From fa9a3a0afba71852d9e18b01909b8981ef3d4496 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Tue, 19 Dec 2023 00:40:18 -0800
Subject: [PATCH 01/12] Handle HTTP 103 Early Hints

---
 http-client/Network/HTTP/Client/Connection.hs |  6 ++++
 http-client/Network/HTTP/Client/Headers.hs    | 33 +++++++++++++++----
 .../Network/HTTP/Client/HeadersSpec.hs        | 18 ++++++++++
 3 files changed, 51 insertions(+), 6 deletions(-)

diff --git a/http-client/Network/HTTP/Client/Connection.hs b/http-client/Network/HTTP/Client/Connection.hs
index f4c42df7..a57da553 100644
--- a/http-client/Network/HTTP/Client/Connection.hs
+++ b/http-client/Network/HTTP/Client/Connection.hs
@@ -5,6 +5,7 @@ module Network.HTTP.Client.Connection
     ( connectionReadLine
     , connectionReadLineWith
     , connectionDropTillBlankLine
+    , connectionUnreadLine
     , dummyConnection
     , openSocketConnection
     , openSocketConnectionSize
@@ -60,6 +61,11 @@ connectionReadLineWith mhl conn bs0 =
                 unless (S.null y) $! connectionUnread conn y
                 return $! killCR $! S.concat $! front [x]
 
+connectionUnreadLine :: Connection -> ByteString -> IO ()
+connectionUnreadLine conn line = do
+  connectionUnread conn (S.pack [charCR, charLF])
+  connectionUnread conn line
+
 charLF, charCR :: Word8
 charLF = 10
 charCR = 13
diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index 087653d6..f11452f6 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -1,4 +1,6 @@
 {-# LANGUAGE DisambiguateRecordFields #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ViewPatterns #-}
 module Network.HTTP.Client.Headers
@@ -45,11 +47,17 @@ parseStatusHeaders mhl conn timeout' cont
             Just  s -> return s
             Nothing -> sendBody >> getStatus
 
+    nextStatusHeaders :: IO (Maybe StatusHeaders)
     nextStatusHeaders = do
         (s, v) <- nextStatusLine mhl
-        if statusCode s == 100
-            then connectionDropTillBlankLine mhl conn >> return Nothing
-            else Just . StatusHeaders s v A.<$> parseHeaders (0 :: Int) id
+        if | statusCode s == 100 -> connectionDropTillBlankLine mhl conn >> return Nothing
+           | statusCode s == 103 -> do
+               linkHeaders <- parseHeadersUntilFailure 0 id
+               nextStatusHeaders >>= \case
+                   Nothing -> return Nothing
+                   Just (StatusHeaders s' v' reqHeaders) ->
+                       return $ Just $ StatusHeaders s' v' (linkHeaders <> reqHeaders)
+           | otherwise -> Just . StatusHeaders s v A.<$> parseHeaders 0 id
 
     nextStatusLine :: Maybe MaxHeaderLength -> IO (Status, HttpVersion)
     nextStatusLine mhl = do
@@ -82,14 +90,14 @@ parseStatusHeaders mhl conn timeout' cont
             Just (i, "") -> Just i
             _ -> Nothing
 
+    parseHeaders :: Int -> ([Header] -> [Header]) -> IO [Header]
     parseHeaders 100 _ = throwHttp OverlongHeaders
     parseHeaders count front = do
         line <- connectionReadLine mhl conn
         if S.null line
             then return $ front []
-            else do
-                mheader <- parseHeader line
-                case mheader of
+            else
+                parseHeader line >>= \case
                     Just header ->
                         parseHeaders (count + 1) $ front . (header:)
                     Nothing ->
@@ -97,6 +105,19 @@ parseStatusHeaders mhl conn timeout' cont
                         -- an exception, ignore it for robustness.
                         parseHeaders count front
 
+    parseHeadersUntilFailure :: Int -> ([Header] -> [Header]) -> IO [Header]
+    parseHeadersUntilFailure 100 _ = throwHttp OverlongHeaders
+    parseHeadersUntilFailure count front = do
+        line <- connectionReadLine mhl conn
+        if S.null line
+            then return $ front []
+            else
+                parseHeader line >>= \case
+                    Just header -> parseHeadersUntilFailure (count + 1) $ front . (header:)
+                    Nothing -> do
+                      connectionUnreadLine conn line
+                      return $ front []
+
     parseHeader :: S.ByteString -> IO (Maybe Header)
     parseHeader bs = do
         let (key, bs2) = S.break (== charColon) bs
diff --git a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
index 08304b9f..a3284612 100644
--- a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
+++ b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
@@ -60,3 +60,21 @@ spec = describe "HeadersSpec" $ do
         statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [ ("foo", "bar") ]
         out >>= (`shouldBe` [])
         inp >>= (`shouldBe` ["result"])
+
+    it "103 early hints" $ do
+        let input =
+                [ "HTTP/1.1 103 Early Hints\r\n"
+                , "Link: </foo.js>\r\n"
+                , "Link: </bar.js>\r\n\r\n"
+                , "HTTP/1.1 200 OK\r\n"
+                , "Content-Type: text/html\r\n\r\n"
+                , "<div></div>"
+                ]
+        (conn, _, inp) <- dummyConnection input
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing Nothing
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [
+          ("Link", "</foo.js>")
+          , ("Link", "</bar.js>")
+          , ("Content-Type", "text/html")
+          ]
+        inp >>= (`shouldBe` ["<div></div>"])

