golang reverseproxy 代码
文件路径：/src/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 (
"context"
"fmt"
"io"
"log"
"mime"
"net"
"net/http"
"net/http/internal/ascii"
"net/textproto"
"net/url"
"strings"
"sync"
"time"
"golang.org/x/net/http/httpguts"
)
/ ReverseProxy is an HTTP Handler that takes an incoming request and
/ sends it to another server, proxying the response back to the
/ client.
/
/ ReverseProxy by default sets the client IP as the value of the
/ X-Forwarded-For header.
/
/ If an X-Forwarded-For header already exists, the client IP is
/ appended to the existing values. As a special case, if the header
/ exists in the Request.Header map but has a nil value (such as when
/ set by the Director func), the X-Forwarded-For header is
/ not modified.
/
/ To prevent IP spoofing, be sure to delete any pre-existing
/ X-Forwarded-For header coming from the client or
/ an untrusted proxy.
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)
/ 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.
/ A negative value means to flush immediately
/ after each write to the client.
/ The FlushInterval is ignored when ReverseProxy
/ recognizes a response as a streaming response, or
/ if its ContentLength is -1; for such responses, writes
/ are flushed to the client immediately.
FlushInterval time.Duration
/ ErrorLog specifies an optional logger for errors
/ that occur when attempting to proxy the request.
/ If nil, logging is done via the log package's standard logger.
ErrorLog *log.Logger
/ BufferPool optionally specifies a buffer pool to
/ get byte slices for use by io.CopyBuffer when
/ copying HTTP response bodies.
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 is an optional function that handles errors
/ reaching the backend or errors from ModifyResponse.
/
/ If nil, the default is to log the provided error and return
/ a 502 Status Bad Gateway response.
ErrorHandler func(http.ResponseWriter, *http.Request, error)
}
/ A BufferPool is an interface for getting and returning temporary
/ byte slices for use by io.CopyBuffer.
type BufferPool interface {
Get() []byte
Put([]byte)
}
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
}
func joinURLPath(a, b *url.URL) (path, rawpath string) {
if a.RawPath == "" && b.RawPath == "" {
return singleJoiningSlash(a.Path, b.Path), ""
}
/ Same as singleJoiningSlash, but uses EscapedPath to determine
/ whether a slash should be added
apath := a.EscapedPath()
bpath := b.EscapedPath()
aslash := strings.HasSuffix(apath, "/")
bslash := strings.HasPrefix(bpath, "/")
switch {
case aslash && bslash:
return a.Path + b.Path[1:], apath + bpath[1:]
case !aslash && !bslash:
return a.Path + "/" + b.Path, apath + "/" + bpath
}
return a.Path + b.Path, apath + bpath
}
/ 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, req.URL.RawPath = joinURLPath(target, req.URL)
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}
}
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.
/ As of RFC 7230, hop-by-hop headers are required to appear in the
/ Connection header field. These are the headers defined by the
/ obsoleted RFC 2616 (section 13.5.1) and are used for backward
/ compatibility.
var hopHeaders = []string{
"Connection",
"Proxy-Connection", / non-standard but still sent by libcurl and rejected by e.g. google
"Keep-Alive",
"Proxy-Authenticate",
"Proxy-Authorization",
"Te", / canonicalized version of "TE"
"Trailer", / not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
"Transfer-Encoding",
"Upgrade",
}
func (p *ReverseProxy) defaultErrorHandler(rw http.ResponseWriter, req *http.Request, err error) {
p.logf("http: proxy error: %v", err)
rw.WriteHeader(http.StatusBadGateway)
}
func (p *ReverseProxy) getErrorHandler() func(http.ResponseWriter, *http.Request, error) {
if p.ErrorHandler != nil {
return p.ErrorHandler
}
return p.defaultErrorHandler
}
/ modifyResponse conditionally runs the optional ModifyResponse hook
/ and reports whether the request should proceed.
func (p *ReverseProxy) modifyResponse(rw http.ResponseWriter, res *http.Response, req *http.Request) bool {
if p.ModifyResponse == nil {
return true
}
if err := p.ModifyResponse(res); err != nil {
res.Body.Close()
p.getErrorHandler()(rw, req, err)
return false
}
return true
}
func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
transport := p.Transport
if transport == nil {
transport = http.DefaultTransport
}
ctx := req.Context()
if ctx.Done() != nil {
/ CloseNotifier predates context.Context, and has been
/ entirely superseded by it. If the request contains
/ a Context that carries a cancellation signal, don't
/ bother spinning up a goroutine to watch the CloseNotify
/ channel (if any).
/
/ If the request Context has a nil Done channel (which
/ means it is either context.Background, or a custom
/ Context implementation with no cancellation signal),
/ then consult the CloseNotifier if available.
