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470 lines
22 KiB
C
470 lines
22 KiB
C
/* gznorm.c -- normalize a gzip stream
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* Copyright (C) 2018 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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* Version 1.0 7 Oct 2018 Mark Adler */
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// gznorm takes a gzip stream, potentially containing multiple members, and
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// converts it to a gzip stream with a single member. In addition the gzip
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// header is normalized, removing the file name and time stamp, and setting the
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// other header contents (XFL, OS) to fixed values. gznorm does not recompress
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// the data, so it is fast, but no advantage is gained from the history that
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// could be available across member boundaries.
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#include <stdio.h> // fread, fwrite, putc, fflush, ferror, fprintf,
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// vsnprintf, stdout, stderr, NULL, FILE
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#include <stdlib.h> // malloc, free
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#include <string.h> // strerror
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#include <errno.h> // errno
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#include <stdarg.h> // va_list, va_start, va_end
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#include "zlib.h" // inflateInit2, inflate, inflateReset, inflateEnd,
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// z_stream, z_off_t, crc32_combine, Z_NULL, Z_BLOCK,
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// Z_OK, Z_STREAM_END, Z_BUF_ERROR, Z_DATA_ERROR,
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// Z_MEM_ERROR
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#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
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# include <fcntl.h>
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# include <io.h>
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# define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
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#else
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# define SET_BINARY_MODE(file)
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#endif
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#define local static
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// printf to an allocated string. Return the string, or NULL if the printf or
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// allocation fails.
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local char *aprintf(char *fmt, ...) {
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// Get the length of the result of the printf.
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va_list args;
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va_start(args, fmt);
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int len = vsnprintf(NULL, 0, fmt, args);
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va_end(args);
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if (len < 0)
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return NULL;
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// Allocate the required space and printf to it.
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char *str = malloc(len + 1);
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if (str == NULL)
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return NULL;
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va_start(args, fmt);
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vsnprintf(str, len + 1, fmt, args);
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va_end(args);
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return str;
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}
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// Return with an error, putting an allocated error message in *err. Doing an
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// inflateEnd() on an already ended state, or one with state set to Z_NULL, is
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// permitted.
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#define BYE(...) \
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do { \
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inflateEnd(&strm); \
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*err = aprintf(__VA_ARGS__); \
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return 1; \
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} while (0)
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// Chunk size for buffered reads and for decompression. Twice this many bytes
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// will be allocated on the stack by gzip_normalize(). Must fit in an unsigned.
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#define CHUNK 16384
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// Read a gzip stream from in and write an equivalent normalized gzip stream to
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// out. If given no input, an empty gzip stream will be written. If successful,
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// 0 is returned, and *err is set to NULL. On error, 1 is returned, where the
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// details of the error are returned in *err, a pointer to an allocated string.
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//
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// The input may be a stream with multiple gzip members, which is converted to
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// a single gzip member on the output. Each gzip member is decompressed at the
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// level of deflate blocks. This enables clearing the last-block bit, shifting
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// the compressed data to concatenate to the previous member's compressed data,
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// which can end at an arbitrary bit boundary, and identifying stored blocks in
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// order to resynchronize those to byte boundaries. The deflate compressed data
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// is terminated with a 10-bit empty fixed block. If any members on the input
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// end with a 10-bit empty fixed block, then that block is excised from the
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// stream. This avoids appending empty fixed blocks for every normalization,
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// and assures that gzip_normalize applied a second time will not change the
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// input. The pad bits after stored block headers and after the final deflate
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// block are all forced to zeros.
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local int gzip_normalize(FILE *in, FILE *out, char **err) {
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// initialize the inflate engine to process a gzip member
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z_stream strm;
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strm.zalloc = Z_NULL;
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strm.zfree = Z_NULL;
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strm.opaque = Z_NULL;
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strm.avail_in = 0;
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strm.next_in = Z_NULL;
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if (inflateInit2(&strm, 15 + 16) != Z_OK)
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BYE("out of memory");
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// State while processing the input gzip stream.
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enum { // BETWEEN -> HEAD -> BLOCK -> TAIL -> BETWEEN -> ...
