Buffer Objects

ISA handles data in data buffers. Each data buffer is represented by a buffer object. By using pointers to the buffer object, various components, such as a series of filters can use the same data without the need to copy data. Avoiding copying data improves performance.

A buffer's size is defined in two ways:

• Allocated size
• Actual size

The allocated size is the buffer's capacity in bytes and does not reflect data actually stored in the buffer. When a buffer is created and filled by a filter, it begins with a defined allocated size. The actual size is the number of bytes of data the buffer currently holds.

A filter can perform the following buffer management activities:

• Read into a buffer directly from a memory pointer by using the IFWXIOBuffer::Append method.
• Read a buffer by using the IFWXIOBuffer::GetBufferAndSize method.
• Read a portion of a buffer by using the IFWXIOBuffer::ReadAt method.
• Send data from a buffer to another buffer by using the IFWXIOBuffer::SendToBuffer method.
• Manipulate the memory directly by using the IFWXIOBuffer::GetBufferAndSize method. This operation can only be performed by the buffer owner (the filter that created the buffer).
• Reset the buffer size by using IFWXIOBuffer::SetDataSize method.

For more information about these methods, see IFWXIOBuffer.

Buffer objects implement the IFWXIOBuffer interface.

Using the IFWXIOBuffer interface, information about the buffer can be retrieved and the buffer can be modified. For examples of how the Firewall service uses the IFWXIOBuffer interface, see Basic Filter Interfaces.