refactor: Add consteval ParseHex(const char (&s)[Size])

Introduces FixedVec<T, size_t> type:
* Returning std::vector from a consteval/constexpr function makes dynamically allocated memory cross the constexpr/runtime barrier, which is not allowed.
* std::array would work if it wasn't for the sake that the previous ParseHex() supported whitespace intermingled with the hex string. This requires introducing a container with a variable size() that doesn't need to be calculated before the function is invoked.

src/bench/bech32.cpp

@@ -13,7 +13,7 @@
 
 static void Bech32Encode(benchmark::Bench& bench)
 {
-    std::vector<uint8_t> v = ParseHex("c97f5a67ec381b760aeaf67573bc164845ff39a3bb26a1cee401ac67243b48db");
+    constexpr FixedVec<uint8_t, 32> v = ParseHex("c97f5a67ec381b760aeaf67573bc164845ff39a3bb26a1cee401ac67243b48db");
     std::vector<unsigned char> tmp = {0};
     tmp.reserve(1 + 32 * 8 / 5);
     ConvertBits<8, 5, true>([&](unsigned char c) { tmp.push_back(c); }, v.begin(), v.end());

src/kernel/chainparams.cpp

@@ -297,7 +297,7 @@ class SigNetParams : public CChainParams {
         vSeeds.clear();
 
         if (!options.challenge) {
-            bin = ParseHex("512103ad5e0edad18cb1f0fc0d28a3d4f1f3e445640337489abb10404f2d1e086be430210359ef5021964fe22d6f8e05b2463c9540ce96883fe3b278760f048f5189f2e6c452ae");
+            bin = ParseHex("512103ad5e0edad18cb1f0fc0d28a3d4f1f3e445640337489abb10404f2d1e086be430210359ef5021964fe22d6f8e05b2463c9540ce96883fe3b278760f048f5189f2e6c452ae").to_dynamic();
             vSeeds.emplace_back("seed.signet.bitcoin.sprovoost.nl.");
             vSeeds.emplace_back("seed.signet.achownodes.xyz."); // Ava Chow, only supports x1, x5, x9, x49, x809, x849, xd, x400, x404, x408, x448, xc08, xc48, x40c
 

src/pubkey.cpp

@@ -190,14 +190,7 @@ int ecdsa_signature_parse_der_lax(secp256k1_ecdsa_signature* sig, const unsigned
  *  For an example script for calculating H, refer to the unit tests in
  *  ./test/functional/test_framework/crypto/secp256k1.py
  */
-static const std::vector<unsigned char> NUMS_H_DATA{ParseHex("50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0")};
-const XOnlyPubKey XOnlyPubKey::NUMS_H{NUMS_H_DATA};
-
-XOnlyPubKey::XOnlyPubKey(Span<const unsigned char> bytes)
-{
-    assert(bytes.size() == 32);
-    std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
-}
+constexpr XOnlyPubKey XOnlyPubKey::NUMS_H{ParseHex("50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0")};
 
 std::vector<CKeyID> XOnlyPubKey::GetKeyIDs() const
 {

src/pubkey.h

@@ -254,7 +254,11 @@ class XOnlyPubKey
     bool IsNull() const { return m_keydata.IsNull(); }
 
     /** Construct an x-only pubkey from exactly 32 bytes. */
-    explicit XOnlyPubKey(Span<const unsigned char> bytes);
+    constexpr explicit XOnlyPubKey(Span<const unsigned char> bytes)
+    {
+        assert(bytes.size() == 32);
+        std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
+    }
 
     /** Construct an x-only pubkey from a normal pubkey. */
     explicit XOnlyPubKey(const CPubKey& pubkey) : XOnlyPubKey(Span{pubkey}.subspan(1, 32)) {}

src/script/script.h

@@ -463,7 +463,7 @@ class CScript : public CScriptBase
         return *this;
     }
 
-    CScript& operator<<(const std::vector<unsigned char>& b) LIFETIMEBOUND
+    CScript& operator<<(std::span<const unsigned char> b) LIFETIMEBOUND
     {
         if (b.size() < OP_PUSHDATA1)
         {

src/test/base58_tests.cpp

@@ -72,7 +72,7 @@ BOOST_AUTO_TEST_CASE(base58_DecodeBase58)
     // check that DecodeBase58 skips whitespace, but still fails with unexpected non-whitespace at the end.
     BOOST_CHECK(!DecodeBase58(" \t\n\v\f\r skip \r\f\v\n\t a", result, 3));
     BOOST_CHECK( DecodeBase58(" \t\n\v\f\r skip \r\f\v\n\t ", result, 3));
-    std::vector<unsigned char> expected = ParseHex("971a55");
+    constexpr FixedVec<unsigned char, 3> expected = ParseHex("971a55");
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
 