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BETWEEN, // between gzip members (must end in this state)
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HEAD, // reading a gzip header
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BLOCK, // reading deflate blocks
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TAIL // reading a gzip trailer
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} state = BETWEEN; // current component being processed
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unsigned long crc = 0; // accumulated CRC of uncompressed data
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unsigned long len = 0; // accumulated length of uncompressed data
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unsigned long buf = 0; // deflate stream bit buffer of num bits
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int num = 0; // number of bits in buf (at bottom)
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// Write a canonical gzip header (no mod time, file name, comment, extra
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// block, or extra flags, and OS is marked as unknown).
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fwrite("\x1f\x8b\x08\0\0\0\0\0\0\xff", 1, 10, out);
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// Process the gzip stream from in until reaching the end of the input,
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// encountering invalid input, or experiencing an i/o error.
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int more; // true if not at the end of the input
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do {
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// State inside this loop.
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unsigned char *put; // next input buffer location to process
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int prev; // number of bits from previous block in
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// the bit buffer, or -1 if not at the
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// start of a block
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unsigned long long memb; // uncompressed length of member
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size_t tail; // number of trailer bytes read (0..8)
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unsigned long part; // accumulated trailer component
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// Get the next chunk of input from in.
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unsigned char dat[CHUNK];
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strm.avail_in = fread(dat, 1, CHUNK, in);
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if (strm.avail_in == 0)
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break;
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more = strm.avail_in == CHUNK;
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strm.next_in = put = dat;
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// Run that chunk of input through the inflate engine to exhaustion.
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do {
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// At this point it is assured that strm.avail_in > 0.
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// Inflate until the end of a gzip component (header, deflate
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// block, trailer) is reached, or until all of the chunk is
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// consumed. The resulting decompressed data is discarded, though
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// the total size of the decompressed data in each member is
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// tracked, for the calculation of the total CRC.
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do {
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// inflate and handle any errors
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unsigned char scrap[CHUNK];
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strm.avail_out = CHUNK;
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strm.next_out = scrap;
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int ret = inflate(&strm, Z_BLOCK);
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if (ret == Z_MEM_ERROR)
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BYE("out of memory");
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if (ret == Z_DATA_ERROR)
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BYE("input invalid: %s", strm.msg);
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if (ret != Z_OK && ret != Z_BUF_ERROR && ret != Z_STREAM_END)
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BYE("internal error");
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// Update the number of uncompressed bytes generated in this
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// member. The actual count (not modulo 2^32) is required to
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// correctly compute the total CRC.
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unsigned got = CHUNK - strm.avail_out;
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memb += got;
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if (memb < got)
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BYE("overflow error");
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// Continue to process this chunk until it is consumed, or
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// until the end of a component (header, deflate block, or
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// trailer) is reached.
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} while (strm.avail_out == 0 && (strm.data_type & 0x80) == 0);
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// Since strm.avail_in was > 0 for the inflate call, some input was
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// just consumed. It is therefore assured that put < strm.next_in.
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// Disposition the consumed component or part of a component.
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switch (state) {
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case BETWEEN:
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state = HEAD;
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// Fall through to HEAD when some or all of the header is
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// processed.
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case HEAD:
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// Discard the header.
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if (strm.data_type & 0x80) {
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// End of header reached -- deflate blocks follow.
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put = strm.next_in;
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prev = num;
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memb = 0;
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state = BLOCK;
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}
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break;
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case BLOCK:
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// Copy the deflate stream to the output, but with the
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// last-block-bit cleared. Re-synchronize stored block
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// headers to the output byte boundaries. The bytes at
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// put..strm.next_in-1 is the compressed data that has been
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// processed and is ready to be copied to the output.
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// At this point, it is assured that new compressed data is
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// available, i.e., put < strm.next_in. If prev is -1, then
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// that compressed data starts in the middle of a deflate
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// block. If prev is not -1, then the bits in the bit
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// buffer, possibly combined with the bits in *put, contain
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// the three-bit header of the new deflate block. In that
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// case, prev is the number of bits from the previous block
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// that remain in the bit buffer. Since num is the number
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// of bits in the bit buffer, we have that num - prev is
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// the number of bits from the new block currently in the
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// bit buffer.
