xprotocol

README

XProtocol Development Guide

This guide is written for potential developer who wants to extend their own RPC protocols in XProtocol framework.

Introduction

Make sure you have already known the basic architecture of MOSN.

XProtocol framework is designed for making extension of new protocols much easier. The framwork providing stream-level common behaviour template and protocol-level interfaces for typical RPC protocols, like SOFABolt and Dubbo.

All you need is to write protocol-level extension and implements the interfaces defined by XProtocol.

TODO: pic

Quick-start

In the section, "x_example" protocol(code folder: pkg/protocol/xprotocol/example) will be taken as example to demonstrates how to develop a brand new protocol with XProtocol framework.

Generally speaking, There are three steps:

1. Confirm the protocol format
2. Define packet models
3. Define protocol behaviours

Confirm the protocol format

First of all, take a glance at the protocol format. All of the following works are dependent with the protocol design itself.

/**
 * Request command
 * 0     1     2           4           6           8          10           12          14         16
 * +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
 * |magic| type| dir |      requestId        |     payloadLength     |     payload bytes ...       |
 * +-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
 *
 * Response command
 * 0     1     2     3     4           6           8          10           12          14         16
 * +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
 * |magic| type| dir |      requestId        |   status  |      payloadLength    | payload bytes ..|
 * +-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
 */

Once the format is determined, we should be aware of the binary bytes format, the packet model layout and how to encode/decode them.

Define packet models

Based on the protocol format, now we can define our packet models. Models will be treated as programmable objects in higher-level, like in Proxy and Router module. In particular, XProtocol framework defined a standard set of interfaces to abstract the ability XProtocol needed. Packet models should implement the interfaces by case.

Define model structure

Usually the struct is determined by the protocol format, keep the logical mapping between them.

type Request struct {
	Type       byte
	RequestId  uint32
	PayloadLen uint32
	Payload    []byte
	Content    types.IoBuffer
}

type Response struct {
	Request
	Status uint16
}

Implement XProtocol interfaces

Request and response should implement the XFrame and XRespFrame interface, XProtocol framework is dependent on the abilities provided by the interfaces, such as Multiplexing and HeartbeatPredicate.

Multiplexing provides the ability to distinguish multi-requests in single-connection by recognize 'request-id' semantics. And HeartbeatPredicate provides the ability to judge if current frame is a heartbeat, which is usually used to make connection keepalive

// XFrame represents the minimal programmable object of the protocol.
type XFrame interface {
	// TODO: make multiplexing optional, and maybe we can support PING-PONG protocol in this framework.
	Multiplexing

	HeartbeatPredicate

	GetStreamType() StreamType

	GetHeader() types.HeaderMap

	GetData() types.IoBuffer
}

// XRespFrame expose response status code based on the XFrame
type XRespFrame interface {
	XFrame

	GetStatusCode() uint32
}

Define protocol behaviours

Beside the concrete packet frame, XProtocol framework also need some ability which should provided by the general protocol. And this is also represent in the interface form as following:

// XProtocol provides extra ability(Heartbeater, Hijacker) to interacts with the proxy framework based on the Protocol interface.
// e.g. A request which cannot find route should be responded with a error response like '404 Not Found', that is what Hijacker
// interface exactly provides.
type XProtocol interface {
	types.Protocol

	Heartbeater

	Hijacker
}

What you need is to implement the protocol and register it into XProtocol framework.

func init() {
	xprotocol.RegisterProtocol(ProtocolName, &proto{})
}

At last, don't forget to import your implementation at the entry point cmd/mosn/main and speficy the sub protocol in configuration.

import _ "mosn.io/mosn/pkg/protocol/xprotocol/example"

...
{
  "type": "proxy",
  "config": {
    "downstream_protocol": "X",
    "upstream_protocol": "X",
    "router_config_name": "router",
    "extend_config": {
      "sub_protocol": "x_example"
    }
  }
}
...

That's it, the 'x_example' protocol is done!

Tips, Tricks and Hacks

Stateless codec with MOSN goroutine model

No blocking

The most common goroutine model for I/O multiplexing codec is like the following:

• FrameReader: responsible for continually read data from connection, and parse the raw data into frame. Frames will be pass to the FrameProcessor by channels.
• FrameProcessor: responsible for continually read frames from FrameReader, and process the frames properly.

And the codec logic is embed in the FrameReader, usually write as blocking mode(Take the benefit of golang netpoll mode). So the logic flow is like:

1. (entry code) FrameReader: start frame decode loop.
2. FrameReader: blocking read data util it meets the minimal length(usually the length of frame header).
3. FrameReader: parse the header and blocking read data util it meets the length of a whole frame.
4. FrameReader: frame parse success, pass it to FrameProcessor by channel.

