minetest/src/util/base64.cpp

/*
base64.cpp and base64.h

Copyright (C) 2004-2008 René Nyffenegger
Stricter validation added by the Minetest Contributors.

This source code is provided 'as-is', without any express or implied
warranty. In no event will the author be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

1. The origin of this source code must not be misrepresented; you must not
   claim that you wrote the original source code. If you use this source code
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be
   misrepresented as being the original source code.

3. This notice may not be removed or altered from any source distribution.

René Nyffenegger rene.nyffenegger@adp-gmbh.ch

*/

#include "base64.h"
#include <iostream>

static const std::string base64_chars =
		"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
		"abcdefghijklmnopqrstuvwxyz"
		"0123456789+/";

static const std::string base64_chars_padding_1 = "AEIMQUYcgkosw048";
static const std::string base64_chars_padding_2 = "AQgw";

static inline bool is_base64(unsigned char c)
{
	return (c >= '0' && c <= '9')
			|| (c >= 'A' && c <= 'Z')
			|| (c >= 'a' && c <= 'z')
			|| c == '+' || c == '/';
}

bool base64_is_valid(std::string_view s)
{
	size_t i = 0;
	for (; i < s.size(); ++i)
		if (!is_base64(s[i]))
			break;
	unsigned char padding = 3 - ((i + 3) % 4);
	if ((padding == 1 && base64_chars_padding_1.find(s[i - 1]) == s.npos)
			|| (padding == 2 && base64_chars_padding_2.find(s[i - 1]) == s.npos)
			|| padding == 3)
		return false;
	int actual_padding = s.size() - i;
	// omission of padding characters is allowed
	if (actual_padding == 0)
		return true;

	// remaining characters (max. 2) may only be padding
	for (; i < s.size(); ++i)
		if (s[i] != '=')
			return false;
	// number of padding characters needs to match
	return padding == actual_padding;
}

std::string base64_encode(std::string_view s)
{
	const unsigned char *bytes_to_encode = reinterpret_cast<const unsigned char*>(s.data());
	size_t in_len = s.size();

	std::string ret;
	ret.reserve(in_len + in_len / 3);

	int i = 0;
	int j = 0;
	unsigned char char_array_3[3];
	unsigned char char_array_4[4];

	while (in_len--) {
		char_array_3[i++] = *(bytes_to_encode++);
		if (i == 3) {
			char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
			char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
			char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
			char_array_4[3] = char_array_3[2] & 0x3f;

			for(i = 0; (i <4) ; i++)
				ret += base64_chars[char_array_4[i]];
			i = 0;
		}
	}

	if (i)
	{
		for(j = i; j < 3; j++)
			char_array_3[j] = '\0';

		char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
		char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
		char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
		char_array_4[3] = char_array_3[2] & 0x3f;

		for (j = 0; (j < i + 1); j++)
			ret += base64_chars[char_array_4[j]];

	// Don't pad it with =
		/*while((i++ < 3))
			ret += '=';*/

	}

	return ret;
}

std::string base64_decode(std::string_view encoded_string)
{
	int in_len = encoded_string.size();
	int i = 0;
	int j = 0;
	int in_ = 0;
	unsigned char char_array_4[4], char_array_3[3];
	std::string ret;
	ret.reserve(in_len / 4 * 3);

	while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
		char_array_4[i++] = encoded_string[in_]; in_++;
		if (i ==4) {
			for (i = 0; i <4; i++)
				char_array_4[i] = base64_chars.find(char_array_4[i]);

			char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
			char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
			char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

			for (i = 0; (i < 3); i++)
				ret += char_array_3[i];
			i = 0;
		}
	}

	if (i) {
		for (j = i; j <4; j++)
			char_array_4[j] = 0;

		for (j = 0; j <4; j++)
			char_array_4[j] = base64_chars.find(char_array_4[j]);

		char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
		char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
		char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

		for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
	}

	return ret;
}