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Overview
Comment: | Add the fossildelta.c extension in ext/misc with implementations of the Fossil delta functions. |
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b80cafa6f8a5c6ff1dc9efd2f670777a |
User & Date: | drh 2019-02-19 18:39:16.475 |
Context
2019-02-19
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20:19 | Add the delta_parse(DELTA) table-valued function to the fossildelta extension. (check-in: d91fcc267b user: drh tags: trunk) | |
18:39 | Add the fossildelta.c extension in ext/misc with implementations of the Fossil delta functions. (check-in: b80cafa6f8 user: drh tags: trunk) | |
17:45 | Fix a potential memory leak in RBU if the rbu_fossil_delta() SQL function is misused. Misuse never happens in a working RBU system, so this is not a particularly important fix. (check-in: 12517d1b15 user: drh tags: trunk) | |
Changes
Added ext/misc/fossildelta.c.
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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 the delta functions used by Fossil. */ #include <string.h> #include <assert.h> #include <stdlib.h> #include "sqlite3ext.h" SQLITE_EXTENSION_INIT1 /* ** The "u32" type must be an unsigned 32-bit integer. Adjust this */ typedef unsigned int u32; /* ** Must be a 16-bit value */ typedef short int s16; typedef unsigned short int u16; /* ** The width of a hash window in bytes. The algorithm only works if this ** is a power of 2. */ #define NHASH 16 /* ** The current state of the rolling hash. ** ** z[] holds the values that have been hashed. z[] is a circular buffer. ** z[i] is the first entry and z[(i+NHASH-1)%NHASH] is the last entry of ** the window. ** ** Hash.a is the sum of all elements of hash.z[]. Hash.b is a weighted ** sum. Hash.b is z[i]*NHASH + z[i+1]*(NHASH-1) + ... + z[i+NHASH-1]*1. ** (Each index for z[] should be module NHASH, of course. The %NHASH operator ** is omitted in the prior expression for brevity.) */ typedef struct hash hash; struct hash { u16 a, b; /* Hash values */ u16 i; /* Start of the hash window */ char z[NHASH]; /* The values that have been hashed */ }; /* ** Initialize the rolling hash using the first NHASH characters of z[] */ static void hash_init(hash *pHash, const char *z){ u16 a, b, i; a = b = z[0]; for(i=1; i<NHASH; i++){ a += z[i]; b += a; } memcpy(pHash->z, z, NHASH); pHash->a = a & 0xffff; pHash->b = b & 0xffff; pHash->i = 0; } /* ** Advance the rolling hash by a single character "c" */ static void hash_next(hash *pHash, int c){ u16 old = pHash->z[pHash->i]; pHash->z[pHash->i] = c; pHash->i = (pHash->i+1)&(NHASH-1); pHash->a = pHash->a - old + c; pHash->b = pHash->b - NHASH*old + pHash->a; } /* ** Return a 32-bit hash value */ static u32 hash_32bit(hash *pHash){ return (pHash->a & 0xffff) | (((u32)(pHash->b & 0xffff))<<16); } /* ** Compute a hash on NHASH bytes. ** ** This routine is intended to be equivalent to: ** hash h; ** hash_init(&h, zInput); ** return hash_32bit(&h); */ static u32 hash_once(const char *z){ u16 a, b, i; a = b = z[0]; for(i=1; i<NHASH; i++){ a += z[i]; b += a; } return a | (((u32)b)<<16); } /* ** Write an base-64 integer into the given buffer. */ static void putInt(unsigned int v, char **pz){ static const char zDigits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~"; /* 123456789 123456789 123456789 123456789 123456789 123456789 123 */ int i, j; char zBuf[20]; if( v==0 ){ *(*pz)++ = '0'; return; } for(i=0; v>0; i++, v>>=6){ zBuf[i] = zDigits[v&0x3f]; } for(j=i-1; j>=0; j--){ *(*pz)++ = zBuf[j]; } } /* ** Read bytes from *pz and convert them into a positive integer. When ** finished, leave *pz pointing to the first character past the end of ** the integer. The *pLen parameter holds the length of the string ** in *pz and is decremented once for each character in the integer. */ static unsigned int getInt(const char **pz, int *pLen){ static const signed char zValue[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, -1, -1, -1, -1, 36, -1, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, -1, -1, -1, 63, -1, }; unsigned int v = 0; int c; unsigned char *z = (unsigned char*)*pz; unsigned char *zStart = z; while( (c = zValue[0x7f&*(z++)])>=0 ){ v = (v<<6) + c; } z--; *pLen -= z - zStart; *pz = (char*)z; return v; } /* ** Return the number digits in the base-64 representation of a positive integer */ static int digit_count(int v){ unsigned int i, x; for(i=1, x=64; v>=x; i++, x <<= 6){} return i; } #ifdef __GNUC__ # define GCC_VERSION (__GNUC__*1000000+__GNUC_MINOR__*1000+__GNUC_PATCHLEVEL__) #else # define GCC_VERSION 0 #endif /* ** Compute a 32-bit big-endian checksum on the N-byte buffer. If the ** buffer is not a multiple of 4 bytes length, compute the sum that would ** have occurred if the buffer was padded with zeros to the next multiple ** of four bytes. */ static unsigned int checksum(const char *zIn, size_t N){ static const int byteOrderTest = 1; const unsigned char *z = (const unsigned char *)zIn; const unsigned char *zEnd = (const unsigned char*)&zIn[N&~3]; unsigned sum = 0; assert( (z - (const unsigned char*)0)%4==0 ); /* Four-byte alignment */ if( 0==*(char*)&byteOrderTest ){ /* This is a big-endian machine */ while( z<zEnd ){ sum += *(unsigned*)z; z += 4; } }else{ /* A little-endian machine */ #if GCC_VERSION>=4003000 while( z<zEnd ){ sum += __builtin_bswap32(*(unsigned*)z); z += 4; } #elif defined(_MSC_VER) && _MSC_VER>=1300 while( z<zEnd ){ sum += _byteswap_ulong(*(unsigned*)z); z += 4; } #else unsigned sum0 = 0; unsigned sum1 = 0; unsigned sum2 = 0; while(N >= 16){ sum0 += ((unsigned)z[0] + z[4] + z[8] + z[12]); sum1 += ((unsigned)z[1] + z[5] + z[9] + z[13]); sum2 += ((unsigned)z[2] + z[6] + z[10]+ z[14]); sum += ((unsigned)z[3] + z[7] + z[11]+ z[15]); z += 16; N -= 16; } while(N >= 4){ sum0 += z[0]; sum1 += z[1]; sum2 += z[2]; sum += z[3]; z += 4; N -= 4; } sum += (sum2 << 8) + (sum1 << 16) + (sum0 << 24); #endif } switch(N&3){ case 3: sum += (z[2] << 8); case 2: sum += (z[1] << 16); case 1: sum += (z[0] << 24); default: ; } return sum; } /* ** Create a new delta. ** ** The delta is written into a preallocated buffer, zDelta, which ** should be at least 60 bytes longer than the target file, zOut. ** The delta string will be NUL-terminated, but it might also contain ** embedded NUL characters if either the zSrc or zOut files are ** binary. This function returns the length of the delta string ** in bytes, excluding the final NUL terminator character. ** ** Output Format: ** ** The delta begins with a base64 number followed by a newline. This ** number is the number of bytes in the TARGET file. Thus, given a ** delta file z, a program can compute the size of the output file ** simply by reading the first line and decoding the base-64 number ** found there. The delta_output_size() routine does exactly this. ** ** After the initial size number, the delta consists of a series of ** literal text segments and commands to copy from the SOURCE file. ** A copy command looks like this: ** ** NNN@MMM, ** ** where NNN is the number