From 76e46f7ba9b6f62832454ddcc65e65bc0d8c1768 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Tue, 19 Dec 2023 01:14:48 -0800
Subject: [PATCH 02/12] Put early hints into `responseEarlyHints` field

---
 http-client/Network/HTTP/Client/Headers.hs    |  8 ++++----
 http-client/Network/HTTP/Client/Manager.hs    |  2 +-
 http-client/Network/HTTP/Client/Response.hs   |  3 ++-
 http-client/Network/HTTP/Client/Types.hs      |  7 ++++++-
 .../Network/HTTP/Client/HeadersSpec.hs        | 19 ++++++++++---------
 5 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index f11452f6..7379a005 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -52,12 +52,12 @@ parseStatusHeaders mhl conn timeout' cont
         (s, v) <- nextStatusLine mhl
         if | statusCode s == 100 -> connectionDropTillBlankLine mhl conn >> return Nothing
            | statusCode s == 103 -> do
-               linkHeaders <- parseHeadersUntilFailure 0 id
+               earlyHeaders <- parseHeadersUntilFailure 0 id
                nextStatusHeaders >>= \case
                    Nothing -> return Nothing
-                   Just (StatusHeaders s' v' reqHeaders) ->
-                       return $ Just $ StatusHeaders s' v' (linkHeaders <> reqHeaders)
-           | otherwise -> Just . StatusHeaders s v A.<$> parseHeaders 0 id
+                   Just (StatusHeaders s' v' earlyHeaders' reqHeaders) ->
+                       return $ Just $ StatusHeaders s' v' (earlyHeaders <> earlyHeaders') reqHeaders
+           | otherwise -> (Just <$>) $ StatusHeaders s v mempty A.<$> parseHeaders 0 id
 
     nextStatusLine :: Maybe MaxHeaderLength -> IO (Status, HttpVersion)
     nextStatusLine mhl = do
diff --git a/http-client/Network/HTTP/Client/Manager.hs b/http-client/Network/HTTP/Client/Manager.hs
index 57462f1e..fbf4eb04 100644
--- a/http-client/Network/HTTP/Client/Manager.hs
+++ b/http-client/Network/HTTP/Client/Manager.hs
@@ -259,7 +259,7 @@ mkCreateConnection ms = do
                     , "\r\n"
                     ]
                 parse conn = do
-                    StatusHeaders status _ _ <- parseStatusHeaders (managerMaxHeaderLength ms) conn Nothing Nothing
+                    StatusHeaders status _ _ _ <- parseStatusHeaders (managerMaxHeaderLength ms) conn Nothing Nothing
                     unless (status == status200) $
                         throwHttp $ ProxyConnectException ultHost ultPort status
                 in tlsProxyConnection
diff --git a/http-client/Network/HTTP/Client/Response.hs b/http-client/Network/HTTP/Client/Response.hs
index 242723fc..7c589e90 100644
--- a/http-client/Network/HTTP/Client/Response.hs
+++ b/http-client/Network/HTTP/Client/Response.hs
@@ -121,7 +121,7 @@ getResponse :: Maybe MaxHeaderLength
             -> IO (Response BodyReader)
 getResponse mhl timeout' req@(Request {..}) mconn cont = do
     let conn = managedResource mconn
-    StatusHeaders s version hs <- parseStatusHeaders mhl conn timeout' cont
+    StatusHeaders s version earlyHs hs <- parseStatusHeaders mhl conn timeout' cont
     let mcl = lookup "content-length" hs >>= readPositiveInt . S8.unpack
         isChunked = ("transfer-encoding", CI.mk "chunked") `elem` map (second CI.mk) hs
 
@@ -162,6 +162,7 @@ getResponse mhl timeout' req@(Request {..}) mconn cont = do
         , responseCookieJar = Data.Monoid.mempty
         , responseClose' = ResponseClose (cleanup False)
         , responseOriginalRequest = req {requestBody = ""}
+        , responseEarlyHints = earlyHs
         }
 
 -- | Does this response have no body?
diff --git a/http-client/Network/HTTP/Client/Types.hs b/http-client/Network/HTTP/Client/Types.hs
index 7a142cfc..8c8d0bfc 100644
--- a/http-client/Network/HTTP/Client/Types.hs
+++ b/http-client/Network/HTTP/Client/Types.hs
@@ -90,7 +90,7 @@ data Connection = Connection
     }
     deriving T.Typeable
 
