Added test for multi header, HttpObjectDecoder performance improvement for multi header, removed empty else block.

Motivation:

For multi-line headers HttpObjectDecoder uses StringBuilder.append(a).append(b) pattern that could be easily replaced with regular a + b. Also oparations with a and b moved out from concat operation to make it friendly for StringOptimizeConcat optimization and thus - faster.

Modification:

StringBuilder.append(a).append(b) reaplced with a + b. Operations with a and b moved out from concat oparation.

Result:
Code simpler to read and faster.

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

@@ -574,12 +574,11 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
             do {
                 char firstChar = line.charAt(0);
                 if (name != null && (firstChar == ' ' || firstChar == '\t')) {
+                    //please do not make one line from below code
+                    //as it breaks +XX:OptimizeStringConcat optimization
                     String trimmedLine = line.toString().trim();
-                    StringBuilder buf = new StringBuilder(value.length() + trimmedLine.length() + 1);
+                    String valueStr = String.valueOf(value);
-                    buf.append(value)
+                    value = valueStr + ' ' + trimmedLine;
-                       .append(' ')
-                       .append(trimmedLine);
-                    value = buf.toString();
                 } else {
                     if (name != null) {
                         headers.add(name, value);
@@ -641,14 +640,11 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
                     List<String> current = trailer.trailingHeaders().getAll(lastHeader);
                     if (!current.isEmpty()) {
                         int lastPos = current.size() - 1;
+                        //please do not make one line from below code
+                        //as it breaks +XX:OptimizeStringConcat optimization
                         String lineTrimmed = line.toString().trim();
-                        CharSequence currentLastPos = current.get(lastPos);
+                        String currentLastPos = current.get(lastPos);
-                        StringBuilder b = new StringBuilder(currentLastPos.length() + lineTrimmed.length());
+                        current.set(lastPos, currentLastPos + lineTrimmed);
-                        b.append(currentLastPos)
-                         .append(lineTrimmed);
-                        current.set(lastPos, b.toString());
-                    } else {
-                        // Content-Length, Transfer-Encoding, or Trailer
                     }
                 } else {
                     splitHeader(line);

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

@@ -174,6 +174,29 @@ public class HttpRequestDecoderTest {
         assertNull(channel.readInbound());
     }
 
+    @Test
+    public void testMultiLineHeader() {
+        EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());
+        String crlf = "\r\n";
+        String request =  "GET /some/path HTTP/1.1" + crlf +
+                "Host: localhost" + crlf +
+                "MyTestHeader: part1" + crlf +
+                "              newLinePart2" + crlf +
+                "MyTestHeader2: part21" + crlf +
+                "\t            newLinePart22"
+                + crlf + crlf;
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer(request, CharsetUtil.US_ASCII)));
+        HttpRequest req = channel.readInbound();
+        assertEquals("part1 newLinePart2", req.headers().get(of("MyTestHeader")));
+        assertEquals("part21 newLinePart22", req.headers().get(of("MyTestHeader2")));
+
+        LastHttpContent c = channel.readInbound();
+        c.release();
+
+        assertFalse(channel.finish());
+        assertNull(channel.readInbound());
+    }
+
     @Test
     public void testEmptyHeaderValue() {
         EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());
@@ -181,7 +204,7 @@ public class HttpRequestDecoderTest {
         String request =  "GET /some/path HTTP/1.1" + crlf +
                 "Host: localhost" + crlf +
                 "EmptyHeader:" + crlf + crlf;
-        channel.writeInbound(Unpooled.wrappedBuffer(request.getBytes(CharsetUtil.US_ASCII)));
+        channel.writeInbound(Unpooled.copiedBuffer(request, CharsetUtil.US_ASCII));
         HttpRequest req = channel.readInbound();
         assertEquals("", req.headers().get(of("EmptyHeader")));
     }