cmd/tipgodoc: make tipgodoc run on App Engine Managed VMs

At least in theory. We don't totally have it working yet. It does
run locally in the dev environment, though, which should be the same
as production, since it builds the Docker container locally.
But we're getting problems when pushing it to production.

Also some minor tweaks to the code with Andrew.

Change-Id: Id192669dbc8d3f86d9c8dad79764abd66e983895
Reviewed-on: https://go-review.googlesource.com/1761
Reviewed-by: Andrew Gerrand <adg@golang.org>

cmd/tipgodoc/Dockerfile

@@ -0,0 +1,16 @@
+# Dockerfile extending the generic Go image with application files for a
+# single application.
+FROM google/appengine-go
+
+RUN apt-get update
+RUN apt-get install --no-install-recommends -y -q curl build-essential git
+RUN mkdir /goroot && curl https://storage.googleapis.com/golang/go1.2.2.linux-amd64.tar.gz | tar xvzf - -C /goroot --strip-components=1
+RUN mkdir /gopath
+
+ENV GOROOT /goroot
+ENV GOPATH /gopath
+ENV PATH $PATH:$GOROOT/bin:$GOPATH/bin
+
+WORKDIR /app
+ADD . /app
+RUN /bin/bash /app/_ah/build.sh

cmd/tipgodoc/app.yaml

@@ -0,0 +1,15 @@
+version: tip
+runtime: go
+api_version: go1
+vm: true
+
+manual_scaling:
+  instances: 1
+
+handlers:
+- url: /.*
+  script: _go_app
+
+health_check:
+  enable_health_check: False
+

cmd/tipgodoc/tip.go

@@ -9,7 +9,6 @@ package main
 import (
 	"bufio"
 	"encoding/json"
-	"flag"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -26,23 +25,16 @@ import (
 
 const metaURL = "https://go.googlesource.com/?b=master&format=JSON"
 
-var (
-	pollInterval = flag.Duration("poll", 10*time.Second, "Remote repo poll interval")
-	listenAddr   = flag.String("listen", "localhost:8080", "HTTP listen address")
-)
-
-func main() {
-	flag.Parse()
+func init() {
 	p := new(Proxy)
 	go p.run()
 	http.Handle("/", p)
-	log.Fatal(http.ListenAndServe(*listenAddr, nil))
 }
 
 type Proxy struct {
-	mu    sync.Mutex // owns the followin'
+	mu    sync.Mutex // protects the followin'
 	proxy *httputil.ReverseProxy
-	last  string // signature of gorepo+toolsrepo
+	cur   string // signature of gorepo+toolsrepo
 	side  string
 }
 
@@ -51,7 +43,7 @@ func (p *Proxy) run() {
 	p.side = "a"
 	for {
 		p.poll()
-		time.Sleep(*pollInterval)
+		time.Sleep(30 * time.Second)
 	}
 }
 
@@ -62,15 +54,18 @@ func (p *Proxy) poll() {
 		return
 	}
 
+	sig := heads["go"] + "-" + heads["tools"]
+
 	p.mu.Lock()
+	changes := sig != p.cur
 	curSide := p.side
-	lastSig := p.last
+	p.cur = sig
 	p.mu.Unlock()
 
-	sig := heads["go"] + "-" + heads["tools"]
-	if sig == lastSig {
+	if !changes {
 		return
 	}
+
 	newSide := "b"
 	if curSide == "b" {
 		newSide = "a"
@@ -91,7 +86,6 @@ func (p *Proxy) poll() {
 	}
 	p.side = newSide
 	p.proxy = httputil.NewSingleHostReverseProxy(u)
-	p.last = sig
 }
 
 func initSide(side, goHash, toolsHash string) (hostport string, err error) {
@@ -112,7 +106,7 @@ func initSide(side, goHash, toolsHash string) (hostport string, err error) {
 
 	env := []string{"GOROOT=" + goDir, "GOPATH=" + filepath.Join(dir, "gopath")}
 
-	make := exec.Command("./make.bash")
+	make := exec.Command(filepath.Join(goDir, "src/make.bash"))
 	make.Stdout = os.Stdout
 	make.Stderr = os.Stderr
 	make.Dir = filepath.Join(goDir, "src")
@@ -209,7 +203,7 @@ func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	proxy := p.proxy
 	p.mu.Unlock()
 	if proxy == nil {
-		http.Error(w, "not ready", http.StatusInternalServerError)
+		http.Error(w, "tip.golang.org is currently starting up, compiling tip", http.StatusInternalServerError)
 		return
 	}
 	proxy.ServeHTTP(w, r)
@@ -218,7 +212,7 @@ func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 func (p *Proxy) serveStatus(w http.ResponseWriter, r *http.Request) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
-	fmt.Fprintf(w, "side=%v\nlast=%v\n", p.side, p.last)
+	fmt.Fprintf(w, "side=%v\ncurrent=%v\n", p.side, p.cur)
 }
 
 // gerritMetaMap returns the map from repo name (e.g. "go") to its