| // 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" |
| "net" |
| "net/http" |
| "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. |
| 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; |
| // 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 |
| } |
| |
| // 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} |
| } |
| |
| 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 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 |
| } |
| |
| p.Director(outreq) |
| outreq.Close = false |
| |
| reqUpType := upgradeType(outreq.Header) |
| 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 { |
| hv := outreq.Header.Get(h) |
| if hv == "" { |
| continue |
| } |
| if h == "Te" && hv == "trailers" { |
| // 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) |
| continue |
| } |
| outreq.Header.Del(h) |
| } |
| |
| // 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. |
| 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 { |
| 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(req, 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 = strings.TrimSpace(sf); sf != "" { |
| h.Del(sf) |
| } |
| } |
| } |
| } |
| |
| // flushInterval returns the p.FlushInterval value, conditionally |
| // overriding its value for a specific request/response. |
| func (p *ReverseProxy) flushInterval(req *http.Request, 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 resCT == "text/event-stream" { |
| return -1 // negative means immediately |
| } |
| |
| // TODO: more specific cases? e.g. res.ContentLength == -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 ...interface{}) { |
| 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 strings.ToLower(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 reqUpType != resUpType { |
| p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType)) |
| return |
| } |
| |
| copyHeader(res.Header, rw.Header()) |
| |
| 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 |
| } |
| defer backConn.Close() |
| 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() |
| 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 |
| return |
| } |
| |
| // 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 |
| } |