server h2c upgrade fail when request doesn't have connection header (n…

…etty#11569)

__Motivation__
Since request.headers().getAll() will never return null. And the check null condition will not work as expected.

__Modification__

Add isEmpty() checking as well.

__Result__

Fixes netty#11568

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

@@ -323,7 +323,7 @@ private boolean upgrade(final ChannelHandlerContext ctx, final FullHttpRequest r
         // Make sure the CONNECTION header is present.
         List<String> connectionHeaderValues = request.headers().getAll(HttpHeaderNames.CONNECTION);
 
-        if (connectionHeaderValues == null) {
+        if (connectionHeaderValues == null || connectionHeaderValues.isEmpty()) {
             return false;
         }
 

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

@@ -31,6 +31,7 @@
 import io.netty.handler.codec.http.HttpServerUpgradeHandler.UpgradeCodec;
 import io.netty.handler.codec.http.HttpServerUpgradeHandler.UpgradeCodecFactory;
 import io.netty.util.CharsetUtil;
+import io.netty.util.ReferenceCountUtil;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -189,4 +190,42 @@ protected boolean shouldHandleUpgradeRequest(HttpRequest req) {
         assertNull(channel.readOutbound());
         assertFalse(channel.finishAndReleaseAll());
     }
+
+    @Test
+    public void upgradeFail() {
+        final HttpServerCodec httpServerCodec = new HttpServerCodec();
+        final UpgradeCodecFactory factory = new UpgradeCodecFactory() {
+            @Override
+            public UpgradeCodec newUpgradeCodec(CharSequence protocol) {
+                return new TestUpgradeCodec();
+            }
+        };
+
+        HttpServerUpgradeHandler upgradeHandler = new HttpServerUpgradeHandler(httpServerCodec, factory);
+
+        EmbeddedChannel channel = new EmbeddedChannel(httpServerCodec, upgradeHandler);
+
+        // Build a h2c upgrade request, but without connection header.
+        String upgradeString = "GET / HTTP/1.1\r\n" +
+                               "Host: example.com\r\n" +
+                               "Upgrade: h2c\r\n\r\n";
+        ByteBuf upgrade = Unpooled.copiedBuffer(upgradeString, CharsetUtil.US_ASCII);
+
+        assertTrue(channel.writeInbound(upgrade));
+        assertNotNull(channel.pipeline().get(HttpServerCodec.class));
+        assertNotNull(channel.pipeline().get(HttpServerUpgradeHandler.class)); // Should not be removed.
+        assertNull(channel.pipeline().get("marker"));
+
+        HttpRequest req = channel.readInbound();
+        assertEquals(HttpVersion.HTTP_1_1, req.protocolVersion());
+        assertTrue(req.headers().contains(HttpHeaderNames.UPGRADE, "h2c", false));
+        assertFalse(req.headers().contains(HttpHeaderNames.CONNECTION));
+        ReferenceCountUtil.release(req);
+        assertNull(channel.readInbound());
+
+        // No response should be written because we're just passing through.
+        channel.flushOutbound();
+        assertNull(channel.readOutbound());
+        assertFalse(channel.finishAndReleaseAll());
+    }
 }