net/textproto: accept bad MIME headers as browsers do

Accept certain non-compliant response headers
(in particular, when spaces preceed the colon).
All major browser and curl seem to support this,
and at least one webserver seems to send these.

*shrug*

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5690059

src/pkg/net/textproto/reader.go

@@ -454,10 +454,14 @@ func (r *Reader) ReadMIMEHeader() (MIMEHeader, error) {
 
 		// Key ends at first colon; must not have spaces.
 		i := bytes.IndexByte(kv, ':')
-		if i < 0 || bytes.IndexByte(kv[0:i], ' ') >= 0 {
+		if i < 0 {
 			return m, ProtocolError("malformed MIME header line: " + string(kv))
 		}
-		key := CanonicalMIMEHeaderKey(string(kv[0:i]))
+		key := string(kv[0:i])
+		if strings.Index(key, " ") >= 0 {
+			key = strings.TrimRight(key, " ")
+		}
+		key = CanonicalMIMEHeaderKey(key)
 
 		// Skip initial spaces in value.
 		i++ // skip colon
@@ -503,6 +507,11 @@ MustRewrite:
 	a := []byte(s)
 	upper := true
 	for i, v := range a {
+		if v == ' ' {
+			a[i] = '-'
+			upper = true
+			continue
+		}
 		if upper && 'a' <= v && v <= 'z' {
 			a[i] = v + 'A' - 'a'
 		}

src/pkg/net/textproto/reader_test.go

@@ -164,6 +164,29 @@ func TestLargeReadMIMEHeader(t *testing.T) {
 	}
 }
 
+// Test that we read slightly-bogus MIME headers seen in the wild,
+// with spaces before colons, and spaces in keys.
+func TestReadMIMEHeaderNonCompliant(t *testing.T) {
+	// Invalid HTTP response header as sent by an Axis security
+	// camera: (this is handled by IE, Firefox, Chrome, curl, etc.)
+	r := reader("Foo: bar\r\n" +
+		"Content-Language: en\r\n" +
+		"SID : 0\r\n" +
+		"Audio Mode : None\r\n" +
+		"Privilege : 127\r\n\r\n")
+	m, err := r.ReadMIMEHeader()
+	want := MIMEHeader{
+		"Foo":              {"bar"},
+		"Content-Language": {"en"},
+		"Sid":              {"0"},
+		"Audio-Mode":       {"None"},
+		"Privilege":        {"127"},
+	}
+	if !reflect.DeepEqual(m, want) || err != nil {
+		t.Fatalf("ReadMIMEHeader =\n%v, %v; want:\n%v", m, err, want)
+	}
+}
+
 type readResponseTest struct {
 	in       string
 	inCode   int