Merge bitcoin/bitcoin#23451: span: Add std::byte helpers

faa3ec2304051be7cfbe301cfbfbda3faf7514fc span: Add std::byte helpers (MarcoFalke)
fa18038f519db76befb9a7bd0b1540143bfeb12b refactor: Use ignore helper when unserializing an invalid pubkey (MarcoFalke)
fabe18d0b39b4b918bf60e3a313eaa36fb4067f2 Use value_type in CDataStream where possible (MarcoFalke)

Pull request description:

  This adds (currently unused) span std::byte helpers, so that they can be used in new code.

  The refactors are also required for https://github.com/bitcoin/bitcoin/pull/23438, but they are split up because the other pull doesn't compile with msvc right now.

  The third commit is not needed for the other pull, but still nice.

ACKs for top commit:
  klementtan:
    reACK  faa3ec2. Verified that all the new `std::byte` helper functions are tested.
  laanwj:
    Code review ACK faa3ec2304051be7cfbe301cfbfbda3faf7514fc

Tree-SHA512: b1f6af39f03ea4dfebf20d4a8538fa993a6104e7fc92ddf0c4606a7efc3ca9a8c1a4741d98a1418569c11bb9ce9258bf0c0c06d93d85ed7e208902a2db04e407

8 files changed, 67 insertions, 24 deletions

diff --git a/src/pubkey.h b/src/pubkey.h
index f174ad8d85..ae6356c246 100644
--- a/src/pubkey.h
+++ b/src/pubkey.h
@@ -141,7 +141,7 @@ public:
     template <typename Stream>
     void Unserialize(Stream& s)
     {
-        unsigned int len = ::ReadCompactSize(s);
+        const unsigned int len(::ReadCompactSize(s));
         if (len <= SIZE) {
             s.read((char*)vch, len);
             if (len != size()) {
@@ -149,9 +149,7 @@ public:
             }
         } else {
             // invalid pubkey, skip available data
-            char dummy;
-            while (len--)
-                s.read(&dummy, 1);
+            s.ignore(len);
             Invalidate();
         }
     }
diff --git a/src/span.h b/src/span.h
index 1e347846d8..746e41f2f4 100644
--- a/src/span.h
+++ b/src/span.h
@@ -184,6 +184,7 @@ public:
         return m_data[m_size - 1];
     }
     constexpr std::size_t size() const noexcept { return m_size; }
+    constexpr std::size_t size_bytes() const noexcept { return sizeof(C) * m_size; }
     constexpr bool empty() const noexcept { return size() == 0; }
     CONSTEXPR_IF_NOT_DEBUG C& operator[](std::size_t pos) const noexcept
     {
@@ -240,11 +241,35 @@ T& SpanPopBack(Span<T>& span)
     return back;
 }
 
+// From C++20 as_bytes and as_writeable_bytes
+template <typename T>
+Span<const std::byte> AsBytes(Span<T> s) noexcept
+{
+    return {reinterpret_cast<const std::byte*>(s.data()), s.size_bytes()};
+}
+template <typename T>
+Span<std::byte> AsWritableBytes(Span<T> s) noexcept
+{
+    return {reinterpret_cast<std::byte*>(s.data()), s.size_bytes()};
+}
+
+template <typename V>
+Span<const std::byte> MakeByteSpan(V&& v) noexcept
+{
+    return AsBytes(MakeSpan(std::forward<V>(v)));
+}
+template <typename V>
+Span<std::byte> MakeWritableByteSpan(V&& v) noexcept
+{
+    return AsWritableBytes(MakeSpan(std::forward<V>(v)));
+}
+
 // Helper functions to safely cast to unsigned char pointers.
 inline unsigned char* UCharCast(char* c) { return (unsigned char*)c; }
 inline unsigned char* UCharCast(unsigned char* c) { return c; }
 inline const unsigned char* UCharCast(const char* c) { return (unsigned char*)c; }
 inline const unsigned char* UCharCast(const unsigned char* c) { return c; }
+inline const unsigned char* UCharCast(const std::byte* c) { return reinterpret_cast<const unsigned char*>(c); }
 