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// If strm.data_type & 0xc0 is 0x80, then the last byte of
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// the available compressed data includes the last bits of
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// the end of a deflate block. In that case, that last byte
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// also has strm.data_type & 0x1f bits of the next deflate
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// block, in the range 0..7. If strm.data_type & 0xc0 is
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// 0xc0, then the last byte of the compressed data is the
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// end of the deflate stream, followed by strm.data_type &
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// 0x1f pad bits, also in the range 0..7.
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// Set bits to the number of bits not yet consumed from the
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// last byte. If we are at the end of the block, bits is
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// either the number of bits in the last byte belonging to
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// the next block, or the number of pad bits after the
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// final block. In either of those cases, bits is in the
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// range 0..7.
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; // (required due to C syntax oddity)
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int bits = strm.data_type & 0x1f;
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if (prev != -1) {
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// We are at the start of a new block. Clear the last
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// block bit, and check for special cases. If it is a
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// stored block, then emit the header and pad to the
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// next byte boundary. If it is a final, empty fixed
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// block, then excise it.
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// Some or all of the three header bits for this block
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// may already be in the bit buffer. Load any remaining
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// header bits into the bit buffer.
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if (num - prev < 3) {
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buf += (unsigned long)*put++ << num;
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num += 8;
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}
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// Set last to have a 1 in the position of the last
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// block bit in the bit buffer.
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unsigned long last = (unsigned long)1 << prev;
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if (((buf >> prev) & 7) == 3) {
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// This is a final fixed block. Load at least ten
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// bits from this block, including the header, into
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// the bit buffer. We already have at least three,
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// so at most one more byte needs to be loaded.
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if (num - prev < 10) {
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if (put == strm.next_in)
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// Need to go get and process more input.
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// We'll end up back here to finish this.
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break;
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buf += (unsigned long)*put++ << num;
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num += 8;
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}
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if (((buf >> prev) & 0x3ff) == 3) {
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// That final fixed block is empty. Delete it
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// to avoid adding an empty block every time a
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// gzip stream is normalized.
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num = prev;
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buf &= last - 1; // zero the pad bits
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}
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}
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else if (((buf >> prev) & 6) == 0) {
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// This is a stored block. Flush to the next
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// byte boundary after the three-bit header.
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num = (prev + 10) & ~7;
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buf &= last - 1; // zero the pad bits
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}
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// Clear the last block bit.
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buf &= ~last;
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// Write out complete bytes in the bit buffer.
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while (num >= 8) {
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putc(buf, out);
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buf >>= 8;
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num -= 8;
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}
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// If no more bytes left to process, then we have
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// consumed the byte that had bits from the next block.
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if (put == strm.next_in)
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bits = 0;
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}
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// We are done handling the deflate block header. Now copy
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// all or almost all of the remaining compressed data that
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// has been processed so far. Don't copy one byte at the
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// end if it contains bits from the next deflate block or
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// pad bits at the end of a deflate block.
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// mix is 1 if we are at the end of a deflate block, and if
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// some of the bits in the last byte follow this block. mix
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// is 0 if we are in the middle of a deflate block, if the
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// deflate block ended on a byte boundary, or if all of the
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// compressed data processed so far has been consumed.
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int mix = (strm.data_type & 0x80) && bits;
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// Copy all of the processed compressed data to the output,
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// except for the last byte if it contains bits from the
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// next deflate block or pad bits at the end of the deflate
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// stream. Copy the data after shifting in num bits from
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// buf in front of it, leaving num bits from the end of the
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// compressed data in buf when done.
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unsigned char *end = strm.next_in - mix;
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if (put < end) {
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if (num)
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// Insert num bits from buf before the data being
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// copied.
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do {
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buf += (unsigned)(*put++) << num;
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putc(buf, out);
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buf >>= 8;
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} while (put < end);
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else {
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// No shifting needed -- write directly.
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fwrite(put, 1, end - put, out);
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put = end;
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}
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}
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// Process the last processed byte if it wasn't written.
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if (mix) {
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// Load the last byte into the bit buffer.