-data StatusHeaders = StatusHeaders Status HttpVersion RequestHeaders
+data StatusHeaders = StatusHeaders Status HttpVersion RequestHeaders RequestHeaders
     deriving (Show, Eq, Ord, T.Typeable)
 
 -- | A newtype wrapper which is not exported from this library but is an
@@ -715,6 +715,11 @@ data Response body = Response
     -- via @getOriginalRequest@ instead.
     --
     -- Since 0.7.8
+    , responseEarlyHints :: ResponseHeaders
+    -- ^ Early response headers sent by the server, as part of an HTTP
+    -- 103 Early Hints section.
+    --
+    -- Since 0.7.16
     }
     deriving (Show, T.Typeable, Functor, Data.Foldable.Foldable, Data.Traversable.Traversable)
 
diff --git a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
index a3284612..6f96cf6a 100644
--- a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
+++ b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
@@ -21,7 +21,7 @@ spec = describe "HeadersSpec" $ do
                 ]
         (connection, _, _) <- dummyConnection input
         statusHeaders <- parseStatusHeaders Nothing connection Nothing Nothing
-        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1)
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) mempty
             [ ("foo", "bar")
             , ("baz", "bin")
             ]
@@ -35,7 +35,7 @@ spec = describe "HeadersSpec" $ do
         (conn, out, _) <- dummyConnection input
         let sendBody = connectionWrite conn "data"
         statusHeaders <- parseStatusHeaders Nothing conn Nothing (Just sendBody)
-        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [ ("foo", "bar") ]
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [] [ ("foo", "bar") ]
         out >>= (`shouldBe` ["data"])
 
     it "Expect: 100-continue (failure)" $ do
@@ -45,7 +45,7 @@ spec = describe "HeadersSpec" $ do
         (conn, out, _) <- dummyConnection input
         let sendBody = connectionWrite conn "data"
         statusHeaders <- parseStatusHeaders Nothing conn Nothing (Just sendBody)
-        statusHeaders `shouldBe` StatusHeaders status417 (HttpVersion 1 1) []
+        statusHeaders `shouldBe` StatusHeaders status417 (HttpVersion 1 1) [] []
         out >>= (`shouldBe` [])
 
     it "100 Continue without expectation is OK" $ do
@@ -57,7 +57,7 @@ spec = describe "HeadersSpec" $ do
                 ]
         (conn, out, inp) <- dummyConnection input
         statusHeaders <- parseStatusHeaders Nothing conn Nothing Nothing
-        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [ ("foo", "bar") ]
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [] [ ("foo", "bar") ]
         out >>= (`shouldBe` [])
         inp >>= (`shouldBe` ["result"])
 
@@ -72,9 +72,10 @@ spec = describe "HeadersSpec" $ do
                 ]
         (conn, _, inp) <- dummyConnection input
         statusHeaders <- parseStatusHeaders Nothing conn Nothing Nothing
-        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [
-          ("Link", "</foo.js>")
-          , ("Link", "</bar.js>")
-          , ("Content-Type", "text/html")
-          ]
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1)
+            [("Link", "</foo.js>")
+            , ("Link", "</bar.js>")
+            ]
+            [("Content-Type", "text/html")
+            ]
         inp >>= (`shouldBe` ["<div></div>"])

From 07043c23e67add25419aa54fa351d9bc239b2199 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Tue, 19 Dec 2023 01:18:24 -0800
Subject: [PATCH 03/12] Expose responseEarlyHints constructor

---
 http-client/Network/HTTP/Client.hs   | 1 +
 http-conduit/Network/HTTP/Conduit.hs | 1 +
 2 files changed, 2 insertions(+)

diff --git a/http-client/Network/HTTP/Client.hs b/http-client/Network/HTTP/Client.hs
index 813c85ca..34e6c315 100644
--- a/http-client/Network/HTTP/Client.hs
+++ b/http-client/Network/HTTP/Client.hs
@@ -184,6 +184,7 @@ module Network.HTTP.Client
     , responseBody
     , responseCookieJar
     , getOriginalRequest
+    , responseEarlyHints
     , throwErrorStatusCodes
       -- ** Response body
     , BodyReader
diff --git a/http-conduit/Network/HTTP/Conduit.hs b/http-conduit/Network/HTTP/Conduit.hs
index 5f0dc07f..ba6f88db 100644
--- a/http-conduit/Network/HTTP/Conduit.hs
+++ b/http-conduit/Network/HTTP/Conduit.hs
@@ -179,6 +179,7 @@ module Network.HTTP.Conduit
     , responseHeaders
     , responseBody
     , responseCookieJar
+    , responseEarlyHints
       -- * Manager
     , Manager
     , newManager

From f51be27fca9f762c9cecbce1f20692b90660e0cc Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Fri, 22 Dec 2023 00:26:43 -0700
Subject: [PATCH 04/12] Bump cabal file version to 0.7.16 and update
 ChangeLog.md

