[haiku-appserver] Re: communication

Hi,

Adi Oanca wrote on Tue, 07 Jun 2005 16:49:07 +0300:
> > Anyway, I've looked over the messaging, and this is what I think is 
> > problematic:
> > a) Attach() may fail and cause a partial message to be sent (since 
> > we 
> > don't do proper error checking)
> 
>       Where?

Right where for example a NULL string was passed to AddString(). The 
string was never added (the error was not checked), and the message was 
only partial. On the server side, wrong data was read, because the 
correct data was at a different offset.

DarkWyrm wrote on Tue, 07 Jun 2005 09:14:12 -0400 EDT:
> I've been mulling over how to fix PortLink properly, and there is 
> another issue with PortLink as it is. There are occasions where a 
> message protocol has been changed on one side and not the other, and 
> the client or the server crashes, hangs, or starts using weird data. 

I think BPortLink as a low overhead design is fine. Just think of all 
the additional type info and field names going over the port. No, sub-
optimal.

We have fixed size messages and variable size messages. One way to 
solve "client/server code out of sync problem" would be to have a file 
similar to ServerProtocol.h with defined structs for most or even all 
messages. A struct can be added to the port link in one operation, and 
therefor error checking is much easier. It would be more efficient too, 
since we would not have to check if we need more buffer size for each 
and every single uint8 that is Attach()ed. Client and Server code don't 
get out of sync because the struct is defined and usage is checked by 
the compiler. Dynamically sized messages will probably fit into this 
picture too.

Best regards,
-Stephan

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