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buf += (unsigned)(*put++) << num;
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num += 8;
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if (strm.data_type & 0x40) {
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// We are at the end of the deflate stream and
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// there are bits pad bits. Discard the pad bits
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// and write a byte to the output, if available.
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// Leave the num bits left over in buf to prepend
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// to the next deflate stream.
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num -= bits;
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if (num >= 8) {
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putc(buf, out);
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num -= 8;
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buf >>= 8;
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}
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// Force the pad bits in the bit buffer to zeros.
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buf &= ((unsigned long)1 << num) - 1;
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// Don't need to set prev here since going to TAIL.
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}
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else
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// At the end of an internal deflate block. Leave
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// the last byte in the bit buffer to examine on
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// the next entry to BLOCK, when more bits from the
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// next block will be available.
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prev = num - bits; // number of bits in buffer
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// from current block
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}
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// Don't have a byte left over, so we are in the middle of
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// a deflate block, or the deflate block ended on a byte
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// boundary. Set prev appropriately for the next entry into
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// BLOCK.
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else if (strm.data_type & 0x80)
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// The block ended on a byte boundary, so no header
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// bits are in the bit buffer.
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prev = num;
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else
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// In the middle of a deflate block, so no header here.
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prev = -1;
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// Check for the end of the deflate stream.
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if ((strm.data_type & 0xc0) == 0xc0) {
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// That ends the deflate stream on the input side, the
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// pad bits were discarded, and any remaining bits from
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// the last block in the stream are saved in the bit
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// buffer to prepend to the next stream. Process the
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// gzip trailer next.
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tail = 0;
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part = 0;
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state = TAIL;
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}
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break;
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case TAIL:
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// Accumulate available trailer bytes to update the total
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// CRC and the total uncompressed length.
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do {
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part = (part >> 8) + ((unsigned long)(*put++) << 24);
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tail++;
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if (tail == 4) {
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// Update the total CRC.
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z_off_t len2 = memb;
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if (len2 < 0 || (unsigned long long)len2 != memb)
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BYE("overflow error");
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crc = crc ? crc32_combine(crc, part, len2) : part;
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part = 0;
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}
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else if (tail == 8) {
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// Update the total uncompressed length. (It's ok
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// if this sum is done modulo 2^32.)
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len += part;
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// At the end of a member. Set up to inflate an
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// immediately following gzip member. (If we made
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// it this far, then the trailer was valid.)
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if (inflateReset(&strm) != Z_OK)
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BYE("internal error");
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state = BETWEEN;
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break;
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}
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} while (put < strm.next_in);
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break;
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}
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// Process the input buffer until completely consumed.
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} while (strm.avail_in > 0);
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// Process input until end of file, invalid input, or i/o error.
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} while (more);
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// Done with the inflate engine.
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inflateEnd(&strm);
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// Verify the validity of the input.
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if (state != BETWEEN)
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BYE("input invalid: incomplete gzip stream");
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// Write the remaining deflate stream bits, followed by a terminating
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// deflate fixed block.
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buf += (unsigned long)3 << num;
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putc(buf, out);
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putc(buf >> 8, out);
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if (num > 6)
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putc(0, out);
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// Write the gzip trailer, which is the CRC and the uncompressed length
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// modulo 2^32, both in little-endian order.
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putc(crc, out);
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putc(crc >> 8, out);
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putc(crc >> 16, out);
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putc(crc >> 24, out);
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putc(len, out);
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putc(len >> 8, out);
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putc(len >> 16, out);
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putc(len >> 24, out);
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fflush(out);
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// Check for any i/o errors.
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if (ferror(in) || ferror(out))
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BYE("i/o error: %s", strerror(errno));
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// All good!
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*err = NULL;
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return 0;
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}
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// Normalize the gzip stream on stdin, writing the result to stdout.
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int main(void) {
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// Avoid end-of-line conversions on evil operating systems.
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SET_BINARY_MODE(stdin);
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SET_BINARY_MODE(stdout);
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// Normalize from stdin to stdout, returning 1 on error, 0 if ok.
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char *err;
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int ret = gzip_normalize(stdin, stdout, &err);
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if (ret)
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fprintf(stderr, "gznorm error: %s\n", err);
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free(err);
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return ret;
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}
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