} else if cn, ok := rw.(http.CloseNotifier); ok {
var cancel context.CancelFunc
ctx, cancel = context.WithCancel(ctx)
defer cancel()
notifyChan := cn.CloseNotify()
go func() {
select {
case <-notifyChan:
cancel()
case <-ctx.Done():
}
}()
}
outreq := req.Clone(ctx)
if req.ContentLength == 0 {
outreq.Body = nil / Issue 16036: nil Body for http.Transport retries
}
if outreq.Body != nil {
/ Reading from the request body after returning from a handler is not
/ allowed, and the RoundTrip goroutine that reads the Body can outlive
/ this handler. This can lead to a crash if the handler panics (see
/ Issue 46866). Although calling Close doesn't guarantee there isn't
/ any Read in flight after the handle returns, in practice it's safe to
/ read after closing it.
defer outreq.Body.Close()
}
if outreq.Header == nil {
outreq.Header = make(http.Header) / Issue 33142: historical behavior was to always allocate
}
p.Director(outreq)
outreq.Close = false
reqUpType := upgradeType(outreq.Header)
if !ascii.IsPrint(reqUpType) {
p.getErrorHandler()(rw, req, fmt.Errorf("client tried to switch to invalid protocol %q", reqUpType))
return
}
removeConnectionHeaders(outreq.Header)
/ 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.
for _, h := range hopHeaders {
outreq.Header.Del(h)
}
/ Issue 21096: tell backend applications that care about trailer support
/ that we support trailers. (We do, but we don't go out of our way to
/ advertise that unless the incoming client request thought it was worth
/ mentioning.) Note that we look at req.Header, not outreq.Header, since
/ the latter has passed through removeConnectionHeaders.
if httpguts.HeaderValuesContainsToken(req.Header["Te"], "trailers") {
outreq.Header.Set("Te", "trailers")
}
/ After stripping all the hop-by-hop connection headers above, add back any
/ necessary for protocol upgrades, such as for websockets.
if reqUpType != "" {
outreq.Header.Set("Connection", "Upgrade")
outreq.Header.Set("Upgrade", reqUpType)
}
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.
prior, ok := outreq.Header["X-Forwarded-For"]
omit := ok && prior == nil / Issue 38079: nil now means don't populate the header
if len(prior) > 0 {
clientIP = strings.Join(prior, ", ") + ", " + clientIP
}
if !omit {
outreq.Header.Set("X-Forwarded-For", clientIP)
}
}
res, err := transport.RoundTrip(outreq)
if err != nil {
p.getErrorHandler()(rw, outreq, err)
return
}
/ Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
if res.StatusCode == http.StatusSwitchingProtocols {
if !p.modifyResponse(rw, res, outreq) {
return
}
p.handleUpgradeResponse(rw, outreq, res)
return
}
removeConnectionHeaders(res.Header)
for _, h := range hopHeaders {
res.Header.Del(h)
}
if !p.modifyResponse(rw, res, outreq) {
return
}
copyHeader(rw.Header(), res.Header)
/ The "Trailer" header isn't included in the Transport's response,
/ at least for *http.Transport. Build it up from Trailer.
announcedTrailers := len(res.Trailer)
if announcedTrailers > 0 {
trailerKeys := make([]string, 0, len(res.Trailer))
for k := range res.Trailer {
trailerKeys = append(trailerKeys, k)
}
rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
}
rw.WriteHeader(res.StatusCode)
err = p.copyResponse(rw, res.Body, p.flushInterval(res))
if err != nil {
defer res.Body.Close()
/ Since we're streaming the response, if we run into an error all we can do
/ is abort the request. Issue 23643: ReverseProxy should use ErrAbortHandler
/ on read error while copying body.
if !shouldPanicOnCopyError(req) {
p.logf("suppressing panic for copyResponse error in test; copy error: %v", err)
return
}
panic(http.ErrAbortHandler)
}
res.Body.Close() / close now, instead of defer, to populate res.Trailer
if len(res.Trailer) > 0 {
/ Force chunking if we saw a response trailer.
/ This prevents net/http from calculating the length for short
/ bodies and adding a Content-Length.
if fl, ok := rw.(http.Flusher); ok {
fl.Flush()
}
}
if len(res.Trailer) == announcedTrailers {
copyHeader(rw.Header(), res.Trailer)
return
}
for k, vv := range res.Trailer {
k = http.TrailerPrefix + k
for _, v := range vv {
rw.Header().Add(k, v)
}
}
}
var inOurTests bool / whether we're in our own tests
/ shouldPanicOnCopyError reports whether the reverse proxy should
/ panic with http.ErrAbortHandler. This is the right thing to do by
/ default, but Go 1.10 and earlier did not, so existing unit tests
/ weren't expecting panics. Only panic in our own tests, or when
/ running under the HTTP server.
func shouldPanicOnCopyError(req *http.Request) bool {
if inOurTests {
/ Our tests know to handle this panic.
return true
}
if req.Context().Value(http.ServerContextKey) != nil {
/ We seem to be running under an HTTP server, so
/ it'll recover the panic.
return true
}
/ Otherwise act like Go 1.10 and earlier to not break
/ existing tests.
return false
}
/ removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
/ See RFC 7230, section 6.1
func removeConnectionHeaders(h http.Header) {
for _, f := range h["Connection"] {
for _, sf := range strings.Split(f, ",") {
if sf = textproto.TrimString(sf); sf != "" {
h.Del(sf)
}
}
}
}
/ flushInterval returns the p.FlushInterval value, conditionally
/ overriding its value for a specific request/response.
func (p *ReverseProxy) flushInterval(res *http.Response) time.Duration {
resCT := res.Header.Get("Content-Type")
/ For Server-Sent Events responses, flush immediately.
