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zlib/examples/gznorm.c  view on Meta::CPAN

#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 <fcntl.h>
#  include <io.h>
#  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)