net/http: avoid a bunch of unnecessary CanonicalHeaderKey calls

CanonicalHeaderKey didn't allocate, but it did use unnecessary
CPU in the hot path, deciding it didn't need to allocate.

I considered using constants for all these common header keys
but I didn't think it would be prettier. "Content-Length" looks
better than contentLength or hdrContentLength, etc.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/6255053

src/pkg/net/http/header.go

@@ -36,6 +36,14 @@ func (h Header) Get(key string) string {
 	return textproto.MIMEHeader(h).Get(key)
 }
 
+// get is like Get, but key must already be in CanonicalHeaderKey form.
+func (h Header) get(key string) string {
+	if v := h[key]; len(v) > 0 {
+		return v[0]
+	}
+	return ""
+}
+
 // Del deletes the values associated with key.
 func (h Header) Del(key string) {
 	textproto.MIMEHeader(h).Del(key)

src/pkg/net/http/request.go

@@ -513,7 +513,7 @@ func ReadRequest(b *bufio.Reader) (req *Request, err error) {
 	// the same.  In the second case, any Host line is ignored.
 	req.Host = req.URL.Host
 	if req.Host == "" {
-		req.Host = req.Header.Get("Host")
+		req.Host = req.Header.get("Host")
 	}
 	req.Header.Del("Host")
 
@@ -732,16 +732,16 @@ func (r *Request) FormFile(key string) (multipart.File, *multipart.FileHeader, e
 }
 
 func (r *Request) expectsContinue() bool {
-	return hasToken(r.Header.Get("Expect"), "100-continue")
+	return hasToken(r.Header.get("Expect"), "100-continue")
 }
 
 func (r *Request) wantsHttp10KeepAlive() bool {
 	if r.ProtoMajor != 1 || r.ProtoMinor != 0 {
 		return false
 	}
-	return hasToken(r.Header.Get("Connection"), "keep-alive")
+	return hasToken(r.Header.get("Connection"), "keep-alive")
 }
 
 func (r *Request) wantsClose() bool {
-	return hasToken(r.Header.Get("Connection"), "close")
+	return hasToken(r.Header.get("Connection"), "close")
 }

src/pkg/net/http/server.go

@@ -287,7 +287,7 @@ func (w *response) WriteHeader(code int) {
 	// Check for a explicit (and valid) Content-Length header.
 	var hasCL bool
 	var contentLength int64
-	if clenStr := w.header.Get("Content-Length"); clenStr != "" {
+	if clenStr := w.header.get("Content-Length"); clenStr != "" {
 		var err error
 		contentLength, err = strconv.ParseInt(clenStr, 10, 64)
 		if err == nil {
@@ -307,7 +307,7 @@ func (w *response) WriteHeader(code int) {
 		w.closeAfterReply = true
 	}
 
-	if w.header.Get("Connection") == "close" {
+	if w.header.get("Connection") == "close" {
 		w.closeAfterReply = true
 	}
 
@@ -331,7 +331,7 @@ func (w *response) WriteHeader(code int) {
 	if code == StatusNotModified {
 		// Must not have body.
 		for _, header := range []string{"Content-Type", "Content-Length", "Transfer-Encoding"} {
-			if w.header.Get(header) != "" {
+			if w.header.get(header) != "" {
 				// TODO: return an error if WriteHeader gets a return parameter
 				// or set a flag on w to make future Writes() write an error page?
 				// for now just log and drop the header.
@@ -341,7 +341,7 @@ func (w *response) WriteHeader(code int) {
 		}
 	} else {
 		// If no content type, apply sniffing algorithm to body.
-		if w.header.Get("Content-Type") == "" && w.req.Method != "HEAD" {
+		if w.header.get("Content-Type") == "" && w.req.Method != "HEAD" {
 			w.needSniff = true
 		}
 	}
@@ -350,7 +350,7 @@ func (w *response) WriteHeader(code int) {
 		w.Header().Set("Date", time.Now().UTC().Format(TimeFormat))
 	}
 
-	te := w.header.Get("Transfer-Encoding")
+	te := w.header.get("Transfer-Encoding")
 	hasTE := te != ""
 	if hasCL && hasTE && te != "identity" {
 		// TODO: return an error if WriteHeader gets a return parameter
@@ -390,7 +390,7 @@ func (w *response) WriteHeader(code int) {
 		return
 	}
 
-	if w.closeAfterReply && !hasToken(w.header.Get("Connection"), "close") {
+	if w.closeAfterReply && !hasToken(w.header.get("Connection"), "close") {
 		w.header.Set("Connection", "close")
 	}
 
@@ -515,8 +515,8 @@ func (w *response) finishRequest() {
 	// If this was an HTTP/1.0 request with keep-alive and we sent a Content-Length
 	// back, we can make this a keep-alive response ...
 	if w.req.wantsHttp10KeepAlive() {
-		sentLength := w.header.Get("Content-Length") != ""
-		if sentLength && w.header.Get("Connection") == "keep-alive" {
+		sentLength := w.header.get("Content-Length") != ""
+		if sentLength && w.header.get("Connection") == "keep-alive" {
 			w.closeAfterReply = false
 		}
 	}
@@ -628,7 +628,7 @@ func (c *conn) serve() {
 				break
 			}
 			req.Header.Del("Expect")
-		} else if req.Header.Get("Expect") != "" {
+		} else if req.Header.get("Expect") != "" {
 			// TODO(bradfitz): let ServeHTTP handlers handle
 			// requests with non-standard expectation[s]? Seems
 			// theoretical at best, and doesn't fit into the

src/pkg/net/http/transfer.go

@@ -432,7 +432,7 @@ func fixLength(isResponse bool, status int, requestMethod string, header Header,
 	}
 
 	// Logic based on Content-Length
-	cl := strings.TrimSpace(header.Get("Content-Length"))
+	cl := strings.TrimSpace(header.get("Content-Length"))
 	if cl != "" {
 		n, err := strconv.ParseInt(cl, 10, 64)
 		if err != nil || n < 0 {
@@ -454,7 +454,7 @@ func fixLength(isResponse bool, status int, requestMethod string, header Header,
 	// Logic based on media type. The purpose of the following code is just
 	// to detect whether the unsupported "multipart/byteranges" is being
 	// used. A proper Content-Type parser is needed in the future.
-	if strings.Contains(strings.ToLower(header.Get("Content-Type")), "multipart/byteranges") {
+	if strings.Contains(strings.ToLower(header.get("Content-Type")), "multipart/byteranges") {
 		return -1, ErrNotSupported
 	}
 
@@ -469,14 +469,14 @@ func shouldClose(major, minor int, header Header) bool {
 	if major < 1 {
 		return true
 	} else if major == 1 && minor == 0 {
-		if !strings.Contains(strings.ToLower(header.Get("Connection")), "keep-alive") {
+		if !strings.Contains(strings.ToLower(header.get("Connection")), "keep-alive") {
 			return true
 		}
 		return false
 	} else {
 		// TODO: Should split on commas, toss surrounding white space,
 		// and check each field.
-		if strings.ToLower(header.Get("Connection")) == "close" {
+		if strings.ToLower(header.get("Connection")) == "close" {
 			header.Del("Connection")
 			return true
 		}
@@ -486,7 +486,7 @@ func shouldClose(major, minor int, header Header) bool {
 
 // Parse the trailer header
 func fixTrailer(header Header, te []string) (Header, error) {
-	raw := header.Get("Trailer")
+	raw := header.get("Trailer")
 	if raw == "" {
 		return nil, nil
 	}