wasi: implements fd_filestat_set_size and fd_filestat_set_times (#1082)

This implements fd_filestat_set_size and fd_filestat_set_times, which
passes one more test in the rust wasi-testsuite.

Signed-off-by: Adrian Cole <adrian@tetrate.io>
Co-authored-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/sysfs/dirfs_test.go

@@ -369,6 +369,88 @@ func TestDirFS_Open(t *testing.T) {
 	})
 }
 
+func TestDirFS_Truncate(t *testing.T) {
+	content := []byte("123456")
+
+	tests := []struct {
+		name            string
+		size            int64
+		expectedContent []byte
+		expectedErr     error
+	}{
+		{
+			name:            "one less",
+			size:            5,
+			expectedContent: []byte("12345"),
+		},
+		{
+			name:            "same",
+			size:            6,
+			expectedContent: content,
+		},
+		{
+			name:            "zero",
+			size:            0,
+			expectedContent: []byte(""),
+		},
+		{
+			name:            "larger",
+			size:            106,
+			expectedContent: append(content, make([]byte, 100)...),
+		},
+	}
+
+	for _, tt := range tests {
+		tc := tt
+		t.Run(tc.name, func(t *testing.T) {
+			tmpDir := t.TempDir()
+			testFS := NewDirFS(tmpDir)
+
+			name := "truncate"
+			realPath := pathutil.Join(tmpDir, name)
+			require.NoError(t, os.WriteFile(realPath, content, 0o0600))
+
+			err := testFS.Truncate(name, tc.size)
+			require.NoError(t, err)
+
+			actual, err := os.ReadFile(realPath)
+			require.NoError(t, err)
+			require.Equal(t, tc.expectedContent, actual)
+		})
+	}
+
+	tmpDir := t.TempDir()
+	testFS := NewDirFS(tmpDir)
+
+	name := "truncate"
+	realPath := pathutil.Join(tmpDir, name)
+
+	if runtime.GOOS != "windows" {
+		// TODO: os.Truncate on windows can create the file even when it
+		// doesn't exist.
+		t.Run("doesn't exist", func(t *testing.T) {
+			err := testFS.Truncate(name, 0)
+			require.Equal(t, syscall.ENOENT, err)
+		})
+	}
+
+	t.Run("not file", func(t *testing.T) {
+		require.NoError(t, os.Mkdir(realPath, 0o700))
+
+		err := testFS.Truncate(name, 0)
+		require.Equal(t, syscall.EISDIR, err)
+
+		require.NoError(t, os.Remove(realPath))
+	})
+
+	t.Run("negative", func(t *testing.T) {
+		require.NoError(t, os.WriteFile(realPath, []byte{}, 0o600))
+
+		err := testFS.Truncate(name, -1)
+		require.Equal(t, syscall.EINVAL, err)
+	})
+}
+
 func TestDirFS_TestFS(t *testing.T) {
 	t.Parallel()