From 7ea123c915d331ba62a7ca2ff33a34fe3932d572 Mon Sep 17 00:00:00 2001
From: blinkthethings <blinkthethings@gmail.com>
Date: Thu, 24 Dec 2020 21:42:14 -0500
Subject: [PATCH] Handle upper or mixed case modhex input

---
 modhex.go      | 49 +++++++++++++++++++++++++++++++------------------
 modhex_test.go | 13 ++++++++++++-
 2 files changed, 43 insertions(+), 19 deletions(-)

diff --git a/modhex.go b/modhex.go
index e92e719..92cfdc1 100644
--- a/modhex.go
+++ b/modhex.go
@@ -4,6 +4,7 @@ package modhex
 import (
 	"errors"
 	"fmt"
+	"strings"
 )
 
 const modhexTable = "cbdefghijklnrtuv"
@@ -24,20 +25,31 @@ func EncodedLen(n int) int {
 }
 
 // Encode encodes src into EncodedLen(len(src)) bytes of dst.
-// It returns the number of bytes written to dst, but this is
-// always EncodedLen(len(src)).
-// Encode implements modhex encoding.
+//
+// Encode returns the number of bytes written to dst, but this is always
+// EncodedLen(len(src)).
 func Encode(dst, src []byte) int {
-	i := 0
+	// keep track of the number of bytes written to dst
+	len := 0
+
+	// convert each byte of src and store in dst
 	for _, v := range src {
-		dst[i] = modhexTable[v>>4]
-		dst[i+1] = modhexTable[v&0x0f]
-		i += 2
+		// convert the upper nibble to modhex
+		// and store it into dst
+		dst[len] = modhexTable[v>>4]
+		len++
+
+		// convert the lower nibble to modhex
+		// and store it into dst
+		dst[len] = modhexTable[v&0x0f]
+		len++
 	}
-	return len(src) * 2
+
+	// return the number of bytes written
+	return len
 }
 
-// EncodeToString returns the modhex encoding of src.
+// EncodeToString returns the modhex encoding of src as a string.
 func EncodeToString(src []byte) string {
 	// make a new slice to hold the encoded bytes
 	dst := make([]byte, EncodedLen(len(src)))
@@ -58,10 +70,9 @@ func DecodedLen(n int) int {
 // Decode decodes src into DecodedLen(len(src)) bytes, returning
 // the actual number of bytes written to dst.
 //
-// Decode expects that src contains only modhex characters and that
-// src has an even length.
-// If the input is malformed, Decode returns the number
-// of bytes decoded before the error.
+// Decode expects that src contains only modhex characters and that src has an
+// even length. If the input is malformed, Decode returns the number of bytes
+// decoded before the error.
 func Decode(dst, src []byte) (int, error) {
 	i, j := 0, 1
 	for ; j < len(src); j += 2 {
@@ -90,13 +101,15 @@ func Decode(dst, src []byte) (int, error) {
 	return i, nil
 }
 
-// DecodeString returns the bytes represesented by the modhex string s.
+// DecodeString returns the bytes represented by the modhex string s.
 //
-// Decode expects that s contains only modhex characters and that s
-// has an even length.
-// If the input is malformed, Decode returns the number
-// of bytes decoded before the error.
+// DecodeString expects that s contains only modhex characters and that s
+// has an even length. If the input is malformed, DecodeString returns the
+// number of bytes decoded before the error.
 func DecodeString(s string) ([]byte, error) {
+	// convert the string to lower case since the map uses lower case
+	s = strings.ToLower(s)
+
 	// convert the input string to an array of bytes
 	src := []byte(s)
 
diff --git a/modhex_test.go b/modhex_test.go
index dde1aaa..f3a877a 100644
--- a/modhex_test.go
+++ b/modhex_test.go
@@ -2,6 +2,7 @@ package modhex
 
 import (
 	"encoding/hex"
+	"strings"
 	"testing"
 )
 
@@ -17,6 +18,16 @@ func TestEncodeHexDecodeHex(t *testing.T) {
 			hex:    "2d344e83",
 		},
 
+		{
+			modhex: "DTEFFUJE",
+			hex:    "2d344e83",
+		},
+
+		{
+			modhex: "dTeFfUjE",
+			hex:    "2d344e83",
+		},
+
 		{
 			modhex: "hknhfjbrjnlnldnhcujvddbikngjrtgh",
 			hex:    "69b6481c8baba2b60e8f22179b58cd56",
@@ -32,7 +43,7 @@ func TestEncodeHexDecodeHex(t *testing.T) {
 		src, _ := hex.DecodeString(tc.hex)
 		modhex := EncodeToString(src)
 
-		if modhex != tc.modhex {
+		if modhex != strings.ToLower(modhex) {
 			t.Errorf("Encode Incorrect: Actual: %s; Expected: %s\n", modhex, tc.modhex)
 		}