From 147f5680bc29e57b5a2d5bbb40fe5878bb4a4744 Mon Sep 17 00:00:00 2001
From: Chris Broadfoot <cbro@golang.org>
Date: Thu, 11 Oct 2018 17:31:38 -0700
Subject: [PATCH] [release-branch.go1.11] godoc/proxy: remove use of
 httputil.ReverseProxy for /share

ReverseProxy doesn't re-set the Request's Host field, only
Request.URL.Host.
The HTTP/2 client prefers Request.Host over Request.URL.Host, so this
results in the request being sent back to the host that originally
accepted the request.
This results in an infinite redirect (and consumption of many connections to
itself).
See Issue golang/go#28168 for details.

Replace it with a simple proxy that drops all the headers (except
Content-Type).

I tried setting the proxy.Director, but it still didn't work. Could do
with some more investigation.

Fixes golang/go#28134.

Change-Id: I5051ce72a379dcacfbe8484f58f8cf7d9385024d
Reviewed-on: https://go-review.googlesource.com/c/141718
Run-TryBot: Chris Broadfoot <cbro@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 837e80568c097270a86b7410b4b6d2f8de427d2e)
Reviewed-on: https://go-review.googlesource.com/c/153858
Run-TryBot: Andrew Bonventre <andybons@golang.org>
---
 cmd/godoc/regtest_test.go | 16 ++++++++++++++++
 godoc/proxy/proxy.go      | 33 +++++++++++++++++++++++----------
 2 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/cmd/godoc/regtest_test.go b/cmd/godoc/regtest_test.go
index 7e760170..f7c7219a 100644
--- a/cmd/godoc/regtest_test.go
+++ b/cmd/godoc/regtest_test.go
@@ -36,6 +36,7 @@ func TestLiveServer(t *testing.T) {
 		Regexp      string
 		NoAnalytics bool // expect the response to not contain GA.
 		PostBody    string
+		StatusCode  int // if 0, expect 2xx status code.
 	}{
 		{
 			Path:      "/doc/faq",
@@ -65,6 +66,7 @@ func TestLiveServer(t *testing.T) {
 			Substring:   "bdb10cf",
 			Message:     "no change redirect - hg to git mapping not registered?",
 			NoAnalytics: true,
+			StatusCode:  302,
 		},
 		{
 			Path:      "/dl/",
@@ -81,6 +83,7 @@ func TestLiveServer(t *testing.T) {
 			Path:        "/s/go2design",
 			Regexp:      "proposal.*Found",
 			NoAnalytics: true,
+			StatusCode:  302,
 		},
 		{
 			Message:   "incorrect search result - broken index?",
@@ -105,6 +108,12 @@ func TestLiveServer(t *testing.T) {
 			Regexp:      `^{"Errors":"","Events":\[{"Message":"A","Kind":"stdout","Delay":0},{"Message":"B","Kind":"stdout","Delay":1000000000}\]}$`,
 			NoAnalytics: true,
 		},
+		{
+			Path:        "/share",
+			PostBody:    "package main",
+			Substring:   "", // just check it is a 2xx.
+			NoAnalytics: true,
+		},
 	}
 
 	for _, tc := range substringTests {
@@ -126,6 +135,13 @@ func TestLiveServer(t *testing.T) {
 			if err != nil {
 				t.Fatalf("RoundTrip: %v", err)
 			}
+			if tc.StatusCode == 0 {
+				if resp.StatusCode > 299 {
+					t.Errorf("Non-OK status code: %v", resp.StatusCode)
+				}
+			} else if tc.StatusCode != resp.StatusCode {
+				t.Errorf("StatusCode; got %v, want %v", resp.StatusCode, tc.StatusCode)
+			}
 			body, err := ioutil.ReadAll(resp.Body)
 			if err != nil {
 				t.Fatalf("ReadAll: %v", err)
diff --git a/godoc/proxy/proxy.go b/godoc/proxy/proxy.go
index f3023727..bd1ef006 100644
--- a/godoc/proxy/proxy.go
+++ b/godoc/proxy/proxy.go
@@ -10,11 +10,10 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
-	"net/http/httputil"
-	"net/url"
 	"strings"
 	"time"
 
@@ -24,13 +23,6 @@ import (
 
 const playgroundURL = "https://play.golang.org"
 
-var proxy *httputil.ReverseProxy
-
-func init() {
-	target, _ := url.Parse(playgroundURL)
-	proxy = httputil.NewSingleHostReverseProxy(target)
-}
-
 type Request struct {
 	Body string
 }
@@ -136,7 +128,28 @@ func share(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
 		return
 	}
-	proxy.ServeHTTP(w, r)
+
+	// HACK(cbro): use a simple proxy rather than httputil.ReverseProxy because of Issue #28168.
+	// TODO: investigate using ReverseProxy with a Director, unsetting whatever's necessary to make that work.
+	req, _ := http.NewRequest("POST", playgroundURL+"/share", r.Body)
+	req.Header.Set("Content-Type", r.Header.Get("Content-Type"))
+	req = req.WithContext(r.Context())
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		log.Printf("ERROR share error: %v", err)
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+	copyHeader := func(k string) {
+		if v := resp.Header.Get(k); v != "" {
+			w.Header().Set(k, v)
+		}
+	}
+	copyHeader("Content-Type")
+	copyHeader("Content-Length")
+	defer resp.Body.Close()
+	w.WriteHeader(resp.StatusCode)
+	io.Copy(w, resp.Body)
 }
 
 func googleCN(r *http.Request) bool {