.
 *
 * In shlib code, any out-of-memory failures will be deferred to time of use;
 * this function is guaranteed to return a valid JsonLexContext.
 */
JsonLexContext *
makeJsonLexContextIncremental(JsonLexContext *lex, int encoding,
                                                          bool need_escapes)
{
        if (lex == NULL)
        {
                lex = ALLOC0(sizeof(JsonLexContext));
                if (!lex)
                        return &failed_oom;

                lex->flags |= JSONLEX_FREE_STRUCT;
        }
        else
                memset(lex, 0, sizeof(JsonLexContext));

        lex->line_number = 1;
        lex->input_encoding = encoding;

        if (!allocate_incremental_state(lex))
        {
                if (lex->flags & JSONLEX_FREE_STRUCT)
                {
                        FREE(lex);
                        return &failed_oom;
                }

                /* lex->inc_state tracks the OOM failure; we can return here. */
                return lex;
        }

        lex->need_escapes = need_escapes;
        if (need_escapes)
        {
                /*
                 * This call can fail in shlib code. We defer error handling to time
                 * of use (json_lex_string()) since we might not need to parse any
                 * strings anyway.
                 */
                lex->strval = jsonapi_makeStringInfo();
                lex->flags |= JSONLEX_FREE_STRVAL;
        }

        return lex;
}

void
setJsonLexContextOwnsTokens(JsonLexContext *lex, bool owned_by_context)
{
        if (lex->incremental && lex->inc_state->started)
        {
                /*
                 * Switching this flag after parsing has already started is a
                 * programming error.
                 */
                Assert(false);
                return;
        }

        if (owned_by_context)
                lex->flags |= JSONLEX_CTX_OWNS_TOKENS;
        else
                lex->flags &= ~JSONLEX_CTX_OWNS_TOKENS;
}

static inline bool
inc_lex_level(JsonLexContext *lex)
{
        if (lex->incremental && (lex->lex_level + 1) >= lex->pstack->stack_size)
        {
                size_t          new_stack_size;
                char       *new_prediction;
                char      **new_fnames;
                bool       *new_fnull;

                new_stack_size = lex->pstack->stack_size + JS_STACK_CHUNK_SIZE;

                new_prediction = REALLOC(lex->pstack->prediction,
                                                                 new_stack_size * JS_MAX_PROD_LEN);
#ifdef JSONAPI_USE_PQEXPBUFFER
                if (!new_prediction)
                        return false;
#endif
                lex->pstack->prediction = new_prediction;

                new_fnames = REALLOC(lex->pstack->fnames,
                                                         new_stack_size * sizeof(char *));
#ifdef JSONAPI_USE_PQEXPBUFFER
                if (!new_fnames)
                        return false;
#endif
                lex->pstack->fnames = new_fnames;

                new_fnull = REALLOC(lex->pstack->fnull, new_stack_size * sizeof(bool));
#ifdef JSONAPI_USE_PQEXPBUFFER
                if (!new_fnull)
                        return false;
#endif
                lex->pstack->fnull = new_fnull;

                lex->pstack->stack_size = new_stack_size;
        }

        lex->lex_level += 1;

        if (lex->incremental)
        {
                /*
                 * Ensure freeJsonLexContext() remains safe even if no fname is
                 * assigned at this level.
                 */
                lex->pstack->fnames[lex->lex_level] = NULL;
        }

        return true;
}

static inline void
dec_lex_level(JsonLexContext *lex)
{
        set_fname(lex, NULL);           /* free the current level's fname, if needed */
        lex->lex_level -= 1;
}

static inline void
push_prediction(JsonParserStack *pstack, td_entry entry)
{
        memcpy(pstack->prediction + pstack->pred_index, entry.prod, entry.len);
        pstack->pred_index += entry.len;
}

static inline char
pop_prediction(JsonParserStack *pstack)
{
        Assert(pstack->pred_index > 0);
        return pstack->prediction[--pstack->pred_index];
}

static inline char
next_prediction(JsonParserStack *pstack)
{
        Assert(pstack->pred_index > 0);
        return pstack->prediction[pstack->pred_index - 1];
}

static inline bool
have_prediction(JsonParserStack *pstack)
{
        return pstack->pred_index > 0;
}

static inline void
set_fname(JsonLexContext *lex, char *fname)
{
        if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
        {
                /*
                 * Don't leak prior fnames. If one hasn't been assigned yet,
                 * inc_lex_level ensured that it's NULL (and therefore safe to free).
                 */
                FREE(lex->pstack->fnames[lex->lex_level]);
        }

        lex->pstack->fnames[lex->lex_level] = fname;
}

static inline char *
get_fname(JsonLexContext *lex)
{
        return lex->pstack->fnames[lex->lex_level];
}

static inline void
set_fnull(JsonLexContext *lex, bool fnull)
{
        lex->pstack->fnull[lex->lex_level] = fnull;
}

static inline bool
get_fnull(JsonLexContext *lex)
{
        return lex->pstack->fnull[lex->lex_level];
}

/*
 * Free memory in a JsonLexContext.
 *
 * There's no need for this if a *lex pointer was given when the object was
 * made, need_escapes was false, and json_errdetail() was not called; or if (in
 * backend environment) a memory context delete/reset is imminent.
 */
void
freeJsonLexContext(JsonLexContext *lex)
{
        static const JsonLexContext empty = {0};

        if (!lex || lex == &failed_oom)
                return;

        if (lex->flags & JSONLEX_FREE_STRVAL)
                jsonapi_destroyStringInfo(lex->strval);

        if (lex->errormsg)
                jsonapi_destroyStringInfo(lex->errormsg);

        if (lex->incremental)
        {
                jsonapi_termStringInfo(&lex->inc_state->partial_token);
                FREE(lex->inc_state);
                FREE(lex->pstack->prediction);

                if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
                {
                        int                     i;

                        /* Clean up any tokens that were left behind. */
                        for (i = 0; i <= lex->lex_level; i++)
                                FREE(lex->pstack->fnames[i]);
                }

                FREE(lex->pstack->fnames);
                FREE(lex->pstack->fnull);
                FREE(lex->pstack->scalar_val);
                FREE(lex->pstack);
        }

        if (lex->flags & JSONLEX_FREE_STRUCT)
                FREE(lex);
        else
                *lex = empty;
}

/*
 * pg_parse_json
 *
 * Publicly visible entry point for the JSON parser.
 *
 * lex is a lexing context, set up for the json to be processed by calling
 * makeJsonLexContext(). sem is a structure of function pointers to semantic
 * action routines to be called at appropriate spots during parsing, and a
 * pointer to a state object to be passed to those routines.
 *
 * If FORCE_JSON_PSTACK is defined then the routine will call the non-recursive
 * JSON parser. This is a useful way to validate that it's doing the right
 * thing at least for non-incremental cases. If this is on we expect to see
 * regression diffs relating to error messages about stack depth, but no
 * other differences.
 */
JsonParseErrorType
pg_parse_json(JsonLexContext *lex, const JsonSemAction *sem)
{
#ifdef FORCE_JSON_PSTACK
        /*
         * We don't need partial token processing, there is only one chunk. But we
         * still need to init the partial token string so that freeJsonLexContext
         * works, so perform the full incremental initialization.
         */
        if (!allocate_incremental_state(lex))
                return JSON_OUT_OF_MEMORY;

        return pg_parse_json_incremental(lex, sem, lex->input, lex->input_length, true);

#else

        JsonTokenType tok;
        JsonParseErrorType result;

        if (lex == &failed_oom)
                return JSON_OUT_OF_MEMORY;
        if (lex->incremental)
                return JSON_INVALID_LEXER_TYPE;

