From 593aa3b2f6a7f7455584594f0b4f6e186635aa0f Mon Sep 17 00:00:00 2001 From: Ben Noordhuis Date: Mon, 29 Jul 2024 22:30:08 +0200 Subject: [PATCH] test: handle zero-length udp datagram (#4344) Under rare but benign circumstances (on XNU), incoming datagrams appear to be dropped by the operating system after libuv has been notified of their arrival but before libuv has had a chance to receive them. Fixes: https://github.com/libuv/libuv/issues/4219 --- test/test-udp-recv-in-a-row.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) diff --git a/test/test-udp-recv-in-a-row.c b/test/test-udp-recv-in-a-row.c index 30745def..0d97e5bf 100644 --- a/test/test-udp-recv-in-a-row.c +++ b/test/test-udp-recv-in-a-row.c @@ -50,11 +50,16 @@ static void sv_recv_cb(uv_udp_t* handle, const uv_buf_t* rcvbuf, const struct sockaddr* addr, unsigned flags) { - if (++ recv_cnt < N) { - ASSERT_EQ(sizeof(send_data), nread); - } else { - ASSERT_OK(nread); - } + /* |nread| can be zero when the kernel drops an incoming datagram after + * marking the file descriptor as readable but before libuv has a chance + * to receive it. Libuv still invokes the uv_udp_recv_cb callback to give + * back the memory from the uv_alloc_cb callback. + * + * See https://github.com/libuv/libuv/issues/4219. + */ + recv_cnt++; + if (nread > 0) + ASSERT_EQ(nread, sizeof(send_data)); } static void check_cb(uv_check_t* handle) { @@ -63,9 +68,11 @@ static void check_cb(uv_check_t* handle) { /** * sv_recv_cb() is called with nread set to zero to indicate * there is no more udp packet in the kernel, so the actual - * recv_cnt is one larger than N. + * recv_cnt is up to one larger than N. UDP being what it is, + * packets can get dropped so don't assume an exact count. */ - ASSERT_EQ(N+1, recv_cnt); + ASSERT_GE(recv_cnt, 1); + ASSERT_LE(recv_cnt, N+1); check_cb_called = 1; /* we are done */