http: fix HTTP shutdown panicking

cmd/chihaya/main.go

@@ -124,7 +124,7 @@ func rootCmdRun(cmd *cobra.Command, args []string) error {
 				close(shutdown)
 				closed = true
 			} else {
-				log.Infoln(bufErr)
+				log.Errorln(bufErr)
 			}
 			bufErr = err
 		}
@@ -175,7 +175,7 @@ func startFrontends(httpConfig httpfrontend.Config, udpConfig udpfrontend.Config
 		go func() {
 			log.Infoln("started serving HTTP on", httpConfig.Addr)
 			if err := httpFrontend.ListenAndServe(); err != nil {
-				errChan <- errors.New("failed to cleanly shutdown HTTP frontend: " + err.Error())
+				errChan <- err
 			}
 		}()
 	}
@@ -186,7 +186,7 @@ func startFrontends(httpConfig httpfrontend.Config, udpConfig udpfrontend.Config
 		go func() {
 			log.Infoln("started serving UDP on", udpConfig.Addr)
 			if err := udpFrontend.ListenAndServe(); err != nil {
-				errChan <- errors.New("failed to cleanly shutdown UDP frontend: " + err.Error())
+				errChan <- err
 			}
 		}()
 	}

frontend/http/frontend.go

@@ -5,6 +5,7 @@ package http
 import (
 	"context"
 	"crypto/tls"
+	"errors"
 	"net"
 	"net/http"
 	"time"
@@ -144,10 +145,8 @@ func (t *Frontend) ListenAndServe() error {
 	}
 
 	// Start the HTTP server and gracefully handle any network errors.
-	if err := t.s.ListenAndServe(); err != nil {
+	if err := t.s.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-		if opErr, ok := err.(*net.OpError); !ok || (ok && opErr.Op != "accept") {
+		return errors.New("http: failed to run HTTP server: " + err.Error())
-			panic("http: failed to gracefully run HTTP server: " + err.Error())
-		}
 	}
 
 	return nil