base64.hpp

/*
    SPDX-License-Identifier: MIT
    Copyright © 2016-2023 Amebis
*/
 
#pragma once
 
#include "compat.hpp"
#include "stream.hpp"
#include <cstdint>
#include <string>
#include <vector>
 
 
namespace stdex
{
#if _HAS_CXX17
    inline
#endif
    const char base64_enc_lookup[64] = {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
        'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
        'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
        'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
    };
 
#if _HAS_CXX17
    inline
#endif
    const uint8_t base64_dec_lookup[256] = {
    /*           0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F  */
    /* 0 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* 1 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* 2 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,  62, 255, 255, 255,  63,
    /* 3 */     52,  53,  54,  55,  56,  57,  58,  59,  60,  61, 255, 255, 255,  64, 255, 255,
    /* 4 */    255,   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
    /* 5 */     15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25, 255, 255, 255, 255, 255,
    /* 6 */    255,  26,  27,  28,  29,  30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,
    /* 7 */     41,  42,  43,  44,  45,  46,  47,  48,  49,  50,  51, 255, 255, 255, 255, 255,
    /* 8 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* 9 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* A */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* B */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* C */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* D */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* E */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    /* F */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255
    };
 
    class base64_enc
    {
    public:
        base64_enc() noexcept : m_num(0)
        {
            m_buf[0] = 0;
            m_buf[1] = 0;
            m_buf[2] = 0;
        }
 
        template<class _Elem, class _Traits, class _Ax>
        void encode(_Inout_ std::basic_string<_Elem, _Traits, _Ax> &out, _In_bytecount_(size) const void *data, _In_ size_t size, _In_opt_ bool is_last = true)
        {
            _Assume_(data || !size);
 
            // Preallocate output
            out.reserve(out.size() + enc_size(size));
 
            // Convert data character by character.
            for (size_t i = 0;; i++) {
                if (m_num >= 3) {
                    encode(out);
                    m_num = 0;
                }
 
                if (i >= size)
                    break;
 
                m_buf[m_num++] = reinterpret_cast<const uint8_t*>(data)[i];
            }
 
            // If this is the last block, flush the buffer.
            if (is_last && m_num) {
                encode(out, m_num);
                m_num = 0;
            }
        }
 
        void clear() noexcept
        {
            m_num = 0;
        }
 
        size_t enc_size(_In_ size_t size) const noexcept
        {
            return ((m_num + size + 2)/3)*4;
        }
 
    protected:
        template<class _Elem, class _Traits, class _Ax>
        void encode(_Inout_ std::basic_string<_Elem, _Traits, _Ax> &out)
        {
            out += base64_enc_lookup[                    m_buf[0] >> 2         ];
            out += base64_enc_lookup[((m_buf[0] << 4) | (m_buf[1] >> 4)) & 0x3f];
            out += base64_enc_lookup[((m_buf[1] << 2) | (m_buf[2] >> 6)) & 0x3f];
            out += base64_enc_lookup[                    m_buf[2]        & 0x3f];
        }
 
        template<class _Elem, class _Traits, class _Ax>
        void encode(_Inout_ std::basic_string<_Elem, _Traits, _Ax> &out, _In_ size_t size)
        {
            if (size > 0) {
                out += base64_enc_lookup[m_buf[0] >> 2];
                if (size > 1) {
                    out += base64_enc_lookup[((m_buf[0] << 4) | (m_buf[1] >> 4)) & 0x3f];
                    if (size > 2) {
                        out += base64_enc_lookup[((m_buf[1] << 2) | (m_buf[2] >> 6)) & 0x3f];
                        out += base64_enc_lookup[m_buf[2] & 0x3f];
                    } else {
                        out += base64_enc_lookup[(m_buf[1] << 2) & 0x3f];
                        out += '=';
                    }
                } else {
                    out += base64_enc_lookup[(m_buf[0] << 4) & 0x3f];
                    out += '=';
                    out += '=';
                }
            } else {
                out += '=';
                out += '=';
                out += '=';
                out += '=';
            }
        }
 
    protected:
        uint8_t m_buf[3]; 
        size_t m_num;     
    };
 