        /* get the initial token */
        result = json_lex(lex);
        if (result != JSON_SUCCESS)
                return result;

        tok = lex_peek(lex);

        /* parse by recursive descent */
        switch (tok)
        {
                case JSON_TOKEN_OBJECT_START:
                        result = parse_object(lex, sem);
                        break;
                case JSON_TOKEN_ARRAY_START:
                        result = parse_array(lex, sem);
                        break;
                default:
                        result = parse_scalar(lex, sem);        /* json can be a bare scalar */
        }

        if (result == JSON_SUCCESS)
                result = lex_expect(JSON_PARSE_END, lex, JSON_TOKEN_END);

        return result;
#endif
}

/*
 * json_count_array_elements
 *
 * Returns number of array elements in lex context at start of array token
 * until end of array token at same nesting level.
 *
 * Designed to be called from array_start routines.
 */
JsonParseErrorType
json_count_array_elements(JsonLexContext *lex, int *elements)
{
        JsonLexContext copylex;
        int                     count;
        JsonParseErrorType result;

        if (lex == &failed_oom)
                return JSON_OUT_OF_MEMORY;

        /*
         * It's safe to do this with a shallow copy because the lexical routines
         * don't scribble on the input. They do scribble on the other pointers
         * etc, so doing this with a copy makes that safe.
         */
        memcpy(&copylex, lex, sizeof(JsonLexContext));
        copylex.need_escapes = false;   /* not interested in values here */
        copylex.lex_level++;

        count = 0;
        result = lex_expect(JSON_PARSE_ARRAY_START, &copylex,
                                                JSON_TOKEN_ARRAY_START);
        if (result != JSON_SUCCESS)
                return result;
        if (lex_peek(&copylex) != JSON_TOKEN_ARRAY_END)
        {
                while (1)
                {
                        count++;
                        result = parse_array_element(&copylex, &nullSemAction);
                        if (result != JSON_SUCCESS)
                                return result;
                        if (copylex.token_type != JSON_TOKEN_COMMA)
                                break;
                        result = json_lex(&copylex);
                        if (result != JSON_SUCCESS)
                                return result;
                }
        }
        result = lex_expect(JSON_PARSE_ARRAY_NEXT, &copylex,
                                                JSON_TOKEN_ARRAY_END);
        if (result != JSON_SUCCESS)
                return result;

        *elements = count;
        return JSON_SUCCESS;
}

/*
 * pg_parse_json_incremental
 *
 * Routine for incremental parsing of json. This uses the non-recursive top
 * down method of the Dragon Book Algorithm 4.3. It's somewhat slower than
 * the Recursive Descent pattern used above, so we only use it for incremental
 * parsing of JSON.
 *
 * The lexing context needs to be set up by a call to
 * makeJsonLexContextIncremental(). sem is a structure of function pointers
 * to semantic action routines, which should function exactly as those used
 * in the recursive descent parser.
 *
 * This routine can be called repeatedly with chunks of JSON. On the final
 * chunk is_last must be set to true. len is the length of the json chunk,
 * which does not need to be null terminated.
 */
JsonParseErrorType
pg_parse_json_incremental(JsonLexContext *lex,
                                                  const JsonSemAction *sem,
                                                  const char *json,
                                                  size_t len,
                                                  bool is_last)
{
        JsonTokenType tok;
        JsonParseErrorType result;
        JsonParseContext ctx = JSON_PARSE_VALUE;
        JsonParserStack *pstack = lex->pstack;

        if (lex == &failed_oom || lex->inc_state == &failed_inc_oom)
                return JSON_OUT_OF_MEMORY;
        if (!lex->incremental)
                return JSON_INVALID_LEXER_TYPE;

        lex->input = lex->token_terminator = lex->line_start = json;
        lex->input_length = len;
        lex->inc_state->is_last_chunk = is_last;
        lex->inc_state->started = true;

        /* get the initial token */
        result = json_lex(lex);
        if (result != JSON_SUCCESS)
                return result;

        tok = lex_peek(lex);

        /* use prediction stack for incremental parsing */

        if (!have_prediction(pstack))
        {
                td_entry        goal = TD_ENTRY(JSON_PROD_GOAL);

                push_prediction(pstack, goal);
        }

        while (have_prediction(pstack))
        {
                char            top = pop_prediction(pstack);
                td_entry        entry;

                /*
                 * these first two branches are the guts of the Table Driven method
                 */
                if (top == tok)
                {
                        /*
                         * tok can only be a terminal symbol, so top must be too. the
                         * token matches the top of the stack, so get the next token.
                         */
                        if (tok < JSON_TOKEN_END)
                        {
                                result = json_lex(lex);
                                if (result != JSON_SUCCESS)
                                        return result;
                                tok = lex_peek(lex);
                        }
                }
                else if (IS_NT(top) && (entry = td_parser_table[OFS(top)][tok]).prod != NULL)
                {
                        /*
                         * the token is in the director set for a production of the
                         * non-terminal at the top of the stack, so push the reversed RHS
                         * of the production onto the stack.
                         */
                        push_prediction(pstack, entry);
                }
                else if (IS_SEM(top))
                {
                        /*
                         * top is a semantic action marker, so take action accordingly.
                         * It's important to have these markers in the prediction stack
                         * before any token they might need so we don't advance the token
                         * prematurely. Note in a couple of cases we need to do something
                         * both before and after the token.
                         */
                        switch (top)
                        {
                                case JSON_SEM_OSTART:
                                        {
                                                json_struct_action ostart = sem->object_start;

                                                if (lex->lex_level >= JSON_TD_MAX_STACK)
                                                        return JSON_NESTING_TOO_DEEP;

                                                if (ostart != NULL)
                                                {
                                                        result = (*ostart) (sem->semstate);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }

                                                if (!inc_lex_level(lex))
                                                        return JSON_OUT_OF_MEMORY;
                                        }
                                        break;
                                case JSON_SEM_OEND:
                                        {
                                                json_struct_action oend = sem->object_end;

                                                dec_lex_level(lex);
                                                if (oend != NULL)
                                                {
                                                        result = (*oend) (sem->semstate);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_ASTART:
                                        {
                                                json_struct_action astart = sem->array_start;

                                                if (lex->lex_level >= JSON_TD_MAX_STACK)
                                                        return JSON_NESTING_TOO_DEEP;

                                                if (astart != NULL)
                                                {
                                                        result = (*astart) (sem->semstate);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }

                                                if (!inc_lex_level(lex))
                                                        return JSON_OUT_OF_MEMORY;
                                        }
                                        break;
                                case JSON_SEM_AEND:
                                        {
                                                json_struct_action aend = sem->array_end;

                                                dec_lex_level(lex);
                                                if (aend != NULL)
                                                {
                                                        result = (*aend) (sem->semstate);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_OFIELD_INIT:
                                        {
                                                /*
                                                 * all we do here is save out the field name. We have
                                                 * to wait to get past the ':' to see if the next
                                                 * value is null so we can call the semantic routine
                                                 */
                                                char       *fname = NULL;
                                                json_ofield_action ostart = sem->object_field_start;
                                                json_ofield_action oend = sem->object_field_end;

                                                if ((ostart != NULL || oend != NULL) && lex->need_escapes)
                                                {
                                                        fname = STRDUP(lex->strval->data);
                                                        if (fname == NULL)
                                                                return JSON_OUT_OF_MEMORY;
                                                }
                                                set_fname(lex, fname);
                                        }
                                        break;
                                case JSON_SEM_OFIELD_START:
                                        {
                                                /*
                                                 * the current token should be the first token of the
                                                 * value
                                                 */
                                                bool            isnull = tok == JSON_TOKEN_NULL;
                                                json_ofield_action ostart = sem->object_field_start;