---
 http-client/ChangeLog.md      | 4 ++++
 http-client/http-client.cabal | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/http-client/ChangeLog.md b/http-client/ChangeLog.md
index fc45385d..99242993 100644
--- a/http-client/ChangeLog.md
+++ b/http-client/ChangeLog.md
@@ -1,5 +1,9 @@
 # Changelog for http-client
 
+## 0.7.16
+
+* Add `responseEarlyHints` field to `Response`, containing any HTTP 103 Early Hints headers from the server.
+
 ## 0.7.15
 
 * Adds `shouldStripHeaderOnRedirectIfOnDifferentHostOnly` option to `Request` [#520](https://github.com/snoyberg/http-client/pull/520)
diff --git a/http-client/http-client.cabal b/http-client/http-client.cabal
index a6c6bbdb..f8d4f0d4 100644
--- a/http-client/http-client.cabal
+++ b/http-client/http-client.cabal
@@ -1,5 +1,5 @@
 name:                http-client
-version:             0.7.15
+version:             0.7.16
 synopsis:            An HTTP client engine
 description:         Hackage documentation generation is not reliable. For up to date documentation, please see: <http://www.stackage.org/package/http-client>.
 homepage:            https://github.com/snoyberg/http-client

From 1dfea22390ee974d05262785c1cbe9ec90e236b3 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Thu, 28 Dec 2023 11:25:39 -0700
Subject: [PATCH 05/12] Plumb early hints callback through and add test

---
 http-client/Network/HTTP/Client/Headers.hs    |  4 +--
 http-client/Network/HTTP/Client/Manager.hs    |  2 +-
 http-client/Network/HTTP/Client/Request.hs    |  1 +
 http-client/Network/HTTP/Client/Response.hs   |  2 +-
 http-client/Network/HTTP/Client/Types.hs      |  5 ++++
 .../Network/HTTP/Client/HeadersSpec.hs        | 26 +++++++++++++++----
 6 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index 7379a005..2ef98818 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -28,8 +28,8 @@ charColon = 58
 charPeriod = 46
 
 
-parseStatusHeaders :: Maybe MaxHeaderLength -> Connection -> Maybe Int -> Maybe (IO ()) -> IO StatusHeaders
-parseStatusHeaders mhl conn timeout' cont
+parseStatusHeaders :: Maybe MaxHeaderLength -> Connection -> Maybe Int -> (Header -> IO ()) -> Maybe (IO ()) -> IO StatusHeaders
+parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
     | Just k <- cont = getStatusExpectContinue k
     | otherwise      = getStatus
   where
diff --git a/http-client/Network/HTTP/Client/Manager.hs b/http-client/Network/HTTP/Client/Manager.hs
index fbf4eb04..fc21ac90 100644
--- a/http-client/Network/HTTP/Client/Manager.hs
+++ b/http-client/Network/HTTP/Client/Manager.hs
@@ -259,7 +259,7 @@ mkCreateConnection ms = do
                     , "\r\n"
                     ]
                 parse conn = do
-                    StatusHeaders status _ _ _ <- parseStatusHeaders (managerMaxHeaderLength ms) conn Nothing Nothing
+                    StatusHeaders status _ _ _ <- parseStatusHeaders (managerMaxHeaderLength ms) conn Nothing (\_ -> return ()) Nothing
                     unless (status == status200) $
                         throwHttp $ ProxyConnectException ultHost ultPort status
                 in tlsProxyConnection
diff --git a/http-client/Network/HTTP/Client/Request.hs b/http-client/Network/HTTP/Client/Request.hs
index f6f3fad2..55647a34 100644
--- a/http-client/Network/HTTP/Client/Request.hs
+++ b/http-client/Network/HTTP/Client/Request.hs
@@ -306,6 +306,7 @@ defaultRequest = Request
         , shouldStripHeaderOnRedirectIfOnDifferentHostOnly = False
         , proxySecureMode = ProxySecureWithConnect
         , redactHeaders = Set.singleton "Authorization"
+        , earlyHintHeaderReceived = \_ -> return ()
         }
 
 -- | Parses a URL via 'parseRequest_'
diff --git a/http-client/Network/HTTP/Client/Response.hs b/http-client/Network/HTTP/Client/Response.hs
index 7c589e90..d4d593d5 100644
--- a/http-client/Network/HTTP/Client/Response.hs
+++ b/http-client/Network/HTTP/Client/Response.hs
@@ -121,7 +121,7 @@ getResponse :: Maybe MaxHeaderLength
             -> IO (Response BodyReader)
 getResponse mhl timeout' req@(Request {..}) mconn cont = do
     let conn = managedResource mconn
-    StatusHeaders s version earlyHs hs <- parseStatusHeaders mhl conn timeout' cont
+    StatusHeaders s version earlyHs hs <- parseStatusHeaders mhl conn timeout' earlyHintHeaderReceived cont
     let mcl = lookup "content-length" hs >>= readPositiveInt . S8.unpack
         isChunked = ("transfer-encoding", CI.mk "chunked") `elem` map (second CI.mk) hs
 
