/* gznorm.c -- normalize a gzip stream * Copyright (C) 2018 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h
* Version 1.0 7 Oct 2018 Mark Adler */
// gznorm takes a gzip stream, potentially containing multiple members, and // converts it to a gzip stream with a single member. In addition the gzip // header is normalized, removing the file name and time stamp, and setting the // other header contents (XFL, OS) to fixed values. gznorm does not recompress // the data, so it is fast, but no advantage is gained from the history that // could be available across member boundaries.
// printf to an allocated string. Return the string, or NULL if the printf or // allocation fails.
local char *aprintf(char *fmt, ...) { // Get the length of the result of the printf.
va_list args;
va_start(args, fmt); int len = vsnprintf(NULL, 0, fmt, args);
va_end(args); if (len < 0) return NULL;
// Allocate the required space and printf to it. char *str = malloc(len + 1); if (str == NULL) return NULL;
va_start(args, fmt);
vsnprintf(str, len + 1, fmt, args);
va_end(args); return str;
}
// Return with an error, putting an allocated error message in *err. Doing an // inflateEnd() on an already ended state, or one with state set to Z_NULL, is // permitted. #define BYE(...) \ do { \
inflateEnd(&strm); \
*err = aprintf(__VA_ARGS__); \ return 1; \
} while (0)
// Chunk size for buffered reads and for decompression. Twice this many bytes // will be allocated on the stack by gzip_normalize(). Must fit in an unsigned. #define CHUNK 16384
// Read a gzip stream from in and write an equivalent normalized gzip stream to // out. If given no input, an empty gzip stream will be written. If successful, // 0 is returned, and *err is set to NULL. On error, 1 is returned, where the // details of the error are returned in *err, a pointer to an allocated string. // // The input may be a stream with multiple gzip members, which is converted to // a single gzip member on the output. Each gzip member is decompressed at the // level of deflate blocks. This enables clearing the last-block bit, shifting // the compressed data to concatenate to the previous member's compressed data, // which can end at an arbitrary bit boundary, and identifying stored blocks in // order to resynchronize those to byte boundaries. The deflate compressed data // is terminated with a 10-bit empty fixed block. If any members on the input // end with a 10-bit empty fixed block, then that block is excised from the // stream. This avoids appending empty fixed blocks for every normalization, // and assures that gzip_normalize applied a second time will not change the // input. The pad bits after stored block headers and after the final deflate // block are all forced to zeros.
local int gzip_normalize(FILE *in, FILE *out, char **err) { // initialize the inflate engine to process a gzip member
z_stream strm;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;
strm.avail_in = 0;
strm.next_in = Z_NULL; if (inflateInit2(&strm, 15 + 16) != Z_OK)
BYE("out of memory");
// State while processing the input gzip stream. enum { // BETWEEN -> HEAD -> BLOCK -> TAIL -> BETWEEN -> ...
BETWEEN, // between gzip members (must end in this state)
HEAD, // reading a gzip header
BLOCK, // reading deflate blocks
TAIL // reading a gzip trailer
} state = BETWEEN; // current component being processed unsignedlong crc = 0; // accumulated CRC of uncompressed data unsignedlong len = 0; // accumulated length of uncompressed data unsignedlong buf = 0; // deflate stream bit buffer of num bits int num = 0; // number of bits in buf (at bottom)
// Write a canonical gzip header (no mod time, file name, comment, extra // block, or extra flags, and OS is marked as unknown).
fwrite("\x1f\x8b\x08\0\0\0\0\0\0\xff", 1, 10, out);
// Process the gzip stream from in until reaching the end of the input, // encountering invalid input, or experiencing an i/o error. int more; // true if not at the end of the input do { // State inside this loop. unsignedchar *put; // next input buffer location to process int prev; // number of bits from previous block in // the bit buffer, or -1 if not at the // start of a block unsignedlonglong memb; // uncompressed length of member
size_t tail; // number of trailer bytes read (0..8) unsignedlong part; // accumulated trailer component
// Get the next chunk of input from in. unsignedchar dat[CHUNK];
strm.avail_in = fread(dat, 1, CHUNK, in); if (strm.avail_in == 0) break;
more = strm.avail_in == CHUNK;
strm.next_in = put = dat;
// Run that chunk of input through the inflate engine to exhaustion. do { // At this point it is assured that strm.avail_in > 0.
