Switch to our own Base64 implementation

Written in modern C++, it strictly adheres to the Base64 specification.

This means that the lack of padding is rejected when decoding.
The alternate alphabet that is used for URLs is handled just fine.

A benchmark would be nice to have, once we switch to a proper test framework.

include/mumble/Base64.hpp

@@ -3,30 +3,159 @@
 // that can be found in the LICENSE file at the root of the
 // Mumble source tree or at <https://www.mumble.info/LICENSE>.
 
+// Inspired by https://renenyffenegger.ch/notes/development/Base64/Encoding-and-decoding-base-64-with-cpp.
+
 #ifndef MUMBLE_BASE64_HPP
 #define MUMBLE_BASE64_HPP
 
-#include "Macros.hpp"
-#include "NonCopyable.hpp"
 #include "Types.hpp"
 
-#include <memory>
+#include <array>
+#include <cmath>
+#include <limits>
+#include <stdexcept>
+
+#include <gsl/span>
+
+static constexpr std::byte operator+(const std::byte lhs, const std::byte rhs) {
+	const auto ret = std::to_integer< uint8_t >(lhs) + std::to_integer< uint8_t >(rhs);
+	return std::byte(ret);
+}
+
+// The standard doesn't overload this operator with both operands as std::byte...
+static constexpr std::byte operator<<(const std::byte lhs, const std::byte rhs) {
+	return lhs << std::to_integer< uint8_t >(rhs);
+}
 
 namespace mumble {
-class MUMBLE_EXPORT Base64 : NonCopyable {
+class Base64 {
 public:
-	class P;
+	using StrView      = gsl::span< char >;
+	using StrViewConst = gsl::span< const char >;
+
+	static constexpr size_t decode(BufView out, StrViewConst in) {
+		if (in.empty()) {
+			return 0;
+		}
+
+		if (in.size() % 4) {
+			throw std::invalid_argument("Input is not a multiple of 4!");
+		}
+
+		const size_t size = decodedSize(in);
+		if (out.size() < size) {
+			throw std::invalid_argument("Insufficient output buffer size!");
+		}
+
+		for (; !in.empty(); out = out.subspan(3), in = in.subspan(4)) {
+			out[0] = (charToByte(in[0]) << std::byte(2)) + ((charToByte(in[1]) & std::byte(0x30)) >> 4);
+
+			if (in[2] == '=') {
+				break;
+			}
+
+			out[1] =
+				((charToByte(in[1]) & std::byte(0x0f)) << std::byte(4)) + ((charToByte(in[2]) & std::byte(0x3c)) >> 2);
+
+			if (in[3] == '=') {
+				break;
+			}
+
+			out[2] = ((charToByte(in[2]) & std::byte(0x03)) << std::byte(6)) + charToByte(in[3]);
+		}
+
+		return size;
+	}
 
-	Base64();
-	virtual ~Base64();
+	static constexpr size_t encode(StrView out, BufViewConst in) {
+		if (in.empty()) {
+			return 0;
+		}
 
-	virtual explicit operator bool();
+		const size_t size = encodedSize(in);
+		if (out.size() < size) {
+			throw std::invalid_argument("Insufficient output buffer size!");
+		}
 
-	virtual size_t decode(const BufView out, const BufViewConst in);
-	static size_t encode(const BufView out, const BufViewConst in);
+		for (; !in.empty(); out = out.subspan(4)) {
+			out[0] = byteToChar((in[0] & std::byte(0xfc)) >> 2);
+
+			if (in.size() >= 2) {
+				out[1] = byteToChar(((in[0] & std::byte(0x03)) << 4) + ((in[1] & std::byte(0xf0)) >> 4));
+
+				if (in.size() >= 3) {
+					out[2] = byteToChar(((in[1] & std::byte(0x0f)) << 2) + ((in[2] & std::byte(0xc0)) >> 6));
+					out[3] = byteToChar(in[2] & std::byte(0x3f));
+				} else {
+					out[2] = byteToChar((in[1] & std::byte(0x0f)) << 2);
+					out[3] = PAD_CHAR;
+				}
+			} else {
+				out[1] = byteToChar((in[0] & std::byte(0x03)) << 4);
+				out[2] = PAD_CHAR;
+				out[3] = PAD_CHAR;
+			}
+
+			// All data blocks are guaranteed to be 3 bytes except the last one.
+			in = in.subspan(std::min(size_t{ 3 }, in.size()));
+		}
+
+		return size;
+	}
+
+	static constexpr size_t decodedSize(const StrViewConst in) {
+		size_t size = (in.size() / 4) * 3;
+		// Base64 can have up to 2 pad characters, in order to make the string a multiple of 4.
+		// In order to calculate the exact output size we have to ignore padding.
+		if (auto iter = in.rbegin(); *iter == PAD_CHAR) {
+			size -= *++iter == PAD_CHAR ? 2U : 1U;
+		}
+
+		return size;
+	}
+
+	static constexpr size_t encodedSize(const BufViewConst in) {
+		// ceil((float) a / 3) == (a + 2) / 3, assuming a is an integer.
+		return ((in.size() + 2) / 3) * 4;
+	}
 
