Improve HTTP parsing long look-ahead (#11486)

Use ByteBuffer.getLong to look for entire request (GET / HTTP/1.1) or response (HTTP/1.1 200 OK) line with 2 long lookups.  Failing that, a single long lookup is sufficient to determine the common methods and/or HttpVersion.

* Cleanup generator also

* Added a fallback int lookup

jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpGenerator.java

@@ -195,7 +195,7 @@ public Result generateRequest(MetaData.Request info, ByteBuffer header, ByteBuff
                 int pos = BufferUtil.flipToFill(header);
                 try
                 {
-                    // generate ResponseLine
+                    // generate request line
                     generateRequestLine(info, header);
 
                     if (info.getHttpVersion() == HttpVersion.HTTP_0_9)
@@ -520,7 +520,7 @@ private void generateResponseLine(MetaData.Response response, ByteBuffer header)
         String reason = response.getReason();
         if (preprepared != null)
         {
-            if (reason == null)
+            if (reason == null || preprepared._reason.equals(reason))
                 header.put(preprepared._responseLine);
             else
             {
@@ -779,11 +779,9 @@ private static void putContentLength(ByteBuffer header, long contentLength)
         }
     }
 
+    @Deprecated(forRemoval = true)
     public static byte[] getReasonBuffer(int code)
     {
-        PreparedResponse status = code < __preprepared.length ? __preprepared[code] : null;
-        if (status != null)
-            return status._reason;
         return null;
     }
 
@@ -807,9 +805,16 @@ public String toString()
     // Build cache of response lines for status
     private static class PreparedResponse
     {
-        byte[] _reason;
-        byte[] _schemeCode;
-        byte[] _responseLine;
+        final String _reason;
+        final byte[] _schemeCode;
+        final byte[] _responseLine;
+
+        private PreparedResponse(String reason, byte[] schemeCode, byte[] responseLine)
+        {
+            _reason = reason;
+            _schemeCode = schemeCode;
+            _responseLine = responseLine;
+        }
     }
 
     private static final PreparedResponse[] __preprepared = new PreparedResponse[HttpStatus.MAX_CODE + 1];
@@ -838,10 +843,7 @@ private static class PreparedResponse
             line[versionLength + 5 + reason.length()] = HttpTokens.CARRIAGE_RETURN;
             line[versionLength + 6 + reason.length()] = HttpTokens.LINE_FEED;
 
-            __preprepared[i] = new PreparedResponse();
-            __preprepared[i]._schemeCode = Arrays.copyOfRange(line, 0, versionLength + 5);
-            __preprepared[i]._reason = Arrays.copyOfRange(line, versionLength + 5, line.length - 2);
-            __preprepared[i]._responseLine = line;
+            __preprepared[i] = new PreparedResponse(reason, Arrays.copyOfRange(line, 0, versionLength + 5), line);
         }
     }
 

jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpMethod.java

@@ -163,34 +163,34 @@ public String toString()
     public static HttpMethod lookAheadGet(ByteBuffer buffer)
     {
         int len = buffer.remaining();
-        // Short cut for 3 char methods, mostly for GET optimisation
-        if (len > 3)
-        {
-            switch (buffer.getInt(buffer.position()))
-            {
-                case ACL_AS_INT:
-                    return ACL;
-                case GET_AS_INT:
-                    return GET;
-                case PRI_AS_INT:
-                    return PRI;
-                case PUT_AS_INT:
-                    return PUT;
-                case POST_AS_INT:
-                    if (len > 4 && buffer.get(buffer.position() + 4) == ' ')
-                        return POST;
-                    break;
-                case HEAD_AS_INT:
-                    if (len > 4 && buffer.get(buffer.position() + 4) == ' ')
-                        return HEAD;
-                    break;
-                default:
-                    break;
-            }
-        }
+        // Shortcut for 3 or 4 char methods, mostly for GET optimisation
+        if (len > 4)
+            return lookAheadGet(buffer, buffer.getInt(buffer.position()));
         return LOOK_AHEAD.getBest(buffer, 0, len);
     }
 
+    /**
+     * Optimized lookup to find a method name and trailing space in a byte array.
+     *
+     * @param buffer buffer containing ISO-8859-1 characters, it is not modified, which must have at least 5 bytes remaining
+     * @param lookAhead The integer representation of the first 4 bytes of the buffer that has previously been fetched
+     *                  with the equivalent of {@code buffer.getInt(buffer.position())}
+     * @return An HttpMethod if a match or null if no easy match.
+     */
+    static HttpMethod lookAheadGet(ByteBuffer buffer, int lookAhead)
+    {
+        return switch (lookAhead)
+        {
+            case ACL_AS_INT -> ACL;
+            case GET_AS_INT -> GET;
+            case PRI_AS_INT -> PRI;
+            case PUT_AS_INT -> PUT;
+            case POST_AS_INT -> (buffer.get(buffer.position() + 4) == ' ') ? POST : LOOK_AHEAD.getBest(buffer, 0, buffer.remaining());
+            case HEAD_AS_INT -> (buffer.get(buffer.position() + 4) == ' ') ? HEAD : LOOK_AHEAD.getBest(buffer, 0, buffer.remaining());
+            default -> LOOK_AHEAD.getBest(buffer, 0, buffer.remaining());
+        };
+    }
+
     /**
      * Converts the given String parameter to an HttpMethod.
      * The string may differ from the Enum name as a '-'  in the method