/*
** 2014-06-13
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
******************************************************************************
**
** This SQLite extension implements SQL compression functions
** compress() and uncompress() using ZLIB.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <zlib.h>
/*
** Implementation of the "compress(X)" SQL function. The input X is
** compressed using zLib and the output is returned.
**
** The output is a BLOB that begins with a variable-length integer that
** is the input size in bytes (the size of X before compression). The
** variable-length integer is implemented as 1 to 5 bytes. There are
** seven bits per integer stored in the lower seven bits of each byte.
** More significant bits occur first. The most significant bit (0x80)
** is a flag to indicate the end of the integer.
**
** This function, SQLAR, and ZIP all use the same "deflate" compression
** algorithm, but each is subtly different:
**
** * ZIP uses raw deflate.
**
** * SQLAR uses the "zlib format" which is raw deflate with a two-byte
** algorithm-identification header and a four-byte checksum at the end.
**
** * This utility uses the "zlib format" like SQLAR, but adds the variable-
** length integer uncompressed size value at the beginning.
**
** This function might be extended in the future to support compression
** formats other than deflate, by providing a different algorithm-id
** mark following the variable-length integer size parameter.
*/
static void compressFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
const unsigned char *pIn;
unsigned char *pOut;
unsigned int nIn;
unsigned long int nOut;
unsigned char x[8];
int rc;
int i, j;
pIn = sqlite3_value_blob(argv[0]);
nIn = sqlite3_value_bytes(argv[0]);
nOut = 13 + nIn + (nIn+999)/1000;
pOut = sqlite3_malloc( nOut+5 );
for(i=4; i>=0; i--){
x[i] = (nIn >> (7*(4-i)))&0x7f;
}
for(i=0; i<4 && x[i]==0; i++){}
for(j=0; i<=4; i++, j++) pOut[j] = x[i];
pOut[j-1] |= 0x80;
rc = compress(&pOut[j], &nOut, pIn, nIn);
if( rc==Z_OK ){
sqlite3_result_blob(context, pOut, nOut+j, sqlite3_free);
}else{
sqlite3_free(pOut);
}
}
/*
** Implementation of the "uncompress(X)" SQL function. The argument X
** is a blob which was obtained from compress(Y). The output will be
** the value Y.
*/
static void uncompressFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
const unsigned char *pIn;
unsigned char *pOut;
unsigned int nIn;
unsigned long int nOut;
int rc;
int i;
pIn = sqlite3_value_blob(argv[0]);
nIn = sqlite3_value_bytes(argv[0]);
nOut = 0;
for(i=0; i<nIn && i<5; i++){
nOut = (nOut<<7) | (pIn[i]&0x7f);
if( (pIn[i]&0x80)!=0 ){ i++; break; }
}
pOut = sqlite3_malloc( nOut+1 );
rc = uncompress(pOut, &nOut, &pIn[i], nIn-i);
if( rc==Z_OK ){
sqlite3_result_blob(context, pOut, nOut, sqlite3_free);
}else{
sqlite3_free(pOut);
}
}
#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_compress_init(
sqlite3 *db,
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
(void)pzErrMsg; /* Unused parameter */
rc = sqlite3_create_function(db, "compress", 1,
SQLITE_UTF8 | SQLITE_INNOCUOUS,
0, compressFunc, 0, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(db, "uncompress", 1,
SQLITE_UTF8 | SQLITE_INNOCUOUS | SQLITE_DETERMINISTIC,
0, uncompressFunc, 0, 0);
}
return rc;
}