Merge bitcoin/bitcoin#25227: Handle invalid hex encoding in ParseHex

faab273e060d27e166b5fb7fe7692614ec9e5c76 util: Return empty vector on invalid hex encoding (MarcoFalke)
fa3549a77bf6a15d8309d36056237f3126baf721 test: Add hex parse unit tests (MarcoFalke)

Pull request description:

  Seems a bit confusing to happily accept random bytes and pretend they are hex encoded strings.

ACKs for top commit:
  stickies-v:
    re-ACK faab273e060d27e166b5fb7fe7692614ec9e5c76

Tree-SHA512: a808135f744f50aece03d4bf5a71481c7bdca1fcdd0d5b113abdb0c8b382bf81cafee6d17c239041fb49b59f4e19970f24a475378e7f711c3a47d6438de2bdab

2 files changed, 12 insertions, 5 deletions

diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index 45a01429e1..03459dcf20 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -78,18 +78,19 @@ bool IsHexNumber(std::string_view str)
 }
 
 template <typename Byte>
-std::vector<Byte> ParseHex(std::string_view str)
+std::optional<std::vector<Byte>> TryParseHex(std::string_view str)
 {
     std::vector<Byte> vch;
     auto it = str.begin();
-    while (it != str.end() && it + 1 != str.end()) {
+    while (it != str.end()) {
         if (IsSpace(*it)) {
             ++it;
             continue;
         }
         auto c1 = HexDigit(*(it++));
+        if (it == str.end()) return std::nullopt;
         auto c2 = HexDigit(*(it++));
-        if (c1 < 0 || c2 < 0) break;
+        if (c1 < 0 || c2 < 0) return std::nullopt;
         vch.push_back(Byte(c1 << 4) | Byte(c2));
     }
     return vch;
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index 626e48f499..05e7b957c4 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -57,9 +57,15 @@ enum class ByteUnit : uint64_t {
 * @return           A new string without unsafe chars
 */
 std::string SanitizeString(std::string_view str, int rule = SAFE_CHARS_DEFAULT);
-/** Parse the hex string into bytes (uint8_t or std::byte). Ignores whitespace. */
+/** Parse the hex string into bytes (uint8_t or std::byte). Ignores whitespace. Returns nullopt on invalid input. */
+template <typename Byte = std::byte>
+std::optional<std::vector<Byte>> TryParseHex(std::string_view str);
+/** Like TryParseHex, but returns an empty vector on invalid input. */
 template <typename Byte = uint8_t>
-std::vector<Byte> ParseHex(std::string_view str);
+std::vector<Byte> ParseHex(std::string_view hex_str)
+{
+    return TryParseHex<Byte>(hex_str).value_or(std::vector<Byte>{});
+}
 signed char HexDigit(char c);
 /* Returns true if each character in str is a hex character, and has an even
  * number of hex digits.*/