From 1ee2a1913e79e010733991d8373b2517abf0d91b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Bj=C3=B6rklund?= <mbj4668@gmail.com>
Date: Mon, 19 Apr 2021 20:03:57 +0200
Subject: Handle any zero-sized Data in http:data with fin

Amended to make the test case hit the problem.
---
 src/gun_http.erl   |  6 +++---
 test/gun_SUITE.erl | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/gun_http.erl b/src/gun_http.erl
index d928b18..b38cc74 100644
--- a/src/gun_http.erl
+++ b/src/gun_http.erl
@@ -692,10 +692,10 @@ data(State=#http_state{socket=Socket, transport=Transport, version=Version,
 			DataLength = iolist_size(Data),
 			case Out of
 				body_chunked when Version =:= 'HTTP/1.1', IsFin =:= fin ->
-					case Data of
-						<<>> ->
+					if
+						DataLength =:= 0 ->
 							Transport:send(Socket, cow_http_te:last_chunk());
-						_ ->
+						true ->
 							Transport:send(Socket, [
 								cow_http_te:chunk(Data),
 								cow_http_te:last_chunk()
diff --git a/test/gun_SUITE.erl b/test/gun_SUITE.erl
index 1a15b01..ad39317 100644
--- a/test/gun_SUITE.erl
+++ b/test/gun_SUITE.erl
@@ -107,6 +107,21 @@ ignore_empty_data_http(_) ->
 	1 = length(Zero),
 	gun:close(Pid).
 
+ignore_empty_data_fin_http(_) ->
+	doc("When gun:data/4 is called with fin and empty data, it must send a final empty chunk."),
+	{ok, OriginPid, OriginPort} = init_origin(tcp, http),
+	{ok, Pid} = gun:open("localhost", OriginPort),
+	{ok, http} = gun:await_up(Pid),
+	handshake_completed = receive_from(OriginPid),
+	Ref = gun:post(Pid, "/", []),
+	gun:data(Pid, Ref, nofin, "hello"),
+	gun:data(Pid, Ref, fin, ["", <<>>]),
+	Data = receive_all_from(OriginPid, 500),
+	Lines = binary:split(Data, <<"\r\n">>, [global]),
+	Zero = [Z || <<"0">> = Z <- Lines],
+	1 = length(Zero),
+	gun:close(Pid).
+
 ignore_empty_data_http2(_) ->
 	doc("When gun:data/4 is called with nofin and empty data, it must be ignored."),
 	{ok, OriginPid, OriginPort} = init_origin(tcp, http2),
-- 
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