     BOOST_CHECK(DecodeBase58Check("3vQB7B6MrGQZaxCuFg4oh"s, result, 100));

src/test/bloom_tests.cpp

@@ -43,7 +43,7 @@ BOOST_AUTO_TEST_CASE(bloom_create_insert_serialize)
     DataStream stream{};
     stream << filter;
 
-    std::vector<uint8_t> expected = ParseHex("03614e9b050000000000000001");
+    constexpr FixedVec<uint8_t, 13> expected = ParseHex("03614e9b050000000000000001");
     auto result{MakeUCharSpan(stream)};
 
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
@@ -70,7 +70,7 @@ BOOST_AUTO_TEST_CASE(bloom_create_insert_serialize_with_tweak)
     DataStream stream{};
     stream << filter;
 
-    std::vector<uint8_t> expected = ParseHex("03ce4299050000000100008001");
+    constexpr FixedVec<uint8_t, 13> expected = ParseHex("03ce4299050000000100008001");
     auto result{MakeUCharSpan(stream)};
 
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
@@ -91,7 +91,7 @@ BOOST_AUTO_TEST_CASE(bloom_create_insert_key)
     DataStream stream{};
     stream << filter;
 
-    std::vector<unsigned char> expected = ParseHex("038fc16b080000000000000001");
+    constexpr FixedVec<unsigned char, 13> expected = ParseHex("038fc16b080000000000000001");
     auto result{MakeUCharSpan(stream)};
 
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
@@ -352,7 +352,7 @@ BOOST_AUTO_TEST_CASE(merkle_block_3_and_serialize)
     DataStream merkleStream{};
     merkleStream << merkleBlock;
 
-    std::vector<uint8_t> expected = ParseHex("0100000079cda856b143d9db2c1caff01d1aecc8630d30625d10e8b4b8b0000000000000b50cc069d6a3e33e3ff84a5c41d9d3febe7c770fdcc96b2c3ff60abe184f196367291b4d4c86041b8fa45d630100000001b50cc069d6a3e33e3ff84a5c41d9d3febe7c770fdcc96b2c3ff60abe184f19630101");
+    constexpr FixedVec<uint8_t, 119> expected = ParseHex("0100000079cda856b143d9db2c1caff01d1aecc8630d30625d10e8b4b8b0000000000000b50cc069d6a3e33e3ff84a5c41d9d3febe7c770fdcc96b2c3ff60abe184f196367291b4d4c86041b8fa45d630100000001b50cc069d6a3e33e3ff84a5c41d9d3febe7c770fdcc96b2c3ff60abe184f19630101");
     auto result{MakeUCharSpan(merkleStream)};
 
     BOOST_CHECK_EQUAL_COLLECTIONS(expected.begin(), expected.end(), result.begin(), result.end());

src/test/key_tests.cpp

@@ -338,7 +338,7 @@ BOOST_AUTO_TEST_CASE(key_ellswift)
 
 BOOST_AUTO_TEST_CASE(bip341_test_h)
 {
-    std::vector<unsigned char> G_uncompressed = ParseHex("0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8");
+    constexpr FixedVec<unsigned char, 65> G_uncompressed = ParseHex("0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8");
     HashWriter hw;
     hw.write(MakeByteSpan(G_uncompressed));
     XOnlyPubKey H{hw.GetSHA256()};

src/test/miniscript_tests.cpp

@@ -642,12 +642,12 @@ BOOST_AUTO_TEST_CASE(fixed_tests)
 
     // Misc unit tests
     // A Script with a non minimal push is invalid
-    std::vector<unsigned char> nonminpush = ParseHex("0000210232780000feff00ffffffffffff21ff005f00ae21ae00000000060602060406564c2102320000060900fe00005f00ae21ae00100000060606060606000000000000000000000000000000000000000000000000000000000000000000");
+    constexpr FixedVec<unsigned char, 96> nonminpush = ParseHex("0000210232780000feff00ffffffffffff21ff005f00ae21ae00000000060602060406564c2102320000060900fe00005f00ae21ae00100000060606060606000000000000000000000000000000000000000000000000000000000000000000");
     const CScript nonminpush_script(nonminpush.begin(), nonminpush.end());
     BOOST_CHECK(miniscript::FromScript(nonminpush_script, wsh_converter) == nullptr);
     BOOST_CHECK(miniscript::FromScript(nonminpush_script, tap_converter) == nullptr);
     // A non-minimal VERIFY (<key> CHECKSIG VERIFY 1)
-    std::vector<unsigned char> nonminverify = ParseHex("2103a0434d9e47f3c86235477c7b1ae6ae5d3442d49b1943c2b752a68e2a47e247c7ac6951");
+    constexpr FixedVec<unsigned char, 37> nonminverify = ParseHex("2103a0434d9e47f3c86235477c7b1ae6ae5d3442d49b1943c2b752a68e2a47e247c7ac6951");
     const CScript nonminverify_script(nonminverify.begin(), nonminverify.end());
     BOOST_CHECK(miniscript::FromScript(nonminverify_script, wsh_converter) == nullptr);
     BOOST_CHECK(miniscript::FromScript(nonminverify_script, tap_converter) == nullptr);

