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From Alex Stapleton <>
Subject Re: mod_ssl and Transfer-Encoding: chunked wastes ~58 bytes per chunk.
Date Fri, 21 Aug 2009 08:22:59 GMT
2009/8/21 Alex Stapleton <>:
> 2009/8/20 Roy T. Fielding <>:
>> On Aug 20, 2009, at 2:01 AM, Alex Stapleton wrote:
>>> 2009/8/19 Roy T. Fielding <>:
>>>> On Aug 19, 2009, at 9:53 AM, Alex Stapleton wrote:
>>>>> (This has been cross posted to users@. I apologise if this mail isn't
>>>>> relevant to the dev list.)
>>>>> First some background. We use Apache HTTPD 2.0 over a high-latency,
>>>>> high packet loss GPRS WAN. The cost per byte is tangible. We use SSL.
>>>>> We also use Transfer-Encoding: chunked sometimes. This is a machine
>>>>> monitoring application. We are using iframe streaming to push real
>>>>> time data to operators browsers.
>>>>> I have noticed after much faffing around with wireshark that httpd
>>>>> will transmit 3 Application Data fragments for each chunk in a chunked
>>>>> HTTP stream. The fragments are the HTTP chunk size, the chunk data,
>>>>> and then a CRLF. All fragments in an SSL session are rounded to the
>>>>> length of the ciphers block size. This results in the 4+2 bytes for
>>>>> the chunk frame ending up being 64 bytes of data over TCP. A waste of
>>>>> 58 bytes per chunk in this case.
>>>> That's odd -- we don't do this with non-SSL writes (last I checked).
>>>> Perhaps we are relying on a TCP cork for the non-SSL case?
>>>> What is your operating system and platform?
>>> I initially discovered this issue on a fairly old Ubuntu 6 machine
>>> running httpd 2.0.55-4ubuntu4.1. I have since recreated it on my OS X
>>> 10.5 iMac using httpd 2.0.64 from MacPorts. I suppose I should also
>>> point out that I am using PHP 5.2.9 to generate the chunked data. If
>>> there's a way of doing chunked output using "plain" Apache let me know
>>> and I can test that too if needed.
>> Er, have you tested it with 2.2.x?  The likelihood of us making any
>> non-security changes to the 2.0.x branch is extremely small.
> I have tested with 2.2.11 from MacPorts on my iMac and it also
> exhibits this behaviour. I'll try and do a 2.2.13 build to test with
> :)

Confirmed on 2.2.13.

>> Apache does chunked output by default if no content-length is
>> provided and the client says it is HTTP/1.1.
>> ....Roy

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