Improve TLS handshake error logging.

pkg/proxyserver/proxyserver.go

@@ -84,9 +84,7 @@ func (server *Server) serveConn(conn net.Conn) {
 			io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
 		}
 
-		if errors.Is(err, context.Canceled) ||
-			errors.Is(err, io.EOF) ||
-			errors.Is(err, syscall.ECONNRESET) {
+		if isNetworkOrClientError(err) {
 			server.vlogf("tls handshake failed (%s), client error: %s", conn.RemoteAddr(), err)
 		} else {
 			server.logf("tls handshake error (%s): %s", conn.RemoteAddr(), err)
@@ -312,3 +310,13 @@ func tlsRecordHeaderLooksLikeHTTP(hdr [5]byte) bool {
 	}
 	return false
 }
+
+func isNetworkOrClientError(err error) bool {
+	var netOpErr *net.OpError
+	return errors.Is(err, context.Canceled) ||
+		errors.Is(err, context.DeadlineExceeded) ||
+		errors.Is(err, io.EOF) ||
+		errors.Is(err, syscall.ECONNRESET) ||
+		// https://github.com/golang/go/blob/release-branch.go1.22/src/crypto/tls/conn.go#L724
+		(errors.As(err, &netOpErr) && netOpErr.Op == "remote error")
+}

pkg/proxyserver/proxyserver_test.go

@@ -0,0 +1,38 @@
+package proxyserver
+
+import (
+	"fmt"
+	"net"
+	"testing"
+)
+
+func TestIsNetworkOrClientError(t *testing.T) {
+	// https://github.com/golang/go/blob/release-branch.go1.22/src/crypto/tls/alert.go#L77
+	alert := fmt.Errorf("unknown certificate authority")
+	// https://github.com/golang/go/blob/release-branch.go1.22/src/crypto/tls/conn.go#L724
+	err := setErrorLocked(&net.OpError{Op: "remote error", Err: alert})
+	if isNetworkOrClientError(err) == false {
+		t.Error("expected tls alert record is client error, got false")
+	}
+
+	if isNetworkOrClientError(fmt.Errorf("some random error")) {
+		t.Error("expected random error is not client error, got true")
+	}
+}
+
+type permanentError struct {
+	err net.Error
+}
+
+func (e *permanentError) Error() string   { return e.err.Error() }
+func (e *permanentError) Unwrap() error   { return e.err }
+func (e *permanentError) Timeout() bool   { return e.err.Timeout() }
+func (e *permanentError) Temporary() bool { return false }
+
+func setErrorLocked(err error) error {
+	if e, ok := err.(net.Error); ok {
+		return &permanentError{err: e}
+	} else {
+		return err
+	}
+}