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reverseproxy.go
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reverseproxy.go
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// This file is adapted from code in the net/http/httputil
// package of the Go standard library, which is by the
// Go Authors, and bears this copyright and license info:
//
// 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.
//
// This file has been modified from the standard lib to
// meet the needs of the application.
package proxy
import (
"crypto/tls"
"io"
"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
}
// Though the relevant directive prefix is just "unix:", url.Parse
// will - assuming the regular URL scheme - add additional slashes
// as if "unix" was a request protocol.
// What we need is just the path, so if "unix:/var/run/www.socket"
// was the proxy directive, the parsed hostName would be
// "unix:///var/run/www.socket", hence the ambiguous trimming.
func socketDial(hostName string) func(network, addr string) (conn net.Conn, err error) {
return func(network, addr string) (conn net.Conn, err error) {
return net.Dial("unix", hostName[len("unix://"):])
}
}
// 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.
// Without logic: target's path is "/", incoming is "/api/messages",
// without is "/api", then the target request will be for /messages.
func NewSingleHostReverseProxy(target *url.URL, without string) *ReverseProxy {
targetQuery := target.RawQuery
director := func(req *http.Request) {
if target.Scheme == "unix" {
// to make Dial work with unix URL,
// scheme and host have to be faked
req.URL.Scheme = "http"
req.URL.Host = "socket"
} else {
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 without != "" {
req.URL.Path = strings.TrimPrefix(req.URL.Path, without)
}
}
rp := &ReverseProxy{Director: director}
if target.Scheme == "unix" {
rp.Transport = &http.Transport{
Dial: socketDial(target.String()),
}
}
return rp
}
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",
}
// InsecureTransport is used to facilitate HTTPS proxying
// when it is OK for upstream to be using a bad certificate,
// since this transport skips verification.
var InsecureTransport http.RoundTripper = &http.Transport{
Proxy: http.ProxyFromEnvironment,
Dial: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
}).Dial,
TLSHandshakeTimeout: 10 * time.Second,
TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
}
func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request, extraHeaders http.Header) error {
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)
}
if extraHeaders != nil {
for k, v := range extraHeaders {
outreq.Header[k] = v
}
}
res, err := transport.RoundTrip(outreq)
if err != nil {
return err
}
if res.StatusCode == http.StatusSwitchingProtocols && res.Header.Get("Upgrade") == "websocket" {
res.Body.Close()
hj, ok := rw.(http.Hijacker)
if !ok {
return nil
}
conn, _, err := hj.Hijack()
if err != nil {
return err
}
defer conn.Close()
backendConn, err := net.Dial("tcp", outreq.URL.Host)
if err != nil {
return err
}
defer backendConn.Close()
outreq.Write(backendConn)
go func() {
io.Copy(backendConn, conn) // write tcp stream to backend.
}()
io.Copy(conn, backendConn) // read tcp stream from backend.
} else {
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)
}
return nil
}
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 }