From 7c336961ad6949dad98128eb8dda096780ca3204 Mon Sep 17 00:00:00 2001
From: Dragana Damjanovic <dd.mozilla@gmail.com>
Date: Tue, 4 Aug 2020 12:41:54 +0000
Subject: [PATCH] Bug 1655843 - Prefer HTTP3 connections in the connection
 pool. r=michal,necko-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D85843
---
 netwerk/protocol/http/nsHttpConnectionMgr.cpp | 23 +++++++++++++------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/netwerk/protocol/http/nsHttpConnectionMgr.cpp b/netwerk/protocol/http/nsHttpConnectionMgr.cpp
index e6a91e6434e7..597497ca96f6 100644
--- a/netwerk/protocol/http/nsHttpConnectionMgr.cpp
+++ b/netwerk/protocol/http/nsHttpConnectionMgr.cpp
@@ -839,13 +839,22 @@ void nsHttpConnectionMgr::UpdateCoalescingForNewConn(
   HttpConnectionBase* existingConn =
       FindCoalescableConnection(ent, true, false);
   if (existingConn) {
-    LOG(
-        ("UpdateCoalescingForNewConn() found existing active conn that could "
-         "have served newConn "
-         "graceful close of newConn=%p to migrate to existingConn %p\n",
-         newConn, existingConn));
-    newConn->DontReuse();
-    return;
+    // Prefer http3 connection.
+    if (newConn->UsingHttp3() && existingConn->UsingSpdy()) {
+      LOG(
+          ("UpdateCoalescingForNewConn() found existing active H2 conn that "
+           "could have served newConn, but new connection is H3, therefore "
+           "close the H2 conncetion"));
+      existingConn->DontReuse();
+    } else {
+      LOG(
+          ("UpdateCoalescingForNewConn() found existing active conn that could "
+           "have served newConn "
+           "graceful close of newConn=%p to migrate to existingConn %p\n",
+           newConn, existingConn));
+      newConn->DontReuse();
+      return;
+    }
   }
 
   // This connection might go into the mCoalescingHash for new transactions to