/ The MIME type is defined in https://www.w3.org/TR/eventsource/#text-event-stream
if baseCT, _, _ := mime.ParseMediaType(resCT); baseCT == "text/event-stream" {
return -1 / negative means immediately
}
/ We might have the case of streaming for which Content-Length might be unset.
if res.ContentLength == -1 {
return -1
}
return p.FlushInterval
}
func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
if flushInterval != 0 {
if wf, ok := dst.(writeFlusher); ok {
mlw := &maxLatencyWriter{
dst: wf,
latency: flushInterval,
}
defer mlw.stop()
/ set up initial timer so headers get flushed even if body writes are delayed
mlw.flushPending = true
mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
dst = mlw
}
}
var buf []byte
if p.BufferPool != nil {
buf = p.BufferPool.Get()
defer p.BufferPool.Put(buf)
}
_, err := p.copyBuffer(dst, src, buf)
return err
}
/ copyBuffer returns any write errors or non-EOF read errors, and the amount
/ of bytes written.
func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
if len(buf) == 0 {
buf = make([]byte, 32*1024)
}
var written int64
for {
nr, rerr := src.Read(buf)
if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
}
if nr > 0 {
nw, werr := dst.Write(buf[:nr])
if nw > 0 {
written += int64(nw)
}
if werr != nil {
return written, werr
}
if nr != nw {
return written, io.ErrShortWrite
}
}
if rerr != nil {
if rerr == io.EOF {
rerr = nil
}
return written, rerr
}
}
}
func (p *ReverseProxy) logf(format string, args ...any) {
if p.ErrorLog != nil {
p.ErrorLog.Printf(format, args...)
} else {
log.Printf(format, args...)
}
}
type writeFlusher interface {
io.Writer
http.Flusher
}
type maxLatencyWriter struct {
dst writeFlusher
latency time.Duration / non-zero; negative means to flush immediately
mu sync.Mutex / protects t, flushPending, and dst.Flush
t *time.Timer
flushPending bool
}
func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
m.mu.Lock()
defer m.mu.Unlock()
n, err = m.dst.Write(p)
if m.latency < 0 {
m.dst.Flush()
return
}
if m.flushPending {
return
}
if m.t == nil {
m.t = time.AfterFunc(m.latency, m.delayedFlush)
} else {
m.t.Reset(m.latency)
}
m.flushPending = true
return
}
func (m *maxLatencyWriter) delayedFlush() {
m.mu.Lock()
defer m.mu.Unlock()
if !m.flushPending { / if stop was called but AfterFunc already started this goroutine
return
}
m.dst.Flush()
m.flushPending = false
}
func (m *maxLatencyWriter) stop() {
m.mu.Lock()
defer m.mu.Unlock()
m.flushPending = false
if m.t != nil {
m.t.Stop()
}
}
func upgradeType(h http.Header) string {
if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
return ""
}
return h.Get("Upgrade")
}
func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, res *http.Response) {
reqUpType := upgradeType(req.Header)
resUpType := upgradeType(res.Header)
if !ascii.IsPrint(resUpType) { / We know reqUpType is ASCII, it's checked by the caller.
p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch to invalid protocol %q", resUpType))
}
if !ascii.EqualFold(reqUpType, resUpType) {
p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
return
}
hj, ok := rw.(http.Hijacker)
if !ok {
p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
return
}
backConn, ok := res.Body.(io.ReadWriteCloser)
if !ok {
p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
return
}
backConnCloseCh := make(chan bool)
go func() {
/ Ensure that the cancellation of a request closes the backend.
/ See issue https://golang.org/issue/35559.
select {
case <-req.Context().Done():
case <-backConnCloseCh:
}
backConn.Close()
}()
defer close(backConnCloseCh)
conn, brw, err := hj.Hijack()
if err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))
return
}
defer conn.Close()
copyHeader(rw.Header(), res.Header)
res.Header = rw.Header()
res.Body = nil / so res.Write only writes the headers; we have res.Body in backConn above
if err := res.Write(brw); err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
return
}
if err := brw.Flush(); err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
return
}
errc := make(chan error, 1)
spc := switchProtocolCopier{user: conn, backend: backConn}
go spc.copyToBackend(errc)
go spc.copyFromBackend(errc)
<-errc
}
/ switchProtocolCopier exists so goroutines proxying data back and
/ forth have nice names in stacks.
type switchProtocolCopier struct {
user, backend io.ReadWriter
}
func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
_, err := io.Copy(c.user, c.backend)
errc <- err
}
func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
_, err := io.Copy(c.backend, c.user)
errc <- err
}