                                                set_fnull(lex, isnull);

                                                if (ostart != NULL)
                                                {
                                                        char       *fname = get_fname(lex);

                                                        result = (*ostart) (sem->semstate, fname, isnull);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_OFIELD_END:
                                        {
                                                json_ofield_action oend = sem->object_field_end;

                                                if (oend != NULL)
                                                {
                                                        char       *fname = get_fname(lex);
                                                        bool            isnull = get_fnull(lex);

                                                        result = (*oend) (sem->semstate, fname, isnull);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_AELEM_START:
                                        {
                                                json_aelem_action astart = sem->array_element_start;
                                                bool            isnull = tok == JSON_TOKEN_NULL;

                                                set_fnull(lex, isnull);

                                                if (astart != NULL)
                                                {
                                                        result = (*astart) (sem->semstate, isnull);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_AELEM_END:
                                        {
                                                json_aelem_action aend = sem->array_element_end;

                                                if (aend != NULL)
                                                {
                                                        bool            isnull = get_fnull(lex);

                                                        result = (*aend) (sem->semstate, isnull);
                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                case JSON_SEM_SCALAR_INIT:
                                        {
                                                json_scalar_action sfunc = sem->scalar;

                                                pstack->scalar_val = NULL;

                                                if (sfunc != NULL)
                                                {
                                                        /*
                                                         * extract the de-escaped string value, or the raw
                                                         * lexeme
                                                         */
                                                        /*
                                                         * XXX copied from RD parser but looks like a
                                                         * buglet
                                                         */
                                                        if (tok == JSON_TOKEN_STRING)
                                                        {
                                                                if (lex->need_escapes)
                                                                {
                                                                        pstack->scalar_val = STRDUP(lex->strval->data);
                                                                        if (pstack->scalar_val == NULL)
                                                                                return JSON_OUT_OF_MEMORY;
                                                                }
                                                        }
                                                        else
                                                        {
                                                                ptrdiff_t       tlen = (lex->token_terminator - lex->token_start);

                                                                pstack->scalar_val = ALLOC(tlen + 1);
                                                                if (pstack->scalar_val == NULL)
                                                                        return JSON_OUT_OF_MEMORY;

                                                                memcpy(pstack->scalar_val, lex->token_start, tlen);
                                                                pstack->scalar_val[tlen] = '\0';
                                                        }
                                                        pstack->scalar_tok = tok;
                                                }
                                        }
                                        break;
                                case JSON_SEM_SCALAR_CALL:
                                        {
                                                /*
                                                 * We'd like to be able to get rid of this business of
                                                 * two bits of scalar action, but we can't. It breaks
                                                 * certain semantic actions which expect that when
                                                 * called the lexer has consumed the item. See for
                                                 * example get_scalar() in jsonfuncs.c.
                                                 */
                                                json_scalar_action sfunc = sem->scalar;

                                                if (sfunc != NULL)
                                                {
                                                        result = (*sfunc) (sem->semstate, pstack->scalar_val, pstack->scalar_tok);

                                                        /*
                                                         * Either ownership of the token passed to the
                                                         * callback, or we need to free it now. Either
                                                         * way, clear our pointer to it so it doesn't get
                                                         * freed in the future.
                                                         */
                                                        if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
                                                                FREE(pstack->scalar_val);
                                                        pstack->scalar_val = NULL;

                                                        if (result != JSON_SUCCESS)
                                                                return result;
                                                }
                                        }
                                        break;
                                default:
                                        /* should not happen */
                                        break;
                        }
                }
                else
                {
                        /*
                         * The token didn't match the stack top if it's a terminal nor a
                         * production for the stack top if it's a non-terminal.
                         *
                         * Various cases here are Asserted to be not possible, as the
                         * token would not appear at the top of the prediction stack
                         * unless the lookahead matched.
                         */
                        switch (top)
                        {
                                case JSON_TOKEN_STRING:
                                        if (next_prediction(pstack) == JSON_TOKEN_COLON)
                                                ctx = JSON_PARSE_STRING;
                                        else
                                        {
                                                Assert(false);
                                                ctx = JSON_PARSE_VALUE;
                                        }
                                        break;
                                case JSON_TOKEN_NUMBER:
                                case JSON_TOKEN_TRUE:
                                case JSON_TOKEN_FALSE:
                                case JSON_TOKEN_NULL:
                                case JSON_TOKEN_ARRAY_START:
                                case JSON_TOKEN_OBJECT_START:
                                        Assert(false);
                                        ctx = JSON_PARSE_VALUE;
                                        break;
                                case JSON_TOKEN_ARRAY_END:
                                        Assert(false);
                                        ctx = JSON_PARSE_ARRAY_NEXT;
                                        break;
                                case JSON_TOKEN_OBJECT_END:
                                        Assert(false);
                                        ctx = JSON_PARSE_OBJECT_NEXT;
                                        break;
                                case JSON_TOKEN_COMMA:
                                        Assert(false);
                                        if (next_prediction(pstack) == JSON_TOKEN_STRING)
                                                ctx = JSON_PARSE_OBJECT_NEXT;
                                        else
                                                ctx = JSON_PARSE_ARRAY_NEXT;
                                        break;
                                case JSON_TOKEN_COLON:
                                        ctx = JSON_PARSE_OBJECT_LABEL;
                                        break;
                                case JSON_TOKEN_END:
                                        ctx = JSON_PARSE_END;
                                        break;
                                case JSON_NT_MORE_ARRAY_ELEMENTS:
                                        ctx = JSON_PARSE_ARRAY_NEXT;
                                        break;
                                case JSON_NT_ARRAY_ELEMENTS:
                                        ctx = JSON_PARSE_ARRAY_START;
                                        break;
                                case JSON_NT_MORE_KEY_PAIRS:
                                        ctx = JSON_PARSE_OBJECT_NEXT;
                                        break;
                                case JSON_NT_KEY_PAIRS:
                                        ctx = JSON_PARSE_OBJECT_START;
                                        break;
                                default:
                                        ctx = JSON_PARSE_VALUE;
                        }
                        return report_parse_error(ctx, lex);
                }
        }

        return JSON_SUCCESS;
}

/*
 *      Recursive Descent parse routines. There is one for each structural
 *      element in a json document:
 *        - scalar (string, number, true, false, null)
 *        - array  ( [ ] )
 *        - array element
 *        - object ( { } )
 *        - object field
 */
static inline JsonParseErrorType
parse_scalar(JsonLexContext *lex, const JsonSemAction *sem)
{
        char       *val = NULL;
        json_scalar_action sfunc = sem->scalar;
        JsonTokenType tok = lex_peek(lex);
        JsonParseErrorType result;

        /* a scalar must be a string, a number, true, false, or null */
        if (tok != JSON_TOKEN_STRING && tok != JSON_TOKEN_NUMBER &&
                tok != JSON_TOKEN_TRUE && tok != JSON_TOKEN_FALSE &&
                tok != JSON_TOKEN_NULL)
                return report_parse_error(JSON_PARSE_VALUE, lex);

        /* if no semantic function, just consume the token */
        if (sfunc == NULL)
                return json_lex(lex);

