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+// Copyright 2011 The Go Authors. All rights reserved.
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+// Use of this source code is governed by a BSD-style
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+// license that can be found in the LICENSE file.
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+
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+// HTTP reverse proxy handler
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+
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+package vhost
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+
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+import (
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+ "context"
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+ "io"
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+ "log"
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+ "net"
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+ "net/http"
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+ "net/url"
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+ "strings"
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+ "sync"
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+ "time"
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+)
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+
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+// onExitFlushLoop is a callback set by tests to detect the state of the
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+// flushLoop() goroutine.
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+var onExitFlushLoop func()
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+
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+// ReverseProxy is an HTTP Handler that takes an incoming request and
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+// sends it to another server, proxying the response back to the
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+// client.
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+type ReverseProxy struct {
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+ // Director must be a function which modifies
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+ // the request into a new request to be sent
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+ // using Transport. Its response is then copied
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+ // back to the original client unmodified.
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+ // Director must not access the provided Request
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+ // after returning.
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+ Director func(*http.Request)
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+
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+ // The transport used to perform proxy requests.
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+ // If nil, http.DefaultTransport is used.
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+ Transport http.RoundTripper
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+
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+ // FlushInterval specifies the flush interval
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+ // to flush to the client while copying the
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+ // response body.
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+ // If zero, no periodic flushing is done.
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+ FlushInterval time.Duration
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+
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+ // ErrorLog specifies an optional logger for errors
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+ // that occur when attempting to proxy the request.
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+ // If nil, logging goes to os.Stderr via the log package's
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+ // standard logger.
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+ ErrorLog *log.Logger
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+
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+ // BufferPool optionally specifies a buffer pool to
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+ // get byte slices for use by io.CopyBuffer when
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+ // copying HTTP response bodies.
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+ BufferPool BufferPool
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+
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+ // ModifyResponse is an optional function that
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+ // modifies the Response from the backend.
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+ // If it returns an error, the proxy returns a StatusBadGateway error.
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+ ModifyResponse func(*http.Response) error
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+}
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+
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+// A BufferPool is an interface for getting and returning temporary
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+// byte slices for use by io.CopyBuffer.
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+type BufferPool interface {
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+ Get() []byte
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+ Put([]byte)
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+}
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+
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+func singleJoiningSlash(a, b string) string {
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+ aslash := strings.HasSuffix(a, "/")
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+ bslash := strings.HasPrefix(b, "/")
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+ switch {
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+ case aslash && bslash:
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+ return a + b[1:]
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+ case !aslash && !bslash:
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+ return a + "/" + b
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+ }
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+ return a + b
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+}
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+
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+// NewSingleHostReverseProxy returns a new ReverseProxy that routes
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+// URLs to the scheme, host, and base path provided in target. If the
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+// target's path is "/base" and the incoming request was for "/dir",
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+// the target request will be for /base/dir.
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+// NewSingleHostReverseProxy does not rewrite the Host header.
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+// To rewrite Host headers, use ReverseProxy directly with a custom
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+// Director policy.
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+func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
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+ targetQuery := target.RawQuery
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+ director := func(req *http.Request) {
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+ req.URL.Scheme = target.Scheme
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+ req.URL.Host = target.Host
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+ req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
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+ if targetQuery == "" || req.URL.RawQuery == "" {
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+ req.URL.RawQuery = targetQuery + req.URL.RawQuery
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+ } else {
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+ req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
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+ }
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+ if _, ok := req.Header["User-Agent"]; !ok {
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+ // explicitly disable User-Agent so it's not set to default value
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+ req.Header.Set("User-Agent", "")
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+ }
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+ }
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+ return &ReverseProxy{Director: director}
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+}
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+
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+func copyHeader(dst, src http.Header) {
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+ for k, vv := range src {
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+ for _, v := range vv {
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+ dst.Add(k, v)
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+ }
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+ }
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+}
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+
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+func cloneHeader(h http.Header) http.Header {
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+ h2 := make(http.Header, len(h))
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+ for k, vv := range h {
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+ vv2 := make([]string, len(vv))
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+ copy(vv2, vv)
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+ h2[k] = vv2
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+ }
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+ return h2
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+}
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+
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+// Hop-by-hop headers. These are removed when sent to the backend.
