package reverseproxy 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 goes to os.Stderr 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) } } } func cloneHeader(h http.Header) http.Header { h2 := make(http.Header, len(h)) for k, vv := range h { vv2 := make([]string, len(vv)) copy(vv2, vv) h2[k] = vv2 } return h2 } // 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) (*http.Response, error) { 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.WithContext(ctx) // includes shallow copies of maps, but okay if req.ContentLength == 0 { outreq.Body = nil // Issue 16036: nil Body for http.Transport retries } outreq.Header = cloneHeader(req.Header) 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 nil, err } // Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc) if res.StatusCode == http.StatusSwitchingProtocols { if !p.modifyResponse(rw, res, outreq) { return res, nil } p.handleUpgradeResponse(rw, outreq, res) return res, nil } removeConnectionHeaders(res.Header) for _, h := range hopHeaders { res.Header.Del(h) } if !p.modifyResponse(rw, res, outreq) { return res, nil } 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 nil, err } 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 res, nil } for k, vv := range res.Trailer { k = http.TrailerPrefix + k for _, v := range vv { rw.Header().Add(k, v) } } return res, nil } 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) { if c := h.Get("Connection"); c != "" { for _, f := range strings.Split(c, ",") { if f = strings.TrimSpace(f); f != "" { h.Del(f) } } } } // 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() 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 }