Re: [PATCH v4] selftests: af_unix: Add tests for ECONNRESET and EOF semantics

Sunday Adelodun
2025-11-13T07:11:58Z

On 11/13/25 07:10, Kuniyuki Iwashima wrote:
> On Wed, Nov 12, 2025 at 9:25 PM Sunday Adelodun
> <adelodunolaoluwa@yahoo.com> wrote:
>> On 11/12/25 23:04, Kuniyuki Iwashima wrote:
>>> On Wed, Nov 12, 2025 at 1:20 PM Sunday Adelodun
>>> <adelodunolaoluwa@yahoo.com> wrote:
>>>> Add selftests to verify and document Linux’s intended behaviour for
>>>> UNIX domain sockets (SOCK_STREAM and SOCK_DGRAM) when a peer closes.
>>>> The tests verify that:
>>>>
>>>> 1. SOCK_STREAM returns EOF when the peer closes normally.
>>>> 2. SOCK_STREAM returns ECONNRESET if the peer closes with unread data.
>>>> 3. SOCK_SEQPACKET returns EOF when the peer closes normally.
>>>> 4. SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
>>>> 5. SOCK_DGRAM does not return ECONNRESET when the peer closes.
>>>>
>>>> This follows up on review feedback suggesting a selftest to clarify
>>>> Linux’s semantics.
>>>>
>>>> Suggested-by: Kuniyuki Iwashima <kuniyu@google.com>
>>>> Signed-off-by: Sunday Adelodun <adelodunolaoluwa@yahoo.com>
>>>> ---
>>>> tools/testing/selftests/net/.gitignore | 1 +
>>>> tools/testing/selftests/net/af_unix/Makefile | 1 +
>>>> .../selftests/net/af_unix/unix_connreset.c | 178 ++++++++++++++++++
>>>> 3 files changed, 180 insertions(+)
>>>> create mode 100644 tools/testing/selftests/net/af_unix/unix_connreset.c
>>>>
>>>> diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
>>>> index 439101b518ee..e89a60581a13 100644
>>>> --- a/tools/testing/selftests/net/.gitignore
>>>> +++ b/tools/testing/selftests/net/.gitignore
>>>> @@ -65,3 +65,4 @@ udpgso
>>>> udpgso_bench_rx
>>>> udpgso_bench_tx
>>>> unix_connect
>>>> +unix_connreset
>>>> diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
>>>> index de805cbbdf69..5826a8372451 100644
>>>> --- a/tools/testing/selftests/net/af_unix/Makefile
>>>> +++ b/tools/testing/selftests/net/af_unix/Makefile
>>>> @@ -7,6 +7,7 @@ TEST_GEN_PROGS := \
>>>> scm_pidfd \
>>>> scm_rights \
>>>> unix_connect \
>>>> + unix_connreset \
>>>> # end of TEST_GEN_PROGS
>>>>
>>>> include ../../lib.mk
>>>> diff --git a/tools/testing/selftests/net/af_unix/unix_connreset.c b/tools/testing/selftests/net/af_unix/unix_connreset.c
>>>> new file mode 100644
>>>> index 000000000000..9413f8a0814f
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/net/af_unix/unix_connreset.c
>>>> @@ -0,0 +1,178 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Selftest for AF_UNIX socket close and ECONNRESET behaviour.
>>>> + *
>>>> + * This test verifies:
>>>> + * 1. SOCK_STREAM returns EOF when the peer closes normally.
>>>> + * 2. SOCK_STREAM returns ECONNRESET if peer closes with unread data.
>>>> + * 3. SOCK_SEQPACKET returns EOF when the peer closes normally.
>>>> + * 4. SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
>>>> + * 5. SOCK_DGRAM does not return ECONNRESET when the peer closes.
>>>> + *
>>>> + * These tests document the intended Linux behaviour.
