[#4079] Fix IllegalStateException when HttpContentEncoder is used and 100 Continue response is used.

Motivation:

Whe a 100 Continue response was written an IllegalStateException was produced as soon as the user wrote the following response. This regression was introduced by 41b0080fcc.

Modifications:

- Special handle 100 Continue responses
- Added unit tests

Result:

Fixed regression.

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

@@ -60,6 +60,7 @@ public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpReque
 
     private static final CharSequence ZERO_LENGTH_HEAD = "HEAD";
     private static final CharSequence ZERO_LENGTH_CONNECT = "CONNECT";
+    private static final int CONTINUE_CODE = HttpResponseStatus.CONTINUE.code();
 
     private final Queue<CharSequence> acceptEncodingQueue = new ArrayDeque<CharSequence>();
     private CharSequence acceptEncoding;
@@ -99,12 +100,18 @@ public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpReque
                 assert encoder == null;
 
                 final HttpResponse res = (HttpResponse) msg;
-
+                final int code = res.getStatus().code();
+                if (code == CONTINUE_CODE) {
+                    // We need to not poll the encoding when response with CONTINUE as another response will follow
+                    // for the issued request. See https://github.com/netty/netty/issues/4079
+                    acceptEncoding = null;
+                } else {
                     // Get the list of encodings accepted by the peer.
                     acceptEncoding = acceptEncodingQueue.poll();
                     if (acceptEncoding == null) {
                         throw new IllegalStateException("cannot send more responses than requests");
                     }
+                }
 
                 /*
                  * per rfc2616 4.3 Message Body
@@ -117,7 +124,7 @@ public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpReque
                  *
                  * This code is now inline with HttpClientDecoder.Decoder
                  */
-                if (isPassthru(res, acceptEncoding)) {
+                if (isPassthru(code, acceptEncoding)) {
                     if (isFull) {
                         out.add(ReferenceCountUtil.retain(res));
                     } else {
@@ -198,10 +205,9 @@ public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpReque
         }
     }
 
-    private static boolean isPassthru(HttpResponse res, CharSequence httpMethod) {
-        final int code = res.getStatus().code();
-        boolean expectEmptyBody = httpMethod == ZERO_LENGTH_HEAD || (httpMethod == ZERO_LENGTH_CONNECT && code == 200);
-        return code < 200 || code == 204 || code == 304 || expectEmptyBody;
+    private static boolean isPassthru(int code, CharSequence httpMethod) {
+        return code < 200 || code == 204 || code == 304 ||
+               (httpMethod == ZERO_LENGTH_HEAD || (httpMethod == ZERO_LENGTH_CONNECT && code == 200));
     }
 
     private static void ensureHeaders(HttpObject msg) {

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

@@ -18,10 +18,12 @@ package io.netty.handler.codec.http;
 import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.embedded.EmbeddedChannel;
+import io.netty.handler.codec.EncoderException;
 import io.netty.handler.codec.compression.ZlibWrapper;
 import io.netty.handler.codec.http.HttpHeaders.Names;
 import io.netty.handler.codec.http.HttpHeaders.Values;
 import io.netty.util.CharsetUtil;
+import io.netty.util.ReferenceCountUtil;
 import org.junit.Test;
 
 import static org.hamcrest.CoreMatchers.*;
@@ -292,6 +294,78 @@ public class HttpContentCompressorTest {
         assertThat(ch.readOutbound(), is(nullValue()));
     }
 
+    @Test
+    public void test100Continue() throws Exception {
+        FullHttpRequest request = newRequest();
+        HttpHeaders.set100ContinueExpected(request);
+
+        EmbeddedChannel ch = new EmbeddedChannel(new HttpContentCompressor());
+        ch.writeInbound(request);
+
+        FullHttpResponse continueResponse = new DefaultFullHttpResponse(
+                HttpVersion.HTTP_1_1, HttpResponseStatus.CONTINUE, Unpooled.EMPTY_BUFFER);
+
+        ch.writeOutbound(continueResponse);
+
+        FullHttpResponse res = new DefaultFullHttpResponse(
+                HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.EMPTY_BUFFER);
+        res.trailingHeaders().set("X-Test", "Netty");
+        ch.writeOutbound(res);
+
+        Object o = ch.readOutbound();
+        assertThat(o, is(instanceOf(FullHttpResponse.class)));
+
+        res = (FullHttpResponse) o;
+        assertSame(continueResponse, res);
+        res.release();
+
+        o = ch.readOutbound();
+        assertThat(o, is(instanceOf(FullHttpResponse.class)));
+
+        res = (FullHttpResponse) o;
+        assertThat(res.headers().get(Names.TRANSFER_ENCODING), is(nullValue()));
+
+        // Content encoding shouldn't be modified.
+        assertThat(res.headers().get(Names.CONTENT_ENCODING), is(nullValue()));
+        assertThat(res.content().readableBytes(), is(0));
+        assertThat(res.content().toString(CharsetUtil.US_ASCII), is(""));
+        assertEquals("Netty", res.trailingHeaders().get("X-Test"));
+        assertThat(ch.readOutbound(), is(nullValue()));
+    }
+
+    @Test
+    public void testTooManyResponses() throws Exception {
+        FullHttpRequest request = newRequest();
+        EmbeddedChannel ch = new EmbeddedChannel(new HttpContentCompressor());
+        ch.writeInbound(request);
+
+        ch.writeOutbound(new DefaultFullHttpResponse(
+                HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.EMPTY_BUFFER));
+
+        try {
+            ch.writeOutbound(new DefaultFullHttpResponse(
+                    HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.EMPTY_BUFFER));
+            fail();
+        } catch (EncoderException e) {
+            assertTrue(e.getCause() instanceof IllegalStateException);
+        }
+        assertTrue(ch.finish());
+        for (;;) {
+            Object message = ch.readOutbound();
+            if (message == null) {
+                break;
+            }
+            ReferenceCountUtil.release(message);
+        }
+        for (;;) {
+            Object message = ch.readInbound();
+            if (message == null) {
+                break;
+            }
+            ReferenceCountUtil.release(message);
+        }
+    }
+
     private static FullHttpRequest newRequest() {
         FullHttpRequest req = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/");
         req.headers().set(Names.ACCEPT_ENCODING, "gzip");