But in MOSN its kind different, you cannot directly read from the connection, but interacts with the I/O buffer which MOSN provides.

1. (entry code) ReadGoroutine: start data read loop.
2. ReadGoroutine: read as much as possible, and fill it into the I/O buffer
3. ReadGoroutine: notify the listeners and pass the I/O buffer to them.

In conclusion, your codec codes is running at the read goroutine, and you cannot directly read from net.Conn, which means no netpoll works here. So if your code has blocking part to wait for more data available, the whole read goroutine is blocked and no more data would fill into the I/O buffer, which causes the dead lock.

Buffer management for I/O multiplexing

Alloc new buffer for your data

I/O buffer is managed by the read goroutine, be careful about its lifecycle.For example, while new data is available, read goroutine will notify the ReadFilter listeners, including the codec impls. And decoder will receive a parameter with type types.IoBuffer, which contains the readable data.

After decode finished you will get a protocol-specific model, like bolt.Request. Make sure no pointers/references in the model points to the types.IoBuffer parameter, because it might be recycled by the read goroutine.

Hack of Append headers/data/trailers

Pass your model as headers and ignore data/trailers

The typical stream layer is designed for most common protocols, like HTTP, HTTP/2, etc. So it has the traditional parts for transmission separation: headers, data, trailers. It's good for some scenarios, like upload files by streaming mode, etc.

But for most RPC protocols, there is no need to divide the transmission of the request into several parts. And, the payload size usually is not large, which means streaming is not critical. On the contrary, use append headers/data/trailers for RPC protocols might break the memory recycle usage for the whole request.

So we use a trick here, decorate your model as types.HeaderMap and pass it by append headers. The XProtocol framework would recognize this and ignore append data/trailers.

Documentation

Index

• Variables
• func DecodeHeader(bytes []byte, h *Header) (err error)
• func EncodeHeader(buf types.IoBuffer, h *Header)
• func GetHeaderEncodeLength(h *Header) (size int)
• func GetMapping(name types.ProtocolName) protocol.HTTPMapping
• func GetMatcher(name types.ProtocolName) types.ProtocolMatch
• func RegisterMapping(name types.ProtocolName, mapping protocol.HTTPMapping) error
• func RegisterMatcher(name types.ProtocolName, matcher types.ProtocolMatch) error
• func RegisterProtocol(name types.ProtocolName, protocol XProtocol) error
• type BytesKV
• type GoAwayPredicate
• type Header
  • func (h *Header) Add(Key string, Value string)
  • func (h *Header) ByteSize() (size uint64)
  • func (h *Header) Clone() *Header
  • func (h *Header) Del(Key string)
  • func (h *Header) Get(Key string) (Value string, ok bool)
  • func (h *Header) Range(f func(Key, Value string) bool)
  • func (h *Header) Set(Key string, Value string)
• type HeartbeatPredicate
• type Heartbeater
• type Hijacker
• type Multiplexing
• type ServiceAware
• type StreamType
• type XEngine
  • func NewXEngine(protocols []string) (*XEngine, error)
  • func (engine *XEngine) Match(ctx context.Context, data types.IoBuffer) (types.Protocol, types.MatchResult)
  • func (engine *XEngine) Register(matchFunc types.ProtocolMatch, protocol types.Protocol) error
• type XFrame
• type XProtocol
  • func GetProtocol(name types.ProtocolName) XProtocol
• type XRespFrame

Variables

var (
	ErrNoSubProtocolFound = errors.New("no sub protocol found in context")
	ErrNoDelegateFound    = errors.New("no sub protocol delegate function found")
)

var (
	AlreadyRegistered = "protocol code already registered"
	UnknownType       = "unknown model type"
	UnrecognizedCode  = "unrecognized protocol code"
	NoProtocolCode    = "no protocol code found"

	ErrDupRegistered    = errors.New(AlreadyRegistered)
	ErrUnknownType      = errors.New(UnknownType)
	ErrUnrecognizedCode = errors.New(UnrecognizedCode)
	ErrNoProtocolCode   = errors.New(NoProtocolCode)
)

Error def

Functions

func DecodeHeader

func DecodeHeader(bytes []byte, h *Header) (err error)

func EncodeHeader

func EncodeHeader(buf types.IoBuffer, h *Header)

func GetHeaderEncodeLength

func GetHeaderEncodeLength(h *Header) (size int)

func GetMapping

func GetMapping(name types.ProtocolName) protocol.HTTPMapping

GetMapping return the corresponding HTTP status code mapping function for given name(if was registered)

func GetMatcher

func GetMatcher(name types.ProtocolName) types.ProtocolMatch

GetMatcher return the corresponding matcher for given name(if was registered)

func RegisterMapping

func RegisterMapping(name types.ProtocolName, mapping protocol.HTTPMapping) error

