hex.cpp

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// Copyright (c) 2017-Present, Electroneum
// Copyright (c) 2017-2019, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
//    of conditions and the following disclaimer in the documentation and/or other
//    materials provided with the distribution.
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//    used to endorse or promote products derived from this software without specific
//    prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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#include "hex.h"
 
#include <iterator>
#include <limits>
#include <ostream>
#include <stdexcept>
 
namespace epee
{
  namespace
  {
    template<typename T>
    void write_hex(T&& out, const span<const std::uint8_t> src)
    {
      static constexpr const char hex[] = u8"0123456789abcdef";
      static_assert(sizeof(hex) == 17, "bad string size");
      for (const std::uint8_t byte : src)
      {
        *out = hex[byte >> 4];
        ++out;
        *out = hex[byte & 0x0F];
        ++out;
      }
    }
  }
 
  template<typename T>
  T to_hex::convert(const span<const std::uint8_t> src)
  {
    if (std::numeric_limits<std::size_t>::max() / 2 < src.size())
      throw std::range_error("hex_view::to_string exceeded maximum size");
 
    T out{};
    out.resize(src.size() * 2);
    to_hex::buffer_unchecked((char*)out.data(), src); // can't see the non const version in wipeable_string??
    return out;
  }
 
  std::string to_hex::string(const span<const std::uint8_t> src) { return convert<std::string>(src); }
  epee::wipeable_string to_hex::wipeable_string(const span<const std::uint8_t> src) { return convert<epee::wipeable_string>(src); }
 
  void to_hex::buffer(std::ostream& out, const span<const std::uint8_t> src)
  {
    write_hex(std::ostreambuf_iterator<char>{out}, src);
  }
 
  void to_hex::formatted(std::ostream& out, const span<const std::uint8_t> src)
  {
    out.put('<');
    buffer(out, src);
    out.put('>');
  }
 
  void to_hex::buffer_unchecked(char* out, const span<const std::uint8_t> src) noexcept
  {
    return write_hex(out, src);
  }
 
  std::vector<uint8_t> from_hex::vector(boost::string_ref src)
  {
    // should we include a specific character
    auto include = [](char input) {
        // we ignore spaces and colons
        return !std::isspace(input) && input != ':';
    };
 
    // the number of relevant characters to decode
    auto count = std::count_if(src.begin(), src.end(), include);
 
    // this must be a multiple of two, otherwise we have a truncated input
    if (count % 2) {
      throw std::length_error{ "Invalid hexadecimal input length" };
    }
 
    std::vector<uint8_t> result;
    result.reserve(count / 2);
 
    // the data to work with (std::string is always null-terminated)
    auto data = src.data();
 
    // convert a single hex character to an unsigned integer
    auto char_to_int = [](const char *input) {
      switch (std::tolower(*input)) {
        case '0': return  0;
        case '1': return  1;
        case '2': return  2;
        case '3': return  3;
        case '4': return  4;
        case '5': return  5;
        case '6': return  6;
        case '7': return  7;
        case '8': return  8;
        case '9': return  9;
        case 'a': return 10;
        case 'b': return 11;
        case 'c': return 12;
        case 'd': return 13;
        case 'e': return 14;
        case 'f': return 15;
        default:  throw std::range_error{ "Invalid hexadecimal input" };
      }
    };
 
    // keep going until we reach the end
    while (data[0] != '\0') {
      // skip unwanted characters
      if (!include(data[0])) {
        ++data;
        continue;
      }
 
      // convert two matching characters to int
      auto high = char_to_int(data++);
      auto low  = char_to_int(data++);
 
      result.push_back(high << 4 | low);
    }
 
    return result;
  }
}