add: use SO_REUSEPORT on platform supporting it

Author: mkleczek

CHANGELOG.md

@@ -13,6 +13,7 @@ All notable changes to this project will be documented in this file. From versio
 - Optimize requests with `Prefer: count=exact` that do not use ranges or `db-max-rows` by @laurenceisla in #3957
   + Removed unnecessary double count when building the `Content-Range`.
 - Add config `client_error_verbosity` to customize error verbosity by @taimoorzaeem in #4088, #3980, #3824
+- Use SO_REUSEPORT on platforms supporting it by @mkleczek in #4703 #4694
 
 ### Changed
 

src/PostgREST/App.hs

@@ -63,7 +63,8 @@ import PostgREST.Version              (docsVersion, prettyVersion)
 
 import qualified Data.ByteString.Char8  as BS
 import qualified Data.List              as L
-import           Data.Streaming.Network (bindPortTCP,
+import           Data.Streaming.Network (HostPreference,
+                                         bindPortGenEx, bindPortTCP,
                                          bindRandomPortTCP)
 import qualified Data.Text              as T
 import qualified Network.HTTP.Types     as HTTP
@@ -260,7 +261,7 @@ initSockets AppConfig{..} = do
       (_, sock) <-
         if cfg'port /= 0
           then do
-            sock <- bindPortTCP cfg'port (fromString $ T.unpack cfg'host)
+            sock <- bindPortTCPWithReusePort cfg'port (fromString $ T.unpack cfg'host)
             pure (cfg'port, sock)
           else do
             -- explicitly bind to a random port, returning bound port number
@@ -270,9 +271,21 @@ initSockets AppConfig{..} = do
 
   adminSock <- case cfg'adminPort of
     Just adminPort -> do
-      adminSock <- bindPortTCP adminPort (fromString $ T.unpack cfg'adminHost)
+      adminSock <- bindPortTCPWithReusePort adminPort (fromString $ T.unpack cfg'adminHost)
       pure $ Just adminSock
     Nothing -> pure Nothing
 
   pure (sock, adminSock)
 
+bindPortTCPWithReusePort :: Int -> HostPreference -> IO NS.Socket
+bindPortTCPWithReusePort port hostPreference
+  = do
+    -- Some unix variants can expose ReusePort but reject it at runtime.
+    -- Fall back to the default behavior when that happens.
+    socketWithReusePort <- try (bindPortGenEx reusePortOpts NS.Stream port hostPreference) :: IO (Either SomeException NS.Socket)
+    either (const $ bindPortTCP port hostPreference) listenSocket socketWithReusePort
+  where
+    reusePortOpts = [(NS.ReusePort, 1)]
+    listenSocket sock = do
+      NS.listen sock (max 2048 NS.maxListenQueue)
+      pure sock

test/io/test_io.py

@@ -133,7 +133,6 @@ def test_random_port_bound(defaultenv):
         assert True  # liveness check is done by run(), so we just need to check that it doesn't fail
 
 
-@pytest.mark.xfail(reason="SO_REUSEPORT handover is currently failing")
 def test_so_reuseport_zero_downtime_handover(defaultenv):
     "A second PostgREST instance should take over on the same main/admin ports without request failures."