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// 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"
)
// 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, in
// nanoseconds, to flush to the client while
// coping the response body.
// If zero, no periodic flushing is done.
FlushInterval int64
}
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 {
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 q := req.URL.RawQuery; q != "" {
req.URL.RawPath = req.URL.Path + "?" + q
} else {
req.URL.RawPath = req.URL.Path
}
req.URL.RawQuery = target.RawQuery
}
return &ReverseProxy{Director: director}
}
func copyHeader(dst, src http.Header) {
for k, vv := range src {
for _, v := range vv {
dst.Add(k, v)
}
}
}
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 the connection header to the backend. 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.
if outreq.Header.Get("Connection") != "" {
outreq.Header = make(http.Header)
copyHeader(outreq.Header, req.Header)
outreq.Header.Del("Connection")
}
if clientIp, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
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
}
copyHeader(rw.Header(), res.Header)
rw.WriteHeader(res.StatusCode)
if res.Body != nil {
var dst io.Writer = rw
if p.FlushInterval != 0 {
if wf, ok := rw.(writeFlusher); ok {
dst = &maxLatencyWriter{dst: wf, latency: p.FlushInterval}
}
}
io.Copy(dst, res.Body)
}
}
type writeFlusher interface {
io.Writer
http.Flusher
}
type maxLatencyWriter struct {
dst writeFlusher
latency int64 // nanos
lk sync.Mutex // protects init of done, as well Write + Flush
done chan bool
}
func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
m.lk.Lock()
defer m.lk.Unlock()
if m.done == nil {
m.done = make(chan bool)
go m.flushLoop()
}
n, err = m.dst.Write(p)
if err != nil {
m.done <- true
}
return
}
func (m *maxLatencyWriter) flushLoop() {
t := time.NewTicker(m.latency)
defer t.Stop()
for {
select {
case <-t.C:
m.lk.Lock()
m.dst.Flush()
m.lk.Unlock()
case <-m.done:
return
}
}
panic("unreached")
}
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