>>>> + *
>>>> + */
>>>> +
>>>> +#define _GNU_SOURCE
>>>> +#include <stdlib.h>
>>>> +#include <string.h>
>>>> +#include <fcntl.h>
>>>> +#include <unistd.h>
>>>> +#include <errno.h>
>>>> +#include <sys/socket.h>
>>>> +#include <sys/un.h>
>>>> +#include "../../kselftest_harness.h"
>>>> +
>>>> +#define SOCK_PATH "/tmp/af_unix_connreset.sock"
>>>> +
>>>> +static void remove_socket_file(void)
>>>> +{
>>>> + unlink(SOCK_PATH);
>>>> +}
>>>> +
>>>> +FIXTURE(unix_sock)
>>>> +{
>>>> + int server;
>>>> + int client;
>>>> + int child;
>>>> +};
>>>> +
>>>> +FIXTURE_VARIANT(unix_sock)
>>>> +{
>>>> + int socket_type;
>>>> + const char *name;
>>>> +};
>>>> +
>>>> +FIXTURE_VARIANT_ADD(unix_sock, stream) {
>>>> + .socket_type = SOCK_STREAM,
>>>> + .name = "SOCK_STREAM",
>>>> +};
>>>> +
>>>> +FIXTURE_VARIANT_ADD(unix_sock, dgram) {
>>>> + .socket_type = SOCK_DGRAM,
>>>> + .name = "SOCK_DGRAM",
>>>> +};
>>>> +
>>>> +FIXTURE_VARIANT_ADD(unix_sock, seqpacket) {
>>>> + .socket_type = SOCK_SEQPACKET,
>>>> + .name = "SOCK_SEQPACKET",
>>>> +};
>>>> +
>>>> +FIXTURE_SETUP(unix_sock)
>>>> +{
>>>> + struct sockaddr_un addr = {};
>>>> + int err;
>>>> +
>>>> + addr.sun_family = AF_UNIX;
>>>> + strcpy(addr.sun_path, SOCK_PATH);
>>>> + remove_socket_file();
>>>> +
>>>> + self->server = socket(AF_UNIX, variant->socket_type, 0);
>>>> + ASSERT_LT(-1, self->server);
>>>> +
>>>> + err = bind(self->server, (struct sockaddr *)&addr, sizeof(addr));
>>>> + ASSERT_EQ(0, err);
>>>> +
>>>> + if (variant->socket_type == SOCK_STREAM ||
>>>> + variant->socket_type == SOCK_SEQPACKET) {
>>>> + err = listen(self->server, 1);
>>>> + ASSERT_EQ(0, err);
>>>> + }
>>>> +
>>>> + self->client = socket(AF_UNIX, variant->socket_type | SOCK_NONBLOCK, 0);
>>>> + ASSERT_LT(-1, self->client);
>>>> +
>>>> + err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr));
>>>> + ASSERT_EQ(0, err);
>>>> +}
>>>> +
>>>> +FIXTURE_TEARDOWN(unix_sock)
>>>> +{
>>>> + if ((variant->socket_type == SOCK_STREAM ||
>>>> + variant->socket_type == SOCK_SEQPACKET) & self->child > 0)
>>>> + close(self->child);
>>>> +
>>>> + close(self->client);
>>>> + close(self->server);
>>>> + remove_socket_file();
>>>> +}
>>>> +
>>>> +/* Test 1: peer closes normally */
>>>> +TEST_F(unix_sock, eof)
>>>> +{
>>>> + char buf[16] = {};
>>>> + ssize_t n;
>>>> +
>>>> + if (variant->socket_type == SOCK_STREAM ||
>>>> + variant->socket_type == SOCK_SEQPACKET) {
>>>> + self->child = accept(self->server, NULL, NULL);
>>>> + ASSERT_LT(-1, self->child);
>>>> +
>>>> + close(self->child);
>>>> + } else {
>>>> + close(self->server);
>>>> + }
>>>> +
>>>> + n = recv(self->client, buf, sizeof(buf), 0);
>>>> +
>>>> + if (variant->socket_type == SOCK_STREAM ||
>>>> + variant->socket_type == SOCK_SEQPACKET) {
>>>> + ASSERT_EQ(0, n);
>>>> + } else {
>>>> + ASSERT_EQ(-1, n);
>>>> + ASSERT_EQ(EAGAIN, errno);
>>>> + }
>>>> +}
>>>> +
>>>> +/* Test 2: peer closes with unread data */
>>>> +TEST_F(unix_sock, reset_unread_behavior)
>>>> +{
>>>> + char buf[16] = {};
>>>> + ssize_t n;
>>>> +
>>>> + if (variant->socket_type == SOCK_DGRAM) {
>>>> + /* No real connection, just close the server */
>>>> + close(self->server);
>>>> + } else {
>>>> + /* Establish full connection first */
>>>> + self->child = accept(self->server, NULL, NULL);
>>>> + ASSERT_LT(-1, self->child);
>>>> +
>>>> + /* Send data that will remain unread */
>>>> + send(self->client, "hello", 5, 0);
>>> Could you move this send() before "if (...)" because we want
>>> to test unread_data behaviour for SOCK_DGRAM too ?
