tools/godoc: remove server's dependence on "expvar".

Importing "expvar" exports server variables on /debug/vars by default.  This
raises security concerns in some environments.  Users should opt-in to this
instead.  If users need godoc metrics, we can provide a function in the godoc
package to read them.

Change-Id: Ie12e695d5958b646e82e7e00de651cc1913aa98d
Reviewed-on: https://go-review.googlesource.com/12270
Reviewed-by: Andrew Gerrand <adg@golang.org>

godoc/server.go

@@ -7,7 +7,6 @@ package godoc
 import (
 	"bytes"
 	"encoding/json"
-	"expvar"
 	"fmt"
 	"go/ast"
 	"go/build"
@@ -460,27 +459,18 @@ func (w *writerCapturesErr) Write(p []byte) (int, error) {
 	return n, err
 }
 
-var httpErrors *expvar.Map
-
-func init() {
-	httpErrors = expvar.NewMap("httpWriteErrors").Init()
-}
-
 // applyTemplateToResponseWriter uses an http.ResponseWriter as the io.Writer
 // for the call to template.Execute.  It uses an io.Writer wrapper to capture
-// errors from the underlying http.ResponseWriter.  If an error is found, an
-// expvar will be incremented.  Other template errors will be logged.  This is
-// done to keep from polluting log files with error messages due to networking
-// issues, such as client disconnects and http HEAD protocol violations.
+// errors from the underlying http.ResponseWriter.  Errors are logged only when
+// they come from the template processing and not the Writer; this avoid
+// polluting log files with error messages due to networking issues, such as
+// client disconnects and http HEAD protocol violations.
 func applyTemplateToResponseWriter(rw http.ResponseWriter, t *template.Template, data interface{}) {
 	w := &writerCapturesErr{w: rw}
 	err := t.Execute(w, data)
 	// There are some cases where template.Execute does not return an error when
 	// rw returns an error, and some where it does.  So check w.err first.
-	if w.err != nil {
-		// For http errors, increment an expvar.
-		httpErrors.Add(w.err.Error(), 1)
-	} else if err != nil {
+	if w.err == nil && err != nil {
 		// Log template errors.
 		log.Printf("%s.Execute: %s", t.Name(), err)
 	}

godoc/server_test.go

@@ -1,79 +0,0 @@
-// Copyright 2013 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package godoc
-
-import (
-	"errors"
-	"expvar"
-	"net/http"
-	"net/http/httptest"
-	"testing"
-	"text/template"
-)
-
-var (
-	// NOTE: with no plain-text in the template, template.Execute will not
-	// return an error when http.ResponseWriter.Write does return an error.
-	tmpl = template.Must(template.New("test").Parse("{{.Foo}}"))
-)
-
-type withFoo struct {
-	Foo int
-}
-
-type withoutFoo struct {
-}
-
-type errResponseWriter struct {
-}
-
-func (*errResponseWriter) Header() http.Header {
-	return http.Header{}
-}
-
-func (*errResponseWriter) WriteHeader(int) {
-}
-
-func (*errResponseWriter) Write(p []byte) (int, error) {
-	return 0, errors.New("error")
-}
-
-func TestApplyTemplateToResponseWriter(t *testing.T) {
-	for _, tc := range []struct {
-		desc    string
-		rw      http.ResponseWriter
-		data    interface{}
-		expVars int
-	}{
-		{
-			desc:    "no error",
-			rw:      &httptest.ResponseRecorder{},
-			data:    &withFoo{},
-			expVars: 0,
-		},
-		{
-			desc:    "template error",
-			rw:      &httptest.ResponseRecorder{},
-			data:    &withoutFoo{},
-			expVars: 0,
-		},
-		{
-			desc:    "ResponseWriter error",
-			rw:      &errResponseWriter{},
-			data:    &withFoo{},
-			expVars: 1,
-		},
-	} {
-		httpErrors.Init()
-		applyTemplateToResponseWriter(tc.rw, tmpl, tc.data)
-		gotVars := 0
-		httpErrors.Do(func(expvar.KeyValue) {
-			gotVars++
-		})
-		if gotVars != tc.expVars {
-			t.Errorf("applyTemplateToResponseWriter(%q): got %d vars, want %d", tc.desc, gotVars, tc.expVars)
-		}
-	}
-}