ext/misc/sqlar.c

   1 /*
   2 ** 2017-12-17
   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 ** Utility functions sqlar_compress() and sqlar_uncompress(). Useful
  14 ** for working with sqlar archives and used by the shell tool's built-in
  15 ** sqlar support.
  16 */
  17 #include "sqlite3ext.h"
  18 SQLITE_EXTENSION_INIT1
  19 #include <zlib.h>
  20 #include <assert.h>
  21
  22 /*
  23 ** Implementation of the "sqlar_compress(X)" SQL function.
  24 **
  25 ** If the type of X is SQLITE_BLOB, and compressing that blob using
  26 ** zlib utility function compress() yields a smaller blob, return the
  27 ** compressed blob. Otherwise, return a copy of X.
  28 **
  29 ** SQLar uses the "zlib format" for compressed content.  The zlib format
  30 ** contains a two-byte identification header and a four-byte checksum at
  31 ** the end.  This is different from ZIP which uses the raw deflate format.
  32 **
  33 ** Future enhancements to SQLar might add support for new compression formats.
  34 ** If so, those new formats will be identified by alternative headers in the
  35 ** compressed data.
  36 */
  37 static void sqlarCompressFunc(
  38   sqlite3_context *context,
  39   int argc,
  40   sqlite3_value **argv
  41 ){
  42   assert( argc==1 );
  43   if( sqlite3_value_type(argv[0])==SQLITE_BLOB ){
  44     const Bytef *pData = sqlite3_value_blob(argv[0]);
  45     uLong nData = sqlite3_value_bytes(argv[0]);
  46     uLongf nOut = compressBound(nData);
  47     Bytef *pOut;
  48
  49     pOut = (Bytef*)sqlite3_malloc(nOut);
  50     if( pOut==0 ){
  51       sqlite3_result_error_nomem(context);
  52       return;
  53     }else{
  54       if( Z_OK!=compress(pOut, &nOut, pData, nData) ){
  55         sqlite3_result_error(context, "error in compress()", -1);
  56       }else if( nOut<nData ){
  57         sqlite3_result_blob(context, pOut, nOut, SQLITE_TRANSIENT);
  58       }else{
  59         sqlite3_result_value(context, argv[0]);
  60       }
  61       sqlite3_free(pOut);
  62     }
  63   }else{
  64     sqlite3_result_value(context, argv[0]);
  65   }
  66 }
  67
  68 /*
  69 ** Implementation of the "sqlar_uncompress(X,SZ)" SQL function
  70 **
  71 ** Parameter SZ is interpreted as an integer. If it is less than or
  72 ** equal to zero, then this function returns a copy of X. Or, if
  73 ** SZ is equal to the size of X when interpreted as a blob, also
  74 ** return a copy of X. Otherwise, decompress blob X using zlib
  75 ** utility function uncompress() and return the results (another
  76 ** blob).
  77 */
  78 static void sqlarUncompressFunc(
  79   sqlite3_context *context,
  80   int argc,
  81   sqlite3_value **argv
  82 ){
  83   uLong nData;
  84   sqlite3_int64 sz;
  85
  86   assert( argc==2 );
  87   sz = sqlite3_value_int(argv[1]);
  88
  89   if( sz<=0 || sz==(nData = sqlite3_value_bytes(argv[0])) ){
  90     sqlite3_result_value(context, argv[0]);
  91   }else{
  92     uLongf szf = sz;
  93     const Bytef *pData= sqlite3_value_blob(argv[0]);
  94     Bytef *pOut = sqlite3_malloc(sz);
  95     if( pOut==0 ){
  96       sqlite3_result_error_nomem(context);
  97     }else if( Z_OK!=uncompress(pOut, &szf, pData, nData) ){
  98       sqlite3_result_error(context, "error in uncompress()", -1);
  99     }else{
 100       sqlite3_result_blob(context, pOut, szf, SQLITE_TRANSIENT);
 101     }
 102     sqlite3_free(pOut);
 103   }
 104 }
 105
 106 #ifdef _WIN32
 107 __declspec(dllexport)
 108 #endif
 109 int sqlite3_sqlar_init(
 110   sqlite3 *db,
 111   char **pzErrMsg,
 112   const sqlite3_api_routines *pApi
 113 ){
 114   int rc = SQLITE_OK;
 115   SQLITE_EXTENSION_INIT2(pApi);
 116   (void)pzErrMsg;  /* Unused parameter */
 117   rc = sqlite3_create_function(db, "sqlar_compress", 1,
 118                                SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
 119                                sqlarCompressFunc, 0, 0);
 120   if( rc==SQLITE_OK ){
 121     rc = sqlite3_create_function(db, "sqlar_uncompress", 2,
 122                                  SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
 123                                  sqlarUncompressFunc, 0, 0);
 124   }
 125   return rc;
 126 }