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+// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
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+var hopHeaders = []string{
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+ "Connection",
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+ "Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
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+ "Keep-Alive",
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+ "Proxy-Authenticate",
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+ "Proxy-Authorization",
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+ "Te", // canonicalized version of "TE"
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+ "Trailer", // not Trailers per URL above; http://www.rfc-editor.org/errata_search.php?eid=4522
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+ "Transfer-Encoding",
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+ "Upgrade",
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+}
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+
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+func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
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+ transport := p.Transport
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+ if transport == nil {
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+ transport = http.DefaultTransport
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+ }
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+
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+ ctx := req.Context()
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+ if cn, ok := rw.(http.CloseNotifier); ok {
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+ var cancel context.CancelFunc
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+ ctx, cancel = context.WithCancel(ctx)
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+ defer cancel()
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+ notifyChan := cn.CloseNotify()
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+ go func() {
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+ select {
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+ case <-notifyChan:
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+ cancel()
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+ case <-ctx.Done():
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+ }
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+ }()
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+ }
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+
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+ outreq := req.WithContext(ctx) // includes shallow copies of maps, but okay
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+ if req.ContentLength == 0 {
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+ outreq.Body = nil // Issue 16036: nil Body for http.Transport retries
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+ }
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+
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+ outreq.Header = cloneHeader(req.Header)
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+
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+ // Modify for frp
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+ outreq = outreq.WithContext(context.WithValue(outreq.Context(), "url", req.URL.Path))
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+ outreq = outreq.WithContext(context.WithValue(outreq.Context(), "host", req.Host))
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+
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+ p.Director(outreq)
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+ outreq.Close = false
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+
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+ // Remove hop-by-hop headers listed in the "Connection" header.
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+ // See RFC 2616, section 14.10.
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+ if c := outreq.Header.Get("Connection"); c != "" {
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+ for _, f := range strings.Split(c, ",") {
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+ if f = strings.TrimSpace(f); f != "" {
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+ outreq.Header.Del(f)
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+ }
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+ }
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+ }
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+
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+ // Remove hop-by-hop headers to the backend. Especially
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+ // important is "Connection" because we want a persistent
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+ // connection, regardless of what the client sent to us.
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+ for _, h := range hopHeaders {
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+ if outreq.Header.Get(h) != "" {
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+ outreq.Header.Del(h)
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+ }
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+ }
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+
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+ if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
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+ // If we aren't the first proxy retain prior
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+ // X-Forwarded-For information as a comma+space
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+ // separated list and fold multiple headers into one.
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+ if prior, ok := outreq.Header["X-Forwarded-For"]; ok {
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+ clientIP = strings.Join(prior, ", ") + ", " + clientIP
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+ }
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+ outreq.Header.Set("X-Forwarded-For", clientIP)
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+ }
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+
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+ res, err := transport.RoundTrip(outreq)
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+ if err != nil {
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+ p.logf("http: proxy error: %v", err)
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+ rw.WriteHeader(http.StatusNotFound)
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+ rw.Write([]byte(NotFound))
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+ return
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+ }
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+
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+ // Remove hop-by-hop headers listed in the
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+ // "Connection" header of the response.
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+ if c := res.Header.Get("Connection"); c != "" {
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+ for _, f := range strings.Split(c, ",") {
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+ if f = strings.TrimSpace(f); f != "" {
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+ res.Header.Del(f)
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+ }
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+ }
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+ }
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+
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+ for _, h := range hopHeaders {
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+ res.Header.Del(h)
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+ }
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+
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+ if p.ModifyResponse != nil {
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+ if err := p.ModifyResponse(res); err != nil {
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+ p.logf("http: proxy error: %v", err)
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+ rw.WriteHeader(http.StatusBadGateway)
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+ return
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+ }
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+ }
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+
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+ copyHeader(rw.Header(), res.Header)
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+
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+ // The "Trailer" header isn't included in the Transport's response,
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+ // at least for *http.Transport. Build it up from Trailer.
