decoder: strict mode (#512)

internal/unsafe/unsafe_test.go

@@ -77,3 +77,92 @@ func TestUnsafeSubsliceOffsetInvalid(t *testing.T) {
 		})
 	}
 }
+
+func TestUnsafeBytesRange(t *testing.T) {
+	type fn = func() ([]byte, []byte)
+	examples := []struct {
+		desc     string
+		test     fn
+		expected []byte
+	}{
+		{
+			desc: "simple",
+			test: func() ([]byte, []byte) {
+				full := []byte("hello world")
+				return full[1:3], full[6:8]
+			},
+			expected: []byte("ello wo"),
+		},
+		{
+			desc: "full",
+			test: func() ([]byte, []byte) {
+				full := []byte("hello world")
+				return full[0:1], full[len(full)-1:]
+			},
+			expected: []byte("hello world"),
+		},
+		{
+			desc: "end before start",
+			test: func() ([]byte, []byte) {
+				full := []byte("hello world")
+				return full[len(full)-1:], full[0:1]
+			},
+		},
+		{
+			desc: "nils",
+			test: func() ([]byte, []byte) {
+				return nil, nil
+			},
+		},
+		{
+			desc: "nils start",
+			test: func() ([]byte, []byte) {
+				return nil, []byte("foo")
+			},
+		},
+		{
+			desc: "nils end",
+			test: func() ([]byte, []byte) {
+				return []byte("foo"), nil
+			},
+		},
+		{
+			desc: "start is end",
+			test: func() ([]byte, []byte) {
+				full := []byte("hello world")
+				return full[1:3], full[1:3]
+			},
+			expected: []byte("el"),
+		},
+		{
+			desc: "end contained in start",
+			test: func() ([]byte, []byte) {
+				full := []byte("hello world")
+				return full[1:7], full[2:4]
+			},
+			expected: []byte("ello w"),
+		},
+		{
+			desc: "different backing arrays",
+			test: func() ([]byte, []byte) {
+				one := []byte("hello world")
+				two := []byte("hello world")
+				return one, two
+			},
+		},
+	}
+
+	for _, e := range examples {
+		t.Run(e.desc, func(t *testing.T) {
+			start, end := e.test()
+			if e.expected == nil {
+				require.Panics(t, func() {
+					unsafe.BytesRange(start, end)
+				})
+			} else {
+				res := unsafe.BytesRange(start, end)
+				require.Equal(t, e.expected, res)
+			}
+		})
+	}
+}