Outbound: One endpoint and at most one user only (#5144)

https://github.com/XTLS/Xray-core/pull/5124#issuecomment-3281091009

Fixes https://github.com/XTLS/Xray-core/pull/5124#pullrequestreview-3218097421

infra/conf/socks.go

@@ -86,12 +86,19 @@ func (v *SocksClientConfig) Build() (proto.Message, error) {
 			{
 				Address: v.Address,
 				Port:    v.Port,
-				Users:   []json.RawMessage{{}},
 			},
 		}
+		if len(v.Username) > 0 {
+			v.Servers[0].Users = []json.RawMessage{{}}
+		}
 	}
-	config.Server = make([]*protocol.ServerEndpoint, len(v.Servers))
-	for idx, serverConfig := range v.Servers {
+	if len(v.Servers) != 1 {
+		return nil, errors.New(`SOCKS settings: "servers" should have one and only one member. Multiple endpoints in "servers" should use multiple SOCKS outbounds and routing balancer instead`)
+	}
+	for _, serverConfig := range v.Servers {
+		if len(serverConfig.Users) > 1 {
+			return nil, errors.New(`SOCKS servers: "users" should have one member at most. Multiple members in "users" should use multiple SOCKS outbounds and routing balancer instead`)
+		}
 		server := &protocol.ServerEndpoint{
 			Address: serverConfig.Address.Build(),
 			Port:    uint32(serverConfig.Port),
@@ -116,9 +123,11 @@ func (v *SocksClientConfig) Build() (proto.Message, error) {
 				}
 			}
 			user.Account = serial.ToTypedMessage(account.Build())
-			server.User = append(server.User, user)
+			server.User = user
+			break
 		}
-		config.Server[idx] = server
+		config.Server = server
+		break
 	}
 	return config, nil
 }