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src/encoding.c  view on Meta::CPAN

 * Convert character c to the corresponding 6-bit value. If character c
 * is not a Base64 character, then 0xFF (255) is returned.
 */
static unsigned b64_char_to_byte(int c) {
    unsigned x;

    x = (GE(c, 'A') & LE(c, 'Z') & (c - 'A')) |
        (GE(c, 'a') & LE(c, 'z') & (c - ('a' - 26))) |
        (GE(c, '0') & LE(c, '9') & (c - ('0' - 52))) | (EQ(c, '+') & 62) |
        (EQ(c, '/') & 63);
    return x | (EQ(x, 0) & (EQ(c, 'A') ^ 0xFF));
}

/*
 * Convert some bytes to Base64. 'dst_len' is the length (in characters)
 * of the output buffer 'dst'; if that buffer is not large enough to
 * receive the result (including the terminating 0), then (size_t)-1
 * is returned. Otherwise, the zero-terminated Base64 string is written
 * in the buffer, and the output length (counted WITHOUT the terminating
 * zero) is returned.
 */
static size_t to_base64(char *dst, size_t dst_len, const void *src,
                        size_t src_len) {
    size_t olen;
    const unsigned char *buf;
    unsigned acc, acc_len;

    olen = (src_len / 3) << 2;
    switch (src_len % 3) {
    case 2:
        olen++;
    /* fall through */
    case 1:
        olen += 2;
        break;
    }
    if (dst_len <= olen) {
        return (size_t)-1;
    }
    acc = 0;
    acc_len = 0;
    buf = (const unsigned char *)src;
    while (src_len-- > 0) {
        acc = (acc << 8) + (*buf++);
        acc_len += 8;
        while (acc_len >= 6) {
            acc_len -= 6;
            *dst++ = (char)b64_byte_to_char((acc >> acc_len) & 0x3F);
        }
    }
    if (acc_len > 0) {
        *dst++ = (char)b64_byte_to_char((acc << (6 - acc_len)) & 0x3F);
    }
    *dst++ = 0;
    return olen;
}

/*
 * Decode Base64 chars into bytes. The '*dst_len' value must initially
 * contain the length of the output buffer '*dst'; when the decoding
 * ends, the actual number of decoded bytes is written back in
 * '*dst_len'.
 *
 * Decoding stops when a non-Base64 character is encountered, or when
 * the output buffer capacity is exceeded. If an error occurred (output
 * buffer is too small, invalid last characters leading to unprocessed
 * buffered bits), then NULL is returned; otherwise, the returned value
 * points to the first non-Base64 character in the source stream, which
 * may be the terminating zero.
 */
static const char *from_base64(void *dst, size_t *dst_len, const char *src) {
    size_t len;
    unsigned char *buf;
    unsigned acc, acc_len;

    buf = (unsigned char *)dst;
    len = 0;
    acc = 0;
    acc_len = 0;
    for (;;) {
        unsigned d;

        d = b64_char_to_byte(*src);
        if (d == 0xFF) {
            break;
        }
        src++;
        acc = (acc << 6) + d;
        acc_len += 6;
        if (acc_len >= 8) {
            acc_len -= 8;
            if ((len++) >= *dst_len) {
                return NULL;
            }
            *buf++ = (acc >> acc_len) & 0xFF;
        }
    }

    /*
     * If the input length is equal to 1 modulo 4 (which is
     * invalid), then there will remain 6 unprocessed bits;
     * otherwise, only 0, 2 or 4 bits are buffered. The buffered
     * bits must also all be zero.
     */
    if (acc_len > 4 || (acc & (((unsigned)1 << acc_len) - 1)) != 0) {
        return NULL;
    }
    *dst_len = len;
    return src;
}

/*
 * Decode decimal integer from 'str'; the value is written in '*v'.
 * Returned value is a pointer to the next non-decimal character in the
 * string. If there is no digit at all, or the value encoding is not
 * minimal (extra leading zeros), or the value does not fit in an
 * 'unsigned long', then NULL is returned.
 */
static const char *decode_decimal(const char *str, unsigned long *v) {
    const char *orig;
    unsigned long acc;