src/test/util_tests.cpp

@@ -145,56 +145,65 @@ static const unsigned char ParseHex_expected[65] = {
 };
 BOOST_AUTO_TEST_CASE(parse_hex)
 {
+    // Forces compile time evaluation so we use the correct ParseHex() overload.
+    auto compile_time = [] (auto input) consteval {
+        return input;
+    };
+
     std::vector<unsigned char> result;
     std::vector<unsigned char> expected(ParseHex_expected, ParseHex_expected + sizeof(ParseHex_expected));
     // Basic test vector
-    result = ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f");
+    result = compile_time(ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f")).to_dynamic();
+    BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
+    result = ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f"sv);
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
     result = TryParseHex<uint8_t>("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f").value();
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
 
     // Spaces between bytes must be supported
-    result = ParseHex("12 34 56 78");
-    BOOST_CHECK(result.size() == 4 && result[0] == 0x12 && result[1] == 0x34 && result[2] == 0x56 && result[3] == 0x78);
-    result = TryParseHex<uint8_t>("12 34 56 78").value();
-    BOOST_CHECK(result.size() == 4 && result[0] == 0x12 && result[1] == 0x34 && result[2] == 0x56 && result[3] == 0x78);
+    BOOST_CHECK(std::vector<uint8_t>({0x12, 0x34, 0x56, 0x78}) == compile_time(ParseHex("12 34 56 78")));
+    BOOST_CHECK(std::vector<uint8_t>({0x12, 0x34, 0x56, 0x78}) == ParseHex("12 34 56 78"sv));
+    BOOST_CHECK(std::vector<uint8_t>({0x12, 0x34, 0x56, 0x78}) == TryParseHex<uint8_t>("12 34 56 78").value());
 
     // Leading space must be supported (used in BerkeleyEnvironment::Salvage)
-    result = ParseHex(" 89 34 56 78");
-    BOOST_CHECK(result.size() == 4 && result[0] == 0x89 && result[1] == 0x34 && result[2] == 0x56 && result[3] == 0x78);
-    result = TryParseHex<uint8_t>(" 89 34 56 78").value();
-    BOOST_CHECK(result.size() == 4 && result[0] == 0x89 && result[1] == 0x34 && result[2] == 0x56 && result[3] == 0x78);
+    BOOST_CHECK(std::vector<uint8_t>({0x89, 0x34, 0x56, 0x78}) == compile_time(ParseHex(" 89 34 56 78")));
+    BOOST_CHECK(std::vector<uint8_t>({0x89, 0x34, 0x56, 0x78}) == ParseHex(" 89 34 56 78"sv));
+    BOOST_CHECK(std::vector<uint8_t>({0x89, 0x34, 0x56, 0x78}) == TryParseHex<uint8_t>(" 89 34 56 78").value());
 
     // Mixed case and spaces are supported
-    result = ParseHex("     Ff        aA    ");
-    BOOST_CHECK(result.size() == 2 && result[0] == 0xff && result[1] == 0xaa);
-    result = TryParseHex<uint8_t>("     Ff        aA    ").value();
-    BOOST_CHECK(result.size() == 2 && result[0] == 0xff && result[1] == 0xaa);
+    BOOST_CHECK(std::vector<uint8_t>({0xff, 0xaa}) == compile_time(ParseHex("     Ff        aA    ")));
+    BOOST_CHECK(std::vector<uint8_t>({0xff, 0xaa}) == ParseHex("     Ff        aA    "sv));
+    BOOST_CHECK(std::vector<uint8_t>({0xff, 0xaa}) == TryParseHex<uint8_t>("     Ff        aA    ").value());
 