 // Helper function to safely convert a Span to a Span<[const] unsigned char>.
 template <typename T> constexpr auto UCharSpanCast(Span<T> s) -> Span<typename std::remove_pointer<decltype(UCharCast(s.data()))>::type> { return {UCharCast(s.data()), s.size()}; }
diff --git a/src/streams.h b/src/streams.h
index 31407287ae..9e8f379cd2 100644
--- a/src/streams.h
+++ b/src/streams.h
@@ -226,7 +226,7 @@ public:
         : nType{nTypeIn},
           nVersion{nVersionIn} {}
 
-    explicit CDataStream(Span<const uint8_t> sp, int nTypeIn, int nVersionIn)
+    explicit CDataStream(Span<const value_type> sp, int nTypeIn, int nVersionIn)
         : vch(sp.data(), sp.data() + sp.size()),
           nType{nTypeIn},
           nVersion{nVersionIn} {}
@@ -254,17 +254,17 @@ public:
     iterator end()                                   { return vch.end(); }
     size_type size() const                           { return vch.size() - nReadPos; }
     bool empty() const                               { return vch.size() == nReadPos; }
-    void resize(size_type n, value_type c=0)         { vch.resize(n + nReadPos, c); }
+    void resize(size_type n, value_type c = value_type{}) { vch.resize(n + nReadPos, c); }
     void reserve(size_type n)                        { vch.reserve(n + nReadPos); }
     const_reference operator[](size_type pos) const  { return vch[pos + nReadPos]; }
     reference operator[](size_type pos)              { return vch[pos + nReadPos]; }
     void clear()                                     { vch.clear(); nReadPos = 0; }
-    iterator insert(iterator it, const uint8_t x) { return vch.insert(it, x); }
-    void insert(iterator it, size_type n, const uint8_t x) { vch.insert(it, n, x); }
+    iterator insert(iterator it, const value_type x) { return vch.insert(it, x); }
+    void insert(iterator it, size_type n, const value_type x) { vch.insert(it, n, x); }
     value_type* data()                               { return vch.data() + nReadPos; }
     const value_type* data() const                   { return vch.data() + nReadPos; }
 
-    void insert(iterator it, std::vector<uint8_t>::const_iterator first, std::vector<uint8_t>::const_iterator last)
+    void insert(iterator it, std::vector<value_type>::const_iterator first, std::vector<value_type>::const_iterator last)
     {
         if (last == first) return;
         assert(last - first > 0);
@@ -278,7 +278,7 @@ public:
             vch.insert(it, first, last);
     }
 
-    void insert(iterator it, const char* first, const char* last)
+    void insert(iterator it, const value_type* first, const value_type* last)
     {
         if (last == first) return;
         assert(last - first > 0);
diff --git a/src/test/base64_tests.cpp b/src/test/base64_tests.cpp
index 9d1dfd46f1..c5fce7bec0 100644
--- a/src/test/base64_tests.cpp
+++ b/src/test/base64_tests.cpp
@@ -23,6 +23,16 @@ BOOST_AUTO_TEST_CASE(base64_testvectors)
         BOOST_CHECK_EQUAL(strDec, vstrIn[i]);
     }
 
+    {
+        const std::vector<uint8_t> in_u{0xff, 0x01, 0xff};
+        const std::vector<std::byte> in_b{std::byte{0xff}, std::byte{0x01}, std::byte{0xff}};
+        const std::string in_s{"\xff\x01\xff"};
+        const std::string out_exp{"/wH/"};
+        BOOST_CHECK_EQUAL(EncodeBase64(in_u), out_exp);
+        BOOST_CHECK_EQUAL(EncodeBase64(in_b), out_exp);
+        BOOST_CHECK_EQUAL(EncodeBase64(in_s), out_exp);
+    }
+
     // Decoding strings with embedded NUL characters should fail
     bool failure;
     (void)DecodeBase64("invalid\0"s, &failure);
diff --git a/src/test/streams_tests.cpp b/src/test/streams_tests.cpp
index 54f04d2e67..b8d76c9608 100644
--- a/src/test/streams_tests.cpp
+++ b/src/test/streams_tests.cpp
@@ -172,7 +172,7 @@ BOOST_AUTO_TEST_CASE(streams_serializedata_xor)
     ds.Xor(key);
     BOOST_CHECK_EQUAL(
             std::string(expected_xor.begin(), expected_xor.end()),
-            std::string(ds.begin(), ds.end()));
+            ds.str());
 
     in.push_back('\x0f');
     in.push_back('\xf0');
@@ -189,7 +189,7 @@ BOOST_AUTO_TEST_CASE(streams_serializedata_xor)
     ds.Xor(key);
     BOOST_CHECK_EQUAL(
             std::string(expected_xor.begin(), expected_xor.end()),
-            std::string(ds.begin(), ds.end()));
+            ds.str());
 
