base64.hpp

//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2017 OpenVPN Technologies, Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU General Public License for more details.
//
//    You should have received a copy of the GNU General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// General-purpose base64 encode and decode.

#ifndef OPENVPN_COMMON_BASE64_H
#define OPENVPN_COMMON_BASE64_H

#include <string>
#include <cstring> // for std::memset, std::strlen

#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/extern.hpp>

namespace openvpn {

  class Base64 {

    class UCharWrap
    {
    public:
      UCharWrap(const unsigned char *data, size_t size)
	: data_(data),
	  size_(size)
      {}

      size_t size() const { return size_; }
      unsigned char operator[](const size_t i) const { return data_[i]; }

    private:
      const unsigned char *data_;
      size_t size_;
    };

  public:
    OPENVPN_SIMPLE_EXCEPTION(base64_bad_map);
    OPENVPN_SIMPLE_EXCEPTION(base64_decode_error);

    // altmap is "+/=" by default
    // another possible encoding for URLs: "-_."
    Base64(const char *altmap = nullptr)
    {
      // build encoding map
      {
	unsigned int i;
	unsigned int j = 65;
	for (i = 0; i < 62; ++i)
	  {
	    enc[i] = j++;
	    if (j == 91)
	      j = 97;
	    else if (j == 123)
	      j = 48;
	  }
	if (!altmap)
	  altmap = "+/=";
	if (std::strlen(altmap) != 3)
	  throw base64_bad_map();
	enc[62] = altmap[0];
	enc[63] = altmap[1];
	equal = altmap[2];
      }

      // build decoding map
      {
	std::memset(dec, 0xFF, 128);
	for (unsigned int i = 0; i < 64; ++i)
	  {
	    const unsigned char c = enc[i];
	    if (c >= 128)
	      throw base64_bad_map();
	    dec[c] = i;
	  }
      }
    }

    static size_t decode_size_max(const size_t encode_size)
    {
      return encode_size;
    }

    static size_t encode_size_max(const size_t decode_size)
    {
      return decode_size * 4 / 3 + 4;
    }

    template <typename V>
    std::string encode(const V& data) const
    {
      char *s, *p;
      size_t i;
      unsigned int c;
      const size_t size = data.size();

      p = s = new char[encode_size_max(size)];
      for (i = 0; i < size; ) {
	c = static_cast<unsigned char>(data[i++]) << 8;
	if (i < size)
	  c += static_cast<unsigned char>(data[i]);
	i++;
	c <<= 8;
	if (i < size)
	  c += static_cast<unsigned char>(data[i]);
	i++;
	p[0] = enc[(c & 0x00fc0000) >> 18];
	p[1] = enc[(c & 0x0003f000) >> 12];
	p[2] = enc[(c & 0x00000fc0) >> 6];
	p[3] = enc[c & 0x0000003f];
	if (i > size)
	  p[3] = equal;
	if (i > size + 1)
	  p[2] = equal;
	p += 4;
      }
      *p = '\0';
      const std::string ret(s);
      delete [] s;
      return ret;
    }

    std::string encode(const unsigned char *data, size_t size) const
    {
      return encode(UCharWrap(data, size));
    }

    std::string decode(const std::string& str) const
    {
      std::string ret;
      ret.reserve(str.length());
      decode(ret, str);
      return ret;
    }

    template <typename V>
    void decode(V& dest, const std::string& str) const
    {
      for (const char *p = str.c_str(); *p != '\0' && (*p == equal || is_base64_char(*p)); p += 4)
	{
	  unsigned int marker;
	  const unsigned int val = token_decode(p, marker);
	  dest.push_back((val >> 16) & 0xff);
	  if (marker < 2)
	    dest.push_back((val >> 8) & 0xff);
	  if (marker < 1)
	    dest.push_back(val & 0xff);
	}
    }

    template <typename V>
    bool is_base64(const V& data, const size_t expected_decoded_length) const
    {
      const size_t size = data.size();
      if (size != encoded_len(expected_decoded_length))
	return false;
      const size_t eq_begin = size - num_eq(expected_decoded_length);
      for (size_t i = 0; i < size; ++i)
	{
	  const char c = data[i];
	  if (i < eq_begin)
	    {
	      if (!is_base64_char(c))
		return false;
	    }
	  else
	    {
	      if (c != equal)
		return false;
	    }
	}
      return true;
    }

  private:
    bool is_base64_char(const char c) const
    {
      const size_t idx = c;
      return idx < 128 && dec[idx] != 0xFF;
    }

    unsigned int decode_base64_char(const char c) const
    {
      const size_t idx = c;
      if (idx >= 128)
	throw base64_decode_error();
      const unsigned int v = dec[idx];
      if (v == 0xFF)
	throw base64_decode_error();
      return v;
    }

    unsigned int token_decode(const char *token, unsigned int& marker) const
    {
      size_t i;
      unsigned int val = 0;
      marker = 0; // number of equal chars seen
      if (std::strlen(token) < 4)
	throw base64_decode_error();
      for (i = 0; i < 4; i++)
	{
	  val <<= 6;
	  if (token[i] == equal)
	    marker++;
	  else if (marker > 0)
	    throw base64_decode_error();
	  else
	    val += decode_base64_char(token[i]);
	}
      if (marker > 2)
	throw base64_decode_error();
      return val;
    }

    static size_t encoded_len(const size_t decoded_len)
    {
      return (decoded_len * 4 / 3 + 3) & ~3;
    }

    static size_t num_eq(const size_t decoded_len)
    {
      return (-1 - decoded_len) % 3;
    }

    unsigned char enc[64];
    unsigned char dec[128];
    unsigned char equal;
  };

  // provide a static Base64 object

  OPENVPN_EXTERN const Base64* base64; // GLOBAL
  OPENVPN_EXTERN const Base64* base64_urlsafe; // GLOBAL

  inline void base64_init_static()
  {
    if (!base64)
      base64 = new Base64();
    if (!base64_urlsafe)
      base64_urlsafe = new Base64("-_.");
  }

  inline void base64_uninit_static()
  {
    if (base64)
      {
	delete base64;
	base64 = nullptr;
      }
    if (base64_urlsafe)
      {
	delete base64_urlsafe;
	base64_urlsafe = nullptr;
      }
  }

}

#endif