of bytes to be copied and MMM is the offset ** into the source file of the first byte (both base-64). If NNN is 0 ** it means copy the rest of the input file. Literal text is like this: ** ** NNN:TTTTT ** ** where NNN is the number of bytes of text (base-64) and TTTTT is the text. ** ** The last term is of the form ** ** NNN; ** ** In this case, NNN is a 32-bit bigendian checksum of the output file ** that can be used to verify that the delta applied correctly. All ** numbers are in base-64. ** ** Pure text files generate a pure text delta. Binary files generate a ** delta that may contain some binary data. ** ** Algorithm: ** ** The encoder first builds a hash table to help it find matching ** patterns in the source file. 16-byte chunks of the source file ** sampled at evenly spaced intervals are used to populate the hash ** table. ** ** Next we begin scanning the target file using a sliding 16-byte ** window. The hash of the 16-byte window in the target is used to ** search for a matching section in the source file. When a match ** is found, a copy command is added to the delta. An effort is ** made to extend the matching section to regions that come before ** and after the 16-byte hash window. A copy command is only issued ** if the result would use less space that just quoting the text ** literally. Literal text is added to the delta for sections that ** do not match or which can not be encoded efficiently using copy ** commands. */ static int delta_create( const char *zSrc, /* The source or pattern file */ unsigned int lenSrc, /* Length of the source file */ const char *zOut, /* The target file */ unsigned int lenOut, /* Length of the target file */ char *zDelta /* Write the delta into this buffer */ ){ int i, base; char *zOrigDelta = zDelta; hash h; int nHash; /* Number of hash table entries */ int *landmark; /* Primary hash table */ int *collide; /* Collision chain */ int lastRead = -1; /* Last byte of zSrc read by a COPY command */ /* Add the target file size to the beginning of the delta */ putInt(lenOut, &zDelta); *(zDelta++) = '\n'; /* If the source file is very small, it means that we have no ** chance of ever doing a copy command. Just output a single ** literal segment for the entire target and exit. */ if( lenSrc<=NHASH ){ putInt(lenOut, &zDelta); *(zDelta++) = ':'; memcpy(zDelta, zOut, lenOut); zDelta += lenOut; putInt(checksum(zOut, lenOut), &zDelta); *(zDelta++) = ';'; return zDelta - zOrigDelta; } /* Compute the hash table used to locate matching sections in the ** source file. */ nHash = lenSrc/NHASH; collide = sqlite3_malloc64( (sqlite3_int64)nHash*2*sizeof(int) ); memset(collide, -1, nHash*2*sizeof(int)); landmark = &collide[nHash]; for(i=0; i<lenSrc-NHASH; i+=NHASH){ int hv = hash_once(&zSrc[i]) % nHash; collide[i/NHASH] = landmark[hv]; landmark[hv] = i/NHASH; } /* Begin scanning the target file and generating copy commands and ** literal sections of the delta. */ base = 0; /* We have already generated everything before zOut[base] */ while( base+NHASH<lenOut ){ int iSrc, iBlock; unsigned int bestCnt, bestOfst=0, bestLitsz=0; hash_init(&h, &zOut[base]); i = 0; /* Trying to match a landmark against zOut[base+i] */ bestCnt = 0; while( 1 ){ int hv; int limit = 250; hv = hash_32bit(&h) % nHash; iBlock = landmark[hv]; while( iBlock>=0 && (limit--)>0 ){ /* ** The hash window has identified a potential match against ** landmark block iBlock. But we need to investigate further. ** ** Look for a region in zOut that matches zSrc. Anchor the search ** at