From 5e508a27e9ae10d1592ca0ba051b86dee20352cf Mon Sep 17 00:00:00 2001
From: Kazu Yamamoto <kazu@iij.ad.jp>
Date: Wed, 15 May 2024 16:06:21 +0900
Subject: [PATCH 1/3] ensuring to receive 4 bytes.

---
 warp/Network/Wai/Handler/Warp/Run.hs | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/warp/Network/Wai/Handler/Warp/Run.hs b/warp/Network/Wai/Handler/Warp/Run.hs
index 858d893a2..2065f87e4 100644
--- a/warp/Network/Wai/Handler/Warp/Run.hs
+++ b/warp/Network/Wai/Handler/Warp/Run.hs
@@ -386,8 +386,8 @@ serveConnection conn ii th origAddr transport settings app = do
         if isHTTP2 transport
             then return (True, "")
             else do
-                bs0 <- connRecv conn
-                if S.length bs0 >= 4 && "PRI " `S.isPrefixOf` bs0
+                bs0 <- recv4
+                if "PRI " `S.isPrefixOf` bs0
                     then return (True, bs0)
                     else return (False, bs0)
     if settingsHTTP2Enabled settings && h2
@@ -395,6 +395,18 @@ serveConnection conn ii th origAddr transport settings app = do
             http2 settings ii conn transport app origAddr th bs
         else do
             http1 settings ii conn transport app origAddr th bs
+  where
+    recv4 = do
+        bs0 <- connRecv conn
+        if S.length bs0 >= 4
+           then return bs0
+           else loop bs0
+    loop bs0 = do
+        bs1 <- connRecv conn
+        let bs = bs0 `S.append` bs1
+        if S.length bs >= 4
+           then return bs
+           else loop bs
 
 -- | Set flag FileCloseOnExec flag on a socket (on Unix)
 --

From eb7b730677864b07dc3cd66f823840fe10f5c795 Mon Sep 17 00:00:00 2001
From: Kazu Yamamoto <kazu@iij.ad.jp>
Date: Wed, 22 May 2024 12:56:29 +0900
Subject: [PATCH 2/3] recv4 breaks if "" is received.

---
 warp/Network/Wai/Handler/Warp/Run.hs | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/warp/Network/Wai/Handler/Warp/Run.hs b/warp/Network/Wai/Handler/Warp/Run.hs
index 2065f87e4..e0cd4fd62 100644
--- a/warp/Network/Wai/Handler/Warp/Run.hs
+++ b/warp/Network/Wai/Handler/Warp/Run.hs
@@ -386,7 +386,7 @@ serveConnection conn ii th origAddr transport settings app = do
         if isHTTP2 transport
             then return (True, "")
             else do
-                bs0 <- recv4
+                bs0 <- recv4 ""
                 if "PRI " `S.isPrefixOf` bs0
                     then return (True, bs0)
                     else return (False, bs0)
@@ -396,17 +396,17 @@ serveConnection conn ii th origAddr transport settings app = do
         else do
             http1 settings ii conn transport app origAddr th bs
   where
-    recv4 = do
-        bs0 <- connRecv conn
-        if S.length bs0 >= 4
-           then return bs0
-           else loop bs0
-    loop bs0 = do
+    recv4 bs0 = do
         bs1 <- connRecv conn
-        let bs = bs0 `S.append` bs1
-        if S.length bs >= 4
-           then return bs
-           else loop bs
+        if S.length bs1 == 0 then
+            return bs0
+          else do
+            -- In the case where bs0 is "", (<>) is called unnecessarily.
+            -- But we adopt this logic for simplicity.
+            let bs2 = bs0 <> bs1
+            if S.length bs2 >= 4
+                 then return bs2
+                 else recv4 bs2
 
 -- | Set flag FileCloseOnExec flag on a socket (on Unix)
 --

From 4247e5ef26175ca5714993761452f76d651a548d Mon Sep 17 00:00:00 2001
From: Kazu Yamamoto <kazu@iij.ad.jp>
Date: Thu, 23 May 2024 08:30:50 +0900
Subject: [PATCH 3/3] using null

---
 warp/Network/Wai/Handler/Warp/Run.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/warp/Network/Wai/Handler/Warp/Run.hs b/warp/Network/Wai/Handler/Warp/Run.hs
index e0cd4fd62..0cde00d90 100644
--- a/warp/Network/Wai/Handler/Warp/Run.hs
+++ b/warp/Network/Wai/Handler/Warp/Run.hs
@@ -398,7 +398,7 @@ serveConnection conn ii th origAddr transport settings app = do
   where
     recv4 bs0 = do
         bs1 <- connRecv conn
-        if S.length bs1 == 0 then
+        if S.null bs1 then
             return bs0
           else do
             -- In the case where bs0 is "", (<>) is called unnecessarily.