diff --git a/app/packet_dispatcher.go b/app/packet_dispatcher.go
index dba6bc39..48dcf9e1 100644
--- a/app/packet_dispatcher.go
+++ b/app/packet_dispatcher.go
@@ -5,6 +5,8 @@ import (
 	"github.com/v2ray/v2ray-core/transport/ray"
 )
 
+// PacketDispatcher dispatch a packet and possibly further network payload to
+// its destination.
 type PacketDispatcher interface {
 	DispatchToOutbound(packet v2net.Packet) ray.InboundRay
 }
diff --git a/common/log/log.go b/common/log/log.go
index 0cff1a06..786509e6 100644
--- a/common/log/log.go
+++ b/common/log/log.go
@@ -76,18 +76,22 @@ func SetLogLevel(level LogLevel) {
 	}
 }
 
+// Debug outputs a debug log with given format and optional arguments.
 func Debug(format string, v ...interface{}) {
 	debugLogger.WriteLog("[Debug]", format, v...)
 }
 
+// Info outputs an info log with given format and optional arguments.
 func Info(format string, v ...interface{}) {
 	infoLogger.WriteLog("[Info]", format, v...)
 }
 
+// Warning outputs a warning log with given format and optional arguments.
 func Warning(format string, v ...interface{}) {
 	warningLogger.WriteLog("[Warning]", format, v...)
 }
 
+// Error outputs an error log with given format and optional arguments.
 func Error(format string, v ...interface{}) {
 	errorLogger.WriteLog("[Error]", format, v...)
 }
diff --git a/proxy/inbound_connection.go b/proxy/inbound_connection.go
index 5d648961..2ad25595 100644
--- a/proxy/inbound_connection.go
+++ b/proxy/inbound_connection.go
@@ -4,10 +4,15 @@ import (
 	"github.com/v2ray/v2ray-core/app"
 )
 
+// A InboundConnectionHandlerFactory creates InboundConnectionHandler on demand.
 type InboundConnectionHandlerFactory interface {
+	// Create creates a new InboundConnectionHandler with given configuration.
 	Create(dispatch app.PacketDispatcher, config interface{}) (InboundConnectionHandler, error)
 }
 
+// A InboundConnectionHandler handles inbound network connections to V2Ray.
 type InboundConnectionHandler interface {
+	// Listen starts a InboundConnectionHandler by listen on a specific port. This method is called
+	// exactly once during runtime.
 	Listen(port uint16) error
 }
diff --git a/proxy/outbound_connection.go b/proxy/outbound_connection.go
index 3c8230cf..67fd8996 100644
--- a/proxy/outbound_connection.go
+++ b/proxy/outbound_connection.go
@@ -5,10 +5,14 @@ import (
 	"github.com/v2ray/v2ray-core/transport/ray"
 )
 
+// An OutboundConnectionHandlerFactory creates OutboundConnectionHandler on demand.
 type OutboundConnectionHandlerFactory interface {
+	// Create creates a new OutboundConnectionHandler with given config.
 	Create(config interface{}) (OutboundConnectionHandler, error)
 }
 
+// An OutboundConnectionHandler handles outbound network connection for V2Ray.
 type OutboundConnectionHandler interface {
+	// Dispatch sends one or more Packets to its destination.
 	Dispatch(firstPacket v2net.Packet, ray ray.OutboundRay) error
 }
diff --git a/transport/ray/direct.go b/transport/ray/direct.go
index b70a0c46..88c36ab8 100644
--- a/transport/ray/direct.go
+++ b/transport/ray/direct.go
@@ -8,6 +8,7 @@ const (
 	bufferSize = 16
 )
 
+// NewRay creates a new Ray for direct traffic transport.
 func NewRay() Ray {
 	return &directRay{
 		Input:  make(chan *alloc.Buffer, bufferSize),