diff --git a/http-client/Network/HTTP/Client/Types.hs b/http-client/Network/HTTP/Client/Types.hs
index 8c8d0bfc..5eb0a5b0 100644
--- a/http-client/Network/HTTP/Client/Types.hs
+++ b/http-client/Network/HTTP/Client/Types.hs
@@ -634,6 +634,11 @@ data Request = Request
     -- ^ List of header values being redacted in case we show Request.
     --
     -- @since 0.7.13
+
+    , earlyHintHeaderReceived :: Header -> IO ()
+    -- ^ Called every time an HTTP 103 Early Hints header is received from the server.
+    --
+    -- @since 0.7.16
     }
     deriving T.Typeable
 
diff --git a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
index 6f96cf6a..dbf863bd 100644
--- a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
+++ b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
@@ -1,6 +1,9 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 module Network.HTTP.Client.HeadersSpec where
 
+import           Control.Concurrent.MVar
+import qualified Data.Sequence as Seq
 import           Network.HTTP.Client.Internal
 import           Network.HTTP.Types
 import           Test.Hspec
@@ -20,7 +23,7 @@ spec = describe "HeadersSpec" $ do
                 , "\nignored"
                 ]
         (connection, _, _) <- dummyConnection input
-        statusHeaders <- parseStatusHeaders Nothing connection Nothing Nothing
+        statusHeaders <- parseStatusHeaders Nothing connection Nothing (\_ -> return ()) Nothing
         statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) mempty
             [ ("foo", "bar")
             , ("baz", "bin")
@@ -34,7 +37,7 @@ spec = describe "HeadersSpec" $ do
                 ]
         (conn, out, _) <- dummyConnection input
         let sendBody = connectionWrite conn "data"
-        statusHeaders <- parseStatusHeaders Nothing conn Nothing (Just sendBody)
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing (\_ -> return ()) (Just sendBody)
         statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [] [ ("foo", "bar") ]
         out >>= (`shouldBe` ["data"])
 
@@ -44,7 +47,7 @@ spec = describe "HeadersSpec" $ do
                 ]
         (conn, out, _) <- dummyConnection input
         let sendBody = connectionWrite conn "data"
-        statusHeaders <- parseStatusHeaders Nothing conn Nothing (Just sendBody)
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing (\_ -> return ()) (Just sendBody)
         statusHeaders `shouldBe` StatusHeaders status417 (HttpVersion 1 1) [] []
         out >>= (`shouldBe` [])
 
@@ -56,7 +59,7 @@ spec = describe "HeadersSpec" $ do
                 , "result"
                 ]
         (conn, out, inp) <- dummyConnection input
-        statusHeaders <- parseStatusHeaders Nothing conn Nothing Nothing
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing (\_ -> return ()) Nothing
         statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1) [] [ ("foo", "bar") ]
         out >>= (`shouldBe` [])
         inp >>= (`shouldBe` ["result"])
@@ -71,11 +74,24 @@ spec = describe "HeadersSpec" $ do
                 , "<div></div>"
                 ]
         (conn, _, inp) <- dummyConnection input
-        statusHeaders <- parseStatusHeaders Nothing conn Nothing Nothing
+
+        callbackResults :: MVar (Seq.Seq Header) <- newMVar mempty
+        let onEarlyHintHeader h = modifyMVar_ callbackResults (return . (Seq.|> h))
+
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing onEarlyHintHeader Nothing
         statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1)
             [("Link", "</foo.js>")
             , ("Link", "</bar.js>")
             ]
             [("Content-Type", "text/html")
             ]
+
         inp >>= (`shouldBe` ["<div></div>"])
+
+        readMVar callbackResults
+          >>= ( `shouldBe`
+                  Seq.fromList
+                    [ ("Link", "</foo.js>"),
+                      ("Link", "</bar.js>")
+                    ]
+              )

From 4c56e9558a5d60e610d02f281408c87f229fea01 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Thu, 28 Dec 2023 11:28:19 -0700
Subject: [PATCH 06/12] Call early hint callback in Headers.hs

---
 http-client/Network/HTTP/Client/Headers.hs | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index 2ef98818..13bc1d19 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -52,7 +52,7 @@ parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
         (s, v) <- nextStatusLine mhl
         if | statusCode s == 100 -> connectionDropTillBlankLine mhl conn >> return Nothing
            | statusCode s == 103 -> do
-               earlyHeaders <- parseHeadersUntilFailure 0 id
+               earlyHeaders <- parseEarlyHintHeadersUntilFailure 0 id
                nextStatusHeaders >>= \case
                    Nothing -> return Nothing
                    Just (StatusHeaders s' v' earlyHeaders' reqHeaders) ->
@@ -105,15 +105,17 @@ parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
                         -- an exception, ignore it for robustness.
                         parseHeaders count front
 
