fix(proxy): log pprof serve errors instead of clean shutdowns

proxy/proxy.go

@@ -120,13 +120,7 @@ func (p *Server) Start() error {
 			return fmt.Errorf("failed to listen on port %v for pprof server: %v", p.pprofPort, err)
 		}
 
-		go func() {
-			p.logger.Info("Serving pprof on existing listener", "port", p.pprofPort)
-			if err := p.pprofServer.Serve(ln); err != nil && errors.Is(err, http.ErrServerClosed) {
-				p.logger.Error("pprof server error", "error", err)
-			}
-		}()
-
+		go p.servePprof(ln)
 	}
 
 	var err error
@@ -158,6 +152,16 @@ func (p *Server) Start() error {
 	return nil
 }
 
+// servePprof serves pprof on ln until the pprof server is shut down. Serve
+// always returns a non-nil error, and http.ErrServerClosed is the expected
+// result of Stop, so only other errors are logged.
+func (p *Server) servePprof(ln net.Listener) {
+	p.logger.Info("Serving pprof on existing listener", "port", p.pprofPort)
+	if err := p.pprofServer.Serve(ln); err != nil && !errors.Is(err, http.ErrServerClosed) {
+		p.logger.Error("pprof server error", "error", err)
+	}
+}
+
 // Stops proxy server
 func (p *Server) Stop() error {
 	if p.isStopped() {

proxy/proxy_test.go

@@ -1,7 +1,14 @@
 package proxy
 
 import (
+	"bytes"
+	"context"
+	"log/slog"
+	"net"
+	"net/http"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 // TestProxyServerBasicHTTP tests basic HTTP request handling
@@ -63,3 +70,44 @@ func TestProxyServerBasicHTTPS(t *testing.T) {
 		pt.ExpectDeny("https://localhost:8080/", "example.com")
 	})
 }
+
+// TestServePprofLogsOnlyUnexpectedErrors verifies that a normal pprof
+// shutdown is not reported as an error, while a real serve failure is.
+func TestServePprofLogsOnlyUnexpectedErrors(t *testing.T) {
+	newServer := func(logs *bytes.Buffer) *Server {
+		return &Server{
+			logger:      slog.New(slog.NewTextHandler(logs, nil)),
+			pprofServer: &http.Server{},
+		}
+	}
+
+	t.Run("ShutdownIsNotAnError", func(t *testing.T) {
+		var logs bytes.Buffer
+		p := newServer(&logs)
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		require.NoError(t, err)
+
+		done := make(chan struct{})
+		go func() {
+			p.servePprof(ln)
+			close(done)
+		}()
+		require.NoError(t, p.pprofServer.Shutdown(context.Background()))
+		<-done
+
+		require.NotContains(t, logs.String(), "pprof server error")
+	})
+
+	t.Run("ServeFailureIsLogged", func(t *testing.T) {
+		var logs bytes.Buffer
+		p := newServer(&logs)
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		require.NoError(t, err)
+		// Serve fails immediately on a closed listener.
+		require.NoError(t, ln.Close())
+
+		p.servePprof(ln)
+
+		require.Contains(t, logs.String(), "pprof server error")
+	})
+}