go-libp2p 入門 example

• 官網： https://libp2p.io/
• 代碼：https://github.com/libp2p/go-libp2p

Install go-libp2p

go get -u -d github.com/libp2p/go-libp2p/...
cd $GOPATH/src/github.com/libp2p/go-libp2p
make
make deps

官網給出了安裝說明：

go get 中 -u 表示下載最新版的依賴，-d 表示只下載不安裝，當然你需要先安裝 golang 才能使用 go get ，這裡推薦安裝 1.10.x 版本

golang安裝包 : https://studygolang.com/dl

make 時需要下載 gx 組件，如果想直接用 make 來下載最好還是先“科學上網”，如果直接在 github 上下載安裝 gx 則無需擔心 “科學上網問題”

make deps 是要下載全部依賴了，這裡會用 gx 來完成下載，第一次用時你會發現他要到 ipfs.io 去 get 依賴包，但是即便“科學上網”了也還是無法訪問，其實只要在本地先啟動一個 ipfs 節點就可以了，他會優先在本地的 ipfs 節點擷取資源

IPFS 的下載和安裝 ： https://ipfs.io/docs/install/

啟動命令： ipfs daemon

然後再去 make deps 經過漫長的等待，即可完成依賴的安裝

很多小夥伴是不是都在這一步放棄了 go-libp2p 呀？其實我也挺討厭這個 gx 的，不如 govendor 用著舒服，不幸的是想繼續探索 go-libp2p 你就必須要掌握 gx 的用法，並且要去習慣使用 gx

gx教程：https://github.com/whyrusleeping/gx

安裝還是比較容易的，一定要粗略的看一遍說明書再去看代碼和例子，否則很難發現它的美

libp2p 說明書: https://github.com/libp2p/specs

Example

PingService

使用 libp2p 做服務是我們學習的目的，通過 PingService 來入門是個不錯的選擇，簡單看一下 PingService 的代碼，你會發現實現一個服務非常簡單， host.Host 介面是核心

PingService : http://github.com/libp2p/go-libp2p/p2p/protocol/ping/ping.go

......const ID = "/ipfs/ping/1.0.0"type PingService struct {    Host host.Host}func NewPingService(h host.Host) *PingService {    ps := &PingService{h}    h.SetStreamHandler(ID, ps.PingHandler)    return ps}func (p *PingService) PingHandler(s inet.Stream) {    ......}func (ps *PingService) Ping(ctx context.Context, p peer.ID) (<-chan time.Duration, error) {    s, err := ps.Host.NewStream(ctx, p, ID)    ......}......

這個程式碼片段示範如何通過 host.Host 介面構建一個服務，Host 介面描述如下：

Host is an object participating in a p2p network, which implements protocols or provides services. It handles requests like a Server, and issues requests like a Client. It is called Host because it is both Server and Client (and Peer may be confusing).

在文章的結尾貼出了 Host 介面的代碼，這個服務主要使用下面這兩個方法

• SetStreamHandler(pid protocol.ID, handler inet.StreamHandler)
  首先通過 Host.SetStreamHandler 來為 "/ipfs/ping/1.0.0" 協議指定 callback 方法，這裡指定了 PingHandler 方法，參數中的 inet.Stream 介面對 io 介面做了擴充，這裡要做的就是當請求到來時對 s 的輸入資料流做讀操作

• NewStream(ctx context.Context, p peer.ID, pids ...protocol.ID) (inet.Stream, error)
  在 Ping 方法被調用時首先通過 NewStream 開啟了一個流，在 p2p 網路中開啟流都是有目標的，這個目標就是 peer.ID ,因為這個 peer 上可能會註冊很多服務，所以也要指明服務ID，就是參數中的 protocol.ID ，剩下的工作就是向 s 的輸出資料流中寫入資料包了。

TODO : 調用 PingService

感覺上調用一個服務比編寫一個服務複雜的多，
首先NewHost就是一個非常複雜的操作，參數中的 Network 介面我們用 Swarm 來填充，那麼 swarm 又是什麼呢？它在這裡是 Network 介面的一個實現，
Host 介面有兩個實現，我們用 BasicHost 來執行個體化 Host 介面.