zSrc[iSrc] and zOut[base+i]. Do not include anything prior to ** zOut[base] or after zOut[outLen] nor anything after zSrc[srcLen]. ** ** Set cnt equal to the length of the match and set ofst so that ** zSrc[ofst] is the first element of the match. litsz is the number ** of characters between zOut[base] and the beginning of the match. ** sz will be the overhead (in bytes) needed to encode the copy ** command. Only generate copy command if the overhead of the ** copy command is less than the amount of literal text to be copied. */ int cnt, ofst, litsz; int j, k, x, y; int sz; int limitX; /* Beginning at iSrc, match forwards as far as we can. j counts ** the number of characters that match */ iSrc = iBlock*NHASH; y = base+i; limitX = ( lenSrc-iSrc <= lenOut-y ) ? lenSrc : iSrc + lenOut - y; for(x=iSrc; x<limitX; x++, y++){ if( zSrc[x]!=zOut[y] ) break; } j = x - iSrc - 1; /* Beginning at iSrc-1, match backwards as far as we can. k counts ** the number of characters that match */ for(k=1; k<iSrc && k<=i; k++){ if( zSrc[iSrc-k]!=zOut[base+i-k] ) break; } k--; /* Compute the offset and size of the matching region */ ofst = iSrc-k; cnt = j+k+1; litsz = i-k; /* Number of bytes of literal text before the copy */ /* sz will hold the number of bytes needed to encode the "insert" ** command and the copy command, not counting the "insert" text */ sz = digit_count(i-k)+digit_count(cnt)+digit_count(ofst)+3; if( cnt>=sz && cnt>bestCnt ){ /* Remember this match only if it is the best so far and it ** does not increase the file size */ bestCnt = cnt; bestOfst = iSrc-k; bestLitsz = litsz; } /* Check the next matching block */ iBlock = collide[iBlock]; } /* We have a copy command that does not cause the delta to be larger ** than a literal insert. So add the copy command to the delta. */ if( bestCnt>0 ){ if( bestLitsz>0 ){ /* Add an insert command before the copy */ putInt(bestLitsz,&zDelta); *(zDelta++) = ':'; memcpy(zDelta, &zOut[base], bestLitsz); zDelta += bestLitsz; base += bestLitsz; } base += bestCnt; putInt(bestCnt, &zDelta); *(zDelta++) = '@'; putInt(bestOfst, &zDelta); *(zDelta++) = ','; if( bestOfst + bestCnt -1 > lastRead ){ lastRead = bestOfst + bestCnt - 1; } bestCnt = 0; break; } /* If we reach this point, it means no match is found so far */ if( base+i+NHASH>=lenOut ){ /* We have reached the end of the file and have not found any ** matches. Do an "insert" for everything that does not match */ putInt(lenOut-base, &zDelta); *(zDelta++) = ':'; memcpy(zDelta, &zOut[base], lenOut-base); zDelta += lenOut-base; base = lenOut; break; } /* Advance the hash by one character. Keep looking for a match */ hash_next(&h, zOut[base+i+NHASH]); i++; } } /* Output a final "insert" record to get all the text at the end of ** the file that does not match anything in the source file. */ if( base<lenOut ){ putInt(lenOut-base, &zDelta); *(zDelta++) = ':'; memcpy(zDelta, &zOut[base], lenOut-base); zDelta += lenOut-base; } /* Output the final checksum record. */ putInt(checksum(zOut, lenOut), &zDelta); *(zDelta++) = ';'; sqlite3_free(collide); return zDelta - zOrigDelta; } /* ** Return the size (in bytes) of the output from applying ** a delta. ** ** This routine is provided so that an procedure that is able ** to call delta_apply() can learn how much space is required ** for the output and hence allocate nor more space that is really ** needed. */ static int delta_output_size(const char *zDelta, int lenDelta){ int size; size = getInt(&zDelta, &lenDelta); if( *zDelta!