        /* extract the de-escaped string value, or the raw lexeme */
        if (lex_peek(lex) == JSON_TOKEN_STRING)
        {
                if (lex->need_escapes)
                {
                        val = STRDUP(lex->strval->data);
                        if (val == NULL)
                                return JSON_OUT_OF_MEMORY;
                }
        }
        else
        {
                int                     len = (lex->token_terminator - lex->token_start);

                val = ALLOC(len + 1);
                if (val == NULL)
                        return JSON_OUT_OF_MEMORY;

                memcpy(val, lex->token_start, len);
                val[len] = '\0';
        }

        /* consume the token */
        result = json_lex(lex);
        if (result != JSON_SUCCESS)
        {
                FREE(val);
                return result;
        }

        /* invoke the callback, which may take ownership of val */
        result = (*sfunc) (sem->semstate, val, tok);

        if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
                FREE(val);

        return result;
}

static JsonParseErrorType
parse_object_field(JsonLexContext *lex, const JsonSemAction *sem)
{
        /*
         * An object field is "fieldname" : value where value can be a scalar,
         * object or array.  Note: in user-facing docs and error messages, we
         * generally call a field name a "key".
         */

        char       *fname = NULL;
        json_ofield_action ostart = sem->object_field_start;
        json_ofield_action oend = sem->object_field_end;
        bool            isnull;
        JsonTokenType tok;
        JsonParseErrorType result;

        if (lex_peek(lex) != JSON_TOKEN_STRING)
                return report_parse_error(JSON_PARSE_STRING, lex);
        if ((ostart != NULL || oend != NULL) && lex->need_escapes)
        {
                fname = STRDUP(lex->strval->data);
                if (fname == NULL)
                        return JSON_OUT_OF_MEMORY;
        }
        result = json_lex(lex);
        if (result != JSON_SUCCESS)
        {
                FREE(fname);
                return result;
        }

        result = lex_expect(JSON_PARSE_OBJECT_LABEL, lex, JSON_TOKEN_COLON);
        if (result != JSON_SUCCESS)
        {
                FREE(fname);
                return result;
        }

        tok = lex_peek(lex);
        isnull = tok == JSON_TOKEN_NULL;

        if (ostart != NULL)
        {
                result = (*ostart) (sem->semstate, fname, isnull);
                if (result != JSON_SUCCESS)
                        goto ofield_cleanup;
        }

        switch (tok)
        {
                case JSON_TOKEN_OBJECT_START:
                        result = parse_object(lex, sem);
                        break;
                case JSON_TOKEN_ARRAY_START:
                        result = parse_array(lex, sem);
                        break;
                default:
                        result = parse_scalar(lex, sem);
        }
        if (result != JSON_SUCCESS)
                goto ofield_cleanup;

        if (oend != NULL)
        {
                result = (*oend) (sem->semstate, fname, isnull);
                if (result != JSON_SUCCESS)
                        goto ofield_cleanup;
        }

ofield_cleanup:
        if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
                FREE(fname);
        return result;
}

static JsonParseErrorType
parse_object(JsonLexContext *lex, const JsonSemAction *sem)
{
        /*
         * an object is a possibly empty sequence of object fields, separated by
         * commas and surrounded by curly braces.
         */
        json_struct_action ostart = sem->object_start;
        json_struct_action oend = sem->object_end;
        JsonTokenType tok;
        JsonParseErrorType result;

#ifndef FRONTEND

        /*
         * TODO: clients need some way to put a bound on stack growth. Parse level
         * limits maybe?
         */
        check_stack_depth();
#endif

        if (ostart != NULL)
        {
                result = (*ostart) (sem->semstate);
                if (result != JSON_SUCCESS)
                        return result;
        }

        /*
         * Data inside an object is at a higher nesting level than the object
         * itself. Note that we increment this after we call the semantic routine
         * for the object start and restore it before we call the routine for the
         * object end.
         */
        lex->lex_level++;

        Assert(lex_peek(lex) == JSON_TOKEN_OBJECT_START);
        result = json_lex(lex);
        if (result != JSON_SUCCESS)
                return result;

        tok = lex_peek(lex);
        switch (tok)
        {
                case JSON_TOKEN_STRING:
                        result = parse_object_field(lex, sem);
                        while (result == JSON_SUCCESS && lex_peek(lex) == JSON_TOKEN_COMMA)
                        {
                                result = json_lex(lex);
                                if (result != JSON_SUCCESS)
                                        break;
                                result = parse_object_field(lex, sem);
                        }
                        break;
                case JSON_TOKEN_OBJECT_END:
                        break;
                default:
                        /* case of an invalid initial token inside the object */
                        result = report_parse_error(JSON_PARSE_OBJECT_START, lex);
        }
        if (result != JSON_SUCCESS)
                return result;

        result = lex_expect(JSON_PARSE_OBJECT_NEXT, lex, JSON_TOKEN_OBJECT_END);
        if (result != JSON_SUCCESS)
                return result;

        lex->lex_level--;

        if (oend != NULL)
        {
                result = (*oend) (sem->semstate);
                if (result != JSON_SUCCESS)
                        return result;
        }

        return JSON_SUCCESS;
}

static JsonParseErrorType
parse_array_element(JsonLexContext *lex, const JsonSemAction *sem)
{
        json_aelem_action astart = sem->array_element_start;
        json_aelem_action aend = sem->array_element_end;
        JsonTokenType tok = lex_peek(lex);
        JsonParseErrorType result;
        bool            isnull;

        isnull = tok == JSON_TOKEN_NULL;

        if (astart != NULL)
        {
                result = (*astart) (sem->semstate, isnull);
                if (result != JSON_SUCCESS)
                        return result;
        }

        /* an array element is any object, array or scalar */
        switch (tok)
        {
                case JSON_TOKEN_OBJECT_START:
                        result = parse_object(lex, sem);
                        break;
                case JSON_TOKEN_ARRAY_START:
                        result = parse_array(lex, sem);
                        break;
                default:
                        result = parse_scalar(lex, sem);
        }

        if (result != JSON_SUCCESS)
                return result;

        if (aend != NULL)
        {
                result = (*aend) (sem->semstate, isnull);
                if (result != JSON_SUCCESS)
                        return result;
        }

        return JSON_SUCCESS;
}

static JsonParseErrorType
parse_array(JsonLexContext *lex, const JsonSemAction *sem)
{
        /*
         * an array is a possibly empty sequence of array elements, separated by
         * commas and surrounded by square brackets.
         */
        json_struct_action astart = sem->array_start;
        json_struct_action aend = sem->array_end;
        JsonParseErrorType result;

#ifndef FRONTEND
        check_stack_depth();
#endif

        if (astart != NULL)
        {
                result = (*astart) (sem->semstate);
                if (result != JSON_SUCCESS)
                        return result;
        }

