Allowing space for packet headers in Wintun Tx/Rx

[David Woodhouse]

On 12 April 2021 12:38:30 BST, Simon Rozman <simon at rozman.si> wrote:
>> > We'll also need to be able to WintunAllocateSendPacket() of the
>full
>> > possible MTU, then receive and decrypt into that, and send only the
>> > actual size of the packet we received.
>
>How about this:
>https://git.zx2c4.com/wintun/commit/?id=03b6cd410c8963d1888966edf31fdc35a4c8b523
>
>Should be backward compatible. Tested with the existing stable
>wireguard-windows release 0.3.10.

Looks good; thanks. However...

>> 2) Some VPN protocols concatenate multiple packets into a single
>> aggregate on the wire. On Linux we can decrypt, truncate, and send to
>> the tunnel interface without further copying.
>> 
>> Case (1) can be handled with overallocate-and-shrink. Case (2) is
>pretty
>> rare among the protocols that OpenConnect supports, so fallback to
>> memcpy seems fine.

Case (2) is fairly easy to handle when the L3 packet size doesn't use up the whole TUN_PACKET size, isn't it? We can loop and consume multiple smaller packets?

-- 
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