use a trampoline to get to the spicy _x functions

internal/msgx/msgx_darwin_test.go

@@ -0,0 +1,69 @@
+//go:build !ios
+
+package msgx
+
+import (
+	"bytes"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
+)
+
+// TestAvailable pins that dlsym finds both calls in this macOS's libSystem, so the batched paths are live.
+func TestAvailable(t *testing.T) {
+	assert.True(t, Available())
+}
+
+// TestSendRecvRoundTrip pins the libSystem calling path end to end: a batch goes out through sendmsg_x in one
+// call and comes back through recvmsg_x in one call, each message whole, in order, with Datalen set.
+func TestSendRecvRoundTrip(t *testing.T) {
+	fds, err := unix.Socketpair(unix.AF_UNIX, unix.SOCK_DGRAM, 0)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		_ = unix.Close(fds[0])
+		_ = unix.Close(fds[1])
+	})
+	// A dropped datagram fails the receive instead of hanging it.
+	require.NoError(t, unix.SetsockoptTimeval(fds[1], unix.SOL_SOCKET, unix.SO_RCVTIMEO, &unix.Timeval{Sec: 2}))
+
+	const n = 5
+	var want [n][]byte
+	var iovs [n]unix.Iovec
+	hdrs := make([]Hdr, n)
+	for i := range n {
+		want[i] = bytes.Repeat([]byte{byte(i + 1)}, 10+i)
+		iovs[i] = unix.Iovec{Base: &want[i][0]}
+		iovs[i].SetLen(len(want[i]))
+		hdrs[i] = Hdr{Iov: &iovs[i], Iovlen: 1}
+	}
+	sent, errno := Send(uintptr(fds[0]), hdrs, 0)
+	require.Zero(t, errno)
+	require.Equal(t, n, sent)
+
+	var bufs [n + 1][64]byte
+	var riovs [n + 1]unix.Iovec
+	rhdrs := make([]Hdr, n+1)
+	for i := range rhdrs {
+		riovs[i] = unix.Iovec{Base: &bufs[i][0]}
+		riovs[i].SetLen(len(bufs[i]))
+		rhdrs[i] = Hdr{Iov: &riovs[i], Iovlen: 1}
+	}
+	got, errno := Recv(uintptr(fds[1]), rhdrs, 0)
+	require.Zero(t, errno)
+	require.Equal(t, n, got)
+	for i := range n {
+		l := int(rhdrs[i].Datalen)
+		assert.Equal(t, want[i], bufs[i][:l], "message %d", i)
+	}
+}
+
+// TestEmptyBatch pins that an empty batch is refused before it reaches the kernel.
+func TestEmptyBatch(t *testing.T) {
+	_, errno := Send(0, nil, 0)
+	assert.Equal(t, syscall.EINVAL, errno)
+	_, errno = Recv(0, nil, 0)
+	assert.Equal(t, syscall.EINVAL, errno)
+}