diff --git a/examples/README.examples b/examples/README.examples index 56a3171..42d9414 100644 --- a/examples/README.examples +++ b/examples/README.examples @@ -34,6 +34,10 @@ gzlog.h and deflateSetDictionary() - illustrates use of a gzip header extra field +gznorm.c + normalize a gzip file by combining members into a single member + - demonstrates how to concatenate deflate streams using Z_BLOCK + zlib_how.html painfully comprehensive description of zpipe.c (see below) - describes in excruciating detail the use of deflate() and inflate() diff --git a/examples/gznorm.c b/examples/gznorm.c new file mode 100644 index 0000000..68e0a0f --- /dev/null +++ b/examples/gznorm.c @@ -0,0 +1,470 @@ +/* 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. + +#include // fread, fwrite, putc, fflush, ferror, fprintf, + // vsnprintf, stdout, stderr, NULL, FILE +#include // malloc, free +#include // strerror +#include // errno +#include // va_list, va_start, va_end +#include "zlib.h" // inflateInit2, inflate, inflateReset, inflateEnd, + // z_stream, z_off_t, crc32_combine, Z_NULL, Z_BLOCK, + // Z_OK, Z_STREAM_END, Z_BUF_ERROR, Z_DATA_ERROR, + // Z_MEM_ERROR + +#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__) +# include +# include +# define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY) +#else +# define SET_BINARY_MODE(file) +#endif + +#define local static + +// 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 + unsigned long crc = 0; // accumulated CRC of uncompressed data + unsigned long len = 0; // accumulated length of uncompressed data + unsigned long 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. + unsigned char *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 + unsigned long long memb; // uncompressed length of member + size_t tail; // number of trailer bytes read (0..8) + unsigned long part; // accumulated trailer component + + // Get the next chunk of input from in. + unsigned char 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 + unsigned char 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 += (unsigned long)*put++ << num; + num += 8; + } + + // Set last to have a 1 in the position of the last + // block bit in the bit buffer. + unsigned long last = (unsigned long)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 += (unsigned long)*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 + } + } + else if (((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. + unsigned char *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 &= ((unsigned long)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. + else if (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) + ((unsigned long)(*put++) << 24); + tail++; + if (tail == 4) { + // Update the total CRC. + z_off_t len2 = memb; + if (len2 < 0 || (unsigned long long)len2 != memb) + BYE("overflow error"); + crc = crc ? crc32_combine(crc, part, len2) : part; + part = 0; + } + else if (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 += (unsigned long)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; +}