        /*
         * Data inside an array is at a higher nesting level than the array
         * itself. Note that we increment this after we call the semantic routine
         * for the array start and restore it before we call the routine for the
         * array end.
         */
        lex->lex_level++;

        result = lex_expect(JSON_PARSE_ARRAY_START, lex, JSON_TOKEN_ARRAY_START);
        if (result == JSON_SUCCESS && lex_peek(lex) != JSON_TOKEN_ARRAY_END)
        {
                result = parse_array_element(lex, sem);

                while (result == JSON_SUCCESS && lex_peek(lex) == JSON_TOKEN_COMMA)
                {
                        result = json_lex(lex);
                        if (result != JSON_SUCCESS)
                                break;
                        result = parse_array_element(lex, sem);
                }
        }
        if (result != JSON_SUCCESS)
                return result;

        result = lex_expect(JSON_PARSE_ARRAY_NEXT, lex, JSON_TOKEN_ARRAY_END);
        if (result != JSON_SUCCESS)
                return result;

        lex->lex_level--;

        if (aend != NULL)
        {
                result = (*aend) (sem->semstate);
                if (result != JSON_SUCCESS)
                        return result;
        }

        return JSON_SUCCESS;
}

/*
 * Lex one token from the input stream.
 *
 * When doing incremental parsing, we can reach the end of the input string
 * without having (or knowing we have) a complete token. If it's not the
 * final chunk of input, the partial token is then saved to the lex
 * structure's ptok StringInfo. On subsequent calls input is appended to this
 * buffer until we have something that we think is a complete token,
 * which is then lexed using a recursive call to json_lex. Processing then
 * continues as normal on subsequent calls.
 *
 * Note than when doing incremental processing, the lex.prev_token_terminator
 * should not be relied on. It could point into a previous input chunk or
 * worse.
 */
JsonParseErrorType
json_lex(JsonLexContext *lex)
{
        const char *s;
        const char *const end = lex->input + lex->input_length;
        JsonParseErrorType result;

        if (lex == &failed_oom || lex->inc_state == &failed_inc_oom)
                return JSON_OUT_OF_MEMORY;

        if (lex->incremental)
        {
                if (lex->inc_state->partial_completed)
                {
                        /*
                         * We just lexed a completed partial token on the last call, so
                         * reset everything
                         */
                        jsonapi_resetStringInfo(&(lex->inc_state->partial_token));
                        lex->token_terminator = lex->input;
                        lex->inc_state->partial_completed = false;
                }

#ifdef JSONAPI_USE_PQEXPBUFFER
                /* Make sure our partial token buffer is valid before using it below. */
                if (PQExpBufferDataBroken(lex->inc_state->partial_token))
                        return JSON_OUT_OF_MEMORY;
#endif
        }

        s = lex->token_terminator;

        if (lex->incremental && lex->inc_state->partial_token.len)
        {
                /*
                 * We have a partial token. Extend it and if completed lex it by a
                 * recursive call
                 */
                jsonapi_StrValType *ptok = &(lex->inc_state->partial_token);
                size_t          added = 0;
                bool            tok_done = false;
                JsonLexContext dummy_lex = {0};
                JsonParseErrorType partial_result;

                if (ptok->data[0] == '"')
                {
                        /*
                         * It's a string. Accumulate characters until we reach an
                         * unescaped '"'.
                         */
                        int                     escapes = 0;

                        for (int i = ptok->len - 1; i > 0; i--)
                        {
                                /* count the trailing backslashes on the partial token */
                                if (ptok->data[i] == '\\')
                                        escapes++;
                                else
                                        break;
                        }

                        for (size_t i = 0; i < lex->input_length; i++)
                        {
                                char            c = lex->input[i];

                                jsonapi_appendStringInfoCharMacro(ptok, c);
                                added++;
                                if (c == '"' && escapes % 2 == 0)
                                {
                                        tok_done = true;
                                        break;
                                }
                                if (c == '\\')
                                        escapes++;
                                else
                                        escapes = 0;
                        }
                }
                else
                {
                        /* not a string */
                        char            c = ptok->data[0];

                        if (c == '-' || (c >= '0' && c <= '9'))
                        {
                                /* for numbers look for possible numeric continuations */

                                bool            numend = false;

                                for (size_t i = 0; i < lex->input_length && !numend; i++)
                                {
                                        char            cc = lex->input[i];

                                        switch (cc)
                                        {
                                                case '+':
                                                case '-':
                                                case 'e':
                                                case 'E':
                                                case '0':
                                                case '1':
                                                case '2':
                                                case '3':
                                                case '4':
                                                case '5':
                                                case '6':
                                                case '7':
                                                case '8':
                                                case '9':
                                                        {
                                                                jsonapi_appendStringInfoCharMacro(ptok, cc);
                                                                added++;
                                                        }
                                                        break;
                                                default:
                                                        numend = true;
                                        }
                                }
                        }

                        /*
                         * Add any remaining alphanumeric chars. This takes care of the
                         * {null, false, true} literals as well as any trailing
                         * alphanumeric junk on non-string tokens.
                         */
                        for (size_t i = added; i < lex->input_length; i++)
                        {
                                char            cc = lex->input[i];

                                if (JSON_ALPHANUMERIC_CHAR(cc))
                                {
                                        jsonapi_appendStringInfoCharMacro(ptok, cc);
                                        added++;
                                }
                                else
                                {
                                        tok_done = true;
                                        break;
                                }
                        }
                        if (added == lex->input_length &&
                                lex->inc_state->is_last_chunk)
                        {
                                tok_done = true;
                        }
                }

                if (!tok_done)
                {
                        /* We should have consumed the whole chunk in this case. */
                        Assert(added == lex->input_length);

                        if (!lex->inc_state->is_last_chunk)
                                return JSON_INCOMPLETE;

                        /* json_errdetail() needs access to the accumulated token. */
                        lex->token_start = ptok->data;
                        lex->token_terminator = ptok->data + ptok->len;
                        return JSON_INVALID_TOKEN;
                }

                /*
                 * Everything up to lex->input[added] has been added to the partial
                 * token, so move the input past it.
                 */
                lex->input += added;
                lex->input_length -= added;

                dummy_lex.input = dummy_lex.token_terminator =
                        dummy_lex.line_start = ptok->data;
                dummy_lex.line_number = lex->line_number;
                dummy_lex.input_length = ptok->len;
                dummy_lex.input_encoding = lex->input_encoding;
                dummy_lex.incremental = false;
                dummy_lex.need_escapes = lex->need_escapes;
                dummy_lex.strval = lex->strval;

                partial_result = json_lex(&dummy_lex);

                /*
                 * We either have a complete token or an error. In either case we need
                 * to point to the partial token data for the semantic or error
                 * routines. If it's not an error we'll readjust on the next call to
                 * json_lex.
                 */
                lex->token_type = dummy_lex.token_type;
                lex->line_number = dummy_lex.line_number;

                /*
                 * We know the prev_token_terminator must be back in some previous
                 * piece of input, so we just make it NULL.
                 */
                lex->prev_token_terminator = NULL;

                /*
                 * Normally token_start would be ptok->data, but it could be later,
                 * see json_lex_string's handling of invalid escapes.
                 */
                lex->token_start = dummy_lex.token_start;
                lex->token_terminator = dummy_lex.token_terminator;
                if (partial_result == JSON_SUCCESS)
                {
                        /* make sure we've used all the input */
                        if (lex->token_terminator - lex->token_start != ptok->len)
                        {
                                Assert(false);
                                return JSON_INVALID_TOKEN;
                        }

                        lex->inc_state->partial_completed = true;
                }
                return partial_result;
                /* end of partial token processing */
        }

        /* Skip leading whitespace. */
        while (s < end && (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r'))
        {
                if (*s++ == '\n')
                {
                        ++lex->line_number;
                        lex->line_start = s;
                }
        }
        lex->token_start = s;

