Cache Accept headers on HTTP 1.1 requests (netty#13824)

Motivation:

The Accept header is frequently used on HTTP 1.1 requests: there's no
point to allocate a fresh new AsciiString while decoding HTTP requests
on them

Modification:

Add Accept caching while decoding HTTP 1.1 requests

Result:

Less garbage and faster HTTP request decoding

codec-http/src/main/java/io/netty/handler/codec/http/HttpRequestDecoder.java

@@ -90,6 +90,7 @@
  */
 public class HttpRequestDecoder extends HttpObjectDecoder {
 
+    private static final AsciiString Accept = AsciiString.cached("Accept");
     private static final AsciiString Host = AsciiString.cached("Host");
     private static final AsciiString Connection = AsciiString.cached("Connection");
     private static final AsciiString ContentType = AsciiString.cached("Content-Type");
@@ -118,6 +119,9 @@ public class HttpRequestDecoder extends HttpObjectDecoder {
     private static final long LENGTH_AS_LONG = 'L' | 'e' << 8 | 'n' << 16 | 'g' << 24 |
             (long) 't' << 32 | (long) 'h' << 40;
 
+    private static final long ACCEPT_AS_LONG = 'A' | 'c' << 8 | 'c' << 16 | 'e' << 24 |
+            (long) 'p' << 32 | (long) 't' << 40;
+
     /**
      * Creates a new instance with the default
      * {@code maxInitialLineLength (4096)}, {@code maxHeaderSize (8192)}, and
@@ -200,10 +204,14 @@ protected HttpMessage createMessage(String[] initialLine) throws Exception {
     @Override
     protected AsciiString splitHeaderName(final byte[] sb, final int start, final int length) {
         final byte firstChar = sb[start];
-        if (firstChar == 'H' && length == 4) {
-            if (isHost(sb, start)) {
+        if (firstChar == 'H') {
+            if (length == 4 && isHost(sb, start)) {
                 return Host;
             }
+        } else if (firstChar == 'A') {
+            if (length == 6 && isAccept(sb, start)) {
+                return Accept;
+            }
         } else if (firstChar == 'C') {
             if (length == 10) {
                 if (isConnection(sb, start)) {
@@ -222,6 +230,16 @@ protected AsciiString splitHeaderName(final byte[] sb, final int start, final in
         return super.splitHeaderName(sb, start, length);
     }
 
+    private static boolean isAccept(byte[] sb, int start) {
+        final long maybeAccept = sb[start] |
+                sb[start + 1] << 8 |
+                sb[start + 2] << 16 |
+                sb[start + 3] << 24 |
+                (long) sb[start + 4] << 32 |
+                (long) sb[start + 5] << 40;
+        return maybeAccept == ACCEPT_AS_LONG;
+    }
+
     private static boolean isHost(byte[] sb, int start) {
         final int maybeHost = sb[start] |
                 sb[start + 1] << 8 |

codec-http/src/test/java/io/netty/handler/codec/http/HttpRequestDecoderTest.java

@@ -60,6 +60,7 @@ private static byte[] createContent(String... lineDelimiters) {
                 "Upgrade: WebSocket" + lineDelimiter2 +
                 "Connection: Upgrade" + lineDelimiter +
                 "Host: localhost" + lineDelimiter2 +
+                "Accept: */*" + lineDelimiter +
                 "Origin: http://localhost:8080" + lineDelimiter +
                 "Sec-WebSocket-Key1: 10  28 8V7 8 48     0" + lineDelimiter2 +
                 "Sec-WebSocket-Key2: 8 Xt754O3Q3QW 0   _60" + lineDelimiter +
@@ -114,10 +115,11 @@ private static void testDecodeWholeRequestAtOnce(byte[] content, int maxHeaderSi
     }
 
     private static void checkHeaders(HttpHeaders headers) {
-        assertEquals(7, headers.names().size());
+        assertEquals(8, headers.names().size());
         checkHeader(headers, "Upgrade", "WebSocket");
         checkHeader(headers, "Connection", "Upgrade");
         checkHeader(headers, "Host", "localhost");
+        checkHeader(headers, "Accept", "*/*");
         checkHeader(headers, "Origin", "http://localhost:8080");
         checkHeader(headers, "Sec-WebSocket-Key1", "10  28 8V7 8 48     0");
         checkHeader(headers, "Sec-WebSocket-Key2", "8 Xt754O3Q3QW 0   _60");