util: Add ParseHex<std::byte>() helper

src/test/fuzz/hex.cpp

@@ -25,6 +25,8 @@ FUZZ_TARGET_INIT(hex, initialize_hex)
 {
     const std::string random_hex_string(buffer.begin(), buffer.end());
     const std::vector<unsigned char> data = ParseHex(random_hex_string);
+    const std::vector<std::byte> bytes{ParseHex<std::byte>(random_hex_string)};
+    assert(AsBytes(Span{data}) == Span{bytes});
     const std::string hex_data = HexStr(data);
     if (IsHex(random_hex_string)) {
         assert(ToLower(random_hex_string) == hex_data);

src/util/strencodings.cpp

@@ -76,9 +76,10 @@ bool IsHexNumber(std::string_view str)
     return str.size() > 0;
 }
 
-std::vector<unsigned char> ParseHex(std::string_view str)
+template <typename Byte>
+std::vector<Byte> ParseHex(std::string_view str)
 {
-    std::vector<unsigned char> vch;
+    std::vector<Byte> vch;
     auto it = str.begin();
     while (it != str.end() && it + 1 != str.end()) {
         if (IsSpace(*it)) {
@@ -88,10 +89,12 @@ std::vector<unsigned char> ParseHex(std::string_view str)
         auto c1 = HexDigit(*(it++));
         auto c2 = HexDigit(*(it++));
         if (c1 < 0 || c2 < 0) break;
-        vch.push_back(uint8_t(c1 << 4) | c2);
+        vch.push_back(Byte(c1 << 4) | Byte(c2));
     }
     return vch;
 }
+template std::vector<std::byte> ParseHex(std::string_view);
+template std::vector<uint8_t> ParseHex(std::string_view);
 
 void SplitHostPort(std::string_view in, uint16_t& portOut, std::string& hostOut)
 {

src/util/strencodings.h

@@ -55,7 +55,9 @@ enum class ByteUnit : uint64_t {
 * @return           A new string without unsafe chars
 */
 std::string SanitizeString(std::string_view str, int rule = SAFE_CHARS_DEFAULT);
-std::vector<unsigned char> ParseHex(std::string_view str);
+/** Parse the hex string into bytes (uint8_t or std::byte). Ignores whitespace. */
+template <typename Byte = uint8_t>
+std::vector<Byte> ParseHex(std::string_view str);
 signed char HexDigit(char c);
 /* Returns true if each character in str is a hex character, and has an even
  * number of hex digits.*/