-    parseHeadersUntilFailure :: Int -> ([Header] -> [Header]) -> IO [Header]
-    parseHeadersUntilFailure 100 _ = throwHttp OverlongHeaders
-    parseHeadersUntilFailure count front = do
+    parseEarlyHintHeadersUntilFailure :: Int -> ([Header] -> [Header]) -> IO [Header]
+    parseEarlyHintHeadersUntilFailure 100 _ = throwHttp OverlongHeaders
+    parseEarlyHintHeadersUntilFailure count front = do
         line <- connectionReadLine mhl conn
         if S.null line
             then return $ front []
             else
                 parseHeader line >>= \case
-                    Just header -> parseHeadersUntilFailure (count + 1) $ front . (header:)
+                    Just header -> do
+                      onEarlyHintHeader header
+                      parseEarlyHintHeadersUntilFailure (count + 1) $ front . (header:)
                     Nothing -> do
                       connectionUnreadLine conn line
                       return $ front []

From 29bdb3fbd84badbdff1234e08420300935158ac1 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Thu, 28 Dec 2023 11:31:54 -0700
Subject: [PATCH 07/12] Export earlyHintHeaderReceived

---
 http-client/Network/HTTP/Client.hs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/http-client/Network/HTTP/Client.hs b/http-client/Network/HTTP/Client.hs
index 34e6c315..ed6d9d62 100644
--- a/http-client/Network/HTTP/Client.hs
+++ b/http-client/Network/HTTP/Client.hs
@@ -168,6 +168,7 @@ module Network.HTTP.Client
     , cookieJar
     , requestVersion
     , redactHeaders
+    , earlyHintHeaderReceived
       -- ** Request body
     , RequestBody (..)
     , Popper

From 345ed727782e2ed834d7a0d1ca14c3fb3cd81ec8 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Thu, 28 Dec 2023 11:33:41 -0700
Subject: [PATCH 08/12] Update CHANGELOG again

---
 http-client/ChangeLog.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/http-client/ChangeLog.md b/http-client/ChangeLog.md
index 99242993..a44ea58c 100644
--- a/http-client/ChangeLog.md
+++ b/http-client/ChangeLog.md
@@ -2,7 +2,8 @@
 
 ## 0.7.16
 
-* Add `responseEarlyHints` field to `Response`, containing any HTTP 103 Early Hints headers from the server.
+* Add `responseEarlyHints` field to `Response`, containing a list of HTTP 103 Early Hints headers received from the server.
+* Add `earlyHintHeaderReceived` callback to `Request`, which will be called on each HTTP 103 Early Hints header received.
 
 ## 0.7.15
 

From 8daeeddf6d04db04b50dbb67496cee29f47bbcbc Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Fri, 29 Dec 2023 12:59:37 -0700
Subject: [PATCH 09/12] Switch callback signature to [Header] -> IO ()

---
 http-client/ChangeLog.md                      |  4 ++--
 http-client/Network/HTTP/Client.hs            |  2 +-
 http-client/Network/HTTP/Client/Headers.hs    | 22 +++++++++----------
 http-client/Network/HTTP/Client/Request.hs    |  2 +-
 http-client/Network/HTTP/Client/Response.hs   |  2 +-
 http-client/Network/HTTP/Client/Types.hs      |  2 +-
 .../Network/HTTP/Client/HeadersSpec.hs        | 12 +++++-----
 7 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/http-client/ChangeLog.md b/http-client/ChangeLog.md
index a44ea58c..e29dcd5a 100644
--- a/http-client/ChangeLog.md
+++ b/http-client/ChangeLog.md
@@ -2,8 +2,8 @@
 
 ## 0.7.16
 
-* Add `responseEarlyHints` field to `Response`, containing a list of HTTP 103 Early Hints headers received from the server.
-* Add `earlyHintHeaderReceived` callback to `Request`, which will be called on each HTTP 103 Early Hints header received.
+* Add `responseEarlyHints` field to `Response`, containing a list of all HTTP 103 Early Hints headers received from the server.
+* Add `earlyHintHeadersReceived` callback to `Request`, which will be called on each HTTP 103 Early Hints header section received.
 
 ## 0.7.15
 
diff --git a/http-client/Network/HTTP/Client.hs b/http-client/Network/HTTP/Client.hs
index ed6d9d62..ab1b8c06 100644
--- a/http-client/Network/HTTP/Client.hs
+++ b/http-client/Network/HTTP/Client.hs
@@ -168,7 +168,7 @@ module Network.HTTP.Client
     , cookieJar
     , requestVersion
     , redactHeaders
-    , earlyHintHeaderReceived
+    , earlyHintHeadersReceived
       -- ** Request body
     , RequestBody (..)
     , Popper
diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index 13bc1d19..1eab92d0 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -16,11 +16,11 @@ import qualified Data.ByteString.Char8          as S8
 import qualified Data.CaseInsensitive           as CI
 import           Data.Maybe (mapMaybe)
 import           Data.Monoid
+import Data.Word (Word8)
 import           Network.HTTP.Client.Connection
 import           Network.HTTP.Client.Types
-import           System.Timeout                 (timeout)
 import           Network.HTTP.Types
-import Data.Word (Word8)
+import           System.Timeout                 (timeout)
 
 charSpace, charColon, charPeriod :: Word8
 charSpace = 32
@@ -28,8 +28,8 @@ charColon = 58
 charPeriod = 46
 