    class base64_writer : public stdex::stream::converter, protected base64_enc
    {
    public:
        base64_writer(_Inout_ stdex::stream::basic& source, _In_ size_t max_blocks = 19) :
            stdex::stream::converter(source),
            m_max_blocks(max_blocks),
            m_num_blocks(0)
        {}
 
        virtual ~base64_writer()
        {
            // Flush the buffer.
            if (m_num) {
                if (++m_num_blocks > m_max_blocks) {
                    *m_source << '\n';
                    m_num_blocks = 1;
                }
                encode(m_num);
            }
        }
 
        virtual _Success_(return != 0) size_t write(
            _In_reads_bytes_opt_(length) const void* data, _In_ size_t length)
        {
            _Assume_(data || !length);
            for (size_t i = 0;; i++) {
                if (m_num >= 3) {
                    if (++m_num_blocks > m_max_blocks) {
                        *m_source << '\n';
                        m_num_blocks = 1;
                    }
                    encode();
                    if (!m_source->ok()) _Unlikely_ {
                        m_state = m_source->state();
                        return length - i;
                    }
                    m_num = 0;
                }
                if (i >= length) {
                    m_state = stdex::stream::state_t::ok;
                    return length;
                }
                m_buf[m_num++] = reinterpret_cast<const uint8_t*>(data)[i];
            }
        }
 
    protected:
        void encode()
        {
            char out[4];
            out[0] = base64_enc_lookup[                    m_buf[0] >> 2         ];
            out[1] = base64_enc_lookup[((m_buf[0] << 4) | (m_buf[1] >> 4)) & 0x3f];
            out[2] = base64_enc_lookup[((m_buf[1] << 2) | (m_buf[2] >> 6)) & 0x3f];
            out[3] = base64_enc_lookup[                    m_buf[2]        & 0x3f];
            m_source->write_array(out, sizeof(*out), _countof(out));
        }
 
        void encode(_In_ size_t size)
        {
            char out[4];
            if (size > 0) {
                out[0] = base64_enc_lookup[m_buf[0] >> 2];
                if (size > 1) {
                    out[1] = base64_enc_lookup[((m_buf[0] << 4) | (m_buf[1] >> 4)) & 0x3f];
                    if (size > 2) {
                        out[2] = base64_enc_lookup[((m_buf[1] << 2) | (m_buf[2] >> 6)) & 0x3f];
                        out[3] = base64_enc_lookup[m_buf[2] & 0x3f];
                    } else {
                        out[2] = base64_enc_lookup[(m_buf[1] << 2) & 0x3f];
                        out[3] = '=';
                    }
                } else {
                    out[1] = base64_enc_lookup[(m_buf[0] << 4) & 0x3f];
                    out[2] = '=';
                    out[3] = '=';
                }
            } else {
                out[0] = '=';
                out[1] = '=';
                out[2] = '=';
                out[3] = '=';
            }
            m_source->write_array(out, sizeof(*out), _countof(out));
        }
 
    protected:
        size_t
            m_max_blocks, 
            m_num_blocks; 
    };
 
    class base64_dec
    {
    public:
        base64_dec() noexcept : m_num(0)
        {
            m_buf[0] = 0;
            m_buf[1] = 0;
            m_buf[2] = 0;
            m_buf[3] = 0;
        }
 
        template<class _Ty, class _Ax, class _Tchr>
        void decode(_Inout_ std::vector<_Ty, _Ax> &out, _Out_ bool &is_last, _In_z_count_(size) const _Tchr *data, _In_ size_t size)
        {
            is_last = false;
 
            // Trim data size to first terminator.
            for (size_t k = 0; k < size; k++)
                if (!data[k]) { size = k; break; }
 
