Graceful: Allow graceful restart for unix sockets (#9113)

Previously we could not handle graceful restarts for http over unix
sockets. These can now be handled.

modules/graceful/net_unix.go

@@ -16,6 +16,7 @@ import (
 	"sync"
 
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
 )
 
 const (
@@ -165,15 +166,27 @@ func GetListenerUnix(network string, address *net.UnixAddr) (*net.UnixListener,
 		if isSameAddr(l.Addr(), address) {
 			providedListeners = append(providedListeners[:i], providedListeners[i+1:]...)
 			activeListeners = append(activeListeners, l)
-			return l.(*net.UnixListener), nil
+			unixListener := l.(*net.UnixListener)
+			unixListener.SetUnlinkOnClose(true)
+			return unixListener, nil
 		}
 	}
 
 	// make a fresh listener
+	if err := os.Remove(address.Name); err != nil && !os.IsNotExist(err) {
+		return nil, fmt.Errorf("Failed to remove unix socket %s: %v", address.Name, err)
+	}
+
 	l, err := net.ListenUnix(network, address)
 	if err != nil {
 		return nil, err
 	}
+
+	fileMode := os.FileMode(setting.UnixSocketPermission)
+	if err = os.Chmod(address.Name, fileMode); err != nil {
+		return nil, fmt.Errorf("Failed to set permission of unix socket to %s: %v", fileMode.String(), err)
+	}
+
 	activeListeners = append(activeListeners, l)
 	return l, nil
 }