 
-parseStatusHeaders :: Maybe MaxHeaderLength -> Connection -> Maybe Int -> (Header -> IO ()) -> Maybe (IO ()) -> IO StatusHeaders
-parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
+parseStatusHeaders :: Maybe MaxHeaderLength -> Connection -> Maybe Int -> ([Header] -> IO ()) -> Maybe (IO ()) -> IO StatusHeaders
+parseStatusHeaders mhl conn timeout' onEarlyHintHeaders cont
     | Just k <- cont = getStatusExpectContinue k
     | otherwise      = getStatus
   where
@@ -52,11 +52,12 @@ parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
         (s, v) <- nextStatusLine mhl
         if | statusCode s == 100 -> connectionDropTillBlankLine mhl conn >> return Nothing
            | statusCode s == 103 -> do
-               earlyHeaders <- parseEarlyHintHeadersUntilFailure 0 id
-               nextStatusHeaders >>= \case
-                   Nothing -> return Nothing
-                   Just (StatusHeaders s' v' earlyHeaders' reqHeaders) ->
-                       return $ Just $ StatusHeaders s' v' (earlyHeaders <> earlyHeaders') reqHeaders
+                 earlyHeaders <- parseEarlyHintHeadersUntilFailure 0 id
+                 onEarlyHintHeaders earlyHeaders
+                 nextStatusHeaders >>= \case
+                     Nothing -> return Nothing
+                     Just (StatusHeaders s' v' earlyHeaders' reqHeaders) ->
+                         return $ Just $ StatusHeaders s' v' (earlyHeaders <> earlyHeaders') reqHeaders
            | otherwise -> (Just <$>) $ StatusHeaders s v mempty A.<$> parseHeaders 0 id
 
     nextStatusLine :: Maybe MaxHeaderLength -> IO (Status, HttpVersion)
@@ -113,8 +114,7 @@ parseStatusHeaders mhl conn timeout' onEarlyHintHeader cont
             then return $ front []
             else
                 parseHeader line >>= \case
-                    Just header -> do
-                      onEarlyHintHeader header
+                    Just header ->
                       parseEarlyHintHeadersUntilFailure (count + 1) $ front . (header:)
                     Nothing -> do
                       connectionUnreadLine conn line
diff --git a/http-client/Network/HTTP/Client/Request.hs b/http-client/Network/HTTP/Client/Request.hs
index 55647a34..99f37edd 100644
--- a/http-client/Network/HTTP/Client/Request.hs
+++ b/http-client/Network/HTTP/Client/Request.hs
@@ -306,7 +306,7 @@ defaultRequest = Request
         , shouldStripHeaderOnRedirectIfOnDifferentHostOnly = False
         , proxySecureMode = ProxySecureWithConnect
         , redactHeaders = Set.singleton "Authorization"
-        , earlyHintHeaderReceived = \_ -> return ()
+        , earlyHintHeadersReceived = \_ -> return ()
         }
 
 -- | Parses a URL via 'parseRequest_'
diff --git a/http-client/Network/HTTP/Client/Response.hs b/http-client/Network/HTTP/Client/Response.hs
index d4d593d5..ceb878ef 100644
--- a/http-client/Network/HTTP/Client/Response.hs
+++ b/http-client/Network/HTTP/Client/Response.hs
@@ -121,7 +121,7 @@ getResponse :: Maybe MaxHeaderLength
             -> IO (Response BodyReader)
 getResponse mhl timeout' req@(Request {..}) mconn cont = do
     let conn = managedResource mconn
-    StatusHeaders s version earlyHs hs <- parseStatusHeaders mhl conn timeout' earlyHintHeaderReceived cont
+    StatusHeaders s version earlyHs hs <- parseStatusHeaders mhl conn timeout' earlyHintHeadersReceived cont
     let mcl = lookup "content-length" hs >>= readPositiveInt . S8.unpack
         isChunked = ("transfer-encoding", CI.mk "chunked") `elem` map (second CI.mk) hs
 
diff --git a/http-client/Network/HTTP/Client/Types.hs b/http-client/Network/HTTP/Client/Types.hs
index 5eb0a5b0..51a53c52 100644
--- a/http-client/Network/HTTP/Client/Types.hs
+++ b/http-client/Network/HTTP/Client/Types.hs
@@ -635,7 +635,7 @@ data Request = Request
     --
     -- @since 0.7.13
 
-    , earlyHintHeaderReceived :: Header -> IO ()
+    , earlyHintHeadersReceived :: [Header] -> IO ()
     -- ^ Called every time an HTTP 103 Early Hints header is received from the server.
     --
     -- @since 0.7.16
diff --git a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
index dbf863bd..ae639715 100644
--- a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
+++ b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
@@ -75,7 +75,7 @@ spec = describe "HeadersSpec" $ do
                 ]
         (conn, _, inp) <- dummyConnection input
 
