Add simple logging facility.

config.json

@@ -3,5 +3,6 @@
     "server_port":8388,
     "local_port":1080,
     "password":"barfoo!",
-    "timeout":60
+    "timeout":60,
+    "debug":true
 }

shadowsocks/config.go

@@ -20,6 +20,7 @@ type Config struct {
 	LocalPort    int               `json:"local_port"`
 	Password     string            `json:"password"`
 	PortPassword map[string]string `json:"port_password"`
+	Debug        bool              `json:"debug"`
 }
 
 func ParseConfig(path string) *Config {
@@ -36,5 +37,6 @@ func ParseConfig(path string) *Config {
 	if err = json.Unmarshal(data, &config); err != nil {
 		log.Fatal("can not parse config:", err)
 	}
+	Debug = DebugLog(config.Debug)
 	return &config
 }

shadowsocks/config_test.go

@@ -10,6 +10,9 @@ func TestParseConfig1Password(t *testing.T) {
 	if config.Password != "barfoo!" {
 		t.Error("wrong password from config")
 	}
+	if config.Debug != true {
+		t.Error("debug option wrong")
+	}
 }
 
 func TestParseConfigMultiPassword(t *testing.T) {

shadowsocks/log.go

@@ -0,0 +1,24 @@
+package shadowsocks
+
+import (
+	"log"
+	"os"
+)
+
+type DebugLog bool
+
+var Debug DebugLog
+
+var dbgLog = log.New(os.Stdout, "[DEBUG] ", log.Ltime)
+
+func (d DebugLog) Printf(format string, args ...interface{}) {
+	if d {
+		dbgLog.Printf(format, args...)
+	}
+}
+
+func (d DebugLog) Println(args ...interface{}) {
+	if d {
+		dbgLog.Println(args...)
+	}
+}

shadowsocks/testdata/config-one-passwd.json

@@ -3,5 +3,6 @@
     "server_port":8388,
     "local_port":1081,
     "password":"barfoo!",
-    "timeout":60
+    "timeout":60,
+    "debug": true
 }