ext/misc/blobio.c

   1 /*
   2 ** 2019-03-30
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 ******************************************************************************
  12 **
  13 ** An SQL function that uses the incremental BLOB I/O mechanism of SQLite
  14 ** to read or write part of a blob.  This is intended for debugging use
  15 ** in the CLI.
  16 **
  17 **      readblob(SCHEMA,TABLE,COLUMN,ROWID,OFFSET,N)
  18 **
  19 ** Returns N bytes of the blob starting at OFFSET.
  20 **
  21 **      writeblob(SCHEMA,TABLE,COLUMN,ROWID,OFFSET,NEWDATA)
  22 **
  23 ** NEWDATA must be a blob.  The content of NEWDATA overwrites the
  24 ** existing BLOB data at SCHEMA.TABLE.COLUMN for row ROWID beginning
  25 ** at OFFSET bytes into the blob.
  26 */
  27 #include "sqlite3ext.h"
  28 SQLITE_EXTENSION_INIT1
  29 #include <assert.h>
  30 #include <string.h>
  31
  32 static void readblobFunc(
  33   sqlite3_context *context,
  34   int argc,
  35   sqlite3_value **argv
  36 ){
  37   sqlite3_blob *pBlob = 0;
  38   const char *zSchema;
  39   const char *zTable;
  40   const char *zColumn;
  41   sqlite3_int64 iRowid;
  42   int iOfst;
  43   unsigned char *aData;
  44   int nData;
  45   sqlite3 *db;
  46   int rc;
  47
  48   zSchema = (const char*)sqlite3_value_text(argv[0]);
  49   zTable = (const char*)sqlite3_value_text(argv[1]);
  50   if( zTable==0 ){
  51     sqlite3_result_error(context, "bad table name", -1);
  52     return;
  53   }
  54   zColumn = (const char*)sqlite3_value_text(argv[2]);
  55   if( zTable==0 ){
  56     sqlite3_result_error(context, "bad column name", -1);
  57     return;
  58   }
  59   iRowid = sqlite3_value_int64(argv[3]);
  60   iOfst = sqlite3_value_int(argv[4]);
  61   nData = sqlite3_value_int(argv[5]);
  62   if( nData<=0 ) return;
  63   aData = sqlite3_malloc64( nData+1 );
  64   if( aData==0 ){
  65     sqlite3_result_error_nomem(context);
  66     return;
  67   }
  68   db = sqlite3_context_db_handle(context);
  69   rc = sqlite3_blob_open(db, zSchema, zTable, zColumn, iRowid, 0, &pBlob);
  70   if( rc ){
  71     sqlite3_free(aData);
  72     sqlite3_result_error(context, "cannot open BLOB pointer", -1);
  73     return;
  74   }
  75   rc = sqlite3_blob_read(pBlob, aData, nData, iOfst);
  76   sqlite3_blob_close(pBlob);
  77   if( rc ){
  78     sqlite3_free(aData);
  79     sqlite3_result_error(context, "BLOB read failed", -1);
  80   }else{
  81     sqlite3_result_blob(context, aData, nData, sqlite3_free);
  82   }
  83 }
  84
  85 static void writeblobFunc(
  86   sqlite3_context *context,
  87   int argc,
  88   sqlite3_value **argv
  89 ){
  90   sqlite3_blob *pBlob = 0;
  91   const char *zSchema;
  92   const char *zTable;
  93   const char *zColumn;
  94   sqlite3_int64 iRowid;
  95   int iOfst;
  96   unsigned char *aData;
  97   int nData;
  98   sqlite3 *db;
  99   int rc;
 100
 101   zSchema = (const char*)sqlite3_value_text(argv[0]);
 102   zTable = (const char*)sqlite3_value_text(argv[1]);
 103   if( zTable==0 ){
 104     sqlite3_result_error(context, "bad table name", -1);
 105     return;
 106   }
 107   zColumn = (const char*)sqlite3_value_text(argv[2]);
 108   if( zTable==0 ){
 109     sqlite3_result_error(context, "bad column name", -1);
 110     return;
 111   }
 112   iRowid = sqlite3_value_int64(argv[3]);
 113   iOfst = sqlite3_value_int(argv[4]);
 114   if( sqlite3_value_type(argv[5])!=SQLITE_BLOB ){
 115     sqlite3_result_error(context, "6th argument must be a BLOB", -1);
 116     return;
 117   }
 118   nData = sqlite3_value_bytes(argv[5]);
 119   aData = (unsigned char *)sqlite3_value_blob(argv[5]);
 120   db = sqlite3_context_db_handle(context);
 121   rc = sqlite3_blob_open(db, zSchema, zTable, zColumn, iRowid, 1, &pBlob);
 122   if( rc ){
 123     sqlite3_result_error(context, "cannot open BLOB pointer", -1);
 124     return;
 125   }
 126   rc = sqlite3_blob_write(pBlob, aData, nData, iOfst);
 127   sqlite3_blob_close(pBlob);
 128   if( rc ){
 129     sqlite3_result_error(context, "BLOB write failed", -1);
 130   }
 131 }
 132
 133
 134 #ifdef _WIN32
 135 __declspec(dllexport)
 136 #endif
 137 int sqlite3_blobio_init(
 138   sqlite3 *db,
 139   char **pzErrMsg,
 140   const sqlite3_api_routines *pApi
 141 ){
 142   int rc = SQLITE_OK;
 143   SQLITE_EXTENSION_INIT2(pApi);
 144   (void)pzErrMsg;  /* Unused parameter */
 145   rc = sqlite3_create_function(db, "readblob", 6, SQLITE_UTF8, 0,
 146                                readblobFunc, 0, 0);
 147   if( rc==SQLITE_OK ){
 148     rc = sqlite3_create_function(db, "writeblob", 6, SQLITE_UTF8, 0,
 149                                writeblobFunc, 0, 0);
 150   }
 151   return rc;
 152 }