partial bitcoin#23595: Add ParseHex<std::byte>() helper

excludes:
- facd1fb911abfc595a3484ee53397eff515d4c40

src/test/fuzz/hex.cpp

@@ -20,6 +20,8 @@ FUZZ_TARGET(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/test/util_tests.cpp

@@ -149,7 +149,7 @@ static const unsigned char ParseHex_expected[65] = {
     0xde, 0x5c, 0x38, 0x4d, 0xf7, 0xba, 0x0b, 0x8d, 0x57, 0x8a, 0x4c, 0x70, 0x2b, 0x6b, 0xf1, 0x1d,
     0x5f
 };
-BOOST_AUTO_TEST_CASE(util_ParseHex)
+BOOST_AUTO_TEST_CASE(parse_hex)
 {
     std::vector<unsigned char> result;
     std::vector<unsigned char> expected(ParseHex_expected, ParseHex_expected + sizeof(ParseHex_expected));
@@ -165,6 +165,14 @@ BOOST_AUTO_TEST_CASE(util_ParseHex)
     result = ParseHex(" 89 34 56 78");
     BOOST_CHECK(result.size() == 4 && result[0] == 0x89 && result[1] == 0x34 && result[2] == 0x56 && result[3] == 0x78);
 
+    // Embedded null is treated as end
+    const std::string with_embedded_null{" 11 "s
+                                         " \0 "
+                                         " 22 "s};
+    BOOST_CHECK_EQUAL(with_embedded_null.size(), 11);
+    result = ParseHex(with_embedded_null);
+    BOOST_CHECK(result.size() == 1 && result[0] == 0x11);
+
     // Stop parsing at invalid value
     result = ParseHex("1234 invalid 1234");
     BOOST_CHECK(result.size() == 2 && result[0] == 0x12 && result[1] == 0x34);

src/util/strencodings.cpp

@@ -75,10 +75,10 @@ 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)
 {
-    // convert hex dump to vector
-    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 +88,12 @@ 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 in, uint16_t& portOut, std::string& hostOut)
 {

src/util/strencodings.h

@@ -36,7 +36,9 @@ enum SafeChars
 * @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.*/