        /* Determine token type. */
        if (s >= end)
        {
                lex->token_start = NULL;
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s;
                lex->token_type = JSON_TOKEN_END;
        }
        else
        {
                switch (*s)
                {
                                /* Single-character token, some kind of punctuation mark. */
                        case '{':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_OBJECT_START;
                                break;
                        case '}':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_OBJECT_END;
                                break;
                        case '[':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_ARRAY_START;
                                break;
                        case ']':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_ARRAY_END;
                                break;
                        case ',':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_COMMA;
                                break;
                        case ':':
                                lex->prev_token_terminator = lex->token_terminator;
                                lex->token_terminator = s + 1;
                                lex->token_type = JSON_TOKEN_COLON;
                                break;
                        case '"':
                                /* string */
                                result = json_lex_string(lex);
                                if (result != JSON_SUCCESS)
                                        return result;
                                lex->token_type = JSON_TOKEN_STRING;
                                break;
                        case '-':
                                /* Negative number. */
                                result = json_lex_number(lex, s + 1, NULL, NULL);
                                if (result != JSON_SUCCESS)
                                        return result;
                                lex->token_type = JSON_TOKEN_NUMBER;
                                break;
                        case '0':
                        case '1':
                        case '2':
                        case '3':
                        case '4':
                        case '5':
                        case '6':
                        case '7':
                        case '8':
                        case '9':
                                /* Positive number. */
                                result = json_lex_number(lex, s, NULL, NULL);
                                if (result != JSON_SUCCESS)
                                        return result;
                                lex->token_type = JSON_TOKEN_NUMBER;
                                break;
                        default:
                                {
                                        const char *p;

                                        /*
                                         * We're not dealing with a string, number, legal
                                         * punctuation mark, or end of string.  The only legal
                                         * tokens we might find here are true, false, and null,
                                         * but for error reporting purposes we scan until we see a
                                         * non-alphanumeric character.  That way, we can report
                                         * the whole word as an unexpected token, rather than just
                                         * some unintuitive prefix thereof.
                                         */
                                        for (p = s; p < end && JSON_ALPHANUMERIC_CHAR(*p); p++)
                                                 /* skip */ ;

                                        /*
                                         * We got some sort of unexpected punctuation or an
                                         * otherwise unexpected character, so just complain about
                                         * that one character.
                                         */
                                        if (p == s)
                                        {
                                                lex->prev_token_terminator = lex->token_terminator;
                                                lex->token_terminator = s + 1;
                                                return JSON_INVALID_TOKEN;
                                        }

                                        if (lex->incremental && !lex->inc_state->is_last_chunk &&
                                                p == lex->input + lex->input_length)
                                        {
                                                jsonapi_appendBinaryStringInfo(&(lex->inc_state->partial_token), s, end - s);
                                                return JSON_INCOMPLETE;
                                        }

                                        /*
                                         * We've got a real alphanumeric token here.  If it
                                         * happens to be true, false, or null, all is well.  If
                                         * not, error out.
                                         */
                                        lex->prev_token_terminator = lex->token_terminator;
                                        lex->token_terminator = p;
                                        if (p - s == 4)
                                        {
                                                if (memcmp(s, "true", 4) == 0)
                                                        lex->token_type = JSON_TOKEN_TRUE;
                                                else if (memcmp(s, "null", 4) == 0)
                                                        lex->token_type = JSON_TOKEN_NULL;
                                                else
                                                        return JSON_INVALID_TOKEN;
                                        }
                                        else if (p - s == 5 && memcmp(s, "false", 5) == 0)
                                                lex->token_type = JSON_TOKEN_FALSE;
                                        else
                                                return JSON_INVALID_TOKEN;
                                }
                }                                               /* end of switch */
        }

        if (lex->incremental && lex->token_type == JSON_TOKEN_END && !lex->inc_state->is_last_chunk)
                return JSON_INCOMPLETE;
        else
                return JSON_SUCCESS;
}

/*
 * The next token in the input stream is known to be a string; lex it.
 *
 * If lex->strval isn't NULL, fill it with the decoded string.
 * Set lex->token_terminator to the end of the decoded input, and in
 * success cases, transfer its previous value to lex->prev_token_terminator.
 * Return JSON_SUCCESS or an error code.
 *
 * Note: be careful that all error exits advance lex->token_terminator
 * to the point after the character we detected the error on.
 */
static inline JsonParseErrorType
json_lex_string(JsonLexContext *lex)
{
        const char *s;
        const char *const end = lex->input + lex->input_length;
        int                     hi_surrogate = -1;

        /* Convenience macros for error exits */
#define FAIL_OR_INCOMPLETE_AT_CHAR_START(code) \
        do { \
                if (lex->incremental && !lex->inc_state->is_last_chunk) \
                { \
                        jsonapi_appendBinaryStringInfo(&lex->inc_state->partial_token, \
                                                                                   lex->token_start, \
                                                                                   end - lex->token_start); \
                        return JSON_INCOMPLETE; \
                } \
                lex->token_terminator = s; \
                return code; \
        } while (0)
#define FAIL_AT_CHAR_END(code) \
        do { \
                const char         *term = s + pg_encoding_mblen(lex->input_encoding, s); \
                lex->token_terminator = (term <= end) ? term : end; \
                return code; \
        } while (0)

        if (lex->need_escapes)
        {
#ifdef JSONAPI_USE_PQEXPBUFFER
                /* make sure initialization succeeded */
                if (lex->strval == NULL)
                        return JSON_OUT_OF_MEMORY;
#endif
                jsonapi_resetStringInfo(lex->strval);
        }

        Assert(lex->input_length > 0);
        s = lex->token_start;
        for (;;)
        {
                s++;
                /* Premature end of the string. */
                if (s >= end)
                        FAIL_OR_INCOMPLETE_AT_CHAR_START(JSON_INVALID_TOKEN);
                else if (*s == '"')
                        break;
                else if (*s == '\\')
                {
                        /* OK, we have an escape character. */
                        s++;
                        if (s >= end)
                                FAIL_OR_INCOMPLETE_AT_CHAR_START(JSON_INVALID_TOKEN);
                        else if (*s == 'u')
                        {
                                int                     i;
                                int                     ch = 0;

                                for (i = 1; i <= 4; i++)
                                {
                                        s++;
                                        if (s >= end)
                                                FAIL_OR_INCOMPLETE_AT_CHAR_START(JSON_INVALID_TOKEN);
                                        else if (*s >= '0' && *s <= '9')
                                                ch = (ch * 16) + (*s - '0');
                                        else if (*s >= 'a' && *s <= 'f')
                                                ch = (ch * 16) + (*s - 'a') + 10;
                                        else if (*s >= 'A' && *s <= 'F')
                                                ch = (ch * 16) + (*s - 'A') + 10;
                                        else
                                                FAIL_AT_CHAR_END(JSON_UNICODE_ESCAPE_FORMAT);
                                }
                                if (lex->need_escapes)
                                {
                                        /*
                                         * Combine surrogate pairs.
                                         */
                                        if (is_utf16_surrogate_first(ch))
                                        {
                                                if (hi_surrogate != -1)
                                                        FAIL_AT_CHAR_END(JSON_UNICODE_HIGH_SURROGATE);
                                                hi_surrogate = ch;
                                                continue;
                                        }
                                        else if (is_utf16_surrogate_second(ch))
                                        {
                                                if (hi_surrogate == -1)
                                                        FAIL_AT_CHAR_END(JSON_UNICODE_LOW_SURROGATE);
                                                ch = surrogate_pair_to_codepoint(hi_surrogate, ch);
                                                hi_surrogate = -1;
                                        }

                                        if (hi_surrogate != -1)
                                                FAIL_AT_CHAR_END(JSON_UNICODE_LOW_SURROGATE);

                                        /*
                                         * Reject invalid cases.  We can't have a value above
                                         * 0xFFFF here (since we only accepted 4 hex digits
                                         * above), so no need to test for out-of-range chars.
                                         */
                                        if (ch == 0)
                                        {
                                                /* We can't allow this, since our TEXT type doesn't */
                                                FAIL_AT_CHAR_END(JSON_UNICODE_CODE_POINT_ZERO);
                                        }