>>>
>>> Otherwise looks good, so with that fixed:
>>>
>>> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
>>>
>>> Thanks!
>> Thank you for the prompt response.
>> I thought of putting the send before the if the statement , but I was afraid
>> STREAM and SEQPACKET connections won't be accepted before data sending.
> connect() create the paired child socket and accept()
> allocates a file descriptor to expose the socket to user
> space.
Thank you for this explanation.
>
> In that sense, the comment above accept() sounds a
> bit weird ;)
I understand.
I am changing it to
/* Accept client connection */

If this is accepted, I will send v5 immediately

Thank you for your guidance.
>
>
>> I will start working on v5.
>>
>> That part will look like this now:
>> /* Test 2: peer closes with unread data */
>> TEST_F(unix_sock, reset_unread_behavior)
>> {
>> char buf[16] = {};
>> ssize_t n;
>>
>> */* Send data that will remain unread */
>> send(self->client, "hello", 5, 0);*
>>
>> *if (variant->socket_type == SOCK_DGRAM) {
>> /* No real connection, just close the server */
>> close(self->server);
>> } else {
>> /* Establish full connection first */
>> self->child = accept(self->server, NULL, NULL);
>> ASSERT_LT(-1, self->child);
>>
>> /* Peer closes before client reads */
>> close(self->child);
>> }*
>>
>> n = recv(self->client, buf, sizeof(buf), 0);
>> ASSERT_EQ(-1, n);
>>
>> if (variant->socket_type == SOCK_STREAM ||
>> variant->socket_type == SOCK_SEQPACKET) {
>> ASSERT_EQ(ECONNRESET, errno);
>> } else {
>> ASSERT_EQ(EAGAIN, errno);
>> }
>> }
>>
>> Thank you once again.
>>>
>>>> +
>>>> + /* Peer closes before client reads */
>>>> + close(self->child);
>>>> + }
>>>> +
>>>> + n = recv(self->client, buf, sizeof(buf), 0);
>>>> + ASSERT_EQ(-1, n);
>>>> +
>>>> + if (variant->socket_type == SOCK_STREAM ||
>>>> + variant->socket_type == SOCK_SEQPACKET) {
>>>> + ASSERT_EQ(ECONNRESET, errno);
>>>> + } else {
>>>> + ASSERT_EQ(EAGAIN, errno);
>>>> + }
>>>> +}
>>>> +
>>>> +/* Test 3: closing unaccepted (embryo) server socket should reset client. */
>>>> +TEST_F(unix_sock, reset_closed_embryo)
>>>> +{
>>>> + char buf[16] = {};
>>>> + ssize_t n;
>>>> +
>>>> + if (variant->socket_type == SOCK_DGRAM)
>>>> + SKIP(return, "This test only applies to SOCK_STREAM and SOCK_SEQPACKET");
>>>> +
>>>> + /* Close server without accept()ing */
>>>> + close(self->server);
>>>> +
>>>> + n = recv(self->client, buf, sizeof(buf), 0);
>>>> +
>>>> + ASSERT_EQ(-1, n);
>>>> + ASSERT_EQ(ECONNRESET, errno);
>>>> +}
>>>> +
>>>> +TEST_HARNESS_MAIN
>>>> +
>>>> --
>>>> 2.43.0
>>>>