-        callbackResults :: MVar (Seq.Seq Header) <- newMVar mempty
+        callbackResults :: MVar (Seq.Seq [Header]) <- newMVar mempty
         let onEarlyHintHeader h = modifyMVar_ callbackResults (return . (Seq.|> h))
 
         statusHeaders <- parseStatusHeaders Nothing conn Nothing onEarlyHintHeader Nothing
@@ -89,9 +89,7 @@ spec = describe "HeadersSpec" $ do
         inp >>= (`shouldBe` ["<div></div>"])
 
         readMVar callbackResults
-          >>= ( `shouldBe`
-                  Seq.fromList
-                    [ ("Link", "</foo.js>"),
-                      ("Link", "</bar.js>")
-                    ]
-              )
+          >>= (`shouldBe` Seq.fromList [
+                  [("Link", "</foo.js>")
+                  , ("Link", "</bar.js>")
+                  ]])

From 1041fe8645aa34b34007209cd7b771874173be1c Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Fri, 29 Dec 2023 13:02:06 -0700
Subject: [PATCH 10/12] Add test of multiple 103 sections

---
 .../Network/HTTP/Client/HeadersSpec.hs        | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
index ae639715..0d242d44 100644
--- a/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
+++ b/http-client/test-nonet/Network/HTTP/Client/HeadersSpec.hs
@@ -93,3 +93,38 @@ spec = describe "HeadersSpec" $ do
                   [("Link", "</foo.js>")
                   , ("Link", "</bar.js>")
                   ]])
+
+    it "103 early hints (multiple sections)" $ do
+        let input =
+                [ "HTTP/1.1 103 Early Hints\r\n"
+                , "Link: </foo.js>\r\n"
+                , "Link: </bar.js>\r\n\r\n"
+                , "HTTP/1.1 103 Early Hints\r\n"
+                , "Link: </baz.js>\r\n\r\n"
+                , "HTTP/1.1 200 OK\r\n"
+                , "Content-Type: text/html\r\n\r\n"
+                , "<div></div>"
+                ]
+        (conn, _, inp) <- dummyConnection input
+
+        callbackResults :: MVar (Seq.Seq [Header]) <- newMVar mempty
+        let onEarlyHintHeader h = modifyMVar_ callbackResults (return . (Seq.|> h))
+
+        statusHeaders <- parseStatusHeaders Nothing conn Nothing onEarlyHintHeader Nothing
+        statusHeaders `shouldBe` StatusHeaders status200 (HttpVersion 1 1)
+            [("Link", "</foo.js>")
+            , ("Link", "</bar.js>")
+            , ("Link", "</baz.js>")
+            ]
+            [("Content-Type", "text/html")
+            ]
+
+        inp >>= (`shouldBe` ["<div></div>"])
+
+        readMVar callbackResults
+          >>= (`shouldBe` Seq.fromList [
+                  [("Link", "</foo.js>")
+                  , ("Link", "</bar.js>")
+                  ]
+                  , [("Link", "</baz.js>")]
+                  ])

From 4fd5eba28d75c8104eb7b4e3506a2b06560a9516 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Fri, 29 Dec 2023 13:06:26 -0700
Subject: [PATCH 11/12] Fix an import indentation in Headers.hs

---
 http-client/Network/HTTP/Client/Headers.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/http-client/Network/HTTP/Client/Headers.hs b/http-client/Network/HTTP/Client/Headers.hs
index 1eab92d0..fefe808c 100644
--- a/http-client/Network/HTTP/Client/Headers.hs
+++ b/http-client/Network/HTTP/Client/Headers.hs
@@ -16,7 +16,7 @@ import qualified Data.ByteString.Char8          as S8
 import qualified Data.CaseInsensitive           as CI
 import           Data.Maybe (mapMaybe)
 import           Data.Monoid
-import Data.Word (Word8)
+import           Data.Word (Word8)
 import           Network.HTTP.Client.Connection
 import           Network.HTTP.Client.Types
 import           Network.HTTP.Types

From 487bebf535252f7deb163c409598b64461053f87 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Fri, 29 Dec 2023 13:07:59 -0700
Subject: [PATCH 12/12] Update comment in Types.hs

---
 http-client/Network/HTTP/Client/Types.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/http-client/Network/HTTP/Client/Types.hs b/http-client/Network/HTTP/Client/Types.hs
index 51a53c52..646dac79 100644
--- a/http-client/Network/HTTP/Client/Types.hs
+++ b/http-client/Network/HTTP/Client/Types.hs
@@ -636,7 +636,7 @@ data Request = Request
     -- @since 0.7.13
 
     , earlyHintHeadersReceived :: [Header] -> IO ()
-    -- ^ Called every time an HTTP 103 Early Hints header is received from the server.
+    -- ^ Called every time an HTTP 103 Early Hints header section is received from the server.
     --
     -- @since 0.7.16
     }