On Wed, 8 Feb 2023, Jeroen Ooms via curl-library wrote:
HTTP/2 stream 20139 was not closed cleanly before end of the underlying stream
So either they introduced a server bug, or perhaps GitHub is deliberately
blocking abusive behavior due to high concurrency.
My guess: they probably just cut off something (like the connection) instead
of closing down the streams nicely, hence this error.
I am using a multi handle with CURLPIPE_MULTIPLEX and otherwise default
settings. Am I correct that this means libcurl starts 100 concurrent streams
(CURLMOPT_MAX_CONCURRENT_STREAMS), and still make 6 concurrent connections
(CURLMOPT_MAX_HOST_CONNECTIONS) per host, i.e. download 600 files in
parallel? I can imagine that could be considered abusive.
If you have added >= 600 transfers to the multi handle, libcurl will attempt
to do them like that.
This said, we also have a bug in HTTP/2 that makes it not always "fill up" the
connections properly after the first one is saturated. (Fixed in master)
Should I set CURLMOPT_MAX_HOST_CONNECTIONS to 1 in case of http/2
multiplexing? Or is CURLMOPT_MAX_HOST_CONNECTIONS ignored in case of
multiplexing?
It is independent of multiplexing.
One other thing I noticed is that GitHub does not seem to set any
MAX_CONCURRENT_STREAMS, or at least I am not seeing any. For example on
httpbin I see this:
curl -v 'https://httpbin.org/get' --http2
* Connection state changed (MAX_CONCURRENT_STREAMS == 128)!
However for GitHub I don't see such a thing:
curl -v 'https://raw.githubusercontent.com/curl/curl/master/README' --http2
So does this mean libcurl will assume 100 streams is OK?
Yes I believe so.
Is there a way to debug this, and monitor how many active downloads a
multi-handle is making in total (summed over all connections)?
I think libcurl lacks that ability. The 'running_handles' counter the
*perform() function returns include transfers that are queued up. You
basically want running_handles - num_pending.
Maybe we should provide a curl_multi_getinfo() for things like this?
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