1 files changed, 118 insertions, 0 deletions
diff --git a/doc/platform-requirements/recv-zero.c b/doc/platform-requirements/recv-zero.c
new file mode 100644
index 0000000..2a2a561
--- /dev/null
+++ b/doc/platform-requirements/recv-zero.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* recv-zero.c
+ *
+ * Verify that we're able to discard datagrams by recv()ing into a zero-length
+ * buffer.
+ *
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "common.h"
+
+#define DSTPORT	13257U
+
+enum discard_method {
+	DISCARD_NULL_BUF,
+	DISCARD_ZERO_IOV,
+	DISCARD_NULL_IOV,
+	NUM_METHODS,
+};
+
+/* 127.0.0.1:DSTPORT */
+static const struct sockaddr_in lo_dst = SOCKADDR_INIT(INADDR_LOOPBACK, DSTPORT);
+
+static void test_discard(enum discard_method method)
+{
+	struct iovec zero_iov = { .iov_base = NULL, .iov_len = 0, };
+	struct msghdr mh_zero = {
+		.msg_iov = &zero_iov,
+		.msg_iovlen = 1,
+	};
+	struct msghdr mh_null = {
+		.msg_iov = NULL,
+		.msg_iovlen = 0,
+	};
+	long token1, token2;
+	int recv_s, send_s;
+	ssize_t rc;
+
+	token1 = random();
+	token2 = random();
+
+	recv_s = sock_reuseaddr();
+	if (bind(recv_s, (struct sockaddr *)&lo_dst, sizeof(lo_dst)) < 0)
+		die("bind(): %s\n", strerror(errno));
+
+	send_s = sock_reuseaddr();
+	if (connect(send_s, (struct sockaddr *)&lo_dst, sizeof(lo_dst)) < 0)
+		die("connect(): %s\n", strerror(errno));
+
+	send_token(send_s, token1);
+	send_token(send_s, token2);
+
+	switch (method) {
+	case DISCARD_NULL_BUF:
+		/* cppcheck-suppress nullPointer */
+		rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
+		if (rc < 0)
+			die("discarding recv(): %s\n", strerror(errno));
+		break;
+
+	case DISCARD_ZERO_IOV:
+		rc = recvmsg(recv_s, &mh_zero, MSG_DONTWAIT);
+		if (rc < 0)
+			die("recvmsg() with zero-length buffer: %s\n",
+			    strerror(errno));
+		if (!((unsigned)mh_zero.msg_flags & MSG_TRUNC))
+			die("Missing MSG_TRUNC flag\n");
+		break;
+
+	case DISCARD_NULL_IOV:
+		rc = recvmsg(recv_s, &mh_null, MSG_DONTWAIT);
+		if (rc < 0)
+			die("recvmsg() with zero-length iov: %s\n",
+			    strerror(errno));
+		if (!((unsigned)mh_null.msg_flags & MSG_TRUNC))
+			die("Missing MSG_TRUNC flag\n");
+		break;
+
+	default:
+		die("Bad method\n");
+	}
+
+	recv_token(recv_s, token2);
+
+	/* cppcheck-suppress nullPointer */
+	rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
+	if (rc < 0 && errno != EAGAIN)
+		die("redundant discarding recv(): %s\n", strerror(errno));
+	if (rc >= 0)
+		die("Unexpected receive: rc=%zd\n", rc);
+}
+
+int main(int argc, char *argv[])
+{
+	enum discard_method method;
+
+	(void)argc;
+	(void)argv;
+
+	for (method = 0; method < NUM_METHODS; method++)
+		test_discard(method);
+
+	printf("Discarding datagrams with 0-length receives seems to work\n");
+
+	exit(0);
+}