Edit report at https://bugs.php.net/bug.php?id=44164&edit=1
ID: 44164
Updated by: cataphr...@php.net
Reported by: mplomer at gmx dot de
Summary: Handle "Content-Length" HTTP header when
zlib.output_compression active
-Status: Assigned
+Status: Closed
Type: Bug
Package: *General Issues
Operating System: *
PHP Version: 5.2.5
Assigned To: cataphract
Block user comment: N
Private report: N
Previous Comments:
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[2013-08-01 14:51:09] m...@php.net
https://github.com/php/php-src/pull/400
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[2013-08-01 14:19:34] m...@php.net
Why is this open, despite the patch being still applied to SAPI.c?
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[2012-02-16 10:00:14] daniel at code-emitter dot com
FYI: This issue is still causing problems.
http://tracker.phpbb.com/browse/PHPBB3-10648
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[2010-12-17 19:18:15] panczel dot levente at groware dot hu
Thanks, you are absolutely right pointing at my error: my suggestion would not
work in situations where a Content-Length header was mandatory or referenced
uncompressed body length. The partial response 206, as I understand, doesnât
make Content-Length mandatory. In fact the last line might be omitted from your
example and that is still a valid response. But since Content-Length is not
mandatory in this case either, I think my thesis still works.
I have not found any explicit remarks in the specification on how offsets and
Content-Encoding should interact. As I see now all fields are about the
document-entity (the one that the script handles and knows well) except for
Content-Encoding and Content-Length fields which are about the representation
of the message body. So Content-Length always shows the decimal number of
octets transferred in the message bodyâs final byte-stream, and
Content-Encoding has to be reversed before other processing (like matching it
to the requested rangeâs size) takes place.
For all response types where Content-Length is mandatory, I agree with you,
that compression should be turned off (possibly after trying to fit in the
initial 1 buffer that I think is allocated anyways). But we know that in case
of response 200 it is not mandatory, and as I see, for 206 neither. So at least
these responses could follow my thesis (and any others currently do not require
a Content-Length field).
> The problem is the zlib.output_compression is not presented as an output
> handler that rewrites the response and creates a new entity. It is presented
> as an inoffensive performance option that compresses the output for better
> performance.
Yes, it rewrites the response; but no, it does not create a new entity. I think
thatâs just what
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.11 references by
âwithout losing the identity of its underlying media typeâ. So to send a
compressed body, one just has to adjust the Content-Encoding field and take
care that Content-Length is not invalid. I feel that changing these headers
isnât more intrusive than altering body octets, since they do not affect
other content and headers in the message, except for Transfer-Encoding which I
suppose that zlib compression correctly adjusts to. I think chunked
Transfer-Encoding is relevant for two reasons. If received from the script, it
has to be assembled before compression. And it might be used to maintain
persistent connections (e.g. 1 compressed buffer in each chunk) where
compression was not able to tell the Content-Length in advance.
Please understand that Iâm not pushing for any of these features, just think
that this topic still has potential for inspiring improvement and finding rare
bugs.
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[2010-12-17 16:35:30] cataphr...@php.net
> Thatâs an error. Both scripts set the correct CL (that they know very well),
> just the way the specification says they SHOULD. I donât agree that it would
> be the responsibility of the script to counteract the setting (zlib output
> compression in this case) of the executing framework (PHP in this case). If
> the scripts should take care for every such situation then using the header()
> would be completely illegal, because a future output handler might interact
> with the output in such a way that invalidates the headers set. This isnât a
> portable phylosophy since it implicitly requires the script being aware of
> every aspects of plugins and settings in PHP.
> In fact it is the zlib output handler that was setting the wrong CL header (by
> not removing the deprecated one). As I see, the handler is constructing a new
> response entity instead the one it receives from the script; the consistency
> of
> this response is entirely the responsibility of the handler. As I understand
> this has now been patched so that the handler always removes the CL header,
> and
> by that it assures correctness. Note: hereâs no refutation of the
> correctness
> of the patched handler.
The problem is the zlib.output_compression is not presented as an output
handler that rewrites the response and creates a new entity. It is presented as
an inoffensive performance option that compresses the output for better
performance. And it does so, generally, without the express assent of the
programmer. The programmer can always use ob_gzhandler to force compression.
Your thesis is that the output handler should not be deactivated; instead it
ought to remove the old header and write a new one, whenever possible. This
looks good. But consider this script:
if (empty($_SERVER["HTTP_RANGE"])) {
$offset = 0;
}
else { //violates rfc2616, which demands ignoring the header if invalid
preg_match("/^bytes=(\d+)-/i",$_SERVER["HTTP_RANGE"], $matches);
if (empty($matches[1]))
$offset = 0;
if (is_num_int($matches[1]) && $matches[1] < $filesize && $matches[1]>=0) {
$offset = $matches[1];
if (@fseek($fp,$offset,SEEK_SET) != 0)
InternalError();
header("HTTP/1.1 206 Partial Content");
header("Content-Range: bytes $offset-".($filesize - 1)."/$filesize");
}
elseif ($matches[1] > $filesize) {
header("HTTP/1.1 416 Requested Range Not Satisfiable");
die();
}
else $offset = 0;
}
$conlen = $filesize - $offset;
header("Content-Length: $conlen");
This is no way this script can work correctly under the zlib handler. 206
responses must have a content-length and the offsets are calculated through the
uncompressed size, while under zlib that should be calculated under the
compressed size, which is obviously impossible to know without first
compressing the file.
So actually the only option is to disable the zlib output handler.
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