     // Empty string is supported
-    result = ParseHex("");
-    BOOST_CHECK(result.size() == 0);
-    result = TryParseHex<uint8_t>("").value();
-    BOOST_CHECK(result.size() == 0);
+    BOOST_CHECK(compile_time(ParseHex("")).size() == 0);
+    BOOST_CHECK(ParseHex(""sv).size() == 0);
+    BOOST_CHECK(TryParseHex<uint8_t>("").value().size() == 0);
 
     // Spaces between nibbles is treated as invalid
-    BOOST_CHECK_EQUAL(ParseHex("AAF F").size(), 0);
+    BOOST_CHECK_EQUAL(compile_time(ParseHex("AAF F")).size(), 0);
+    BOOST_CHECK_EQUAL(ParseHex("AAF F"sv).size(), 0);
     BOOST_CHECK(!TryParseHex("AAF F").has_value());
 
     // Embedded null is treated as invalid
-    const std::string with_embedded_null{" 11 "s
-                                         " \0 "
-                                         " 22 "s};
-    BOOST_CHECK_EQUAL(with_embedded_null.size(), 11);
-    BOOST_CHECK_EQUAL(ParseHex(with_embedded_null).size(), 0);
-    BOOST_CHECK(!TryParseHex(with_embedded_null).has_value());
+    constexpr char with_embedded_null[] = " 11 "
+                                          " \0 "
+                                          " 22 ";
+    const std::string_view with_embedded_null_str(with_embedded_null, 11);
+    BOOST_CHECK_EQUAL(sizeof(with_embedded_null), 12);
+    BOOST_CHECK_EQUAL(with_embedded_null_str.size(), 11);
+    BOOST_CHECK_EQUAL(compile_time(ParseHex(with_embedded_null)).size(), 0);
+    BOOST_CHECK_EQUAL(ParseHex(with_embedded_null_str).size(), 0);
+    BOOST_CHECK(!TryParseHex(with_embedded_null_str).has_value());
 
     // Non-hex is treated as invalid
-    BOOST_CHECK_EQUAL(ParseHex("1234 invalid 1234").size(), 0);
+    BOOST_CHECK_EQUAL(compile_time(ParseHex("1234 invalid 1234")).size(), 0);
+    BOOST_CHECK_EQUAL(ParseHex("1234 invalid 1234"sv).size(), 0);
     BOOST_CHECK(!TryParseHex("1234 invalid 1234").has_value());
 
     // Truncated input is treated as invalid
-    BOOST_CHECK_EQUAL(ParseHex("12 3").size(), 0);
+    BOOST_CHECK_EQUAL(compile_time(ParseHex("12 3")).size(), 0);
+    BOOST_CHECK_EQUAL(ParseHex("12 3"sv).size(), 0);
     BOOST_CHECK(!TryParseHex("12 3").has_value());
 }
 

src/util/strencodings.h

@@ -13,6 +13,7 @@
 #include <span.h>
 #include <util/string.h>
 
+#include <algorithm>
 #include <charconv>
 #include <cstddef>
 #include <cstdint>
@@ -67,6 +68,88 @@ std::vector<Byte> ParseHex(std::string_view hex_str)
 {
     return TryParseHex<Byte>(hex_str).value_or(std::vector<Byte>{});
 }
+
+/**
+ * Max size fixed at compile time.
+ * Created to be used on the border between runtime and compile time which a
+ * dynamically allocating std::vector cannot cross.
+ * The type was created in preference over std::array to be able to parse hex
+ * strings at compile time which may contain whitespace, making exact size()
+ * unknown ahead of template instantiation.
+ */
+template<typename T, size_t N>
+class FixedVec
+{
+    std::array<T, N> m_data{};
+    size_t m_size{0};
+
+public:
+    constexpr const T* data() const { return m_data.data(); }
+    constexpr size_t size() const { return m_size; }
+    constexpr const T* begin() const { return data(); }
+    constexpr const T* end() const { return data() + m_size; }
+    constexpr void push_back(const T& v)
+    {
+        assert(m_size < N);
+        m_data[m_size] = v;
+        ++m_size;
+    }
+
+    /// Enables creation of a runtime allocated vector when necessary.
+    // NOT just a plain `operator std::vector<T>()` since we want to expose
+    // allocations.
+    constexpr std::vector<T> to_dynamic() const
+    {
+        return {begin(), end()};
+    }
+};
+
+template <typename T, size_t N>
+constexpr bool operator==(const std::vector<T>& a, const FixedVec<T, N>& b)
+{
+    return std::ranges::equal(a, b);
+}
+
+constexpr inline bool IsSpace(char c) noexcept;
+template <typename Byte = uint8_t, size_t Size>
+consteval FixedVec<Byte, Size / 2> ParseHex(const char (&hex_str)[Size])
+{
+    // Non lookup table version of HexDigit().
+    auto from_hex = [](const uint8_t c) -> std::optional<uint8_t> {
+        if (c >= '0' && c <= '9') {
+            return std::make_optional<uint8_t>(c - '0');
+        } else if (c >= 'a' && c <= 'f') {
+            return std::make_optional<uint8_t>(c - uint8_t{'a' - 0xA});
+        } else if (c >= 'A' && c <= 'F') {
+            return std::make_optional<uint8_t>(c - uint8_t{'A' - 0xA});
+        } else {
+            return std::nullopt;
+        }
+    };
+
+    FixedVec<Byte, Size / 2> rv;
+    size_t it = 0;
+    while (it < (Size - 1)) { // -1 - Assumes null-term at the end.
+        if (IsSpace(hex_str[it])) {
+            ++it;
+            continue;
+        }
+        auto c1 = from_hex(hex_str[it++]);
+        if (it >= Size)
+            return {};
+        if (!c1.has_value())
+            return {};
+        auto c1_value = c1.value();
+        c1_value <<= 4;
+        Byte elem{c1_value};
+        auto c2 = from_hex(hex_str[it++]);
+        if (!c2.has_value())
+            return {};
+        elem |= Byte{c2.value()};
+        rv.push_back(elem);
+    }
+    return rv;
+}
 /* Returns true if each character in str is a hex character, and has an even
  * number of hex digits.*/
 bool IsHex(std::string_view str);