     // Multi character key
 
@@ -210,7 +210,7 @@ BOOST_AUTO_TEST_CASE(streams_serializedata_xor)
     ds.Xor(key);
     BOOST_CHECK_EQUAL(
             std::string(expected_xor.begin(), expected_xor.end()),
-            std::string(ds.begin(), ds.end()));
+            ds.str());
 }
 
 BOOST_AUTO_TEST_CASE(streams_buffered_file)
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 4f00a4d69e..76a690fd28 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -151,12 +151,25 @@ BOOST_AUTO_TEST_CASE(util_HexStr)
         HexStr(Span<const unsigned char>(ParseHex_expected, ParseHex_expected)),
         "");
 
-    std::vector<unsigned char> ParseHex_vec(ParseHex_expected, ParseHex_expected + 5);
+    {
+        const std::vector<char> in_s{ParseHex_expected, ParseHex_expected + 5};
+        const Span<const uint8_t> in_u{MakeUCharSpan(in_s)};
+        const Span<const std::byte> in_b{MakeByteSpan(in_s)};
+        const std::string out_exp{"04678afdb0"};
+
+        BOOST_CHECK_EQUAL(HexStr(in_u), out_exp);
+        BOOST_CHECK_EQUAL(HexStr(in_s), out_exp);
+        BOOST_CHECK_EQUAL(HexStr(in_b), out_exp);
+    }
+}
 
-    BOOST_CHECK_EQUAL(
-        HexStr(ParseHex_vec),
-        "04678afdb0"
-    );
+BOOST_AUTO_TEST_CASE(span_write_bytes)
+{
+    std::array mut_arr{uint8_t{0xaa}, uint8_t{0xbb}};
+    const auto mut_bytes{MakeWritableByteSpan(mut_arr)};
+    mut_bytes[1] = std::byte{0x11};
+    BOOST_CHECK_EQUAL(mut_arr.at(0), 0xaa);
+    BOOST_CHECK_EQUAL(mut_arr.at(1), 0x11);
 }
 
 BOOST_AUTO_TEST_CASE(util_Join)
diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index 5e7c99f140..430f1963ea 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -139,11 +139,6 @@ std::string EncodeBase64(Span<const unsigned char> input)
     return str;
 }
 
-std::string EncodeBase64(const std::string& str)
-{
-    return EncodeBase64(MakeUCharSpan(str));
-}
-
 std::vector<unsigned char> DecodeBase64(const char* p, bool* pf_invalid)
 {
     static const int decode64_table[256] =
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index bc0a6233ab..08a5465de1 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -67,7 +67,8 @@ bool IsHexNumber(const std::string& str);
 std::vector<unsigned char> DecodeBase64(const char* p, bool* pf_invalid = nullptr);
 std::string DecodeBase64(const std::string& str, bool* pf_invalid = nullptr);
 std::string EncodeBase64(Span<const unsigned char> input);
-std::string EncodeBase64(const std::string& str);
+inline std::string EncodeBase64(Span<const std::byte> input) { return EncodeBase64(MakeUCharSpan(input)); }
+inline std::string EncodeBase64(const std::string& str) { return EncodeBase64(MakeUCharSpan(str)); }
 std::vector<unsigned char> DecodeBase32(const char* p, bool* pf_invalid = nullptr);
 std::string DecodeBase32(const std::string& str, bool* pf_invalid = nullptr);
 
@@ -206,6 +207,7 @@ std::optional<T> ToIntegral(const std::string& str)
  */
 std::string HexStr(const Span<const uint8_t> s);
 inline std::string HexStr(const Span<const char> s) { return HexStr(MakeUCharSpan(s)); }
+inline std::string HexStr(const Span<const std::byte> s) { return HexStr(MakeUCharSpan(s)); }
 
 /**
  * Format a paragraph of text to a fixed width, adding spaces for