Add app engine app to mirror html docs from chromium.googlesource.com

doc/appengine/main.go

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package crashpad mirrors crashpad documentation from Chromium’s git repo.
+package crashpad
+
+import (
+        "encoding/base64"
+        "fmt"
+        "io"
+        "io/ioutil"
+        "net/http"
+        "net/url"
+        "path"
+        "strings"
+        "time"
+
+        "google.golang.org/appengine"
+        "google.golang.org/appengine/memcache"
+        "google.golang.org/appengine/urlfetch"
+)
+
+const baseURL = "https://chromium.googlesource.com/crashpad/crashpad/+/doc/doc/generated/?format=TEXT"
+
+func init() {
+        http.HandleFunc("/", handler)
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+        ctx := appengine.NewContext(r)
+        client := urlfetch.Client(ctx)
+
+        // Don’t show dotfiles.
+        if strings.HasPrefix(path.Base(r.URL.Path), ".") {
+                http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
+                return
+        }
+
+        u, err := url.Parse(baseURL)
+        if err != nil {
+                http.Error(w, err.Error(), http.StatusInternalServerError)
+                return
+        }
+
+        // Redirect directories to their index pages (/doc/ -> /doc/index.html).
+        if strings.HasSuffix(r.URL.Path, "/") {
+                http.Redirect(w, r, r.URL.Path+"index.html", http.StatusFound)
+                return
+        }
+
+        u.Path = path.Join(u.Path, r.URL.Path)
+        urlStr := u.String()
+
+        item, err := memcache.Get(ctx, urlStr)
+        if err == memcache.ErrCacheMiss {
+                resp, err := client.Get(urlStr)
+                if err != nil {
+                        http.Error(w, err.Error(), http.StatusInternalServerError)
+                        return
+                }
+                defer resp.Body.Close()
+                if resp.StatusCode != http.StatusOK {
+                        w.WriteHeader(resp.StatusCode)
+                        w.Header().Set("Content-Type", "text/html")

[Mark Mentovai, 2015/10/08 21:46:17]

If you’re going to copy the response: carry the Content-Type from the server
too?

+                        io.Copy(w, resp.Body)

[Mark Mentovai, 2015/10/08 21:46:17]

Is it actually kosher to do this? Might leak something we don’t want to expose
publicly.

+                        return
+                }
+                decoder := base64.NewDecoder(base64.StdEncoding, resp.Body)
+                b, err := ioutil.ReadAll(decoder)
+                if err != nil {
+                        http.Error(w, err.Error(), http.StatusInternalServerError)
+                        return
+                }
+                item = &memcache.Item{
+                        Key:        urlStr,
+                        Value:      b,
+                        Expiration: 24 * time.Hour,
+                }
+                if err := memcache.Set(ctx, item); err != nil {
+                        http.Error(w, err.Error(), http.StatusInternalServerError)
+                        return
+                }
+        } else if err != nil {
+                http.Error(w, err.Error(), http.StatusInternalServerError)
+                return
+        }
+
+        w.Header().Set("Content-Type", contentType(path.Base(u.Path)))
+        fmt.Fprintf(w, "%s", item.Value)
+}
+
+var contentTypes = map[string]string{
+        ".html": "text/html",
+        ".css":  "text/css",
+        ".js":   "text/javascript",
+        ".png":  "image/png",
+}
+
+// contentType returns the appropriate content type header for file.
+func contentType(file string) string {
+        for suffix, typ := range contentTypes {
+                if strings.HasSuffix(file, suffix) {
+                        return typ + "; charset=UTF-8"
+                }
+        }
+        return "text/plain; charset=UTF-8"
+}