To: Matt Corallo <lf-lists@mattcorallo.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	Pieter Wuille <pieter.wuille@gmail.com>
References: <ba422d5e-8e96-3475-2a29-80d89fd67322@voskuil.org>
	<CAPg+sBhDjVuN6=tdvUcSY5OCdJD7s3Jp90K1qx0iRX+2WppUQQ@mail.gmail.com>
	<dde5349d-c430-ad57-30c7-77954ff1a94d@voskuil.org>
	<424C9E40-0B90-46A6-9C5E-30AE3E84E119@mattcorallo.com>
	<9ca02a65-23df-5eb4-f9bd-7e05b54ec4ea@voskuil.org>
	<9ECDD902-1D2C-4500-8FC2-4DADF46E4318@mattcorallo.com>
From: Eric Voskuil <eric@voskuil.org>
Message-ID: <0983c823-e517-2821-1398-24bc7467b364@voskuil.org>
Date: Mon, 13 Feb 2017 03:17:11 -0800
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Cc: libbitcoin@lists.dyne.org
Subject: Re: [bitcoin-dev] BIP151 protocol incompatibility
Precedence: list

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On 02/13/2017 03:11 AM, Matt Corallo wrote:
> I believe many, if not all, of those messages are sent irrespective of =
version number.

In the interest of perfect clarity, see your code:

https://github.com/bitcoin/bitcoin/blob/master/src/net_processing.cpp#L13=
72-L1403

Inside of the VERACK handler (i.e. after the handshake) there is a peer
version test before sending SENDCMPCT (and SENDHEADERS).

I have no idea where the fee filter message is sent, if it is sent at
all. But I have *never* seen any control messages arrive before the
handshake is complete.

> In any case, I fail to see how adding any additional messages which
are ignored by old peers amounts to a lack of backward compatibility.

See preceding messages in this thread, I think it's pretty clearly
spelled out.

e

> On February 13, 2017 11:54:23 AM GMT+01:00, Eric Voskuil <eric@voskuil.=
org> wrote:
>> On 02/13/2017 02:16 AM, Matt Corallo wrote:
>>> For the reasons Pieter listed, an explicit part of our version
>> handshake and protocol negotiation is the exchange of otherwise-ignore=
d
>> messages to set up optional features.
>>
>> Only if the peer is at the protocol level that allows the message:
>>
>> compact blocks:
>>
>> https://github.com/bitcoin/bitcoin/blob/master/src/protocol.h#L217-L24=
2
>>
>> fee filter:
>>
>> https://github.com/bitcoin/bitcoin/blob/master/src/protocol.h#L211-L21=
6
>>
>> send headers:
>>
>> https://github.com/bitcoin/bitcoin/blob/master/src/protocol.h#L204-L21=
0
>>
>> filters:
>>
>> https://github.com/bitcoin/bitcoin/blob/master/src/protocol.h#L170-L19=
6
>>
>>> Peers that do not support this ignore such messages, just as if they
>> had indicated they wouldn't support it, see, eg BIP 152's handshake.
>> Not
>> sure why you consider this backwards incompatible, as I would say it's=

>> pretty clearly allowing old nodes to communicate just fine.
>>
>> No, it is not the same as BIP152. Control messages apart from BIP151
>> are
>> not sent until *after* the version is negotiated.
>>
>> I assume that BIP151 is different in this manner because it has a
>> desire
>> to negotiate encryption before any other communications, including
>> version.
>>
>> e


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