fix(receive): a receive 0 should immediately return, not block

The fix is slightly more complex because reading from a closed
socket should still return a closed-error.

fixes: #427
fixes: https://github.com/ledgetech/lua-resty-http/pull/313

1 files changed, 36 insertions, 0 deletions

diff --git a/test/test_receive_zero.lua b/test/test_receive_zero.lua
new file mode 100644
index 0000000..2259910
--- /dev/null
+++ b/test/test_receive_zero.lua
@@ -0,0 +1,36 @@
+-- a TCP receive(0) must never block: requesting zero bytes is trivially
+-- satisfied without touching the transport layer, POSIX recv(fd, buf, 0, 0)
+-- returns immediately regardless of whether data is available.
+local socket = require "socket"
+
+local host, port = "127.0.0.1", "5464"
+
+local server = assert(socket.bind(host, port))
+local client = assert(socket.connect(host, port))
+local peer = assert(server:accept())
+
+client:settimeout(2)
+
+-- no data has been sent by the peer: the read buffer is empty, so if
+-- receive(0) touches the network it will block until the timeout expires
+local t0 = socket.gettime()
+local data, err = client:receive(0)
+local elapsed = socket.gettime() - t0
+
+assert(data == "", "receive(0) on empty buffer returned " .. tostring(data))
+assert(err == nil, "receive(0) on empty buffer returned error " .. tostring(err))
+assert(elapsed < 1, "receive(0) on empty buffer blocked for " .. elapsed .. "s")
+
+-- receive(0) must also not consume any bytes when data *is* available
+assert(peer:send("hello"))
+data, err = client:receive(0)
+assert(data == "", "receive(0) with data pending returned " .. tostring(data))
+assert(err == nil, "receive(0) with data pending returned error " .. tostring(err))
+data = assert(client:receive(5))
+assert(data == "hello", "receive(0) consumed bytes meant for receive(5)")
+
+client:close()
+peer:close()
+server:close()
+
+print("done!")