Docker Swarm程式碼分析筆記（8）——建立Docker API router

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。在上一篇提到的 API Server需要設定 HTTP處理函數：

......server.SetHandler(api.NewPrimary(cl, tlsConfig, &statusHandler{cl, nil, nil}, c.GlobalBool("debug"), c.Bool("cors")))......

api.Server結構體定義如下：

// Server is a Docker API server.type Server struct {    hosts  []string    tlsConfig  *tls.Config    dispatcher *dispatcher}

其中處理HTTP請求的相關方法如下：

// Dispatcher is a meta http.Handler. It acts as an http.Handler and forwards// requests to another http.Handler that can be changed at runtime.type dispatcher struct {    handler http.Handler}// SetHandler changes the underlying handler.func (d *dispatcher) SetHandler(handler http.Handler) {    d.handler = handler}// ServeHTTP forwards requests to the underlying handler.func (d *dispatcher) ServeHTTP(w http.ResponseWriter, r *http.Request) {    if d.handler == nil {        httpError(w, "No dispatcher defined", http.StatusInternalServerError)        return    }    d.handler.ServeHTTP(w, r)}// SetHandler is used to overwrite the HTTP handler for the API.// This can be the api router or a reverse proxy.func (s *Server) SetHandler(handler http.Handler) {    s.dispatcher.SetHandler(handler)}

Server.SetHandler所做的就是把handler賦給Server.dispatcher.handler。handler類型是http.Handler:

type Handler interface {    ServeHTTP(ResponseWriter, *Request)}

api.NewPrimary利用了mux這個project：

// NewPrimary creates a new API router.func NewPrimary(cluster cluster.Cluster, tlsConfig *tls.Config, status StatusHandler, debug, enableCors bool) *mux.Router {    // Register the API events handler in the cluster.    eventsHandler := newEventsHandler()    cluster.RegisterEventHandler(eventsHandler)    context := &context{        cluster:       cluster,        eventsHandler: eventsHandler,        statusHandler: status,        tlsConfig:     tlsConfig,    }    r := mux.NewRouter()    setupPrimaryRouter(r, context, enableCors)    if debug {        profilerSetup(r, "/debug/")    }    return r}

而*mux.Router實現了ServeHTTP這個方法，所以符合http.Handler這個interface：

// ServeHTTP dispatches the handler registered in the matched route.//// When there is a match, the route variables can be retrieved calling// mux.Vars(request).func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {    ......}

api.Server的ListenAndServe()函數定義了新的http.Server變數，利用上面實現的api.Server.dispatcher的ServeHTTP方法來響應HTTP請求：

server = &http.Server{                Addr:    protoAddrParts[1],                Handler: s.dispatcher,            }

再看一下setupPrimaryRouter這個函數：

func setupPrimaryRouter(r *mux.Router, context *context, enableCors bool) {    for method, mappings := range routes {        for route, fct := range mappings {            log.WithFields(log.Fields{"method": method, "route": route}).Debug("Registering HTTP route")            localRoute := route            localFct := fct            wrap := func(w http.ResponseWriter, r *http.Request) {                log.WithFields(log.Fields{"method": r.Method, "uri": r.RequestURI}).Debug("HTTP request received")                if enableCors {                    writeCorsHeaders(w, r)                }                context.apiVersion = mux.Vars(r)["version"]                localFct(context, w, r)            }            localMethod := method            r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).Methods(localMethod).HandlerFunc(wrap)            r.Path(localRoute).Methods(localMethod).HandlerFunc(wrap)            if enableCors {                optionsMethod := "OPTIONS"                optionsFct := optionsHandler                wrap := func(w http.ResponseWriter, r *http.Request) {                    log.WithFields(log.Fields{"method": optionsMethod, "uri": r.RequestURI}).                        Debug("HTTP request received")                    if enableCors {                        writeCorsHeaders(w, r)                    }                    context.apiVersion = mux.Vars(r)["version"]                    optionsFct(context, w, r)                }                r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).                    Methods(optionsMethod).HandlerFunc(wrap)                r.Path(localRoute).Methods(optionsMethod).                    HandlerFunc(wrap)            }        }    }}

其中routes定義如下：

var routes = map[string]map[string]handler{    "HEAD": {        "/containers/{name:.*}/archive": proxyContainer,    },    "GET": {        "/_ping":                          ping,        "/events":                         getEvents,        "/info":                           getInfo,        ......        }    ......}

以

"HEAD": {        "/containers/{name:.*}/archive": proxyContainer,}

為例：
method和localMethod是"HEAD"；
mappings是：

{        "/containers/{name:.*}/archive": proxyContainer,}

route和localRoute是"/containers/{name:.*}/archive"；
fct和localFct是proxyContainer。
所以

r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).Methods(localMethod).HandlerFunc(wrap)r.Path(localRoute).Methods(localMethod).HandlerFunc(wrap)

就是為"/v*/containers/{name:.*}/archive"和"/containers/{name:.*}/archive"這個PATH的"HEAD"操作註冊了wrap函數，而wrap函數則封裝了localFct,也就是proxyContainer函數。 另外，if enableCors部分與上述類似。