Golang如何实现简单的API网关

func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy

// NewSingleHostReverseProxy returns a new ReverseProxy that routes// URLs to the scheme, host, and base path provided in target. If the// target's path is "/base" and the incoming request was for "/dir",// the target request will be for /base/dir.// NewSingleHostReverseProxy does not rewrite the Host header.// To rewrite Host headers, use ReverseProxy directly with a custom// Director policy.func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {

    targetQuery := target.RawQuery

    director := func(req *http.Request) {

        req.URL.Scheme = target.Scheme

        req.URL.Host = target.Host

        req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)

        if targetQuery == "" || req.URL.RawQuery == "" {

            req.URL.RawQuery = targetQuery + req.URL.RawQuery       } else {

            req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery     }

        if _, ok := req.Header["User-Agent"]; !ok {

            // explicitly disable User-Agent so it's not set to default value

            req.Header.Set("User-Agent", "")

        }

    }

    return &ReverseProxy{Director: director}}

// ReverseProxy is an HTTP Handler that takes an incoming request and// sends it to another server, proxying the response back to the// client.type ReverseProxy struct {

    // Director must be a function which modifies

    // the request into a new request to be sent

    // using Transport. Its response is then copied

    // back to the original client unmodified.

    // Director must not access the provided Request

    // after returning.

    Director func(*http.Request)

    Transport http.RoundTripper

    FlushInterval time.Duration

    ErrorLog *log.Logger

    BufferPool BufferPool   // ModifyResponse is an optional function that modifies the

    // Response from the backend. It is called if the backend

    // returns a response at all, with any HTTP status code.

    // If the backend is unreachable, the optional ErrorHandler is

    // called without any call to ModifyResponse.

    //

    // If ModifyResponse returns an error, ErrorHandler is called

    // with its error value. If ErrorHandler is nil, its default

    // implementation is used.

    ModifyResponse func(*http.Response) error

    ErrorHandler func(http.ResponseWriter, *http.Request, error)}