日期：2016年6月16日

Docker Swarm代码分析笔记（8）——创建Docker API router

在上一篇提到的API Server需要设置HTTP处理函数：

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

api.Server结构体定义如下：

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

其中处理HTTP请求的相关方法如下：

// 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赋给Server.dispatcher.handler。handler类型是http.Handler:

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

api.NewPrimary利用了mux这个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实现了ServeHTTP这个方法，所以符合http.Handler这个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()函数定义了新的http.Server变量，利用上面实现的api.Server.dispatcher的ServeHTTP方法来响应HTTP请求：

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

再看一下setupPrimaryRouter这个函数：

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定义如下：

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,
}

为例：
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)

就是为"/v*/containers/{name:.*}/archive"和"/containers/{name:.*}/archive"这个PATH的"HEAD"操作注册了wrap函数，而wrap函数则封装了localFct,也就是proxyContainer函数。 另外，if enableCors部分与上述类似。