TUN-3209: improve performance and reduce allocations during user header serialization from h1 to h2

benchmark                                    old ns/op     new ns/op     delta
BenchmarkH1ResponseToH2ResponseHeaders-4     10360         5048          -51.27%

benchmark                                    old allocs     new allocs     delta
BenchmarkH1ResponseToH2ResponseHeaders-4     135            26             -80.74%

benchmark                                    old bytes     new bytes     delta
BenchmarkH1ResponseToH2ResponseHeaders-4     8543          3667          -57.08%

Author: ipostelnik

h2mux/header.go

@@ -38,11 +38,12 @@ const (
 // HTTP/1 equivalents. See https://tools.ietf.org/html/rfc7540#section-8.1.2.3
 func H2RequestHeadersToH1Request(h2 []Header, h1 *http.Request) error {
 	for _, header := range h2 {
-		if !IsControlHeader(header.Name) {
+		name := strings.ToLower(header.Name)
+		if !IsControlHeader(name) {
 			continue
 		}
 
-		switch strings.ToLower(header.Name) {
+		switch name {
 		case ":method":
 			h1.Method = header.Value
 		case ":scheme":
@@ -116,18 +117,14 @@ func ParseUserHeaders(headerNameToParseFrom string, headers []Header) ([]Header,
 }
 
 func IsControlHeader(headerName string) bool {
-	headerName = strings.ToLower(headerName)
-
 	return headerName == "content-length" ||
 		headerName == "connection" || headerName == "upgrade" || // Websocket headers
 		strings.HasPrefix(headerName, ":") ||
 		strings.HasPrefix(headerName, "cf-")
 }
 
-// IsWebsocketClientHeader returns true if the header name is required by the client to upgrade properly
-func IsWebsocketClientHeader(headerName string) bool {
-	headerName = strings.ToLower(headerName)
-
+// isWebsocketClientHeader returns true if the header name is required by the client to upgrade properly
+func isWebsocketClientHeader(headerName string) bool {
 	return headerName == "sec-websocket-accept" ||
 		headerName == "connection" ||
 		headerName == "upgrade"
@@ -137,56 +134,73 @@ func H1ResponseToH2ResponseHeaders(h1 *http.Response) (h2 []Header) {
 	h2 = []Header{
 		{Name: ":status", Value: strconv.Itoa(h1.StatusCode)},
 	}
-	userHeaders := http.Header{}
+	userHeaders := make(http.Header, len(h1.Header))
 	for header, values := range h1.Header {
-		for _, value := range values {
-			if strings.ToLower(header) == "content-length" {
-				// This header has meaning in HTTP/2 and will be used by the edge,
-				// so it should be sent as an HTTP/2 response header.
-
-				// Since these are http2 headers, they're required to be lowercase
-				h2 = append(h2, Header{Name: strings.ToLower(header), Value: value})
-			} else if !IsControlHeader(header) || IsWebsocketClientHeader(header) {
-				// User headers, on the other hand, must all be serialized so that
-				// HTTP/2 header validation won't be applied to HTTP/1 header values
-				if _, ok := userHeaders[header]; ok {
-					userHeaders[header] = append(userHeaders[header], value)
-				} else {
-					userHeaders[header] = []string{value}
-				}
-			}
+		h2name := strings.ToLower(header)
+		if h2name == "content-length" {
+			// This header has meaning in HTTP/2 and will be used by the edge,
+			// so it should be sent as an HTTP/2 response header.
+
+			// Since these are http2 headers, they're required to be lowercase
+			h2 = append(h2, Header{Name: "content-length", Value: values[0]})
+		} else if !IsControlHeader(h2name) || isWebsocketClientHeader(h2name) {
+			// User headers, on the other hand, must all be serialized so that
+			// HTTP/2 header validation won't be applied to HTTP/1 header values
+			userHeaders[header] = values
 		}
 	}
 
 	// Perform user header serialization and set them in the single header
-	h2 = append(h2, CreateSerializedHeaders(ResponseUserHeadersField, userHeaders)...)
+	h2 = append(h2, Header{ResponseUserHeadersField, SerializeHeaders(userHeaders)})
 
 	return h2
 }
 
 // Serialize HTTP1.x headers by base64-encoding each header name and value,
 // and then joining them in the format of [key:value;]
 func SerializeHeaders(h1Headers http.Header) string {
-	var serializedHeaders []string
+	// compute size of the fully serialized value and largest temp buffer we will need
+	serializedLen := 0
+	maxTempLen := 0
 	for headerName, headerValues := range h1Headers {
 		for _, headerValue := range headerValues {
-			encodedName := make([]byte, headerEncoding.EncodedLen(len(headerName)))
-			headerEncoding.Encode(encodedName, []byte(headerName))
-
-			encodedValue := make([]byte, headerEncoding.EncodedLen(len(headerValue)))
-			headerEncoding.Encode(encodedValue, []byte(headerValue))
-
-			serializedHeaders = append(
-				serializedHeaders,
-				strings.Join(
-					[]string{string(encodedName), string(encodedValue)},
-					":",
-				),
-			)
+			nameLen := headerEncoding.EncodedLen(len(headerName))
+			valueLen := headerEncoding.EncodedLen(len(headerValue))
+			const delims = 2
+			serializedLen += delims + nameLen + valueLen
+			if nameLen > maxTempLen {
+				maxTempLen = nameLen
+			}
+			if valueLen > maxTempLen {
+				maxTempLen = valueLen
+			}
 		}
 	}
+	var buf strings.Builder
+	buf.Grow(serializedLen)
+
+	temp := make([]byte, maxTempLen)
+	writeB64 := func(s string) {
+		n := headerEncoding.EncodedLen(len(s))
+		if n > len(temp) {
+			temp = make([]byte, n)
+		}
+		headerEncoding.Encode(temp[:n], []byte(s))
+		buf.Write(temp[:n])
+	}
 
