common/hexutil: implement TextMarshaler, TextUnmarshaler

This commit makes the wrapper types more generally applicable.
encoding.TextMarshaler is supported by most codec implementations (e.g.
for yaml).

The tests now ensure that package json actually recognizes the custom
marshaler implementation irrespective of how it is implemented.

The Uint type has new tests, too. These are tricky because uint size
depends on the CPU word size. Turns out that there was one incorrect
case where decoding returned ErrUint64Range instead of ErrUintRange.

1 files changed, 45 insertions, 0 deletions

diff --git a/common/hexutil/json_example_test.go b/common/hexutil/json_example_test.go
new file mode 100644
index 000000000..80180d918
--- /dev/null
+++ b/common/hexutil/json_example_test.go
@@ -0,0 +1,45 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package hexutil_test
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+)
+
+type MyType [5]byte
+
+func (v *MyType) UnmarshalText(input []byte) error {
+	return hexutil.UnmarshalFixedText("MyType", input, v[:])
+}
+
+func (v MyType) String() string {
+	return hexutil.Bytes(v[:]).String()
+}
+
+func ExampleUnmarshalFixedText() {
+	var v1, v2 MyType
+	fmt.Println("v1 error:", json.Unmarshal([]byte(`"0x01"`), &v1))
+	fmt.Println("v2 error:", json.Unmarshal([]byte(`"0x0101010101"`), &v2))
+	fmt.Println("v2:", v2)
+	// Output:
+	// v1 error: hex string has length 2, want 10 for MyType
+	// v2 error: <nil>
+	// v2: 0x0101010101
+}