Rebase.

[official-gcc.git] / libgo / go / net / http / httputil / reverseproxy.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// HTTP reverse proxy handler

package httputil

import (
        "io"
        "log"
        "net"
        "net/http"
        "net/url"
        "strings"
        "sync"
        "time"
)

// onExitFlushLoop is a callback set by tests to detect the state of the
// flushLoop() goroutine.
var onExitFlushLoop func()

// 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 func(*http.Request)

        // The transport used to perform proxy requests.
        // If nil, http.DefaultTransport is used.
        Transport http.RoundTripper

        // FlushInterval specifies the flush interval
        // to flush to the client while copying the
        // response body.
        // If zero, no periodic flushing is done.
        FlushInterval time.Duration
}

func singleJoiningSlash(a, b string) string {
        aslash := strings.HasSuffix(a, "/")
        bslash := strings.HasPrefix(b, "/")
        switch {
        case aslash && bslash:
                return a + b[1:]
        case !aslash && !bslash:
                return a + "/" + b
        }
        return a + b
}

// NewSingleHostReverseProxy returns a new ReverseProxy that rewrites
// 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.
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
                }
        }
        return &ReverseProxy{Director: director}
}

func copyHeader(dst, src http.Header) {
        for k, vv := range src {
                for _, v := range vv {
                        dst.Add(k, v)
                }
        }
}

// Hop-by-hop headers. These are removed when sent to the backend.
// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
var hopHeaders = []string{
        "Connection",
        "Keep-Alive",
        "Proxy-Authenticate",
        "Proxy-Authorization",
        "Te", // canonicalized version of "TE"
        "Trailers",
        "Transfer-Encoding",
        "Upgrade",
}

func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
        transport := p.Transport
        if transport == nil {
                transport = http.DefaultTransport
        }

        outreq := new(http.Request)
        *outreq = *req // includes shallow copies of maps, but okay

        p.Director(outreq)
        outreq.Proto = "HTTP/1.1"
        outreq.ProtoMajor = 1
        outreq.ProtoMinor = 1
        outreq.Close = false

        // Remove hop-by-hop headers to the backend.  Especially
        // important is "Connection" because we want a persistent
        // connection, regardless of what the client sent to us.  This
        // is modifying the same underlying map from req (shallow
        // copied above) so we only copy it if necessary.
        copiedHeaders := false
        for _, h := range hopHeaders {
                if outreq.Header.Get(h) != "" {
                        if !copiedHeaders {
                                outreq.Header = make(http.Header)
                                copyHeader(outreq.Header, req.Header)
                                copiedHeaders = true
                        }
                        outreq.Header.Del(h)
                }
        }

        if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
                // If we aren't the first proxy retain prior
                // X-Forwarded-For information as a comma+space
                // separated list and fold multiple headers into one.
                if prior, ok := outreq.Header["X-Forwarded-For"]; ok {
                        clientIP = strings.Join(prior, ", ") + ", " + clientIP
                }
                outreq.Header.Set("X-Forwarded-For", clientIP)
        }

        res, err := transport.RoundTrip(outreq)
        if err != nil {
                log.Printf("http: proxy error: %v", err)
                rw.WriteHeader(http.StatusInternalServerError)
                return
        }
        defer res.Body.Close()

        for _, h := range hopHeaders {
                res.Header.Del(h)
        }

        copyHeader(rw.Header(), res.Header)

        rw.WriteHeader(res.StatusCode)
        p.copyResponse(rw, res.Body)
}

func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
        if p.FlushInterval != 0 {
                if wf, ok := dst.(writeFlusher); ok {
                        mlw := &maxLatencyWriter{
                                dst:     wf,
                                latency: p.FlushInterval,
                                done:    make(chan bool),
                        }
                        go mlw.flushLoop()
                        defer mlw.stop()
                        dst = mlw
                }
        }

        io.Copy(dst, src)
}

type writeFlusher interface {
        io.Writer
        http.Flusher
}

type maxLatencyWriter struct {
        dst     writeFlusher
        latency time.Duration

        lk   sync.Mutex // protects Write + Flush
        done chan bool
}

func (m *maxLatencyWriter) Write(p []byte) (int, error) {
        m.lk.Lock()
        defer m.lk.Unlock()
        return m.dst.Write(p)
}

func (m *maxLatencyWriter) flushLoop() {
        t := time.NewTicker(m.latency)
        defer t.Stop()
        for {
                select {
                case <-m.done:
                        if onExitFlushLoop != nil {
                                onExitFlushLoop()
                        }
                        return
                case <-t.C:
                        m.lk.Lock()
                        m.dst.Flush()
                        m.lk.Unlock()
                }
        }
}

func (m *maxLatencyWriter) stop() { m.done <- true }