-	return strings.Join(serializedHeaders, ";")
+	for headerName, headerValues := range h1Headers {
+		for _, headerValue := range headerValues {
+			if buf.Len() > 0 {
+				buf.WriteByte(';')
+			}
+			writeB64(headerName)
+			buf.WriteByte(':')
+			writeB64(headerValue)
+		}
+	}
+
+	return buf.String()
 }
 
 // Deserialize headers serialized by `SerializeHeader`
@@ -225,18 +239,6 @@ func DeserializeHeaders(serializedHeaders string) ([]Header, error) {
 	return deserialized, nil
 }
 
-func CreateSerializedHeaders(headersField string, headers ...http.Header) []Header {
-	var serializedHeaderChunks []string
-	for _, headerChunk := range headers {
-		serializedHeaderChunks = append(serializedHeaderChunks, SerializeHeaders(headerChunk))
-	}
-
-	return []Header{{
-		headersField,
-		strings.Join(serializedHeaderChunks, ";"),
-	}}
-}
-
 type ResponseMetaHeader struct {
 	Source string `json:"src"`
 }

h2mux/header_test.go

@@ -37,12 +37,19 @@ func TestH2RequestHeadersToH1Request_RegularHeaders(t *testing.T) {
 		"Mock header 2": {"Mock value 2"},
 	}
 
-	headersConversionErr := H2RequestHeadersToH1Request(CreateSerializedHeaders(RequestUserHeadersField, mockHeaders), request)
+	headersConversionErr := H2RequestHeadersToH1Request(createSerializedHeaders(RequestUserHeadersField, mockHeaders), request)
 
 	assert.True(t, reflect.DeepEqual(mockHeaders, request.Header))
 	assert.NoError(t, headersConversionErr)
 }
 
+func createSerializedHeaders(headersField string, headers http.Header) []Header {
+	return []Header{{
+		headersField,
+		SerializeHeaders(headers),
+	}}
+}
+
 func TestH2RequestHeadersToH1Request_NoHeaders(t *testing.T) {
 	request, err := http.NewRequest(http.MethodGet, "http://example.com", nil)
 	assert.NoError(t, err)
@@ -509,40 +516,32 @@ func TestParseHeaders(t *testing.T) {
 	}
 
 	mockHeaders := []Header{
-		{Name: "One", Value: "1"},
+		{Name: "One", Value: "1"}, // will be dropped
 		{Name: "Cf-Two", Value: "cf-value-1"},
 		{Name: "Cf-Two", Value: "cf-value-2"},
 		{Name: RequestUserHeadersField, Value: SerializeHeaders(mockUserHeadersToSerialize)},
 	}
 
 	expectedHeaders := []Header{
+		{Name: "Cf-Two", Value: "cf-value-1"},
+		{Name: "Cf-Two", Value: "cf-value-2"},
 		{Name: "Mock-Header-One", Value: "1"},
 		{Name: "Mock-Header-One", Value: "1.5"},
 		{Name: "Mock-Header-Two", Value: "2"},
 		{Name: "Mock-Header-Three", Value: "3"},
 	}
-	parsedHeaders, err := ParseUserHeaders(RequestUserHeadersField, mockHeaders)
-	assert.NoError(t, err)
-	assert.ElementsMatch(t, expectedHeaders, parsedHeaders)
-}
-
-func TestParseHeadersNoSerializedHeader(t *testing.T) {
-	mockHeaders := []Header{
-		{Name: "One", Value: "1"},
-		{Name: "Cf-Two", Value: "cf-value-1"},
-		{Name: "Cf-Two", Value: "cf-value-2"},
+	h1 := &http.Request{
+		Header: make(http.Header),
 	}
-
-	_, err := ParseUserHeaders(RequestUserHeadersField, mockHeaders)
-	assert.EqualError(t, err, fmt.Sprintf("%s header not found", RequestUserHeadersField))
+	err := H2RequestHeadersToH1Request(mockHeaders, h1)
+	assert.NoError(t, err)
+	assert.ElementsMatch(t, expectedHeaders, stdlibHeaderToH2muxHeader(h1.Header))
 }
 
 func TestIsControlHeader(t *testing.T) {
 	controlHeaders := []string{
 		// Anything that begins with cf-
 		"cf-sample-header",
-		"CF-SAMPLE-HEADER",
-		"Cf-Sample-Header",
 
 		// Any http2 pseudoheader
 		":sample-pseudo-header",
@@ -559,8 +558,8 @@ func TestIsControlHeader(t *testing.T) {
 
 func TestIsNotControlHeader(t *testing.T) {
 	notControlHeaders := []string{
-		"Mock-header",
-		"Another-sample-header",
+		"mock-header",
+		"another-sample-header",
 	}
 
 	for _, header := range notControlHeaders {