Issue when using UNIX socket: Connection #0 is still name resolving, can't reuse

[vasiliy-ul]

Hello. I observe an issue while running some tests that use curl with a unix socket: https://gitlab.com/nbdkit/nbdkit/-/blob/master/tests/test-curl-header-script.c

The tests trigger several HTTP requests. The first one goes well:

nbdkit: debug: curl: load
nbdkit: debug: curl: config key=url, value=http://localhost/disk
nbdkit: debug: curl: config key=header-script, value=if [ $iteration -eq 0 ]; then echo X-Test: hello; fi
echo X-Iteration: $iteration
echo 'X-Empty;'

nbdkit: debug: curl: config key=header-script-renew, value=1
nbdkit: debug: curl: config key=unix-socket-path, value=/tmp/wswOJAjw/sock
nbdkit: debug: curl: config_complete
nbdkit: debug: using thread model: serialize_requests
nbdkit: debug: curl: get_ready
nbdkit: debug: curl: after_fork
nbdkit: curl: debug: curl: preconnect
nbdkit: curl: debug: newstyle negotiation: flags: global 0x3
nbdkit: curl: debug: newstyle negotiation: client flags: 0x3
nbdkit: curl: debug: newstyle negotiation: NBD_OPT_STRUCTURED_REPLY: client requested structured replies
nbdkit: curl: debug: newstyle negotiation: NBD_OPT_GO: client requested export ''
nbdkit: curl: debug: curl: open readonly=0 exportname="" tls=0
nbdkit: curl: debug: curl: default_export readonly=0 tls=0
nbdkit: curl: debug: curl: running header-script
nbdkit: curl: debug: header-script returned 3 header(s)
nbdkit: curl: debug:   Trying /tmp/wswOJAjw/sock:0...
nbdkit: curl: debug: Connected to localhost () port 80 (#0)
nbdkit: curl: debug: C: HEAD /disk HTTP/1.1

while on the second I see error message Connection #0 is still name resolving, can't reuse:

nbdkit: curl: debug: Mark bundle as not supporting multiuse
nbdkit: curl: debug: S: HTTP/1.1 200 OK
nbdkit: curl: debug: S: Accept-rANGES:     bytes
nbdkit: curl: debug: S: Connection: keep-alive
nbdkit: curl: debug: S: Content-Type: application/octet-stream
nbdkit: curl: debug: S: Content-Length: 105923072
nbdkit: curl: debug: S: 
nbdkit: curl: debug: Connection #0 to host localhost left intact
nbdkit: curl: debug: content length: 105923072
nbdkit: curl: debug: accept range supported (for HTTP/HTTPS)
nbdkit: curl: debug: curl: open returned handle 0x55fe754678c0
nbdkit: curl: debug: curl: prepare readonly=0
nbdkit: curl: debug: curl: get_size
nbdkit: curl: debug: curl: can_write
nbdkit: curl: debug: curl: can_zero
nbdkit: curl: debug: curl: can_fast_zero
nbdkit: curl: debug: curl: can_trim
nbdkit: curl: debug: curl: can_fua
nbdkit: curl: debug: curl: can_flush
nbdkit: curl: debug: curl: is_rotational
nbdkit: curl: debug: curl: can_multi_conn
nbdkit: curl: debug: curl: can_cache
nbdkit: curl: debug: curl: can_extents
nbdkit: curl: debug: newstyle negotiation: flags: export 0x8c1
nbdkit: curl: debug: curl: block_size
nbdkit: curl: debug: newstyle negotiation: NBD_OPT_GO: NBD_INFO_BLOCK_SIZE: client requested but no plugin or filter provided block size information, ignoring client request
nbdkit: curl: debug: handshake complete, processing requests serially
nbdkit: curl: debug: curl: pread count=512 offset=0
nbdkit: curl: debug: curl: running header-script
nbdkit: curl: debug: header-script returned 2 header(s)
nbdkit: curl: debug: Found bundle for host: 0x55fe75469050 [serially]
nbdkit: curl: debug: Can not multiplex, even if we wanted to
nbdkit: curl: debug: Connection #0 is still name resolving, can't reuse
nbdkit: curl: debug:   Trying /tmp/wswOJAjw/sock:0...
nbdkit: curl: debug: Connected to localhost () port 80 (#1)
nbdkit: curl: debug: C: GET /disk HTTP/1.1

This eventually causes problems with the test execution. I can reproduce this with libcurl 7.85.0.

After running with a couple of previous versions, eventually I was able to bisect the commit 0f23341.

I am very new to the curl codebase, but it seems to me that after the mentioned change, the primay_ip field is not properly updated anymore when UNIX sockets are used:

curl/lib/url.c

Lines 1253 to 1258 in 83de62b

	if(!check->primary_ip[0]) {
	infof(data,
	"Connection #%ld is still name resolving, can't reuse",
	check->connection_id);
	continue;
	}

Also in the log, the output of Curl_verboseconnect is Connected to localhost () port 80 (#1) and here the primary_ip is empty as well (in ()).

I was able to fix the problem with the bellow patch by handling the newly introduced TRNSPRT_UNIX in Curl_updateconninfo:

diff --git a/lib/connect.c b/lib/connect.c
index c1d8cfd39..d830c00fc 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -774,6 +774,11 @@ void Curl_updateconninfo(struct Curl_easy *data, struct connectdata *conn,
     Curl_conninfo_local(data, sockfd, local_ip, &local_port);
   }
 #endif
+  else if(conn->transport == TRNSPRT_UNIX) {
+    if(!conn->bits.reuse)
+      Curl_conninfo_remote(data, conn, sockfd);
+    Curl_conninfo_local(data, sockfd, local_ip, &local_port);
+  }
 
   /* persist connection info in session handle */
   Curl_persistconninfo(data, conn, local_ip, local_port);

I just wanted to share the patch and get some feedback. Would that be a proper way to fix the issue?

I did this

I expected the following

curl/libcurl version

[curl -V output]

operating system

[bagder]

Thanks for the report and the patch. I think it can be simplified somewhat. Let me make an attempt in a PR that you can test...

[bagder]

Try #9670!

[vasiliy-ul]

Try #9670!

Works fine:

nbdkit: curl: debug: Re-using existing connection #0 with host localhost
nbdkit: curl: debug: Connected to localhost (/tmp/wsUh9Vjj/sock) port 80 (#0)
nbdkit: curl: debug: C: GET /disk HTTP/1.1

[vasiliy-ul]

Thanks for taking care of that!