swoole源码分析之Buffer的write操作

swoole_buffer提供的write操作用于向缓存区的任意内存位置写数据。read/write函数可以直接读写内存。所以使用务必要谨慎，否则可能会破坏现有数据。

swoole_buffer->write(int $offset, string $data)

• $offset 偏移量
• $data 写入的数据

现在我们看下其处理流程。

static PHP_METHOD(swoole_buffer, write)
{
    long offset;
    swString str;

    bzero(&str, sizeof(str));

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ls", &offset, &str.str, &str.length) == FAILURE)
    {
        RETURN_FALSE;
    }

    if (str.length < 1)
    {
        php_error_docref(NULL TSRMLS_CC, E_WARNING, "string to write is empty.");
        RETURN_FALSE;
    }

    swString *buffer = swoole_get_object(getThis());

    if (offset < 0)
    {
        offset = buffer->length - buffer->offset + offset;
    }
    if (offset < 0)
    {
        php_error_docref(NULL TSRMLS_CC, E_WARNING, "offset(%ld) is out of bounds.", offset);
        RETURN_FALSE;
    }

    offset += buffer->offset;

    if ((str.length + offset) > buffer->size && (str.length + offset) > SW_STRING_BUFFER_MAXLEN)
    {
        php_error_docref(NULL TSRMLS_CC, E_WARNING, "buffer size can't exceed %d", SW_STRING_BUFFER_MAXLEN);
        RETURN_FALSE;
    }

    size_t size_old = buffer->size;
    if (swString_write(buffer, offset, &str) == SW_OK)
    {
        if (buffer->size > size_old)
        {
            zend_update_property_long(swoole_buffer_class_entry_ptr, getThis(), ZEND_STRL("capacity"), buffer->size TSRMLS_CC);
        }
        zend_update_property_long(swoole_buffer_class_entry_ptr, getThis(), ZEND_STRL("length"),
                buffer->length - buffer->offset TSRMLS_CC);
        RETURN_LONG(buffer->length - buffer->offset);
    }
    else
    {
        RETURN_FALSE;
    }
}

int swString_write(swString *str, off_t offset, swString *write_str)
{
    int new_length = offset + write_str->length;
    if (new_length > str->size)
    {
        if (swString_extend(str, swoole_size_align(new_length * 2, sysconf(_SC_PAGESIZE))) < 0)
        {
            return SW_ERR;
        }
    }

    memcpy(str->str + offset, write_str->str, write_str->length);

    if (new_length > str->length)
    {
        str->length = new_length;
    }

    return SW_OK;
}