RegisterMapping register the HTTP status code mapping function of the protocol into factory

func RegisterMatcher

func RegisterMatcher(name types.ProtocolName, matcher types.ProtocolMatch) error

RegisterMatcher register the matcher of the protocol into factory

func RegisterProtocol

func RegisterProtocol(name types.ProtocolName, protocol XProtocol) error

RegisterProtocol register the protocol to factory

Types

type BytesKV

type BytesKV struct {
	Key   []byte
	Value []byte
}

BytesKV key-value pair in byte slice

type GoAwayPredicate

type GoAwayPredicate interface {
	IsGoAwayFrame() bool
}

HeartbeatPredicate provides the ability to judge if current is a goaway frmae, which indicates that current connection should be no longer used and turn into the draining state.

type Header

type Header struct {
	Kvs []BytesKV

	Changed bool
}

Header consists of multi key-value pair in byte slice formation. This could reduce the cost of []byte to string for protocol codec.

func (*Header) Add

func (h *Header) Add(Key string, Value string)

func (*Header) ByteSize

func (h *Header) ByteSize() (size uint64)

func (*Header) Clone

func (h *Header) Clone() *Header

func (*Header) Del

func (h *Header) Del(Key string)

func (*Header) Get

func (h *Header) Get(Key string) (Value string, ok bool)

~ HeaderMap

func (*Header) Range

func (h *Header) Range(f func(Key, Value string) bool)

func (*Header) Set

func (h *Header) Set(Key string, Value string)

type HeartbeatPredicate

type HeartbeatPredicate interface {
	IsHeartbeatFrame() bool
}

HeartbeatPredicate provides the ability to judge if current frame is a heartbeat, which is usually used to make connection keepalive

type Heartbeater

type Heartbeater interface {
	// Trigger builds an active heartbeat command
	Trigger(requestId uint64) XFrame

	// Reply builds heartbeat command corresponding to the given requestID
	Reply(request XFrame) XRespFrame
}

HeartbeatBuilder provides the ability to construct proper heartbeat command for xprotocol sub-protocols

type Hijacker

type Hijacker interface {
	// BuildResponse build response with given status code
	Hijack(statusCode uint32) XRespFrame

	// Mapping the http status code, which used by proxy framework into protocol-specific status
	Mapping(httpStatusCode uint32) uint32
}

Hijacker provides the ability to construct proper response command for xprotocol sub-protocols

type Multiplexing

type Multiplexing interface {
	GetRequestId() uint64

	SetRequestId(id uint64)
}

Multiplexing provides the ability to distinguish multi-requests in single-connection by recognize 'request-id' semantics

type ServiceAware

type ServiceAware interface {
	GetServiceName() string

	GetMethodName() string
}

ServiceAware provides the ability to get the most common info for rpc invocation: service name and method name

type StreamType

type StreamType int

StreamType distinguish the stream flow type. Request: stream is a normal request and needs response RequestOneWay: stream is a oneway request and doesn't need response Response: stream is a response to specific request

const (
	Request StreamType = iota
	RequestOneWay
	Response
)

type XEngine

type XEngine struct {
	// contains filtered or unexported fields
}

XEngine is an implementation of the ProtocolEngine interface

func NewXEngine

func NewXEngine(protocols []string) (*XEngine, error)

func (*XEngine) Match

func (engine *XEngine) Match(ctx context.Context, data types.IoBuffer) (types.Protocol, types.MatchResult)

Match use registered matchFunc to recognize corresponding protocol

func (*XEngine) Register

func (engine *XEngine) Register(matchFunc types.ProtocolMatch, protocol types.Protocol) error

Register register protocol, which recognized by the matchFunc

type XFrame

type XFrame interface {
	// TODO: make multiplexing optional, and maybe we can support PING-PONG protocol in this framework.
	Multiplexing

	HeartbeatPredicate

	GetStreamType() StreamType

	GetHeader() types.HeaderMap

	GetData() types.IoBuffer

	SetData(data types.IoBuffer)
}

XFrame represents the minimal programmable object of the protocol.

type XProtocol

type XProtocol interface {
	types.Protocol

	Heartbeater

	Hijacker
}

XProtocol provides extra ability(Heartbeater, Hijacker) to interacts with the proxy framework based on the Protocol interface. e.g. A request which cannot find route should be responded with a error response like '404 Not Found', that is what Hijacker interface exactly provides.

func GetProtocol

func GetProtocol(name types.ProtocolName) XProtocol

GetProtocol return the corresponding protocol for given name(if was registered)

type XRespFrame

type XRespFrame interface {
	XFrame

	GetStatusCode() uint32
}

XRespFrame expose response status code based on the XFrame