// Inflate until the end of a gzip component (header, deflate // block, trailer) is reached, or until all of the chunk is // consumed. The resulting decompressed data is discarded, though // the total size of the decompressed data in each member is // tracked, for the calculation of the total CRC. do { // inflate and handle any errors unsignedchar scrap[CHUNK];
strm.avail_out = CHUNK;
strm.next_out = scrap; int ret = inflate(&strm, Z_BLOCK); if (ret == Z_MEM_ERROR)
BYE("out of memory"); if (ret == Z_DATA_ERROR)
BYE("input invalid: %s", strm.msg); if (ret != Z_OK && ret != Z_BUF_ERROR && ret != Z_STREAM_END)
BYE("internal error");
// Update the number of uncompressed bytes generated in this // member. The actual count (not modulo 2^32) is required to // correctly compute the total CRC. unsigned got = CHUNK - strm.avail_out;
memb += got; if (memb < got)
BYE("overflow error");
// Continue to process this chunk until it is consumed, or // until the end of a component (header, deflate block, or // trailer) is reached.
} while (strm.avail_out == 0 && (strm.data_type & 0x80) == 0);
// Since strm.avail_in was > 0 for the inflate call, some input was // just consumed. It is therefore assured that put < strm.next_in.
// Disposition the consumed component or part of a component. switch (state) { case BETWEEN:
state = HEAD; // Fall through to HEAD when some or all of the header is // processed.
case HEAD: // Discard the header. if (strm.data_type & 0x80) { // End of header reached -- deflate blocks follow.
put = strm.next_in;
prev = num;
memb = 0;
state = BLOCK;
} break;
case BLOCK: // Copy the deflate stream to the output, but with the // last-block-bit cleared. Re-synchronize stored block // headers to the output byte boundaries. The bytes at // put..strm.next_in-1 is the compressed data that has been // processed and is ready to be copied to the output.
// At this point, it is assured that new compressed data is // available, i.e., put < strm.next_in. If prev is -1, then // that compressed data starts in the middle of a deflate // block. If prev is not -1, then the bits in the bit // buffer, possibly combined with the bits in *put, contain // the three-bit header of the new deflate block. In that // case, prev is the number of bits from the previous block // that remain in the bit buffer. Since num is the number // of bits in the bit buffer, we have that num - prev is // the number of bits from the new block currently in the // bit buffer.
// If strm.data_type & 0xc0 is 0x80, then the last byte of // the available compressed data includes the last bits of // the end of a deflate block. In that case, that last byte // also has strm.data_type & 0x1f bits of the next deflate // block, in the range 0..7. If strm.data_type & 0xc0 is // 0xc0, then the last byte of the compressed data is the // end of the deflate stream, followed by strm.data_type & // 0x1f pad bits, also in the range 0..7.
// Set bits to the number of bits not yet consumed from the // last byte. If we are at the end of the block, bits is // either the number of bits in the last byte belonging to // the next block, or the number of pad bits after the // final block. In either of those cases, bits is in the // range 0..7.
; // (required due to C syntax oddity) int bits = strm.data_type & 0x1f;
if (prev != -1) { // We are at the start of a new block. Clear the last // block bit, and check for special cases. If it is a // stored block, then emit the header and pad to the // next byte boundary. If it is a final, empty fixed // block, then excise it.
// Some or all of the three header bits for this block // may already be in the bit buffer. Load any remaining // header bits into the bit buffer. if (num - prev < 3) {
buf += (unsignedlong)*put++ << num;
num += 8;
}
// Set last to have a 1 in the position of the last // block bit in the bit buffer. unsignedlong last = (unsignedlong)1 << prev;
if (((buf >> prev) & 7) == 3) { // This is a final fixed block. Load at least ten // bits from this block, including the header, into // the bit buffer. We already have at least three, // so at most one more byte needs to be loaded. if (num - prev < 10) { if (put == strm.next_in) // Need to go get and process more input. // We'll end up back here to finish this. break;
buf += (unsignedlong)*put++ << num;
num += 8;
} if (((buf >> prev) & 0x3ff) == 3) { // That final fixed block is empty. Delete it // to avoid adding an empty block every time a // gzip stream is normalized.
num = prev;
buf &= last - 1; // zero the pad bits
}
} elseif (((buf >> prev) & 6) == 0) { // This is a stored block. Flush to the next // byte boundary after the three-bit header.
num = (prev + 10) & ~7;
buf &= last - 1; // zero the pad bits
}
// Clear the last block bit.
buf &= ~last;
// Write out complete bytes in the bit buffer. while (num >= 8) {
putc(buf, out);
buf >>= 8;
num -= 8;
}
// If no more bytes left to process, then we have // consumed the byte that had bits from the next block. if (put == strm.next_in)
bits = 0;
}
// We are done handling the deflate block header. Now copy // all or almost all of the remaining compressed data that // has been processed so far. Don't copy one byte at the // end if it contains bits from the next deflate block or // pad bits at the end of a deflate block.