            // Preallocate output
            out.reserve(out.size() + dec_size(size));
 
            for (size_t i = 0;; i++) {
                if (m_num >= 4) {
                    // Buffer full; decode it.
                    size_t nibbles = decode(out);
                    if (nibbles < 3) {
                        is_last = true;
                        break;
                    }
                }
 
                if (i >= size)
                    break;
 
                int x = data[i];
                if ((m_buf[m_num] = x < _countof(base64_dec_lookup) ? base64_dec_lookup[x] : 255) != 255)
                    m_num++;
            }
        }
 
        void clear() noexcept
        {
            m_num = 0;
        }
 
        size_t dec_size(_In_ size_t size) const noexcept
        {
            return ((m_num + size + 3)/4)*3;
        }
 
    protected:
        template<class _Ty, class _Ax>
        size_t decode(_Inout_ std::vector<_Ty, _Ax> &out)
        {
            m_num = 0;
            out.push_back((_Ty)(((m_buf[0] << 2) | (m_buf[1] >> 4)) & 0xff));
            if (m_buf[2] < 64) {
                out.push_back((_Ty)(((m_buf[1] << 4) | (m_buf[2] >> 2)) & 0xff));
                if (m_buf[3] < 64) {
                    out.push_back((_Ty)(((m_buf[2] << 6) | m_buf[3]) & 0xff));
                    return 3;
                } else
                    return 2;
            } else
                return 1;
        }
 
    protected:
        uint8_t m_buf[4]; 
        size_t m_num;     
    };
 
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable: 26495)
#endif
 
    class base64_reader : public stdex::stream::converter, protected base64_dec
    {
    public:
        base64_reader(_Inout_ stdex::stream::basic& source) :
            stdex::stream::converter(source),
            m_temp_off(0),
            m_temp_len(0)
        {}
 
#pragma warning(suppress: 6101) // See [1] below
        virtual _Success_(return != 0 || length == 0) size_t read(
            _Out_writes_bytes_to_opt_(length, return) void* data, _In_ size_t length)
        {
            _Assume_(data || !length);
            for (size_t to_read = length;;) {
                if (m_temp_len >= to_read) {
                    memcpy(data, m_temp + m_temp_off, to_read);
                    m_temp_off += to_read;
                    m_temp_len -= to_read;
                    m_state = stdex::stream::state_t::ok;
                    return length;
                }
                if (m_temp_len) {
                    memcpy(data, m_temp + m_temp_off, m_temp_len);
                    reinterpret_cast<uint8_t*&>(data) += m_temp_len;
                    to_read -= m_temp_len;
                    m_temp_off = 0;
                    m_temp_len = 0;
                }
                // Read one Base64 block (4 chars)
                while (m_num < 4) {
                    uint8_t x;
                    *m_source >> x;
                    if (!m_source->ok()) _Unlikely_ {
                        m_state = m_source->state();
                        return length - to_read; // [1] Code analysis misses `length - to_read` bytes were written to data in previous loop iterations.
                    }
                    if ((m_buf[m_num] = base64_dec_lookup[x]) != 255)
                        m_num++;
                }
                decode();
                if (m_temp_len < 3 && to_read >= 3) {
                    // If Base64 indicates end of data, truncate read to hint the client, end of Base64 data has been reached.
                    memcpy(data, m_temp + m_temp_off, m_temp_len);
                    m_temp_off = 0;
                    m_temp_len = 0;
                    to_read -= m_temp_len;
                    m_state = stdex::stream::state_t::ok;
                    return length - to_read; // [1] Code analysis misses `length - to_read` bytes were written to data in previous loop iterations.
                }
            }
        }
 
    protected:
        void decode()
        {
            m_num = 0;
            m_temp_off = 0;
            m_temp[0] = ((m_buf[0] << 2) | (m_buf[1] >> 4)) & 0xff;
            if (m_buf[2] < 64) {
                m_temp[1] = ((m_buf[1] << 4) | (m_buf[2] >> 2)) & 0xff;
                if (m_buf[3] < 64) {
                    m_temp[2] = ((m_buf[2] << 6) | m_buf[3]) & 0xff;
                    m_temp_len = 3;
                } else
                    m_temp_len = 2;
            } else
                m_temp_len = 1;
        }
 
    protected:
        char m_temp[3]; 
        size_t
            m_temp_off, 
            m_temp_len; 
    };
 
#ifdef _MSC_VER
#pragma warning(pop)
#endif
}