wasi: improve stdin support for nonblocking, fix stdout (#1542)

Signed-off-by: Edoardo Vacchi <evacchi@users.noreply.github.com>

internal/sysfs/file.go

@@ -69,6 +69,17 @@ type stdioFile struct {
 	st fsapi.Stat_t
 }
 
+// SetAppend implements File.SetAppend
+func (f *stdioFile) SetAppend(bool) syscall.Errno {
+	// Ignore for stdio.
+	return 0
+}
+
+// IsAppend implements File.SetAppend
+func (f *stdioFile) IsAppend() bool {
+	return true
+}
+
 // IsDir implements File.IsDir
 func (f *stdioFile) IsDir() (bool, syscall.Errno) {
 	return false, 0

internal/sysfs/file_test.go

@@ -131,6 +131,16 @@ func TestFileSetAppend(t *testing.T) {
 	requireFileContent("wazero6789wazero")
 }
 
+func TestStdioFile_SetAppend(t *testing.T) {
+	// SetAppend should not affect Stdio.
+	file, err := NewStdioFile(false, os.Stdout)
+	require.NoError(t, err)
+	errno := file.SetAppend(true)
+	require.EqualErrno(t, 0, errno)
+	_, errno = file.Write([]byte{})
+	require.EqualErrno(t, 0, errno)
+}
+
 func TestFileIno(t *testing.T) {
 	tmpDir := t.TempDir()
 	dirFS, embedFS, mapFS := dirEmbedMapFS(t, tmpDir)