='\n' ){ /* ERROR: size integer not terminated by "\n" */ return -1; } return size; } /* ** Apply a delta. ** ** The output buffer should be big enough to hold the whole output ** file and a NUL terminator at the end. The delta_output_size() ** routine will determine this size for you. ** ** The delta string should be null-terminated. But the delta string ** may contain embedded NUL characters (if the input and output are ** binary files) so we also have to pass in the length of the delta in ** the lenDelta parameter. ** ** This function returns the size of the output file in bytes (excluding ** the final NUL terminator character). Except, if the delta string is ** malformed or intended for use with a source file other than zSrc, ** then this routine returns -1. ** ** Refer to the delta_create() documentation above for a description ** of the delta file format. */ static int delta_apply( const char *zSrc, /* The source or pattern file */ int lenSrc, /* Length of the source file */ const char *zDelta, /* Delta to apply to the pattern */ int lenDelta, /* Length of the delta */ char *zOut /* Write the output into this preallocated buffer */ ){ unsigned int limit; unsigned int total = 0; #ifdef FOSSIL_ENABLE_DELTA_CKSUM_TEST char *zOrigOut = zOut; #endif limit = getInt(&zDelta, &lenDelta); if( *zDelta!='\n' ){ /* ERROR: size integer not terminated by "\n" */ return -1; } zDelta++; lenDelta--; while( *zDelta && lenDelta>0 ){ unsigned int cnt, ofst; cnt = getInt(&zDelta, &lenDelta); switch( zDelta[0] ){ case '@': { zDelta++; lenDelta--; ofst = getInt(&zDelta, &lenDelta); if( lenDelta>0 && zDelta[0]!=',' ){ /* ERROR: copy command not terminated by ',' */ return -1; } zDelta++; lenDelta--; total += cnt; if( total>limit ){ /* ERROR: copy exceeds output file size */ return -1; } if( ofst+cnt > lenSrc ){ /* ERROR: copy extends past end of input */ return -1; } memcpy(zOut, &zSrc[ofst], cnt); zOut += cnt; break; } case ':': { zDelta++; lenDelta--; total += cnt; if( total>limit ){ /* ERROR: insert command gives an output larger than predicted */ return -1; } if( cnt>lenDelta ){ /* ERROR: insert count exceeds size of delta */ return -1; } memcpy(zOut, zDelta, cnt); zOut += cnt; zDelta += cnt; lenDelta -= cnt; break; } case ';': { zDelta++; lenDelta--; zOut[0] = 0; #ifdef FOSSIL_ENABLE_DELTA_CKSUM_TEST if( cnt!=checksum(zOrigOut, total) ){ /* ERROR: bad checksum */ return -1; } #endif if( total!=limit ){ /* ERROR: generated size does not match predicted size */ return -1; } return total; } default: { /* ERROR: unknown delta operator */ return -1; } } } /* ERROR: unterminated delta */ return -1; } /* ** Analyze a delta. Figure out the total number of bytes copied from ** source to target, and the total number of bytes inserted by the delta, ** and return both numbers. */ static int delta_analyze( const char *zDelta, /* Delta to apply to the pattern */ int lenDelta, /* Length of the delta */ int *pnCopy, /* OUT: Number of bytes copied */ int *pnInsert /* OUT: Number of bytes inserted */ ){ unsigned int nInsert = 0; unsigned int nCopy = 0; (void)getInt(&zDelta, &lenDelta); if( *zDelta!='\n' ){ /* ERROR: size integer not terminated by "\n" */ return -1; } zDelta++; lenDelta--; while( *zDelta && lenDelta>0 ){ unsigned int cnt; cnt = getInt(&zDelta, &lenDelta); switch( zDelta[0] ){ case '@': { zDelta++; lenDelta--; (void)getInt(&zDelta, &lenDelta); if( lenDelta>0 && zDelta[0]!