int aws_base64_decode()

in source/encoding.c [351:413]

• 52 lines of code
• 17 McCabe index (conditional complexity)

int aws_base64_decode(const struct aws_byte_cursor *AWS_RESTRICT to_decode, struct aws_byte_buf *AWS_RESTRICT output) {
    size_t decoded_length = 0;

    if (AWS_UNLIKELY(aws_base64_compute_decoded_len(to_decode, &decoded_length))) {
        return AWS_OP_ERR;
    }

    if (output->capacity < decoded_length) {
        return aws_raise_error(AWS_ERROR_SHORT_BUFFER);
    }

    if (aws_common_private_has_avx2()) {
        size_t result = aws_common_private_base64_decode_sse41(to_decode->ptr, output->buffer, to_decode->len);
        if (result == -1) {
            return aws_raise_error(AWS_ERROR_INVALID_BASE64_STR);
        }

        output->len = result;
        return AWS_OP_SUCCESS;
    }

    int64_t block_count = (int64_t)to_decode->len / 4;
    size_t string_index = 0;
    uint8_t value1 = 0, value2 = 0, value3 = 0, value4 = 0;
    int64_t buffer_index = 0;

    for (int64_t i = 0; i < block_count - 1; ++i) {
        if (AWS_UNLIKELY(
                s_base64_get_decoded_value(to_decode->ptr[string_index++], &value1, 0) ||
                s_base64_get_decoded_value(to_decode->ptr[string_index++], &value2, 0) ||
                s_base64_get_decoded_value(to_decode->ptr[string_index++], &value3, 0) ||
                s_base64_get_decoded_value(to_decode->ptr[string_index++], &value4, 0))) {
            return aws_raise_error(AWS_ERROR_INVALID_BASE64_STR);
        }

        buffer_index = i * 3;
        output->buffer[buffer_index++] = (uint8_t)((value1 << 2) | ((value2 >> 4) & 0x03));
        output->buffer[buffer_index++] = (uint8_t)(((value2 << 4) & 0xF0) | ((value3 >> 2) & 0x0F));
        output->buffer[buffer_index] = (uint8_t)((value3 & 0x03) << 6 | value4);
    }

    buffer_index = (block_count - 1) * 3;

    if (buffer_index >= 0) {
        if (s_base64_get_decoded_value(to_decode->ptr[string_index++], &value1, 0) ||
            s_base64_get_decoded_value(to_decode->ptr[string_index++], &value2, 0) ||
            s_base64_get_decoded_value(to_decode->ptr[string_index++], &value3, 1) ||
            s_base64_get_decoded_value(to_decode->ptr[string_index], &value4, 1)) {
            return aws_raise_error(AWS_ERROR_INVALID_BASE64_STR);
        }

        output->buffer[buffer_index++] = (uint8_t)((value1 << 2) | ((value2 >> 4) & 0x03));

        if (value3 != BASE64_SENTIANAL_VALUE) {
            output->buffer[buffer_index++] = (uint8_t)(((value2 << 4) & 0xF0) | ((value3 >> 2) & 0x0F));
            if (value4 != BASE64_SENTIANAL_VALUE) {
                output->buffer[buffer_index] = (uint8_t)((value3 & 0x03) << 6 | value4);
            }
        }
    }
    output->len = decoded_length;
    return AWS_OP_SUCCESS;
}