From eae5e8163f3b0784848ff0310ba3c8adca0bcb87 Mon Sep 17 00:00:00 2001
From: Anders Svensson <anders@erlang.org>
Date: Fri, 11 Mar 2016 06:07:19 +0100
Subject: Don't ask throttling callback to receive more unless needed

TCP packets can contain more than one message, so only ask to receive
another message if it hasn't already been received.
---
 lib/diameter/src/transport/diameter_tcp.erl | 42 ++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 9 deletions(-)

(limited to 'lib')

diff --git a/lib/diameter/src/transport/diameter_tcp.erl b/lib/diameter/src/transport/diameter_tcp.erl
index d22b0ff320..e317922e7e 100644
--- a/lib/diameter/src/transport/diameter_tcp.erl
+++ b/lib/diameter/src/transport/diameter_tcp.erl
@@ -859,7 +859,17 @@ throttle(#transport{throttled = false} = S) ->
     recv(S);
 
 throttle(#transport{throttle_cb = F, throttled = B} = S) ->
-    throttle(cb(F, B), S).
+    Res = cb(F, B),
+
+    try throttle(Res, S) of
+        #transport{} = NS ->
+            throttle(defrag(NS))
+    catch
+        #transport{throttled = false} = NS ->
+            recv(NS);
+        #transport{} = NS ->
+            NS
+    end.
 
 %% cb/2
 
@@ -873,12 +883,13 @@ cb(F, B) ->
 
 %% Callback says to receive another message.
 throttle(ok, #transport{throttled = true} = S) ->
-    recv(S#transport{throttled = false});
+    throw(S#transport{throttled = false});
 
 %% Callback says to accept a received message.
-throttle(ok, #transport{parent = Pid, throttled = Msg} = S) ->
+throttle(ok, #transport{parent = Pid, throttled = Msg} = S)
+  when is_binary(Msg) ->
     diameter_peer:recv(Pid, Msg),
-    throttle(S#transport{throttled = true});
+    S;
 
 throttle({ok = T, F}, S) ->
     throttle(T, S#transport{throttle_cb = F});
@@ -891,7 +902,7 @@ throttle({ok = T, F}, S) ->
 throttle(NPid, #transport{parent = Pid, throttled = Msg} = S)
   when is_pid(NPid), is_binary(Msg) ->
     diameter_peer:recv(Pid, {Msg, NPid}),
-    throttle(S#transport{throttled = true});
+    S;
 
 throttle({NPid, F}, #transport{throttled = Msg} = S)
   when is_pid(NPid), is_binary(Msg) ->
@@ -900,7 +911,7 @@ throttle({NPid, F}, #transport{throttled = Msg} = S)
 %% Callback to accept a received message says to discard it.
 throttle(discard, #transport{throttled = Msg} = S)
   when is_binary(Msg) ->
-    throttle(S#transport{throttled = true});
+    S;
 
 throttle({discard = T, F}, #transport{throttled = Msg} = S)
   when is_binary(Msg) ->
@@ -911,16 +922,16 @@ throttle({discard = T, F}, #transport{throttled = Msg} = S)
 throttle(Bin, #transport{throttled = Msg} = S)
   when is_binary(Bin), is_binary(Msg) ->
     send(Bin, S),
-    throttle(S#transport{throttled = true});
+    S;
 
 throttle({Bin, F}, #transport{throttled = Msg} = S)
   when is_binary(Bin), is_binary(Msg) ->
     throttle(Bin, S#transport{throttle_cb = F});
 
 %% Callback says to ask again in the specified number of milliseconds.
-throttle({timeout, Tmo}, #transport{} = S) ->
+throttle({timeout, Tmo}, S) ->
     erlang:send_after(Tmo, self(), throttle),
-    S;
+    throw(S);
 
 throttle({timeout = T, Tmo, F}, S) ->
     throttle({T, Tmo}, S#transport{throttle_cb = F});
@@ -928,6 +939,19 @@ throttle({timeout = T, Tmo, F}, S) ->
 throttle(T, #transport{throttle_cb = F}) ->
     ?ERROR({invalid_return, T, F}).
 
+%% defrag/1
+%%
+%% Try to extract another message from packets already read before
+%% another throttling callback.
+
+defrag(#transport{frag = Head} = S) ->
+    case rcv(Head, <<>>) of
+        {Msg, B} ->
+            S#transport{throttled = Msg, frag = B};
+        _ ->
+            S#transport{throttled = true}
+    end.
+
 %% portnr/2
 
 portnr(gen_tcp, Sock) ->
-- 
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