// mix is 1 if we are at the end of a deflate block, and if // some of the bits in the last byte follow this block. mix // is 0 if we are in the middle of a deflate block, if the // deflate block ended on a byte boundary, or if all of the // compressed data processed so far has been consumed. int mix = (strm.data_type & 0x80) && bits;
// Copy all of the processed compressed data to the output, // except for the last byte if it contains bits from the // next deflate block or pad bits at the end of the deflate // stream. Copy the data after shifting in num bits from // buf in front of it, leaving num bits from the end of the // compressed data in buf when done. unsignedchar *end = strm.next_in - mix; if (put < end) { if (num) // Insert num bits from buf before the data being // copied. do {
buf += (unsigned)(*put++) << num;
putc(buf, out);
buf >>= 8;
} while (put < end); else { // No shifting needed -- write directly.
fwrite(put, 1, end - put, out);
put = end;
}
}
// Process the last processed byte if it wasn't written. if (mix) { // Load the last byte into the bit buffer.
buf += (unsigned)(*put++) << num;
num += 8;
if (strm.data_type & 0x40) { // We are at the end of the deflate stream and // there are bits pad bits. Discard the pad bits // and write a byte to the output, if available. // Leave the num bits left over in buf to prepend // to the next deflate stream.
num -= bits; if (num >= 8) {
putc(buf, out);
num -= 8;
buf >>= 8;
}
// Force the pad bits in the bit buffer to zeros.
buf &= ((unsignedlong)1 << num) - 1;
// Don't need to set prev here since going to TAIL.
} else // At the end of an internal deflate block. Leave // the last byte in the bit buffer to examine on // the next entry to BLOCK, when more bits from the // next block will be available.
prev = num - bits; // number of bits in buffer // from current block
}
// Don't have a byte left over, so we are in the middle of // a deflate block, or the deflate block ended on a byte // boundary. Set prev appropriately for the next entry into // BLOCK. elseif (strm.data_type & 0x80) // The block ended on a byte boundary, so no header // bits are in the bit buffer.
prev = num; else // In the middle of a deflate block, so no header here.
prev = -1;
// Check for the end of the deflate stream. if ((strm.data_type & 0xc0) == 0xc0) { // That ends the deflate stream on the input side, the // pad bits were discarded, and any remaining bits from // the last block in the stream are saved in the bit // buffer to prepend to the next stream. Process the // gzip trailer next.
tail = 0;
part = 0;
state = TAIL;
} break;
case TAIL: // Accumulate available trailer bytes to update the total // CRC and the total uncompressed length. do {
part = (part >> 8) + ((unsignedlong)(*put++) << 24);
tail++; if (tail == 4) { // Update the total CRC.
z_off_t len2 = memb; if (len2 < 0 || (unsignedlonglong)len2 != memb)
BYE("overflow error");
crc = crc ? crc32_combine(crc, part, len2) : part;
part = 0;
} elseif (tail == 8) { // Update the total uncompressed length. (It's ok // if this sum is done modulo 2^32.)
len += part;
// At the end of a member. Set up to inflate an // immediately following gzip member. (If we made // it this far, then the trailer was valid.) if (inflateReset(&strm) != Z_OK)
BYE("internal error");
state = BETWEEN; break;
}
} while (put < strm.next_in); break;
}
// Process the input buffer until completely consumed.
} while (strm.avail_in > 0);
// Process input until end of file, invalid input, or i/o error.
} while (more);
// Done with the inflate engine.
inflateEnd(&strm);
// Verify the validity of the input. if (state != BETWEEN)
BYE("input invalid: incomplete gzip stream");
// Write the remaining deflate stream bits, followed by a terminating // deflate fixed block.
buf += (unsignedlong)3 << num;
putc(buf, out);
putc(buf >> 8, out); if (num > 6)
putc(0, out);
// Write the gzip trailer, which is the CRC and the uncompressed length // modulo 2^32, both in little-endian order.
putc(crc, out);
putc(crc >> 8, out);
putc(crc >> 16, out);
putc(crc >> 24, out);
putc(len, out);
putc(len >> 8, out);
putc(len >> 16, out);
putc(len >> 24, out);
fflush(out);
// Check for any i/o errors. if (ferror(in) || ferror(out))
BYE("i/o error: %s", strerror(errno));
// All good!
*err = NULL; return 0;
}
// Normalize the gzip stream on stdin, writing the result to stdout. int main(void) { // Avoid end-of-line conversions on evil operating systems.
SET_BINARY_MODE(stdin);
SET_BINARY_MODE(stdout);
// Normalize from stdin to stdout, returning 1 on error, 0 if ok. char *err; int ret = gzip_normalize(stdin, stdout, &err); if (ret)
fprintf(stderr, "gznorm error: %s\n", err);
free(err); return ret;
}
¤ Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.0.41Bemerkung:
(vorverarbeitet)
¤
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung ist noch experimentell.
