playground: block share functionality from specific countries

This will permit us to serve *.golang.org to Chinese users.

Change-Id: If184760d7f4c9e49a3df3785c15af770958413de
Reviewed-on: https://go-review.googlesource.com/14190
Reviewed-by: Jason Buberel <jbuberel@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

playground/appengine.go

@@ -13,6 +13,10 @@ import (
 	"appengine/urlfetch"
 )
 
+func init() {
+	onAppengine = !appengine.IsDevAppServer()
+}
+
 func client(r *http.Request) *http.Client {
 	return urlfetch.Client(appengine.NewContext(r))
 }

playground/common.go

@@ -9,6 +9,7 @@ package playground // import "golang.org/x/tools/playground"
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -32,6 +33,9 @@ func bounce(w http.ResponseWriter, r *http.Request) {
 }
 
 func passThru(w io.Writer, req *http.Request) error {
+	if req.URL.Path == "/share" && !allowShare(req) {
+		return errors.New("Forbidden")
+	}
 	defer req.Body.Close()
 	url := baseURL + req.URL.Path
 	r, err := client(req).Post(url, req.Header.Get("Content-type"), req.Body)
@@ -44,3 +48,16 @@ func passThru(w io.Writer, req *http.Request) error {
 	}
 	return nil
 }
+
+var onAppengine = false // will be overriden by appengine.go
+
+func allowShare(r *http.Request) bool {
+	if !onAppengine {
+		return true
+	}
+	switch r.Header.Get("X-AppEngine-Country") {
+	case "", "ZZ", "HK", "CN", "RC":
+		return false
+	}
+	return true
+}