add `hex_decode()` to `String`

core/string/ustring.cpp

@@ -1644,6 +1644,35 @@ String String::hex_encode_buffer(const uint8_t *p_buffer, int p_len) {
 	return ret;
 }
 
+Vector<uint8_t> String::hex_decode() const {
+	ERR_FAIL_COND_V_MSG(length() % 2 != 0, Vector<uint8_t>(), "Hexadecimal string of uneven length.");
+
+#define HEX_TO_BYTE(m_output, m_index)                                                                                   \
+	uint8_t m_output;                                                                                                    \
+	c = operator[](m_index);                                                                                             \
+	if (is_digit(c)) {                                                                                                   \
+		m_output = c - '0';                                                                                              \
+	} else if (c >= 'a' && c <= 'f') {                                                                                   \
+		m_output = c - 'a' + 10;                                                                                         \
+	} else if (c >= 'A' && c <= 'F') {                                                                                   \
+		m_output = c - 'A' + 10;                                                                                         \
+	} else {                                                                                                             \
+		ERR_FAIL_V_MSG(Vector<uint8_t>(), "Invalid hexadecimal character \"" + chr(c) + "\" at index " + m_index + "."); \
+	}
+
+	Vector<uint8_t> out;
+	int len = length() / 2;
+	out.resize(len);
+	for (int i = 0; i < len; i++) {
+		char32_t c;
+		HEX_TO_BYTE(first, i * 2);
+		HEX_TO_BYTE(second, i * 2 + 1);
+		out.write[i] = first * 16 + second;
+	}
+	return out;
+#undef HEX_TO_BYTE
+}
+
 void String::print_unicode_error(const String &p_message, bool p_critical) const {
 	if (p_critical) {
 		print_error(vformat("Unicode parsing error, some characters were replaced with spaces: %s", p_message));

core/string/ustring.h

@@ -321,6 +321,8 @@ public:
 	static String chr(char32_t p_char);
 	static String md5(const uint8_t *p_md5);
 	static String hex_encode_buffer(const uint8_t *p_buffer, int p_len);
+	Vector<uint8_t> hex_decode() const;
+
 	bool is_numeric() const;
 
 	double to_float() const;

core/variant/variant_call.cpp

@@ -1734,6 +1734,7 @@ static void _register_variant_builtin_methods() {
 	bind_string_method(to_utf8_buffer, sarray(), varray());
 	bind_string_method(to_utf16_buffer, sarray(), varray());
 	bind_string_method(to_utf32_buffer, sarray(), varray());
+	bind_string_method(hex_decode, sarray(), varray());
 	bind_string_method(to_wchar_buffer, sarray(), varray());
 
 	bind_static_method(String, num_scientific, sarray("number"), varray());

doc/classes/String.xml

@@ -313,6 +313,24 @@
 				[b]Note:[/b] Strings with equal hash values are [i]not[/i] guaranteed to be the same, as a result of hash collisions. On the countrary, strings with different hash values are guaranteed to be different.
 			</description>
 		</method>
+		<method name="hex_decode" qualifiers="const">
+			<return type="PackedByteArray" />
+			<description>
+				Decodes a hexadecimal string as a [PackedByteArray].
+				[codeblocks]
+				[gdscript]
+				var text = "hello world"
+				var encoded = text.to_utf8_buffer().hex_encode() # outputs "68656c6c6f20776f726c64"
+				print(buf.hex_decode().get_string_from_utf8())
+				[/gdscript]
+				[csharp]
+				var text = "hello world";
+				var encoded = text.ToUtf8Buffer().HexEncode(); # outputs "68656c6c6f20776f726c64"
+				GD.Print(buf.HexDecode().GetStringFromUtf8());
+				[/csharp]
+				[/codeblocks]
+			</description>
+		</method>
 		<method name="hex_to_int" qualifiers="const">
 			<return type="int" />
 			<description>

doc/classes/StringName.xml

@@ -296,6 +296,24 @@
 				[b]Note:[/b] Strings with equal hash values are [i]not[/i] guaranteed to be the same, as a result of hash collisions. On the countrary, strings with different hash values are guaranteed to be different.
 			</description>
 		</method>
+		<method name="hex_decode" qualifiers="const">
+			<return type="PackedByteArray" />
+			<description>
+				Decodes a hexadecimal string as a [PackedByteArray].
+				[codeblocks]
+				[gdscript]
+				var text = "hello world"
+				var encoded = text.to_utf8_buffer().hex_encode() # outputs "68656c6c6f20776f726c64"
+				print(buf.hex_decode().get_string_from_utf8())
+				[/gdscript]
+				[csharp]
+				var text = "hello world";
+				var encoded = text.ToUtf8Buffer().HexEncode(); # outputs "68656c6c6f20776f726c64"
+				GD.Print(buf.HexDecode().GetStringFromUtf8());
+				[/csharp]
+				[/codeblocks]
+			</description>
+		</method>
 		<method name="hex_to_int" qualifiers="const">
 			<return type="int" />
 			<description>

modules/mono/glue/GodotSharp/GodotSharp/Core/StringExtensions.cs

@@ -728,6 +728,26 @@ namespace Godot
             return hash;
         }
 
+        /// <summary>
+        /// Decodes a hexadecimal string.
+        /// </summary>
+        /// <param name="instance">The hexadecimal string.</param>
+        /// <returns>The byte array representation of this string.</returns>
+        public static byte[] HexDecode(this string instance)
+        {
+            if (instance.Length % 2 != 0)
+            {
+                throw new ArgumentException("Hexadecimal string of uneven length.", nameof(instance));
+            }
+            int len = instance.Length / 2;
+            byte[] ret = new byte[len];
+            for (int i = 0; i < len; i++)
+            {
+                ret[i] = (byte)int.Parse(instance.AsSpan(i * 2, 2), NumberStyles.AllowHexSpecifier);
+            }
+            return ret;
+        }
+
         /// <summary>
         /// Returns a hexadecimal representation of this byte as a string.
         /// </summary>