[tor-commits] [snowflake/main] Release resources in client Transport.Dial on error.

[cohosh at torproject.org]

commit ae7cc478fd345a1e588f8315ec980809c6806372
Author: David Fifield <david at bamsoftware.com>
Date:   Mon May 24 15:09:29 2021 -0600

    Release resources in client Transport.Dial on error.
    
    Make a stack of cleanup functions to run (as with defer), but clear the
    stack before returning if no error occurs.
    
    Uselessly pushing the stream.Close() cleanup just before clearing the
    stack is an intentional safeguard, for in case additional operations are
    added before the return in the future.
    
    Fixes #40042.
---
 client/lib/snowflake.go | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/client/lib/snowflake.go b/client/lib/snowflake.go
index 6e87b81..f643c0a 100644
--- a/client/lib/snowflake.go
+++ b/client/lib/snowflake.go
@@ -74,11 +74,21 @@ func NewSnowflakeClient(brokerURL, frontDomain string, iceAddresses []string, ke
 // Create a new Snowflake connection. Starts the collection of snowflakes and returns a
 // smux Stream.
 func (t *Transport) Dial() (net.Conn, error) {
+	// Cleanup functions to run before returning, in case of an error.
+	var cleanup []func()
+	defer func() {
+		// Run cleanup in reverse order, as defer does.
+		for i := len(cleanup) - 1; i >= 0; i-- {
+			cleanup[i]()
+		}
+	}()
+
 	// Prepare to collect remote WebRTC peers.
 	snowflakes, err := NewPeers(t.dialer)
 	if err != nil {
 		return nil, err
 	}
+	cleanup = append(cleanup, func() { snowflakes.End() })
 
 	// Use a real logger to periodically output how much traffic is happening.
 	snowflakes.BytesLogger = NewBytesSyncLogger()
@@ -92,15 +102,22 @@ func (t *Transport) Dial() (net.Conn, error) {
 	if err != nil {
 		return nil, err
 	}
+	cleanup = append(cleanup, func() {
+		pconn.Close()
+		sess.Close()
+	})
 
 	// On the smux session we overlay a stream.
 	stream, err := sess.OpenStream()
 	if err != nil {
 		return nil, err
 	}
-
 	// Begin exchanging data.
 	log.Printf("---- SnowflakeConn: begin stream %v ---", stream.ID())
+	cleanup = append(cleanup, func() { stream.Close() })
+
+	// All good, clear the cleanup list.
+	cleanup = nil
 	return &SnowflakeConn{Stream: stream, sess: sess, pconn: pconn, snowflakes: snowflakes}, nil
 }