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rtacconi
Asked: 2009-08-27 06:55:40 +0800 CST

Apache sending Transfer-Encoding: chunked

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There is an Apache server on Solaris that is sending 'Transfer-Encoding: chunked' and not sending the 'Content-Length' header that I have in my PHP (used for downloading files). Do you know a way to prevent this?

Thanks

See: https://stackoverflow.com/questions/1334471/content-length-header-always-zero

I have tried the directive 

 SetEnvIfNoCase Request_URI get_file\.php$ no-gzip dont-vary

and now I get a file with the same file size of the original, but the file is corrupted. Here are the headers received from the server:

http://example.com/output_file_download.php?fileID=130

GET /output_file_download.php?fileID=130 HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.1.2) Gecko/20090729 Firefox/3.5.2 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Cookie: user_id=7C%25R; intrauser=kE06Ub%238+2dHT%29U0t%28B%2A; intrakey=rtacconi; PHPSESSID=5a3f8edff822474f3b95b6a6e5c87ad2


HTTP/1.x 200 OK
Date: Thu, 03 Sep 2009 10:02:05 GMT
Server: Apache
Expires: 0
Cache-Control: private
Pragma: public
Content-Description: File Transfer
Content-Disposition: attachment; filename=alfresco-logo.gif
Content-Transfer-Encoding: binary
Content-Length: 2401
Keep-Alive: timeout=15, max=500
Connection: Keep-Alive
Content-Type: application/octet-stream
apache-2.2

2 Answers

  1. Best Answer

    Chunked output occurs when Apache doesn't know the total output size before sending, as is the case with compressed transfer (Apache compresses data into chunks when they reach a certain size, then despatches them to the browser/requester while the script is still executing). You could be seeing this because you have mod_deflate or mod_gzip active. You can verify if this is your issue here.

    You can disable mod_deflate per file like so (more here)

        SetEnvIfNoCase Request_URI get_file\.php$ no-gzip dont-vary

    It's best left on in general as it greatly increases the speed of data transfer.

    • 4

  2. The Apache 2 output filter will automatically add a content-length header if it sees an end-of-stream marker (EOS) AND nothing has been sent yet. source code:

    if (ctx->data_sent == 0 && eos) {
  ap_set_content_length(r, r->bytes_sent);
}

    If PHP passes any data down to Apache before it sends EOS, then chunking happens. PHP uses a output buffer of 4096 bytes by default. Any page smaller than that will not get chunked.

    Also check if the content is fed via gzip (mod_gzip) and gets compressed apache will then turn to chunked encoding.

    • 3