BasicHost: (github.com/libp2p/go-libp2p/p2p/host/basic/basic_host.go)

第二個參數 net 是 Network 介面類型，我們用 swarm 對象來填充即可得到一個 Host 介面的實現對象// NewHost constructs a new *BasicHost and activates it by attaching its stream and connection handlers to the given [inet.Network](http://inet.Network).func NewHost(ctx context.Context, net inet.Network, opts *HostOpts) (*BasicHost, error) {......

go-libp2p-host 介面

// Host is an object participating in a p2p network, which implements protocols or provides services. It handles requests like a Server, and issues requests like a Client. It is called Host because it is both Server and Client (and Peer may be confusing).type Host interface {   // ID returns the (local) [peer.ID](http://peer.ID) associated with this Host   ID() peer.ID   // Peerstore returns the Host's repository of Peer Addresses and Keys.   Peerstore() pstore.Peerstore   // Returns the listen addresses of the Host   Addrs() []ma.Multiaddr   // Networks returns the Network interface of the Host   Network() inet.Network   // Mux returns the Mux multiplexing incoming streams to protocol handlers   Mux() *msmux.MultistreamMuxer   // Connect ensures there is a connection between this host and the peer with given [peer.ID](http://peer.ID). Connect will absorb the addresses in pi into its internal peerstore. If there is not an active connection, Connect will issue a h.Network.Dial, and block until a connection is open, or an error is returned.    // TODO: Relay + NAT.   Connect(ctx context.Context, pi pstore.PeerInfo) error   // SetStreamHandler sets the protocol handler on the Host's Mux.   // This is equivalent to:   //   host.Mux().SetHandler(proto, handler)   // (Threadsafe)   SetStreamHandler(pid protocol.ID, handler inet.StreamHandler)   // SetStreamHandlerMatch sets the protocol handler on the Host's Mux   // using a matching function for protocol selection.   SetStreamHandlerMatch(protocol.ID, func(string) bool, inet.StreamHandler)   // RemoveStreamHandler removes a handler on the mux that was set by   // SetStreamHandler   RemoveStreamHandler(pid protocol.ID)   // NewStream opens a new stream to given peer p, and writes a p2p/protocol   // header with given [protocol.ID](http://protocol.ID). If there is no connection to p, attempts   // to create one. If ProtocolID is "", writes no header.   // (Threadsafe)   NewStream(ctx context.Context, p peer.ID, pids ...protocol.ID) (inet.Stream, error)   // Close shuts down the host, its Network, and services.   Close() error   // ConnManager returns this hosts connection manager   ConnManager() ifconnmgr.ConnManager}

go-libp2p-net 中的 Network 介面

// Network is the interface used to connect to the outside world. It dials and listens for connections. it uses a Swarm to pool connnections (see swarm pkg, and peerstream.Swarm). Connections are encrypted with a TLS-like protocol.type Network interface {   Dialer   io.Closer   // SetStreamHandler sets the handler for new streams opened by the remote side. This operation is threadsafe.   SetStreamHandler(StreamHandler)   // SetConnHandler sets the handler for new connections opened by the remote side. This operation is threadsafe.   SetConnHandler(ConnHandler)   // NewStream returns a new stream to given peer p. If there is no connection to p, attempts to create one.   NewStream(context.Context, peer.ID) (Stream, error)   // Listen tells the network to start listening on given multiaddrs.   Listen(...ma.Multiaddr) error   // ListenAddresses returns a list of addresses at which this network listens.   ListenAddresses() []ma.Multiaddr   // InterfaceListenAddresses returns a list of addresses at which this network listens. It expands "any interface" addresses (/ip4/0.0.0.0, /ip6/::) to use the known local interfaces.   InterfaceListenAddresses() ([]ma.Multiaddr, error)   // Process returns the network's Process   Process() goprocess.Process}