CODEWITHSUNDEEP
czlib
Pranjal
Pranjal

Reputation: 689

zlib output memory buffer size error

I am trying to compress image data using zlib's compress() function. For this purpose I allocate memory equal to compressBound() of input data to the output buffer. But I keep getting the Z_BUF_ERROR. Why is it happening ?

for (y = 0; y < header.cupsHeight; y ++)
{
    pixdata = malloc(header.cupsBytesPerLine);

    if(pixdata==NULL)
    {
        fprintf(stderr,"error in memory allocation for pixdata\n");
        return -1;
    }
    cupsRasterReadPixels(ras, pixdata, header.cupsBytesPerLine);

    destLen = compressBound(header.cupsBytesPerLine);
    fprintf(stderr, "mem. dest. = %lld\n",destLen);
    write_buffer = malloc(destLen);
    if(write_buffer==NULL)
    {
        fprintf(stderr,"error in memory allocation for write_buffer\n");
        return -1;
    }
    ret = compress(write_buffer, &destLen, pixdata, header.cupsBytesPerLine);
    if (ret != Z_OK)
        zerr(ret);
    fwrite(write_buffer, 1, destLen, stdout);
    free(write_buffer);
        free(pixdata);
    }

Error checking of value returned is performed by this function:

/* report a zlib or i/o error */
void zerr(int ret)
{
    fputs("zpipe: ", stderr);
    switch (ret) {
    case Z_ERRNO:
        fputs("error in source data or output file\n", stderr);
        break;
    case Z_STREAM_ERROR:
        fputs("invalid compression level\n", stderr);
        break;
    case Z_DATA_ERROR:
        fputs("invalid or incomplete deflate data\n", stderr);
        break;
    case Z_MEM_ERROR:
        fputs("out of memory\n", stderr);
        break;
    case Z_VERSION_ERROR:
        fputs("zlib version mismatch!\n", stderr);
        break;
    case Z_BUF_ERROR:
            fputs("error in buffer\n",stderr);
            break;
    }
}

When I run the program each time the compress() function is called, I get zpipe: error in buffer (the last case in zerr() function). Also memory allocation does not fail as I have included the condition for it and it evaluates to false each time the loop is called.

Upvotes: 0

Views: 541

Answers (1)

jxh
jxh

Reputation: 70362

You ask for the memory bound for compressing some number of bytes:

destLen = compressBound(header.cupsBytesPerLine);

But, then you attempt to compress 1 more byte than what you had computed the bound for.

ret = compress(write_buffer, &destLen, pixdata, header.cupsBytesPerLine+1);

Upvotes: 1

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