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+ announcedTrailers := len(res.Trailer)
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+ if announcedTrailers > 0 {
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+ trailerKeys := make([]string, 0, len(res.Trailer))
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+ for k := range res.Trailer {
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+ trailerKeys = append(trailerKeys, k)
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+ }
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+ rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
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+ }
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+
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+ rw.WriteHeader(res.StatusCode)
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+ if len(res.Trailer) > 0 {
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+ // Force chunking if we saw a response trailer.
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+ // This prevents net/http from calculating the length for short
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+ // bodies and adding a Content-Length.
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+ if fl, ok := rw.(http.Flusher); ok {
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+ fl.Flush()
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+ }
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+ }
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+ p.copyResponse(rw, res.Body)
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+ res.Body.Close() // close now, instead of defer, to populate res.Trailer
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+
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+ if len(res.Trailer) == announcedTrailers {
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+ copyHeader(rw.Header(), res.Trailer)
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+ return
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+ }
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+
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+ for k, vv := range res.Trailer {
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+ k = http.TrailerPrefix + k
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+ for _, v := range vv {
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+ rw.Header().Add(k, v)
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+ }
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+ }
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+}
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+
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+func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
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+ if p.FlushInterval != 0 {
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+ if wf, ok := dst.(writeFlusher); ok {
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+ mlw := &maxLatencyWriter{
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+ dst: wf,
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+ latency: p.FlushInterval,
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+ done: make(chan bool),
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+ }
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+ go mlw.flushLoop()
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+ defer mlw.stop()
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+ dst = mlw
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+ }
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+ }
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+
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+ var buf []byte
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+ if p.BufferPool != nil {
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+ buf = p.BufferPool.Get()
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+ }
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+ p.copyBuffer(dst, src, buf)
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+ if p.BufferPool != nil {
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+ p.BufferPool.Put(buf)
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+ }
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+}
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+
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+func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
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+ if len(buf) == 0 {
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+ buf = make([]byte, 32*1024)
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+ }
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+ var written int64
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+ for {
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+ nr, rerr := src.Read(buf)
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+ if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
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+ p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
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+ }
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+ if nr > 0 {
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+ nw, werr := dst.Write(buf[:nr])
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+ if nw > 0 {
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+ written += int64(nw)
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+ }
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+ if werr != nil {
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+ return written, werr
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+ }
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+ if nr != nw {
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+ return written, io.ErrShortWrite
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+ }
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+ }
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+ if rerr != nil {
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+ return written, rerr
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+ }
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+ }
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+}
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+
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+func (p *ReverseProxy) logf(format string, args ...interface{}) {
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+ if p.ErrorLog != nil {
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+ p.ErrorLog.Printf(format, args...)
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+ } else {
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+ log.Printf(format, args...)
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+ }
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+}
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+
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+type writeFlusher interface {
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+ io.Writer
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+ http.Flusher
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+}
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+
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+type maxLatencyWriter struct {
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+ dst writeFlusher
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+ latency time.Duration
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+
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+ mu sync.Mutex // protects Write + Flush
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+ done chan bool
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+}
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+
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+func (m *maxLatencyWriter) Write(p []byte) (int, error) {
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+ m.mu.Lock()
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+ defer m.mu.Unlock()
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+ return m.dst.Write(p)
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+}
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+
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+func (m *maxLatencyWriter) flushLoop() {
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+ t := time.NewTicker(m.latency)
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+ defer t.Stop()
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+ for {
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+ select {
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+ case <-m.done:
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+ if onExitFlushLoop != nil {
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+ onExitFlushLoop()
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+ }
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+ return
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+ case <-t.C:
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+ m.mu.Lock()
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+ m.dst.Flush()
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+ m.mu.Unlock()
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+ }
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+ }
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+}
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+
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+func (m *maxLatencyWriter) stop() { m.done <- true }
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fatedier