 private:
-	std::unique_ptr< P > m_p;
+	using ByteView      = gsl::span< uint8_t >;
+	using ByteViewConst = gsl::span< const uint8_t >;
+
+	static constexpr std::byte charToByte(const char ch) {
+		if (ch >= 'A' && ch <= 'Z')
+			return std::byte(ch - 'A');
+		if (ch >= 'a' && ch <= 'z')
+			return std::byte(ch - 'a' + ('Z' - 'A') + 1);
+		if (ch >= '0' && ch <= '9')
+			return std::byte(ch - '0' + ('Z' - 'A') + ('z' - 'a') + 2);
+		if (ch == '+' || ch == '-')
+			return std::byte(62);
+		if (ch == '/' || ch == '_')
+			return std::byte(63);
+
+		throw std::range_error("");
+	}
+
+	static constexpr char byteToChar(const std::byte byte) {
+		const auto num = std::to_integer< char >(byte);
+
+		if (num <= 25)
+			return num + 'A';
+		if (num >= 26 && num <= 51)
+			return num + 'a' - ('Z' - 'A') - 1;
+		if (num >= 52 && num <= 61)
+			return num + '0' - ('Z' - 'A') - ('z' - 'a') - 2;
+		if (num == 62)
+			return '+';
+		if (num == 63)
+			return '/';
+
+		throw std::range_error("");
+	}
+
+	static constexpr char PAD_CHAR = '=';
 };
 } // namespace mumble
 

src/CMakeLists.txt

@@ -57,8 +57,6 @@ target_include_directories(mumble_library
 
 target_sources(mumble_library
 	PRIVATE
-		"Base64.cpp"
-		"Base64.hpp"
 		"Cert.cpp"
 		"Cert.hpp"
 		"Connection.cpp"

tests/TestBase64/main.cpp

@@ -23,45 +23,35 @@ static constexpr size_t iterations = 1000000;
 
 using namespace mumble;
 
-static std::string decode(Base64 &base64, const Data::Entry &entry) {
-	const BufViewConst in(reinterpret_cast< const std::byte * >(entry.second.data()), entry.second.size());
-
+static std::string decode(const Data::Entry &entry) {
 	std::string ret;
-	ret.resize(base64.decode({}, in));
+	ret.resize(Base64::decodedSize(entry.second));
 
 	const BufView out(reinterpret_cast< std::byte * >(ret.data()), ret.size());
 
-	const auto written = base64.decode(out, in);
+	const auto written = Base64::decode(out, entry.second);
 	if (!written) {
 		return {};
 	}
 
-	ret.resize(written);
-
 	return ret;
 }
 
 static std::string encode(const Data::Entry &entry) {
 	const BufViewConst in(reinterpret_cast< const std::byte * >(entry.first.data()), entry.first.size());
 
 	std::string ret;
-	ret.resize(Base64::encode({}, in) - 1);
-
-	const BufView out(reinterpret_cast< std::byte * >(ret.data()), ret.size());
+	ret.resize(Base64::encodedSize(in));
 
-	const auto written = Base64::encode(out, in);
+	const auto written = Base64::encode(ret, in);
 	if (!written) {
 		return {};
 	}
 
-	ret.resize(written - 1);
-
 	return ret;
 }
 
 static uint8_t thread() {
-	Base64 base64;
-
 	std::random_device device;
 	std::mt19937 algorithm(device());
 	std::uniform_int_distribution< size_t > gen(0, std::tuple_size< Data::Table >() - 1);
@@ -73,7 +63,7 @@ static uint8_t thread() {
 
 		auto entry = Data::ascii[gen(algorithm)];
 
-		auto decoded = decode(base64, entry);
+		auto decoded = decode(entry);
 		if (decoded != entry.first) {
 			return 1;
 		}
@@ -85,7 +75,7 @@ static uint8_t thread() {
 
 		entry = Data::unicode[gen(algorithm)];
 
-		decoded = decode(base64, entry);
+		decoded = decode(entry);
 		if (decoded != entry.first) {
 			return 3;
 		}