                                        /*
                                         * Add the represented character to lex->strval.  In the
                                         * backend, we can let pg_unicode_to_server_noerror()
                                         * handle any required character set conversion; in
                                         * frontend, we can only deal with trivial conversions.
                                         */
#ifndef FRONTEND
                                        {
                                                char            cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];

                                                if (!pg_unicode_to_server_noerror(ch, (unsigned char *) cbuf))
                                                        FAIL_AT_CHAR_END(JSON_UNICODE_UNTRANSLATABLE);
                                                appendStringInfoString(lex->strval, cbuf);
                                        }
#else
                                        if (lex->input_encoding == PG_UTF8)
                                        {
                                                /* OK, we can map the code point to UTF8 easily */
                                                char            utf8str[5];
                                                int                     utf8len;

                                                unicode_to_utf8(ch, (unsigned char *) utf8str);
                                                utf8len = pg_utf_mblen((unsigned char *) utf8str);
                                                jsonapi_appendBinaryStringInfo(lex->strval, utf8str, utf8len);
                                        }
                                        else if (ch <= 0x007f)
                                        {
                                                /* The ASCII range is the same in all encodings */
                                                jsonapi_appendStringInfoChar(lex->strval, (char) ch);
                                        }
                                        else
                                                FAIL_AT_CHAR_END(JSON_UNICODE_HIGH_ESCAPE);
#endif                                                  /* FRONTEND */
                                }
                        }
                        else if (lex->need_escapes)
                        {
                                if (hi_surrogate != -1)
                                        FAIL_AT_CHAR_END(JSON_UNICODE_LOW_SURROGATE);

                                switch (*s)
                                {
                                        case '"':
                                        case '\\':
                                        case '/':
                                                jsonapi_appendStringInfoChar(lex->strval, *s);
                                                break;
                                        case 'b':
                                                jsonapi_appendStringInfoChar(lex->strval, '\b');
                                                break;
                                        case 'f':
                                                jsonapi_appendStringInfoChar(lex->strval, '\f');
                                                break;
                                        case 'n':
                                                jsonapi_appendStringInfoChar(lex->strval, '\n');
                                                break;
                                        case 'r':
                                                jsonapi_appendStringInfoChar(lex->strval, '\r');
                                                break;
                                        case 't':
                                                jsonapi_appendStringInfoChar(lex->strval, '\t');
                                                break;
                                        default:

                                                /*
                                                 * Not a valid string escape, so signal error.  We
                                                 * adjust token_start so that just the escape sequence
                                                 * is reported, not the whole string.
                                                 */
                                                lex->token_start = s;
                                                FAIL_AT_CHAR_END(JSON_ESCAPING_INVALID);
                                }
                        }
                        else if (strchr("\"\\/bfnrt", *s) == NULL)
                        {
                                /*
                                 * Simpler processing if we're not bothered about de-escaping
                                 *
                                 * It's very tempting to remove the strchr() call here and
                                 * replace it with a switch statement, but testing so far has
                                 * shown it's not a performance win.
                                 */
                                lex->token_start = s;
                                FAIL_AT_CHAR_END(JSON_ESCAPING_INVALID);
                        }
                }
                else
                {
                        const char *p = s;

                        if (hi_surrogate != -1)
                                FAIL_AT_CHAR_END(JSON_UNICODE_LOW_SURROGATE);

                        /*
                         * Skip to the first byte that requires special handling, so we
                         * can batch calls to jsonapi_appendBinaryStringInfo.
                         */
                        while (p < end - sizeof(Vector8) &&
                                   !pg_lfind8('\\', (uint8 *) p, sizeof(Vector8)) &&
                                   !pg_lfind8('"', (uint8 *) p, sizeof(Vector8)) &&
                                   !pg_lfind8_le(31, (uint8 *) p, sizeof(Vector8)))
                                p += sizeof(Vector8);

                        for (; p < end; p++)
                        {
                                if (*p == '\\' || *p == '"')
                                        break;
                                else if ((unsigned char) *p <= 31)
                                {
                                        /* Per RFC4627, these characters MUST be escaped. */
                                        /*
                                         * Since *p isn't printable, exclude it from the context
                                         * string
                                         */
                                        lex->token_terminator = p;
                                        return JSON_ESCAPING_REQUIRED;
                                }
                        }

                        if (lex->need_escapes)
                                jsonapi_appendBinaryStringInfo(lex->strval, s, p - s);

                        /*
                         * s will be incremented at the top of the loop, so set it to just
                         * behind our lookahead position
                         */
                        s = p - 1;
                }
        }

        if (hi_surrogate != -1)
        {
                lex->token_terminator = s + 1;
                return JSON_UNICODE_LOW_SURROGATE;
        }

#ifdef JSONAPI_USE_PQEXPBUFFER
        if (lex->need_escapes && PQExpBufferBroken(lex->strval))
                return JSON_OUT_OF_MEMORY;
#endif

        /* Hooray, we found the end of the string! */
        lex->prev_token_terminator = lex->token_terminator;
        lex->token_terminator = s + 1;
        return JSON_SUCCESS;

#undef FAIL_OR_INCOMPLETE_AT_CHAR_START
#undef FAIL_AT_CHAR_END
}

/*
 * The next token in the input stream is known to be a number; lex it.
 *
 * In JSON, a number consists of four parts:
 *
 * (1) An optional minus sign ('-').
 *
 * (2) Either a single '0', or a string of one or more digits that does not
 *         begin with a '0'.
 *
 * (3) An optional decimal part, consisting of a period ('.') followed by
 *         one or more digits.  (Note: While this part can be omitted
 *         completely, it's not OK to have only the decimal point without
 *         any digits afterwards.)
 *
 * (4) An optional exponent part, consisting of 'e' or 'E', optionally
 *         followed by '+' or '-', followed by one or more digits.  (Note:
 *         As with the decimal part, if 'e' or 'E' is present, it must be
 *         followed by at least one digit.)
 *
 * The 's' argument to this function points to the ostensible beginning
 * of part 2 - i.e. the character after any optional minus sign, or the
 * first character of the string if there is none.
 *
 * If num_err is not NULL, we return an error flag to *num_err rather than
 * raising an error for a badly-formed number.  Also, if total_len is not NULL
 * the distance from lex->input to the token end+1 is returned to *total_len.
 */
static inline JsonParseErrorType
json_lex_number(JsonLexContext *lex, const char *s,
                                bool *num_err, size_t *total_len)
{
        bool            error = false;
        int                     len = s - lex->input;

        /* Part (1): leading sign indicator. */
        /* Caller already did this for us; so do nothing. */

        /* Part (2): parse main digit string. */
        if (len < lex->input_length && *s == '0')
        {
                s++;
                len++;
        }
        else if (len < lex->input_length && *s >= '1' && *s <= '9')
        {
                do
                {
                        s++;
                        len++;
                } while (len < lex->input_length && *s >= '0' && *s <= '9');
        }
        else
                error = true;

        /* Part (3): parse optional decimal portion. */
        if (len < lex->input_length && *s == '.')
        {
                s++;
                len++;
                if (len == lex->input_length || *s < '0' || *s > '9')
                        error = true;
                else
                {
                        do
                        {
                                s++;
                                len++;
                        } while (len < lex->input_length && *s >= '0' && *s <= '9');
                }
        }

        /* Part (4): parse optional exponent. */
        if (len < lex->input_length && (*s == 'e' || *s == 'E'))
        {
                s++;
                len++;
                if (len < lex->input_length && (*s == '+' || *s == '-'))
                {
                        s++;
                        len++;
                }
                if (len == lex->input_length || *s < '0' || *s > '9')
                        error = true;
                else
                {
                        do
                        {
                                s++;
                                len++;
                        } while (len < lex->input_length && *s >= '0' && *s <= '9');
                }
        }

