libcurl 7.88.0 - Connection failed maybe due to the refactor of detecting if a connection is dead.

[SendSonS]

With libcurl 7.88.0/7.88.1, we sometimes encountered this issue, that the sending request was 'Expire cleared', it tried to reuse connections but ' Connection died, tried 5 times before giving up'.

Refer to the attached logs:
logs_libcurl_7_87_0.txt
logs_libcurl_7_88_0.txt

There're 6 connections in the cache but they are all dead.
With 7.87.0, when handling a new request, it fount that the connection is already dead before sending data (Connection 2 seems to be dead), then it remove all dead connections.
With 7.88.0, when handling a new request, it did not remove any dead connection before sending data, but failed to send data (we are done reading and this is set to close, stop send), then it retry the next died connection (Connection died, retrying a fresh connect (retry count: 1), finally it failed after retried with 5 times.

We checked the history and found that, before create_conn it will prune_dead_connections, the detecting method was changed at here:
71b7e01#diff-a8a54563608f8155973318f4ddb61d7328dab512b8ff2b5cc48cc76979d4204c

-      dead = SocketIsDead(conn->sock[FIRSTSOCKET]);
+      dead = !Curl_conn_is_alive(data, conn);

Looks like it cannot find the connection that is already dead before sending data.

[icing]

@SendSonS what platform are you running on?

[icing]

Thanks for the report and the logs.

Could your check that #10652 fixes the problem for you as well?

[SendSonS]

Thanks for the report and the logs.

Could your check that #10652 fixes the problem for you as well?

@icing We still see this issue with your patch.
The log is still as same as before, it re-tried to re-use 5 dead connections.

[icing]

I assume the requests involved use https:?

[icing]

Please find in #10690 my latest fix for putting a lid not this issue.

Background: the refactoring from 7.87 to 7.88 failed to properly preserve the handling of pending input on connection reuse. For http connections, having input arriving from a server is considered bad, since the server should not send anything unless there is some issue.

For https: connections the most common case of pending input is a TLS notify close message, e.g. the server was done with it.

The PR restores the previous way of checking for this.

[icing]

@SendSonS could you try the current master?

[SendSonS]

@icing Thanks, we just try against #10690 , and we didn't see this issue again.
We think this issue is fixed now.

[stanhu]

Thanks! We're keen on updating curl to v7.88, but this issue makes us a little hesitant since we have a number of users who use proxy servers.

Will there be a curl 7.88.2 with this fix?

[bagder]

The next release is 8.0.0, due in 6 days.