=',' ){ /* ERROR: copy command not terminated by ',' */ return -1; } zDelta++; lenDelta--; nCopy += cnt; break; } case ':': { zDelta++; lenDelta--; nInsert += cnt; if( cnt>lenDelta ){ /* ERROR: insert count exceeds size of delta */ return -1; } zDelta += cnt; lenDelta -= cnt; break; } case ';': { *pnCopy = nCopy; *pnInsert = nInsert; return 0; } default: { /* ERROR: unknown delta operator */ return -1; } } } /* ERROR: unterminated delta */ return -1; } /* ** SQL functions: fossildelta_create(X,Y) ** ** Return a delta for carrying X into Y. */ static void deltaCreateFunc( sqlite3_context *context, int argc, sqlite3_value **argv ){ const char *aOrig; int nOrig; /* old blob */ const char *aNew; int nNew; /* new blob */ char *aOut; int nOut; /* output delta */ assert( argc==2 ); if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return; if( sqlite3_value_type(argv[1])==SQLITE_NULL ) return; nOrig = sqlite3_value_bytes(argv[0]); aOrig = (const char*)sqlite3_value_blob(argv[0]); nNew = sqlite3_value_bytes(argv[1]); aNew = (const char*)sqlite3_value_blob(argv[1]); aOut = sqlite3_malloc64(nNew+70); if( aOut==0 ){ sqlite3_result_error_nomem(context); }else{ nOut = delta_create(aOrig, nOrig, aNew, nNew, aOut); if( nOut<0 ){ sqlite3_free(aOut); sqlite3_result_error(context, "cannot create fossil delta", -1); }else{ sqlite3_result_blob(context, aOut, nOut, sqlite3_free); } } } /* ** SQL functions: fossildelta_apply(X,D) ** ** Return the result of applying delta D to input X. */ static void deltaApplyFunc( sqlite3_context *context, int argc, sqlite3_value **argv ){ const char *aOrig; int nOrig; /* The X input */ const char *aDelta; int nDelta; /* The input delta (D) */ char *aOut; int nOut, nOut2; /* The output */ assert( argc==2 ); if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return; if( sqlite3_value_type(argv[1])==SQLITE_NULL ) return; nOrig = sqlite3_value_bytes(argv[0]); aOrig = (const char*)sqlite3_value_blob(argv[0]); nDelta = sqlite3_value_bytes(argv[1]); aDelta = (const char*)sqlite3_value_blob(argv[1]); /* Figure out the size of the output */ nOut = delta_output_size(aDelta, nDelta); if( nOut<0 ){ sqlite3_result_error(context, "corrupt fossil delta", -1); return; } aOut = sqlite3_malloc64((sqlite3_int64)nOut+1); if( aOut==0 ){ sqlite3_result_error_nomem(context); }else{ nOut2 = delta_apply(aOrig, nOrig, aDelta, nDelta, aOut); if( nOut2!=nOut ){ sqlite3_free(aOut); sqlite3_result_error(context, "corrupt fossil delta", -1); }else{ sqlite3_result_blob(context, aOut, nOut, sqlite3_free); } } } /* ** SQL functions: fossildelta_output_size(D) ** ** Return the size of the output that results from applying delta D. */ static void deltaOutputSizeFunc( sqlite3_context *context, int argc, sqlite3_value **argv ){ const char *aDelta; int nDelta; /* The input delta (D) */ int nOut; /* Size of output */ assert( argc==1 ); if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return; nDelta = sqlite3_value_bytes(argv[0]); aDelta = (const char*)sqlite3_value_blob(argv[0]); /* Figure out the size of the output */ nOut = delta_output_size(aDelta, nDelta); if( nOut<0 ){ sqlite3_result_error(context, "corrupt fossil delta", -1); return; }else{ sqlite3_result_int(context, nOut); } } #ifdef _WIN32 __declspec(dllexport) #endif int sqlite3_fossildelta_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, "delta_create", 2, SQLITE_UTF8, 0, deltaCreateFunc, 0, 0); if( rc==SQLITE_OK ){ rc = sqlite3_create_function(db, "delta_apply", 2, SQLITE_UTF8, 0, deltaApplyFunc, 0, 0); } if( rc==SQLITE_OK ){ rc = sqlite3_create_function(db, "delta_output_size", 1, SQLITE_UTF8, 0, deltaOutputSizeFunc, 0, 0); } return rc; } |