fix(proxy): don't shutdown 'uc proxy' when a client connection aborts

internal/proxy/proxy.go

@@ -2,11 +2,12 @@ package proxy
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"net"
-	"os"
 	"sync"
+	"syscall"
 	"time"
 )
 
@@ -15,58 +16,53 @@ type Proxy struct {
 	Listener    net.Listener
 	RemoteAddr  string
 	DialContext func(ctx context.Context, network, address string) (net.Conn, error)
+	// OnError is called for errors that occur during proxying individual connections. It may be called concurrently
+	// for different connections.
 	OnError     func(error)
 	activeConns sync.WaitGroup
 }
 
-// deadliner is an interface for listeners that support setting deadlines.
-type deadliner interface {
-	SetDeadline(t time.Time) error
-}
-
 // halfCloser is an interface for connections that support half-close.
 type halfCloser interface {
 	CloseWrite() error
 }
 
-// Run starts the proxy and runs until the context is canceled.
-func (p *Proxy) Run(ctx context.Context) {
+// IsConnectionClosedError reports whether err indicates that a connection was closed or aborted by either peer.
+// Callers can use it to ignore routine connection shutdown or broken pipe errors reported to Proxy.OnError.
+func IsConnectionClosedError(err error) bool {
+	return errors.Is(err, net.ErrClosed) || errors.Is(err, io.ErrClosedPipe) ||
+		errors.Is(err, syscall.EPIPE) || errors.Is(err, syscall.ECONNRESET)
+}
+
+// Run starts the proxy and runs until the context is canceled or the listener fails. It returns nil when the context
+// is canceled. Errors handling individual connections are reported to OnError and do not stop the proxy.
+func (p *Proxy) Run(ctx context.Context) error {
 	if p.DialContext == nil {
 		p.DialContext = (&net.Dialer{}).DialContext
 	}
 
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
 	defer p.Listener.Close()
 
-	// Handle incoming connections until context is canceled.
-Loop:
+	// Closing the listener unblocks Accept when the context is canceled. This works for both TCP and Unix listeners
+	// and avoids polling with listener deadlines.
+	stopClose := context.AfterFunc(ctx, func() {
+		p.Listener.Close()
+	})
+	defer stopClose()
+
+	var runErr error
 	for {
-		select {
-		case <-ctx.Done():
-			break Loop
-		default:
-		}
-
-		// Set a deadline on the listener if supported to check context periodically.
-		if dl, ok := p.Listener.(deadliner); ok {
-			dl.SetDeadline(time.Now().Add(1 * time.Second))
-		}
-
 		conn, err := p.Listener.Accept()
 		if err != nil {
-			if os.IsTimeout(err) {
-				// Just a timeout, continue to check context and accept again.
-				continue
+			if ctx.Err() != nil {
+				break
 			}
 
-			select {
-			case <-ctx.Done():
-				break Loop
-			default:
-				if p.OnError != nil {
-					p.OnError(fmt.Errorf("accept local connection: %w", err))
-				}
-				continue
-			}
+			runErr = fmt.Errorf("accept local connection: %w", err)
+			cancel()
+			break
 		}
 
 		p.activeConns.Add(1)
@@ -75,6 +71,7 @@ Loop:
 
 	// Wait for all connections to finish.
 	p.activeConns.Wait()
+	return runErr
 }
 
 func (p *Proxy) handleConnection(ctx context.Context, localConn net.Conn) {
@@ -87,46 +84,62 @@ func (p *Proxy) handleConnection(ctx context.Context, localConn net.Conn) {
 
 	remoteConn, err := p.DialContext(dialCtx, "tcp", p.RemoteAddr)
 	if err != nil {
-		if p.OnError != nil {
+		if ctx.Err() == nil && p.OnError != nil {
 			p.OnError(fmt.Errorf("connect remote address '%s': %w", p.RemoteAddr, err))
 		}
 		return
 	}
 	defer remoteConn.Close()
 
-	// Bidirectional copy with proper half-close handling.
+	// Closing both connections aborts both copies after cancellation or a copy error. A clean EOF still uses
+	// half-close so the other direction can finish sending any remaining data.
+	closeConnections := func() {
+		localConn.Close()
+		remoteConn.Close()
+	}
+	stopClose := context.AfterFunc(ctx, closeConnections)
+	defer stopClose()
+
 	done := make(chan error, 2)
 
 	go func() {
 		_, err := io.Copy(remoteConn, localConn)
+		if err != nil {
+			done <- err
+			closeConnections()
+			return
+		}
 		// Close write half of remote connection if supported.
 		if hc, ok := remoteConn.(halfCloser); ok {
 			hc.CloseWrite()
 		}
-		done <- err
+		done <- nil
 	}()
 
 	go func() {
 		_, err := io.Copy(localConn, remoteConn)
+		if err != nil {
+			done <- err
+			closeConnections()
+			return
+		}
 		// Close write half of local connection if supported.
 		if hc, ok := localConn.(halfCloser); ok {
 			hc.CloseWrite()
 		}
-		done <- err
+		done <- nil
 	}()
 
-	// Wait for both copies to complete or context cancel.
+	// Wait for both copies to complete. The first error is the original failure because a copy reports it before
+	// closing the connections to unblock the other copy.
+	var copyErr error
 	for range 2 {
-		select {
-		case <-ctx.Done():
-			// Close connections to abort ongoing copies.
-			localConn.Close()
-			remoteConn.Close()
-			return
-		case err = <-done:
-			if err != nil && p.OnError != nil {
-				p.OnError(fmt.Errorf("data copy: %w", err))
-			}
+		if err = <-done; err != nil && copyErr == nil {
+			copyErr = err
 		}
 	}
+
+	if copyErr != nil && ctx.Err() == nil && p.OnError != nil {
+		p.OnError(fmt.Errorf("data copy: %w", copyErr))
+	}
 }