Cleanup host UDS support

This change fixes several issues with the fsgofer host UDS support. Notably, it
adds support for SOCK_SEQPACKET and SOCK_DGRAM sockets [1]. It also fixes
unsafe use of unet.Socket, which could cause a panic if Socket.FD is called
when err != nil, and calls to Socket.FD with nothing to prevent the garbage
collector from destroying and closing the socket.

A set of tests is added to exercise host UDS access. This required extracting
most of the syscall test runner into a library that can be used by custom
tests.

Updates #235
Updates #1003

[1] N.B. SOCK_DGRAM sockets are likely not particularly useful, as a server can
only reply to a client that binds first. We don't allow bind, so these are
unlikely to be used.

PiperOrigin-RevId: 275558502

1 files changed, 12 insertions, 0 deletions

diff --git a/test/syscalls/linux/accept_bind.cc b/test/syscalls/linux/accept_bind.cc
index 1122ea240..328192a05 100644
--- a/test/syscalls/linux/accept_bind.cc
+++ b/test/syscalls/linux/accept_bind.cc
@@ -140,6 +140,18 @@ TEST_P(AllSocketPairTest, Connect) {
               SyscallSucceeds());
 }
 
+TEST_P(AllSocketPairTest, ConnectNonListening) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  ASSERT_THAT(bind(sockets->first_fd(), sockets->first_addr(),
+                   sockets->first_addr_size()),
+              SyscallSucceeds());
+
+  ASSERT_THAT(connect(sockets->second_fd(), sockets->first_addr(),
+                      sockets->first_addr_size()),
+              SyscallFailsWithErrno(ECONNREFUSED));
+}
+
 TEST_P(AllSocketPairTest, ConnectToFilePath) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());