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Asked: 2026-05-12T00:10:40+00:00

I have a very weird problem.. I really do hope someone has an answer

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I have a very weird problem.. I really do hope someone has an answer because I wouldn’t know where else to ask.

I am writing a cgi application in C++ which is executed by Apache and outputs HTML code. I am compressing the HTML output myself – from within my C++ application – since my web host doesn’t support mod_deflate for some reason.

I tested this with Firefox 2, Firefox 3, Opera 9, Opera 10, Google Chrome, Safari, IE6, IE7, IE8, even wget.. It works with ANYTHING except IE8.

IE8 just says “Internet Explorer cannot display the webpage”, with no information whatsoever. I know it’s because of the compression only because it works if I disable it.

Do you know what I’m doing wrong?

I use zlib to compress it, and the exact code is:

    /* Compress it */
int compressed_output_size = content.length() + (content.length() * 0.2) + 16;
char *compressed_output = (char *)Alloc(compressed_output_size);
int compressed_output_length;
Compress(compressed_output, compressed_output_size, (void *)content.c_str(), content.length(), &compressed_output_length);

/* Send the compressed header */
cout << "Content-Encoding: deflate\r\n";
cout << boost::format("Content-Length: %d\r\n") % compressed_output_length;
cgiHeaderContentType("text/html");
cout.write(compressed_output, compressed_output_length);


static void Compress(void *to, size_t to_size, void *from, size_t from_size, int *final_size)
{
int ret;
z_stream stream;

stream.zalloc = Z_NULL;
stream.zfree = Z_NULL;
stream.opaque = Z_NULL;

if ((ret = deflateInit(&stream, CompressionSpeed)) != Z_OK)
    COMPRESSION_ERROR("deflateInit() failed: %d", ret);

stream.next_out = (Bytef *)to;
stream.avail_out = (uInt)to_size;
stream.next_in = (Bytef *)from;
stream.avail_in = (uInt)from_size;

if ((ret = deflate(&stream, Z_NO_FLUSH)) != Z_OK)
    COMPRESSION_ERROR("deflate() failed: %d", ret);

if (stream.avail_in != 0)
    COMPRESSION_ERROR("stream.avail_in is not 0 (it's %d)", stream.avail_in);

if ((ret = deflate(&stream, Z_FINISH)) != Z_STREAM_END)
    COMPRESSION_ERROR("deflate() failed: %d", ret);

if ((ret = deflateEnd(&stream)) != Z_OK)
    COMPRESSION_ERROR("deflateEnd() failed: %d", ret);

if (final_size)
    *final_size = stream.total_out;
return;
}
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1 Answer

  1. Editorial Team

    The gzip and deflate methods aren’t the same… they are very close, but there are some subtle differences with the header, so, if you change your content-encoding, you should also change your parameters to the encoding method (specifically, the window size)!

    See: http://apcmag.com/improve_your_site_with_http_compression.htm

    Probably the other browsers are ignoring your content-encoding specification and doing some automatic recognition, but IE8 is not…

    See: http://www.zlib.net/manual.html#deflateInit2

    Try to use:

    method=Z_DEFLATED
windowBits=-15  (negative so that the header is suppressed)

    And use “gzip” as the content-encoding

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