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