1 files changed, 54 insertions, 0 deletions
diff --git a/pkg/hex/hex.go b/pkg/hex/hex.go
new file mode 100644
index 0000000..1b5e324
--- /dev/null
+++ b/pkg/hex/hex.go
@@ -0,0 +1,54 @@
+// package hex implements a lower-case hex parser.
+package hex
+
+import (
+	"fmt"
+)
+
+const (
+	language = "0123456789abcdef"
+)
+
+// Serialize serializes a buffer as lower-case hex
+func Serialize(buf []byte) string {
+	out := make([]byte, len(buf)*2)
+	for i, b := range buf {
+		offset := i * 2
+		out[offset] = language[b>>4]
+		out[offset+1] = language[b&0x0f]
+	}
+	return string(out)
+}
+
+// Deserialize tries to deserialize a lower-case hex string
+func Deserialize(str string) ([]byte, error) {
+	if len(str)%2 != 0 {
+		return nil, fmt.Errorf("hex: string must have even length")
+	}
+
+	buf := make([]byte, len(str)/2)
+	for i := 0; i < len(buf); i++ {
+		offset := i * 2
+		first, ok := deserializeOne(str[offset])
+		if !ok {
+			return nil, fmt.Errorf("hex: invalid character at index %d: %d", i, first)
+		}
+		second, ok := deserializeOne(str[offset+1])
+		if !ok {
+			return nil, fmt.Errorf("hex: invalid character at index %d: %d", i, second)
+		}
+		buf[i] = first << 4
+		buf[i] = buf[i] | second
+	}
+	return buf, nil
+}
+
+func deserializeOne(b byte) (byte, bool) {
+	if b >= '0' && b <= '9' {
+		return b - '0', true
+	}
+	if b >= 'a' && b <= 'f' {
+		return b - 'a' + 10, true
+	}
+	return 0, false
+}