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Date: Fri, 17 Aug 2012 12:51:33 -0400
Message-ID: <CA+8xBpcLk04m8pX3bA14H4MBamT1-1Exd6EyxOZqER8u9C0WAA@mail.gmail.com>
From: Jeff Garzik <jgarzik@exmulti.com>
To: Pieter Wuille <pieter.wuille@gmail.com>
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Cc: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] BIP 35: add mempool message
Precedence: list

On Fri, Aug 17, 2012 at 9:40 AM, Pieter Wuille <pieter.wuille@gmail.com> wrote:
> On Thu, Aug 16, 2012 at 05:05:58PM -0400, Jeff Garzik wrote:
>> On MSG_MEMTX:  The current version has a much higher Just Works value.
>>
>> On empty "inv":  It is generally better to do something
>> unconditionally, than have a response generated only under certain
>> conditions.
>>
>> And Alan is correct to note that unknown messages are ignored
>> (intentionally, for expansion).  However, unconditionally returning a
>> response has little to do with feature probing/discovery.  It is
>> simply a clear, deterministic indication that processing is complete,
>> for each invocation.
>
> I disagree. Returning an empty "inv" is a very strange way of replying
> "empty mempool". Bitcoin P2P is not a request-response protocol, and
> "inv" messages are sent where there are inventory items to send. The
> reaction to a request (for example "getblocks") can be nothing, or one
> or more "inv" messages if necessary. Special casing an empty "inv" to
> mean empty mempool is trying to hack a request-response system on top
> of the asynchronous system.

OK, just updated 'mempool' branch to not return "inv" if mempool is empty.


> If there is need for confirming the transmission of the mempool is
> complete, the proposal to use a MSG_MEMTX sounds good to me. No client
> will ever receive such an inv without requesting the mempool, and
> implementing handling MSG_MEMTX is trivial.

MSG_MEMTX is not a good idea for this use case.  Just sent a ping(nonce).

Bitcoin P2P processes requests in-order, and responds accordingly.
The remote end may insert asynchronous messages into the response
stream, certainly, but responses to queries are processed and returned
in-order.  A 'getdata' response is fully sent before a 'ping' response
is sent, etc.

-- 
Jeff Garzik
exMULTI, Inc.
jgarzik@exmulti.com