net/http: make ParseForm ignore unknown content types.

Also fix a shadowed error variable bug.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5573072

src/pkg/net/http/request.go

@@ -606,7 +606,7 @@ func (r *Request) ParseForm() (err error) {
 			return errors.New("missing form body")
 		}
 		ct := r.Header.Get("Content-Type")
-		ct, _, err := mime.ParseMediaType(ct)
+		ct, _, err = mime.ParseMediaType(ct)
 		switch {
 		case ct == "application/x-www-form-urlencoded":
 			var reader io.Reader = r.Body
@@ -646,8 +646,6 @@ func (r *Request) ParseForm() (err error) {
 			// Clean this up and write more tests.
 			// request_test.go contains the start of this,
 			// in TestRequestMultipartCallOrder.
-		default:
-			return &badStringError{"unknown Content-Type", ct}
 		}
 	}
 	return err

src/pkg/net/http/request_test.go

@@ -46,28 +46,31 @@ func TestPostQuery(t *testing.T) {
 
 type stringMap map[string][]string
 type parseContentTypeTest struct {
+	shouldError bool
 	contentType stringMap
 }
 
 var parseContentTypeTests = []parseContentTypeTest{
-	{contentType: stringMap{"Content-Type": {"text/plain"}}},
-	{contentType: stringMap{}}, // Non-existent keys are not placed. The value nil is illegal.
-	{contentType: stringMap{"Content-Type": {"text/plain; boundary="}}},
-	{
-		contentType: stringMap{"Content-Type": {"application/unknown"}},
-	},
+	{false, stringMap{"Content-Type": {"text/plain"}}},
+	// Non-existent keys are not placed. The value nil is illegal.
+	{true, stringMap{}},
+	{true, stringMap{"Content-Type": {"text/plain; boundary="}}},
+	{false, stringMap{"Content-Type": {"application/unknown"}}},
 }
 
-func TestParseFormBadContentType(t *testing.T) {
+func TestParseFormUnknownContentType(t *testing.T) {
 	for i, test := range parseContentTypeTests {
 		req := &Request{
 			Method: "POST",
 			Header: Header(test.contentType),
 			Body:   ioutil.NopCloser(bytes.NewBufferString("body")),
 		}
 		err := req.ParseForm()
-		if err == nil {
+		switch {
+		case err == nil && test.shouldError:
 			t.Errorf("test %d should have returned error", i)
+		case err != nil && !test.shouldError:
+			t.Errorf("test %d should not have returned error, got %v", i, err)
 		}
 	}
 }