From ef3a9b0acdc59d0d85de8f844499225ad225360c Mon Sep 17 00:00:00 2001
From: Trustin Lee <t@motd.kr>
Date: Sun, 29 Nov 2015 13:25:52 +0900
Subject: [PATCH] Relax the sanity check in HttpClientUpgradeHandler

Motivation:

HttpClientUpgradeHandler currently throws an IllegalStateException when
the server sends a '101 Switching Protocols' response that has no
'Upgrade' header.

Some servers do not send the 'Upgrade' header on a successful protocol
upgrade and we could safely assume that the server accepted the
requested protocol upgrade in such a case, looking from the response
status code (101)

Modifications:

- Do not throw an IllegalStateException when the server responded 101
  without a 'Upgrade' header
- Note that we still check the equality of the 'Upgrade' header when it
  is present.

Result:

- Fixes #4523
- Better interoperability
---
 .../handler/codec/http/HttpClientUpgradeHandler.java     | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/HttpClientUpgradeHandler.java b/codec-http/src/main/java/io/netty/handler/codec/http/HttpClientUpgradeHandler.java
index b7b3fda8e9..4e96a626bc 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/HttpClientUpgradeHandler.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/HttpClientUpgradeHandler.java
@@ -216,14 +216,9 @@ public class HttpClientUpgradeHandler extends HttpObjectAggregator implements Ch
             }
 
             CharSequence upgradeHeader = response.headers().get(HttpHeaderNames.UPGRADE);
-            if (upgradeHeader == null) {
+            if (upgradeHeader != null && !AsciiString.contentEqualsIgnoreCase(upgradeCodec.protocol(), upgradeHeader)) {
                 throw new IllegalStateException(
-                        "Switching Protocols response missing UPGRADE header");
-            }
-            if (!AsciiString.contentEqualsIgnoreCase(upgradeCodec.protocol(), upgradeHeader)) {
-                throw new IllegalStateException(
-                        "Switching Protocols response with unexpected UPGRADE protocol: "
-                                + upgradeHeader);
+                        "Switching Protocols response with unexpected UPGRADE protocol: " + upgradeHeader);
             }
 
             // Upgrade to the new protocol.