ext/misc/compress.c

   1 /*
   2 ** 2014-06-13
   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 ** This SQLite extension implements SQL compression functions
  14 ** compress() and uncompress() using ZLIB.
  15 */
  16 #include "sqlite3ext.h"
  17 SQLITE_EXTENSION_INIT1
  18 #include <zlib.h>
  19
  20 /*
  21 ** Implementation of the "compress(X)" SQL function.  The input X is
  22 ** compressed using zLib and the output is returned.
  23 **
  24 ** The output is a BLOB that begins with a variable-length integer that
  25 ** is the input size in bytes (the size of X before compression).  The
  26 ** variable-length integer is implemented as 1 to 5 bytes.  There are
  27 ** seven bits per integer stored in the lower seven bits of each byte.
  28 ** More significant bits occur first.  The most significant bit (0x80)
  29 ** is a flag to indicate the end of the integer.
  30 **
  31 ** This function, SQLAR, and ZIP all use the same "deflate" compression
  32 ** algorithm, but each is subtly different:
  33 **
  34 **   *  ZIP uses raw deflate.
  35 **
  36 **   *  SQLAR uses the "zlib format" which is raw deflate with a two-byte
  37 **      algorithm-identification header and a four-byte checksum at the end.
  38 **
  39 **   *  This utility uses the "zlib format" like SQLAR, but adds the variable-
  40 **      length integer uncompressed size value at the beginning.
  41 **
  42 ** This function might be extended in the future to support compression
  43 ** formats other than deflate, by providing a different algorithm-id
  44 ** mark following the variable-length integer size parameter.
  45 */
  46 static void compressFunc(
  47   sqlite3_context *context,
  48   int argc,
  49   sqlite3_value **argv
  50 ){
  51   const unsigned char *pIn;
  52   unsigned char *pOut;
  53   unsigned int nIn;
  54   unsigned long int nOut;
  55   unsigned char x[8];
  56   int rc;
  57   int i, j;
  58
  59   pIn = sqlite3_value_blob(argv[0]);
  60   nIn = sqlite3_value_bytes(argv[0]);
  61   nOut = 13 + nIn + (nIn+999)/1000;
  62   pOut = sqlite3_malloc( nOut+5 );
  63   for(i=4; i>=0; i--){
  64     x[i] = (nIn >> (7*(4-i)))&0x7f;
  65   }
  66   for(i=0; i<4 && x[i]==0; i++){}
  67   for(j=0; i<=4; i++, j++) pOut[j] = x[i];
  68   pOut[j-1] |= 0x80;
  69   rc = compress(&pOut[j], &nOut, pIn, nIn);
  70   if( rc==Z_OK ){
  71     sqlite3_result_blob(context, pOut, nOut+j, sqlite3_free);
  72   }else{
  73     sqlite3_free(pOut);
  74   }
  75 }
  76
  77 /*
  78 ** Implementation of the "uncompress(X)" SQL function.  The argument X
  79 ** is a blob which was obtained from compress(Y).  The output will be
  80 ** the value Y.
  81 */
  82 static void uncompressFunc(
  83   sqlite3_context *context,
  84   int argc,
  85   sqlite3_value **argv
  86 ){
  87   const unsigned char *pIn;
  88   unsigned char *pOut;
  89   unsigned int nIn;
  90   unsigned long int nOut;
  91   int rc;
  92   int i;
  93
  94   pIn = sqlite3_value_blob(argv[0]);
  95   nIn = sqlite3_value_bytes(argv[0]);
  96   nOut = 0;
  97   for(i=0; i<nIn && i<5; i++){
  98     nOut = (nOut<<7) | (pIn[i]&0x7f);
  99     if( (pIn[i]&0x80)!=0 ){ i++; break; }
 100   }
 101   pOut = sqlite3_malloc( nOut+1 );
 102   rc = uncompress(pOut, &nOut, &pIn[i], nIn-i);
 103   if( rc==Z_OK ){
 104     sqlite3_result_blob(context, pOut, nOut, sqlite3_free);
 105   }else{
 106     sqlite3_free(pOut);
 107   }
 108 }
 109
 110
 111 #ifdef _WIN32
 112 __declspec(dllexport)
 113 #endif
 114 int sqlite3_compress_init(
 115   sqlite3 *db,
 116   char **pzErrMsg,
 117   const sqlite3_api_routines *pApi
 118 ){
 119   int rc = SQLITE_OK;
 120   SQLITE_EXTENSION_INIT2(pApi);
 121   (void)pzErrMsg;  /* Unused parameter */
 122   rc = sqlite3_create_function(db, "compress", 1, SQLITE_UTF8, 0,
 123                                compressFunc, 0, 0);
 124   if( rc==SQLITE_OK ){
 125     rc = sqlite3_create_function(db, "uncompress", 1, SQLITE_UTF8, 0,
 126                                  uncompressFunc, 0, 0);
 127   }
 128   return rc;
 129 }