add some hex utilities (#40)

coding/hex.go

@@ -0,0 +1,37 @@
+package coding
+
+import (
+	"encoding/hex"
+	"fmt"
+	"strings"
+)
+
+func DecodeHex(in string) ([]byte, error) {
+	normalized := in
+	if strings.HasPrefix(in, "0x") || strings.HasPrefix(in, "0X") {
+		normalized = normalized[2:]
+	}
+
+	return hex.DecodeString(normalized)
+}
+
+func NormalizeBytesToHex(input []byte) string {
+	return strings.ToLower("0x" + hex.EncodeToString(input))
+}
+
+// PayloadFingerprint pretty prints a hex payload in an identifiable and succint way.
+func PayloadFingerprint(payload []byte) string {
+	if len(payload) == 0 {
+		return NormalizeMaybeEmptyBytes(payload)
+	}
+
+	return fmt.Sprintf("[%s...%s]", hex.EncodeToString(payload[0:4]), hex.EncodeToString(payload[len(payload)-4:]))
+}
+
+// Returns an empty byte slice rather than no output for empty byte arrays
+func NormalizeMaybeEmptyBytes(bytes []byte) string {
+	if len(bytes) > 0 {
+		return hex.EncodeToString(bytes)
+	}
+	return "[]"
+}

coding/hex_test.go

@@ -0,0 +1,32 @@
+package coding_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/tessellated-io/pickaxe/coding"
+)
+
+func TestDecodeHex(t *testing.T) {
+	expected := []byte{0x01, 0x02, 0x03, 0x04, 0xa, 0xb}
+
+	cases := []string{
+		"010203040a0b",
+		"0x010203040a0b",
+		"0X010203040A0B",
+	}
+
+	for _, in := range cases {
+		decoded, err := coding.DecodeHex(in)
+		assert.Nil(t, err, "should not have an error")
+		assert.Equal(t, expected, decoded, "unexpected decoded value")
+	}
+}
+
+func TestNormalizeHex(t *testing.T) {
+	input := []byte{0x00, 0x01, 0x10, 0x11}
+
+	normalized := coding.NormalizeBytesToHex(input)
+
+	assert.Equal(t, "0x00011011", normalized)
+}