src/wallet/crypter.cpp

@@ -11,7 +11,7 @@
 #include <vector>
 
 namespace wallet {
-int CCrypter::BytesToKeySHA512AES(const std::vector<unsigned char>& chSalt, const SecureString& strKeyData, int count, unsigned char *key,unsigned char *iv) const
+int CCrypter::BytesToKeySHA512AES(std::span<const unsigned char> chSalt, const SecureString& strKeyData, int count, unsigned char *key,unsigned char *iv) const
 {
     // This mimics the behavior of openssl's EVP_BytesToKey with an aes256cbc
     // cipher and sha512 message digest. Because sha512's output size (64b) is
@@ -37,7 +37,7 @@ int CCrypter::BytesToKeySHA512AES(const std::vector<unsigned char>& chSalt, cons
     return WALLET_CRYPTO_KEY_SIZE;
 }
 
-bool CCrypter::SetKeyFromPassphrase(const SecureString& strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod)
+bool CCrypter::SetKeyFromPassphrase(const SecureString& strKeyData, std::span<const unsigned char> chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod)
 {
     if (nRounds < 1 || chSalt.size() != WALLET_CRYPTO_SALT_SIZE)
         return false;
@@ -87,7 +87,7 @@ bool CCrypter::Encrypt(const CKeyingMaterial& vchPlaintext, std::vector<unsigned
     return true;
 }
 
-bool CCrypter::Decrypt(const std::vector<unsigned char>& vchCiphertext, CKeyingMaterial& vchPlaintext) const
+bool CCrypter::Decrypt(std::span<const unsigned char> vchCiphertext, CKeyingMaterial& vchPlaintext) const
 {
     if (!fKeySet)
         return false;

src/wallet/crypter.h

@@ -75,12 +75,12 @@ friend class wallet_crypto_tests::TestCrypter; // for test access to chKey/chIV
     std::vector<unsigned char, secure_allocator<unsigned char>> vchIV;
     bool fKeySet;
 
-    int BytesToKeySHA512AES(const std::vector<unsigned char>& chSalt, const SecureString& strKeyData, int count, unsigned char *key,unsigned char *iv) const;
+    int BytesToKeySHA512AES(std::span<const unsigned char> chSalt, const SecureString& strKeyData, int count, unsigned char *key,unsigned char *iv) const;
 
 public:
-    bool SetKeyFromPassphrase(const SecureString &strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod);
+    bool SetKeyFromPassphrase(const SecureString& strKeyData, std::span<const unsigned char> chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod);
     bool Encrypt(const CKeyingMaterial& vchPlaintext, std::vector<unsigned char> &vchCiphertext) const;
-    bool Decrypt(const std::vector<unsigned char>& vchCiphertext, CKeyingMaterial& vchPlaintext) const;
+    bool Decrypt(std::span<const unsigned char> vchCiphertext, CKeyingMaterial& vchPlaintext) const;
     bool SetKey(const CKeyingMaterial& chNewKey, const std::vector<unsigned char>& chNewIV);
 
     void CleanKey()