Re: Asynchronous TCP server -- Misc. questions

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From: Mochuelo (hola_at_que.tal)
Date: 03/17/05 

Date: Thu, 17 Mar 2005 12:14:06 +0100

On Thu, 17 Mar 2005 06:43:30 +0200, "Sean Hederman"
<usemy@blogentry.com> wrote:

>"Mochuelo" <hola@que.tal> wrote in message
>news:ifoh31lcr3irab6kjr5rce7t4nikmqj97m@4ax.com...
>> Hi,
>>
>> I'm working with an asynchronous TCP server. I have a few questions
>> that may seem silly, but I can't get to understand all this.
>>
>> Let's say that BeginAccept will cause the AcceptCallback method being
>> executed, and that BeginReceive will cause the ReadCallback method
>> being execute. I have played a little bit with them, it looks like the
>> AcceptCallback method gets executed right when a (local or remote)
>> client requests to connect to this server. I believe that when the
>> server executes the EndAccept method, it is accepting the connection.
>
>Sort of, it's completing the Begin...End started by BeginAccept.

Yes. But, in that sentence, I was thinking from the client point of
view. The client doesn't see its connection request as being accepted
until the server executes exactly which instruction? I believe it is
EndAccept.

>
>> My first silly question is: Why would the server want to reject a
>> specific connection request, if the Listen method has already
>> specified in advance the maximum number of simultaneous connections I
>> want to allow? Could anyone give me an example of a criterium under
>> which I could want to reject a connection request, assuming the max
>> number of connections has NOT been reached yet?
>
>You might want to reject connections based on all sorts of criteria, eg.
>server load.

Ok, that could be a criterium.

The way to reject a connection is by not calling EndAccept, or by
calling it, and then closing the connection?

>> Can I know the IP of the client, before accepting the connection
>> request?
>
>No, the socket is only available from EndAccept.

So, the only way to keep away from certain "banned" client IPs would
be to first accept, and then close the connection, I guess.

>> Another question is: The help for BeginAccept says, among other
>> things:
>>
>> "Your callback method should implement the EndAccept method. When
>> your application calls BeginAccept, the system uses a separate thread
>> to execute the specified callback method and blocks on EndAccept until
>> a pending connection is retrieved."
>>
>> I don't understand why it says "blocks". ReadCallback is executed
>> right at the beginning of every chunk received, or at the end? If it
>> is executed at the beginning, I could understand the "block". It would
>> block until the end of the chunk is reached, when all the chunk data
>> is finally present in the receive buffer. If ReadCallback is executed
>> at the end of every chunk received, I don't understand the word
>> "block". Could someone help me understand this?
>
>"blocks on EndAccept", not ReadCallback. If you don't specify a ReadCallback
>(i.e. leave it null), then your code would have to call EndAccept manually.
>Once EndAccept is called, assuming it's not finished, your thread will block
>until such time as it is.

Understood. That makes sense.

Again, thanks.

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