From 3cf33c9922d0e54dc631c1576ccbef504f023252 Mon Sep 17 00:00:00 2001
From: Shivaram Lingamneni <slingamn@cs.stanford.edu>
Date: Mon, 23 Jan 2023 07:58:41 -0500
Subject: [PATCH] add support for C hex escapes

---
 ircdog.go           |  1 +
 lib/strings_test.go | 38 ++++++++++++++++++++++++++
 lib/utils.go        | 66 ++++++++++++++++++++++++++++++++++-----------
 3 files changed, 90 insertions(+), 15 deletions(-)
 create mode 100644 lib/strings_test.go

diff --git a/ircdog.go b/ircdog.go
index f4f7be6..cd368ca 100644
--- a/ircdog.go
+++ b/ircdog.go
@@ -81,6 +81,7 @@ Sending Escapes:
 	 Strikethrough | [[S]]    | 0x1e
 	 Underscore    | [[U]]    | 0x1f
 	 Reset         | [[R]]    | 0x0f
+	 C hex escape  | [[\x??]] | 0x??
 	---------------------------------
 
 	These escapes are only enabled in standard mode (not listening mode),
diff --git a/lib/strings_test.go b/lib/strings_test.go
new file mode 100644
index 0000000..f8319aa
--- /dev/null
+++ b/lib/strings_test.go
@@ -0,0 +1,38 @@
+// Copyright (c) 2023 Shivaram Lingamneni <slingamn@cs.stanford.edu>
+// released under the ISC license
+
+package lib
+
+import (
+	"testing"
+)
+
+var replacementTestCases = []struct {
+	input  string
+	output string
+}{
+	{"", ""},
+	{`a`, "a"},
+	{`[`, "["},
+	{`[[`, "[["},
+	{`[[a]]`, "[[a]]"},
+	{`a[[CTCP]]b`, "a\x01b"},
+	{`[[B]]b[[B]]`, "\x02b\x02"},
+	{`a[[\x67]]b`, "a\x67b"},
+	{`[[\x67]]`, "\x67"},
+	{`www[[\x00]]`, "www\x00"},
+	{`www[[\x0D]]`, "www\x0d"},
+	{`www[[\xff]]`, "www\xff"},
+	{`www[[\xFF]]`, "www\xff"},
+	{`[[notanescape]]`, "[[notanescape]]"},
+	{`[[[U]]]`, "[\x1f]"},
+}
+
+func TestReplaceControlCodes(t *testing.T) {
+	for _, testCase := range replacementTestCases {
+		actual := ReplaceControlCodes(testCase.input)
+		if actual != testCase.output {
+			t.Errorf("expected `%s` -> %#v, got %#v", testCase.input, []byte(testCase.output), []byte(actual))
+		}
+	}
+}
diff --git a/lib/utils.go b/lib/utils.go
index 6ab74b9..4e21e85 100644
--- a/lib/utils.go
+++ b/lib/utils.go
@@ -3,18 +3,11 @@
 
 package lib
 
-import "strings"
-
-var controlCodeReplacements = map[string]string{
-	"[[CTCP]]": "\x01",
-	"[[B]]":    "\x02",
-	"[[C]]":    "\x03",
-	"[[M]]":    "\x11",
-	"[[I]]":    "\x1d",
-	"[[S]]":    "\x1e",
-	"[[U]]":    "\x1f",
-	"[[R]]":    "\x0f",
-}
+import (
+	"regexp"
+	"strconv"
+	"strings"
+)
 
 // SplitLineIntoParts splits the given IRC line into separate parts.
 func SplitLineIntoParts(line string) []string {
@@ -64,11 +57,54 @@ func SplitLineIntoParts(line string) []string {
 	return lineParts
 }
 
+var (
+	// e.g., [[\x00]] for \x00, [[\xFF]] or [[\xff]] for \xff
+	hexEscapeRegex = regexp.MustCompile(`^\[\[\\x[0-9a-fA-F]{2}\]\]`)
+)
+
+var controlCodeReplacements = []struct {
+	escape string
+	value  byte
+}{
+	{"[[CTCP]]", '\x01'},
+	{"[[B]]", '\x02'},
+	{"[[C]]", '\x03'},
+	{"[[M]]", '\x11'},
+	{"[[I]]", '\x1d'},
+	{"[[S]]", '\x1e'},
+	{"[[U]]", '\x1f'},
+	{"[[R]]", '\x0f'},
+}
+
 // ReplaceControlCodes applies our control code replacements to the line.
 func ReplaceControlCodes(line string) string {
-	for k, v := range controlCodeReplacements {
-		line = strings.Replace(line, k, v, -1)
+	if idx := strings.Index(line, "[["); idx == -1 {
+		return line
+	}
+
+	var buf strings.Builder
+
+LineLoop:
+	for line != "" {
+		if line[0] == '[' {
+			for _, replacement := range controlCodeReplacements {
+				if strings.HasPrefix(line, replacement.escape) {
+					buf.WriteByte(replacement.value)
+					line = line[len(replacement.escape):]
+					continue LineLoop
+				}
+			}
+			if hexEscapeRegex.MatchString(line) {
+				if val, err := strconv.ParseUint(strings.ToLower(line[4:6]), 16, 8); err == nil {
+					buf.WriteByte(byte(val))
+					line = line[8:]
+					continue LineLoop
+				}
+			}
+		}
+		buf.WriteByte(line[0])
+		line = line[1:]
 	}
 
-	return line
+	return buf.String()
 }