feat: log http proxy error

goproxy actually discard all upstream errors, you can find its error
handling here [1], the upstream error from proxy.connectDial() is always
hidden in the two if branches, and never got logged. we need to log
hysteria layer errors by ourselves.

[1] 8ea89ba920/https.go (L321-L328)

according to some bug reports (such like #404 and the resolve_preference
one report via telegram private message), some users use http proxy, got a
http 502 error without any useful logs.

cmd/client.go

@@ -228,14 +228,19 @@ func client(config *clientConfig) {
 				}
 			}
 			proxy, err := hyHTTP.NewProxyHTTPServer(client, transport.DefaultClientTransport,
-				time.Duration(config.HTTP.Timeout)*time.Second, aclEngine,
+				time.Duration(config.HTTP.Timeout)*time.Second, aclEngine, authFunc,
 				func(reqAddr string, action acl.Action, arg string) {
 					logrus.WithFields(logrus.Fields{
 						"action": actionToString(action, arg),
 						"dst":    defaultIPMasker.Mask(reqAddr),
 					}).Debug("HTTP request")
 				},
-				authFunc)
+				func(reqAddr string, err error) {
+					logrus.WithFields(logrus.Fields{
+						"error": err,
+						"dst":   defaultIPMasker.Mask(reqAddr),
+					}).Info("HTTP error")
+				})
 			if err != nil {
 				logrus.WithField("error", err).Fatal("Failed to initialize HTTP server")
 			}

pkg/http/server.go

@@ -18,8 +18,10 @@ import (
 )
 
 func NewProxyHTTPServer(hyClient *core.Client, transport *transport.ClientTransport, idleTimeout time.Duration,
-	aclEngine *acl.Engine, newDialFunc func(reqAddr string, action acl.Action, arg string),
+	aclEngine *acl.Engine,
 	basicAuthFunc func(user, password string) bool,
+	newDialFunc func(reqAddr string, action acl.Action, arg string),
+	proxyErrorFunc func(reqAddr string, err error),
 ) (*goproxy.ProxyHttpServer, error) {
 	proxy := goproxy.NewProxyHttpServer()
 	proxy.Logger = &nopLogger{}
@@ -46,27 +48,44 @@ func NewProxyHTTPServer(hyClient *core.Client, transport *transport.ClientTransp
 				if resErr != nil {
 					return nil, resErr
 				}
-				return transport.DialTCP(&net.TCPAddr{
+				conn, err := transport.DialTCP(&net.TCPAddr{
 					IP:   ipAddr.IP,
 					Port: int(port),
 					Zone: ipAddr.Zone,
 				})
+				if err != nil {
+					proxyErrorFunc(addr, err)
+				}
+				return conn, err
 			case acl.ActionProxy:
-				return hyClient.DialTCP(addr)
+				conn, err := hyClient.DialTCP(addr)
+				if err != nil {
+					proxyErrorFunc(addr, err)
+				}
+				return conn, err
 			case acl.ActionBlock:
-				return nil, errors.New("blocked by ACL")
+				err := errors.New("blocked by ACL")
+				proxyErrorFunc(addr, err)
+				return nil, err
 			case acl.ActionHijack:
 				hijackIPAddr, err := transport.ResolveIPAddr(arg)
 				if err != nil {
+					proxyErrorFunc(addr, err)
 					return nil, err
 				}
-				return transport.DialTCP(&net.TCPAddr{
+				conn, err := transport.DialTCP(&net.TCPAddr{
 					IP:   hijackIPAddr.IP,
 					Port: int(port),
 					Zone: hijackIPAddr.Zone,
 				})
+				if err != nil {
+					proxyErrorFunc(addr, err)
+				}
+				return conn, err
 			default:
-				return nil, fmt.Errorf("unknown action %d", action)
+				err := fmt.Errorf("unknown action %d", action)
+				proxyErrorFunc(addr, err)
+				return nil, err
 			}
 		},
 		IdleConnTimeout: idleTimeout,