Fix HttpContentEncoder does not handle multiple Accept-Encoding (#9557)

Motivation:
At the current moment HttpContentEncoder handle only first value of multiple accept-encoding headers.

Modification:

Join multiple accept-encoding headers to one separated by comma.

Result:

Fixes #9553

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

@@ -24,11 +24,14 @@ import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.handler.codec.DecoderResult;
 import io.netty.handler.codec.MessageToMessageCodec;
 import io.netty.util.ReferenceCountUtil;
+import io.netty.util.internal.StringUtil;
 
 import java.util.ArrayDeque;
 import java.util.List;
 import java.util.Queue;
 
+import static io.netty.handler.codec.http.HttpHeaderNames.*;
+
 /**
  * Encodes the content of the outbound {@link HttpResponse} and {@link HttpContent}.
  * The original content is replaced with the new content encoded by the
@@ -73,21 +76,30 @@ public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpReque
     }
 
     @Override
-    protected void decode(ChannelHandlerContext ctx, HttpRequest msg, List<Object> out)
-            throws Exception {
-        CharSequence acceptedEncoding = msg.headers().get(HttpHeaderNames.ACCEPT_ENCODING);
-        if (acceptedEncoding == null) {
-            acceptedEncoding = HttpContentDecoder.IDENTITY;
+    protected void decode(ChannelHandlerContext ctx, HttpRequest msg, List<Object> out) throws Exception {
+        CharSequence acceptEncoding;
+        List<String> acceptEncodingHeaders = msg.headers().getAll(ACCEPT_ENCODING);
+        switch (acceptEncodingHeaders.size()) {
+        case 0:
+            acceptEncoding = HttpContentDecoder.IDENTITY;
+            break;
+        case 1:
+            acceptEncoding = acceptEncodingHeaders.get(0);
+            break;
+        default:
+            // Multiple message-header fields https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2
+            acceptEncoding = StringUtil.join(",", acceptEncodingHeaders);
+            break;
         }
 
         HttpMethod method = msg.method();
         if (HttpMethod.HEAD.equals(method)) {
-            acceptedEncoding = ZERO_LENGTH_HEAD;
+            acceptEncoding = ZERO_LENGTH_HEAD;
         } else if (HttpMethod.CONNECT.equals(method)) {
-            acceptedEncoding = ZERO_LENGTH_CONNECT;
+            acceptEncoding = ZERO_LENGTH_CONNECT;
         }
 
-        acceptEncodingQueue.add(acceptedEncoding);
+        acceptEncodingQueue.add(acceptEncoding);
         out.add(ReferenceCountUtil.retain(msg));
     }
 

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

@@ -500,6 +500,39 @@ public class HttpContentCompressorTest {
         assertTrue(ch.finishAndReleaseAll());
     }
 
+    @Test
+    public void testMultipleAcceptEncodingHeaders() {
+        FullHttpRequest request = newRequest();
+        request.headers().set(HttpHeaderNames.ACCEPT_ENCODING, "unknown; q=1.0")
+               .add(HttpHeaderNames.ACCEPT_ENCODING, "gzip; q=0.5")
+               .add(HttpHeaderNames.ACCEPT_ENCODING, "deflate; q=0");
+
+        EmbeddedChannel ch = new EmbeddedChannel(new HttpContentCompressor());
+
+        assertTrue(ch.writeInbound(request));
+
+        FullHttpResponse res = new DefaultFullHttpResponse(
+                HttpVersion.HTTP_1_1, HttpResponseStatus.OK,
+                Unpooled.copiedBuffer("Gzip Win", CharsetUtil.US_ASCII));
+        assertTrue(ch.writeOutbound(res));
+
+        assertEncodedResponse(ch);
+        HttpContent c = ch.readOutbound();
+        assertThat(ByteBufUtil.hexDump(c.content()), is("1f8b080000000000000072afca2c5008cfcc03000000ffff"));
+        c.release();
+
+        c = ch.readOutbound();
+        assertThat(ByteBufUtil.hexDump(c.content()), is("03001f2ebf0f08000000"));
+        c.release();
+
+        LastHttpContent last = ch.readOutbound();
+        assertThat(last.content().readableBytes(), is(0));
+        last.release();
+
+        assertThat(ch.readOutbound(), is(nullValue()));
+        assertTrue(ch.finishAndReleaseAll());
+    }
+
     private static FullHttpRequest newRequest() {
         FullHttpRequest req = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/");
         req.headers().set(HttpHeaderNames.ACCEPT_ENCODING, "gzip");

common/src/main/java/io/netty/util/internal/StringUtil.java

@@ -17,6 +17,7 @@ package io.netty.util.internal;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 
 import static java.util.Objects.requireNonNull;
@@ -597,6 +598,36 @@ public final class StringUtil {
         return start == 0 && end == length - 1 ? value : value.subSequence(start, end + 1);
     }
 
+    /**
+     * Returns a char sequence that contains all {@code elements} joined by a given separator.
+     *
+     * @param separator for each element
+     * @param elements to join together
+     *
+     * @return a char sequence joined by a given separator.
+     */
+    public static CharSequence join(CharSequence separator, Iterable<? extends CharSequence> elements) {
+        ObjectUtil.checkNotNull(separator, "separator");
+        ObjectUtil.checkNotNull(elements, "elements");
+
+        Iterator<? extends CharSequence> iterator = elements.iterator();
+        if (!iterator.hasNext()) {
+            return EMPTY_STRING;
+        }
+
+        CharSequence firstElement = iterator.next();
+        if (!iterator.hasNext()) {
+            return firstElement;
+        }
+
+        StringBuilder builder = new StringBuilder(firstElement);
+        do {
+            builder.append(separator).append(iterator.next());
+        } while (iterator.hasNext());
+
+        return builder;
+    }
+
     /**
      * @return {@code length} if no OWS is found.
      */
@@ -622,4 +653,5 @@ public final class StringUtil {
     private static boolean isOws(char c) {
         return c == SPACE || c == TAB;
     }
+
 }

common/src/test/java/io/netty/util/internal/StringUtilTest.java

@@ -534,4 +534,19 @@ public class StringUtilTest {
         assertEquals("", StringUtil.trimOws("\t ").toString());
         assertEquals("a b", StringUtil.trimOws("\ta b \t").toString());
     }
+
+    @Test
+    public void testJoin() {
+        assertEquals("",
+                     StringUtil.join(",", Collections.<CharSequence>emptyList()).toString());
+        assertEquals("a",
+                     StringUtil.join(",", Collections.singletonList("a")).toString());
+        assertEquals("a,b",
+                     StringUtil.join(",", Arrays.asList("a", "b")).toString());
+        assertEquals("a,b,c",
+                     StringUtil.join(",", Arrays.asList("a", "b", "c")).toString());
+        assertEquals("a,b,c,null,d",
+                     StringUtil.join(",", Arrays.asList("a", "b", "c", null, "d")).toString());
+    }
+
 }