HttpObjectDecoder ignores HTTP trailer header when empty line is rece… (#8799)

* HttpObjectDecoder ignores HTTP trailer header when empty line is received in seperate ByteBuf

Motivation:

When the empty line that termines the trailers was sent in a seperate ByteBuf we did ignore the previous parsed trailers and just returned none.

Modifications:

- Correct respect previous parsed trailers.
- Add unit test.

Result:

Fixes https://github.com/netty/netty/issues/8736

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

@@ -633,13 +633,18 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
         if (line == null) {
             return null;
         }
-        CharSequence lastHeader = null;
-        if (line.length() > 0) {
         LastHttpContent trailer = this.trailer;
+        if (line.length() == 0 && trailer == null) {
+            // We have received the empty line which signals the trailer is complete and did not parse any trailers
+            // before. Just return an empty last content to reduce allocations.
+            return LastHttpContent.EMPTY_LAST_CONTENT;
+        }
+
+        CharSequence lastHeader = null;
         if (trailer == null) {
             trailer = this.trailer = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER, validateHeaders);
         }
-            do {
+        while (line.length() > 0) {
             char firstChar = line.charAt(0);
             if (lastHeader != null && (firstChar == ' ' || firstChar == '\t')) {
                 List<String> current = trailer.trailingHeaders().getAll(lastHeader);
@@ -664,20 +669,16 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
                 name = null;
                 value = null;
             }
-
             line = headerParser.parse(buffer);
             if (line == null) {
                 return null;
             }
-            } while (line.length() > 0);
+        }
 
         this.trailer = null;
         return trailer;
     }
 
-        return LastHttpContent.EMPTY_LAST_CONTENT;
-    }
-
     protected abstract boolean isDecodingRequest();
     protected abstract HttpMessage createMessage(String[] initialLine) throws Exception;
     protected abstract HttpMessage createInvalidMessage();

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

@@ -634,4 +634,33 @@ public class HttpResponseDecoderTest {
         assertThat(message.decoderResult().cause(), instanceOf(PrematureChannelClosureException.class));
         assertNull(channel.readInbound());
     }
+
+    @Test
+    public void testTrailerWithEmptyLineInSeparateBuffer() {
+        HttpResponseDecoder decoder = new HttpResponseDecoder();
+        EmbeddedChannel channel = new EmbeddedChannel(decoder);
+
+        String headers = "HTTP/1.1 200 OK\r\n"
+                + "Transfer-Encoding: chunked\r\n"
+                + "Trailer: My-Trailer\r\n";
+        assertFalse(channel.writeInbound(Unpooled.copiedBuffer(headers.getBytes(CharsetUtil.US_ASCII))));
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer("\r\n".getBytes(CharsetUtil.US_ASCII))));
+
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer("0\r\n", CharsetUtil.US_ASCII)));
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer("My-Trailer: 42\r\n", CharsetUtil.US_ASCII)));
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer("\r\n", CharsetUtil.US_ASCII)));
+
+        HttpResponse response = channel.readInbound();
+        assertEquals(2, response.headers().size());
+        assertEquals("chunked", response.headers().get(HttpHeaderNames.TRANSFER_ENCODING));
+        assertEquals("My-Trailer", response.headers().get(HttpHeaderNames.TRAILER));
+
+        LastHttpContent lastContent = channel.readInbound();
+        assertEquals(1, lastContent.trailingHeaders().size());
+        assertEquals("42", lastContent.trailingHeaders().get("My-Trailer"));
+        assertEquals(0, lastContent.content().readableBytes());
+        lastContent.release();
+
+        assertFalse(channel.finish());
+    }
 }