src/lib/base64.c

/* Copyright (c) 2007-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "base64.h"
#include "buffer.h"

static const char b64enc[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static const unsigned char b64dec[256] = {
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 0-7 */
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 8-15 */
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 16-23 */
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 24-31 */
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 32-39 */
    0xff, 0xff, 0xff, 0x3e, 0xff, 0xff, 0xff, 0x3f, /* 40-47 */
    0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, /* 48-55 */
    0x3c, 0x3d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 56-63 */
    0xff, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, /* 64-71 */
    0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, /* 72-79 */
    0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, /* 80-87 */
    0x17, 0x18, 0x19, 0xff, 0xff, 0xff, 0xff, 0xff, /* 88-95 */
    0xff, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, /* 96-103 */
    0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, /* 104-111 */
    0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, /* 112-119 */
    0x31, 0x32, 0x33, 0xff, 0xff, 0xff, 0xff, 0xff, /* 120-127 */

    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* 128-255 */
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
};

void base64_encode(const void *src, size_t src_size, buffer_t *dest)
{
    const size_t res_size = MAX_BASE64_ENCODED_SIZE(src_size);
    unsigned char *start = buffer_append_space_unsafe(dest, res_size);
    unsigned char *ptr = start;
    const unsigned char *src_c = src;
    size_t src_pos;

    for (src_pos = 0; src_size - src_pos > 2; src_pos += 3, ptr += 4) {
        ptr[0] = b64enc[src_c[src_pos] >> 2];
        ptr[1] = b64enc[((src_c[src_pos] & 0x03) << 4) |
                (src_c[src_pos+1] >> 4)];
        ptr[2] = b64enc[((src_c[src_pos+1] & 0x0f) << 2) |
                ((src_c[src_pos+2] & 0xc0) >> 6)];
        ptr[3] = b64enc[src_c[src_pos+2] & 0x3f];
    }

    i_assert(ptr <= start + res_size);

    switch (src_size - src_pos) {
    case 0:
        break;
    case 1:
        ptr[0] = b64enc[src_c[src_pos] >> 2];
        ptr[1] = b64enc[(src_c[src_pos] & 0x03) << 4];
        ptr[2] = '=';
        ptr[3] = '=';
        break;
    case 2:
        ptr[0] = b64enc[src_c[src_pos] >> 2];
        ptr[1] = b64enc[((src_c[src_pos] & 0x03) << 4) |
                (src_c[src_pos+1] >> 4)];
        ptr[2] = b64enc[((src_c[src_pos+1] & 0x0f) << 2)];
        ptr[3] = '=';
        break;
    default:
        i_unreached();
    }
}

#define IS_EMPTY(c) \
    ((c) == '\n' || (c) == '\r' || (c) == ' ' || (c) == '\t')

int base64_decode(const void *src, size_t src_size,
          size_t *src_pos_r, buffer_t *dest)
{
    const unsigned char *src_c = src;
    size_t src_pos;
    unsigned char input[4], output[3];
    int ret = 1;

    for (src_pos = 0; src_pos+3 < src_size; ) {
        input[0] = b64dec[src_c[src_pos]];
        if (input[0] == 0xff) {
            if (unlikely(!IS_EMPTY(src_c[src_pos]))) {
                ret = -1;
                break;
            }
            src_pos++;
            continue;
        }

        input[1] = b64dec[src_c[src_pos+1]];
        if (unlikely(input[1] == 0xff)) {
            ret = -1;
            break;
        }
        output[0] = (input[0] << 2) | (input[1] >> 4);

        input[2] = b64dec[src_c[src_pos+2]];
        if (input[2] == 0xff) {
            if (unlikely(src_c[src_pos+2] != '=' ||
                     src_c[src_pos+3] != '=')) {
                ret = -1;
                break;
            }
            buffer_append(dest, output, 1);
            ret = 0;
            src_pos += 4;
            break;
        }

        output[1] = (input[1] << 4) | (input[2] >> 2);
        input[3] = b64dec[src_c[src_pos+3]];
        if (input[3] == 0xff) {
            if (unlikely(src_c[src_pos+3] != '=')) {
                ret = -1;
                break;
            }
            buffer_append(dest, output, 2);
            ret = 0;
            src_pos += 4;
            break;
        }

        output[2] = ((input[2] << 6) & 0xc0) | input[3];
        buffer_append(dest, output, 3);
        src_pos += 4;
    }

    for (; src_pos < src_size; src_pos++) {
        if (!IS_EMPTY(src_c[src_pos]))
            break;
    }

    if (src_pos_r != NULL)
        *src_pos_r = src_pos;

    return ret;
}

buffer_t *t_base64_decode_str(const char *str)
{
    buffer_t *buf;
    size_t len = strlen(str);

    buf = t_buffer_create(MAX_BASE64_DECODED_SIZE(len));
    (void)base64_decode(str, len, NULL, buf);
    return buf;
}

bool base64_is_valid_char(char c)
{
    return b64dec[(uint8_t)c] != 0xff;
}