From 31d2586e3296d424e51848ada963299b0da89324 Mon Sep 17 00:00:00 2001
From: Dirk Engling <erdgeist@erdgeist.org>
Date: Fri, 30 Oct 2026 13:23:39 +0100
Subject: Defer accepts until some data actually is there

---
 tests/t_socket.c | 43 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

(limited to 'tests/t_socket.c')

diff --git a/tests/t_socket.c b/tests/t_socket.c
index ab4b785..20a0c0a 100644
--- a/tests/t_socket.c
+++ b/tests/t_socket.c
@@ -78,15 +78,17 @@ static int sock_flag(int s, int level, int option) {
 }
 
 /* Wait for one event, so a test never blocks forever on a lost packet */
-static int wait_for(int s, short events) {
+static int wait_for_ms(int s, short events, int timeout_ms) {
   struct pollfd pfd;
 
   pfd.fd      = s;
   pfd.events  = events;
   pfd.revents = 0;
-  return poll(&pfd, 1, 2000) == 1;
+  return poll(&pfd, 1, timeout_ms) == 1;
 }
 
+static int wait_for(int s, short events) { return wait_for_ms(s, events, 2000); }
+
 /* ------------------------------------------------------------ invariants */
 
 /* Asked for the wildcard address, because a socket bound to one specific
@@ -200,6 +202,42 @@ static void case_a_signal_ends_a_blocking_read(void) {
   close(reader_socket);
 }
 
+/* What a deferred accept is for is a descriptor that already has the request
+   in it, so what is checked is the silence before: a client that has
+   connected but said nothing must not make the listener readable. Kernels
+   that cannot do this say so, and then there is nothing to check. */
+static void case_deferred_accept(void) {
+  struct sockaddr_in6 address;
+  char                ip[16];
+  uint16_t            port = 0;
+  int                 listener, client;
+
+  test_case("a connection that has sent nothing is held back from accept");
+  listener = socket_tcp_listen(ip_loopback, 0, SOCKET_EXCLUSIVE);
+  CHECK(listener != -1);
+  if (socket_defer_accept(listener) == -1) {
+    close(listener);
+    return;
+  }
+  bound_address(listener, ip, &port);
+
+  client = socket(AF_INET6, SOCK_STREAM, 0);
+  CHECK(client != -1);
+  memset(&address, 0, sizeof(address));
+  address.sin6_family = AF_INET6;
+  address.sin6_port   = htons(port);
+  memcpy(&address.sin6_addr, ip_loopback, 16);
+  CHECK_INT(connect(client, (struct sockaddr *)&address, sizeof(address)), 0);
+
+  CHECK_INT(wait_for_ms(listener, POLLIN, 300), 0);
+
+  CHECK_INT((int)write(client, "GET / HTTP/1.0\r\n\r\n", 18), 18);
+  CHECK_INT(wait_for(listener, POLLIN), 1);
+
+  close(client);
+  close(listener);
+}
+
 /* An IPv4 peer must arrive in the v4 mapped form opentracker stores, however
    the kernel chose to report it. Linux fills a v4 mapped sockaddr_in6 here
    and the BSDs fill a plain sockaddr_in, so this is the case that tells the
@@ -352,6 +390,7 @@ void test_socket(void) {
   case_a_signal_ends_a_blocking_read();
   case_udp_v4mapped();
   case_tcp_roundtrip();
+  case_deferred_accept();
   case_connect_refused();
   case_bind_failure();
 #ifdef WANT_SYNC_LIVE
-- 
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