Question

I’m trying to deflate and inflate a text file using zlib-1.2.7 with VC++2010.
I used pipe.c as basis and rewrote the main() in order to set the input/output files.

I’m able to deflate any text file but i can’t inflate large files without getting a Z_DATA_ERROR (-3).

the inf() and def() are not changed from pipe.c.

Here is my main() :

int main (){
    FILE *a, *b, *c;
    int ret;

    //ZIP
    a = fopen("a_data.txt", "r");
    b = fopen("b_compressedData.zip", "w");
    if(a != NULL && b != NULL){
        ret = def(a, b, Z_DEFAULT_COMPRESSION);
        printf("%d\n", ret); 

        if (ret != Z_OK) zerr(ret);

        fclose(a);
        fclose(b);
    }
    //UNZIP
    b = fopen("b_compressedData.zip", "r");
    c = fopen("c_uncompressedData.txt", "w");
    if(c != NULL && b != NULL){
        ret = inf(b, c);
        printf("%d\n", ret); 
        if (ret != Z_OK) zerr(ret);

        fclose(b);
        fclose(c);
    }

    return 0;
}

Here is the inf() function :

int inf(FILE *source, FILE *dest)
{
    int ret;
    unsigned have;
    z_stream strm;
    unsigned char in[CHUNK];
    unsigned char out[CHUNK];

    /* allocate inflate state */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    strm.avail_in = 0;
    strm.next_in = Z_NULL;
    ret = inflateInit(&strm);
    if (ret != Z_OK)
        return ret;

    /* decompress until deflate stream ends or end of file */
    do {
        strm.avail_in = fread(in, 1, CHUNK, source);
        if (ferror(source)) {
            (void)inflateEnd(&strm);
            return Z_ERRNO;
        }
        if (strm.avail_in == 0)
            break;
        strm.next_in = in;

        /* run inflate() on input until output buffer not full */
        do {
            strm.avail_out = CHUNK;
            strm.next_out = out;
            ret = inflate(&strm, Z_NO_FLUSH);
            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
            switch (ret) {
            case Z_NEED_DICT:
                ret = Z_DATA_ERROR;     /* and fall through */
            case Z_DATA_ERROR:
            case Z_MEM_ERROR:
                (void)inflateEnd(&strm);
                return ret;
            }
            have = CHUNK - strm.avail_out;
            if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
                (void)inflateEnd(&strm);
                return Z_ERRNO;
            }
        } while (strm.avail_out == 0);

        /* done when inflate() says it's done */
    } while (ret != Z_STREAM_END);

    /* clean up and return */
    (void)inflateEnd(&strm);
    return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
}

Answer 1

You need to add a "b" in the modes for fopen(), where the b is for binary. E.g. "rb" and "wb". Otherwise on Windows you get end-of-line conversions which mess up binary data.

By the way, you should not call the compressed file .zip since it isn’t. zlib writes zlib-formatted data, or if requested gzip-formatted data. zlib does not write zip-formatted data on its own. There is third-party code for writing zip files, such as in the contrib directory of the zlib source distribution, or in libzip.

I use .zz as the suffix for zlib-formatted data. .gz is the suffix for gzip-formatted data.