[Windows] libcurl 7.88.0 - Immediate connect fail for x.x.x.x: Socket is already connected

[sjadhavar]

I downloaded libcurl version 7.88.0 and used it in my application on Windows box. But I am seeing failure in my application and curl log shows below error.

curl_debug_logger(): == Info: Added my_host_name:1555:x.x.x.x to DNS cache
curl_debug_logger(): == Info: Hostname my_host_name was found in DNS cache
curl_debug_logger(): == Info: Trying x.x.x.x:1555...
curl_debug_logger(): == Info: Immediate connect fail for x.x.x.x: Socket is already connected
curl_debug_logger(): == Info: Failed to connect to my_host_name port 1555 after 0 ms: Couldn't connect to server
curl_debug_logger(): == Info: Closing connection 0

I tried with curl version 7.88.1 too, but same issue. Also issue is seen on Windows platform only, on RHEL it works fine.
If I use curl version 7.87.0 then it works properly.

curl/libcurl version

7.88.0

operating system

Windows

[bagder]

You need to give us more details. How can we reproduce this?

[sjadhavar]

This issue happens only when we use CURLOPT_OPENSOCKETFUNCTION and CURLOPT_SOCKOPTFUNCTION socket options to use the application created sockets by curl library.

In curl 7.87.0 version it was working fine but below commit (available in 7.88.0) broke this functionality.
71b7e01#diff-96ac2b9e301765fa5e816e0c41282610e9c0193a5852cc9bb0ed053b1fc4ef7f

In 7.87.0, if callback method for CURLOPT_SOCKOPTFUNCTION returns CURL_SOCKOPT_ALREADY_CONNECTED then curl library used to return CURLE_OK.

In 7.88.0, now even if callback returns CURL_SOCKOPT_ALREADY_CONNECTED, curl library still tries to connect to socket by invoking method [in file cf-socket.c/ function cf_tcp_connect() ]

/* Connect TCP socket */
rc = do_connect(cf, data, cf->conn->bits.tcp_fastopen);

And then it fails with WSAEISCONN error i.e. ("Socket is already connected").