Re: [libmicrohttpd] Duplicate Content-Length headers set by MHD & application

[Evgeny Grin]

Hi Rob,

Kodi currently using MHD API incorrectly.
There is no need to use MHD_RF_INSANITY_HEADER_CONTENT_LENGTH unless you 
are testing HTTP client with incorrect HTTP response. The flag allow 
application to override MHD automatic value.
There is no need to set `Content-Length` manually. MHD always sets it 
automatically, when this header is needed.

As a member of Kodi-team I'll make a PR with proper fix for Kodi. :)

--
Evgeny

On 20.02.2022 5:23, Rob Kingston wrote:
> Hi there,
>
> Kodi uses MHD for its web interface and JSON API. A recent update on MHD 
> has changed Content-Length headers to be set automatically without 
> throwing any errors or overriding the existing headers when present.
>
> This results in the header being set twice when the application 
> inadvertently sets it. E.g. resulting in headers like:
>
> HTTP/1.1 200 OK
> Date: Sat, 19 Feb 2022 23:59:56 GMT
> Accept-Ranges: none
> Cache-Control: private, max-age=0, no-cache
> Content-Length: 649
> Content-Type: application/json
> Content-Length: 649
>
> Unfortunately, some useragents reject responses where this is set 
> multiple times. Python's aiohttp library is one such useragent that 
> breaks due to this.
>
> There's discussion about handling this in Kodi by conditionally setting 
> the Content-Length headers depending on the version of MHD being run. 
> However it looks like MHD has also recently handled such cases before too:
>
> https://github.com/Karlson2k/libmicrohttpd/commit/16ac89f3beb982dab4f1552ffb94e637b45ca324 
> <https://github.com/Karlson2k/libmicrohttpd/commit/16ac89f3beb982dab4f1552ffb94e637b45ca324>
>
> What is the best way to handle this going forward?
>
> Cheers,
> Rob

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