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Handle HTTP/2 PINGs from servers #1521
As per https://curl.haxx.se/mail/lib-2017-05/0096.html, I've made a fix to allow libcurl to handle HTTP/2 PINGs from servers.
The main portion of this fix is to create a new "connection_check" Curl_handler callback, which can be called with flags to check on a connection (Currently, the only check option is CONNCHECK_ISDEAD, to check if the connection is dead or not).
The existing special case (Curl_rtsp_connisdead) is refactored to use this approach, and http2.c is extended to use a cloned version of Curl_rtsp_connisdead.
By default, libnghttp2 handles PING frames automatically (https://nghttp2.org/documentation/nghttp2_option_set_no_auto_ping_ack.html). The PING frames are handled next time a request is made on an existing HTTP/2 connection.
I've tested it on my local machine - I have a Python script which sends an HTTP/2 PING on a connection 10 seconds after serving a GET request, and a test client which performs a GET every 30 seconds. Before, the second GET would complain about the connection being dead; now, it doesn't mind and reuses the connection.
In terms of getting this tested in the test framework - I tried to run the unit tests for HTTP/2 but I think the tests use nghttpx, which requires a fair few dependencies to compile. Tell you what - I'll try and spin up a VM to see if I can get this tested. I wouldn't want to reduce the code coverage!
I've had a further look at this now and I'm not sure we can test this in a sensible way.
Currently the HTTP/2 tests use the
Even if we do this, there's no way of checking libcurl to see if it's reusing a connection or not - so there's no way of seeing any problems.
I'm not sure where to go. Would it be possible to just get this merged in now, and maybe rethink the HTTP/2 testing strategy in a separate thread?
First, please squash the bugfix commit into one of the other commits, we don't need to see your history or merge commits we already know are broken.
Then, and I'm not sure why this isn't shown in the CI builds but building debug-enabled HTTP/2-enabled on my machine shows:
The function should be made static.