        /*
         * Check for trailing garbage.  As in json_lex(), any alphanumeric stuff
         * here should be considered part of the token for error-reporting
         * purposes.
         */
        for (; len < lex->input_length && JSON_ALPHANUMERIC_CHAR(*s); s++, len++)
                error = true;

        if (total_len != NULL)
                *total_len = len;

        if (lex->incremental && !lex->inc_state->is_last_chunk &&
                len >= lex->input_length)
        {
                jsonapi_appendBinaryStringInfo(&lex->inc_state->partial_token,
                                                                           lex->token_start, s - lex->token_start);
                if (num_err != NULL)
                        *num_err = error;

                return JSON_INCOMPLETE;
        }
        else if (num_err != NULL)
        {
                /* let the caller handle any error */
                *num_err = error;
        }
        else
        {
                /* return token endpoint */
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s;
                /* handle error if any */
                if (error)
                        return JSON_INVALID_TOKEN;
        }

        return JSON_SUCCESS;
}

/*
 * Report a parse error.
 *
 * lex->token_start and lex->token_terminator must identify the current token.
 */
static JsonParseErrorType
report_parse_error(JsonParseContext ctx, JsonLexContext *lex)
{
        /* Handle case where the input ended prematurely. */
        if (lex->token_start == NULL || lex->token_type == JSON_TOKEN_END)
                return JSON_EXPECTED_MORE;

        /* Otherwise choose the error type based on the parsing context. */
        switch (ctx)
        {
                case JSON_PARSE_END:
                        return JSON_EXPECTED_END;
                case JSON_PARSE_VALUE:
                        return JSON_EXPECTED_JSON;
                case JSON_PARSE_STRING:
                        return JSON_EXPECTED_STRING;
                case JSON_PARSE_ARRAY_START:
                        return JSON_EXPECTED_ARRAY_FIRST;
                case JSON_PARSE_ARRAY_NEXT:
                        return JSON_EXPECTED_ARRAY_NEXT;
                case JSON_PARSE_OBJECT_START:
                        return JSON_EXPECTED_OBJECT_FIRST;
                case JSON_PARSE_OBJECT_LABEL:
                        return JSON_EXPECTED_COLON;
                case JSON_PARSE_OBJECT_NEXT:
                        return JSON_EXPECTED_OBJECT_NEXT;
                case JSON_PARSE_OBJECT_COMMA:
                        return JSON_EXPECTED_STRING;
        }

        /*
         * We don't use a default: case, so that the compiler will warn about
         * unhandled enum values.
         */
        Assert(false);
        return JSON_SUCCESS;            /* silence stupider compilers */
}

/*
 * Construct an (already translated) detail message for a JSON error.
 *
 * The returned pointer should not be freed, the allocation is either static
 * or owned by the JsonLexContext.
 */
char *
json_errdetail(JsonParseErrorType error, JsonLexContext *lex)
{
        if (error == JSON_OUT_OF_MEMORY || lex == &failed_oom)
        {
                /* Short circuit. Allocating anything for this case is unhelpful. */
                return _("out of memory");
        }

        if (lex->errormsg)
                jsonapi_resetStringInfo(lex->errormsg);
        else
                lex->errormsg = jsonapi_makeStringInfo();

        /*
         * A helper for error messages that should print the current token. The
         * format must contain exactly one %.*s specifier.
         */
#define json_token_error(lex, format) \
        jsonapi_appendStringInfo((lex)->errormsg, _(format), \
                                                         (int) ((lex)->token_terminator - (lex)->token_start), \
                                                         (lex)->token_start);

        switch (error)
        {
                case JSON_INCOMPLETE:
                case JSON_SUCCESS:
                        /* fall through to the error code after switch */
                        break;
                case JSON_INVALID_LEXER_TYPE:
                        if (lex->incremental)
                                return _("Recursive descent parser cannot use incremental lexer.");
                        else
                                return _("Incremental parser requires incremental lexer.");
                case JSON_NESTING_TOO_DEEP:
                        return (_("JSON nested too deep, maximum permitted depth is 6400."));
                case JSON_ESCAPING_INVALID:
                        json_token_error(lex, "Escape sequence \"\\%.*s\" is invalid.");
                        break;
                case JSON_ESCAPING_REQUIRED:
                        jsonapi_appendStringInfo(lex->errormsg,
                                                                         _("Character with value 0x%02x must be escaped."),
                                                                         (unsigned char) *(lex->token_terminator));
                        break;
                case JSON_EXPECTED_END:
                        json_token_error(lex, "Expected end of input, but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_ARRAY_FIRST:
                        json_token_error(lex, "Expected array element or \"]\", but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_ARRAY_NEXT:
                        json_token_error(lex, "Expected \",\" or \"]\", but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_COLON:
                        json_token_error(lex, "Expected \":\", but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_JSON:
                        json_token_error(lex, "Expected JSON value, but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_MORE:
                        return _("The input string ended unexpectedly.");
                case JSON_EXPECTED_OBJECT_FIRST:
                        json_token_error(lex, "Expected string or \"}\", but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_OBJECT_NEXT:
                        json_token_error(lex, "Expected \",\" or \"}\", but found \"%.*s\".");
                        break;
                case JSON_EXPECTED_STRING:
                        json_token_error(lex, "Expected string, but found \"%.*s\".");
                        break;
                case JSON_INVALID_TOKEN:
                        json_token_error(lex, "Token \"%.*s\" is invalid.");
                        break;
                case JSON_OUT_OF_MEMORY:
                        /* should have been handled above; use the error path */
                        break;
                case JSON_UNICODE_CODE_POINT_ZERO:
                        return _("\\u0000 cannot be converted to text.");
                case JSON_UNICODE_ESCAPE_FORMAT:
                        return _("\"\\u\" must be followed by four hexadecimal digits.");
                case JSON_UNICODE_HIGH_ESCAPE:
                        /* note: this case is only reachable in frontend not backend */
                        return _("Unicode escape values cannot be used for code point values above 007F when the encoding is not UTF8.");
                case JSON_UNICODE_UNTRANSLATABLE:

                        /*
                         * Note: this case is only reachable in backend and not frontend.
                         * #ifdef it away so the frontend doesn't try to link against
                         * backend functionality.
                         */
#ifndef FRONTEND
                        return psprintf(_("Unicode escape value could not be translated to the server's encoding %s."),
                                                        GetDatabaseEncodingName());
#else
                        Assert(false);
                        break;
#endif
                case JSON_UNICODE_HIGH_SURROGATE:
                        return _("Unicode high surrogate must not follow a high surrogate.");
                case JSON_UNICODE_LOW_SURROGATE:
                        return _("Unicode low surrogate must follow a high surrogate.");
                case JSON_SEM_ACTION_FAILED:
                        /* fall through to the error code after switch */
                        break;
        }
#undef json_token_error

        /* Note that lex->errormsg can be NULL in shlib code. */
        if (lex->errormsg && lex->errormsg->len == 0)
        {
                /*
                 * We don't use a default: case, so that the compiler will warn about
                 * unhandled enum values.  But this needs to be here anyway to cover
                 * the possibility of an incorrect input.
                 */
                jsonapi_appendStringInfo(lex->errormsg,
                                                                 "unexpected json parse error type: %d",
                                                                 (int) error);
        }

#ifdef JSONAPI_USE_PQEXPBUFFER
        if (PQExpBufferBroken(lex->errormsg))
                return _("out of memory while constructing error description");
#endif

        return lex->errormsg->data;
}