Re: [bitcoin-dev] Removal of reject network messages from Bitcoin Core (BIP61)

From: Andreas Schildbach <andreas@schildbach•de>
To: bitcoin-dev@lists•linuxfoundation.org
Subject: Re: [bitcoin-dev] Removal of reject network messages from Bitcoin Core (BIP61)
Date: Thu, 7 Mar 2019 18:58:01 +0100	[thread overview]
Message-ID: <q5rm39$87ck$1@blaine.gmane.org> (raw)
In-Reply-To: <78CAF294-56E2-477C-B46F-C65A56357820@sprovoost.nl>

Yes, I'm talking about P2P connections.

First and foremost, reject messages are an indication that the
transaction isn't going to confirm. Without these messages, we'd need to
revert to pre-BIP61 behaviour of using a timeout for reception of
network confirmations.

Regarding the content, these cases are useful to distinguish:

- Not enough fee
- UTXO already spent
- Tx validity/standardness (e.g. invalid signature)

While the last one in theority wouldn't be necessary if you produced
your software bug-free to begin with, this just isn't how software
development works. Developers need any indication they can get.

The first two happen even in the ideal case. Fees are impossible to
predict, and unintentional double spends happen because users clone
their wallet state.

On 07/03/2019 14.59, Sjors Provoost via bitcoin-dev wrote:
> Can you elaborate a bit on what kind of reject messages your users are getting? I assume the users wallet connects directly to the Bitcoin p2p network?
> 
> What does the wallet do when a transaction is rejected? Does it forget about it (that seems unsafe) or compose another one (with overlapping inputs)?
> 
> Sjors
> 
>> Op 6 mrt. 2019, om 17:49 heeft Andreas Schildbach via bitcoin-dev <bitcoin-dev@lists•linuxfoundation.org> het volgende geschreven:
>>
>> Reject messages cannot be replaced for debugging user problems. At least
>> unless you plan to make RPC or bitcoind logfiles available via the P2P
>> protocol (both probably not a good idea).
>>
>> The typical case is, I get mailed a wallet logfile with reject messages
>> and that's all I have. I cannot access the bitcoind logfile(s) of the
>> node(s) that generated the reject message in the first place. Nor can I
>> access their RPC interface.
>>
>> I strongly suggest re-enabling reject messages by default before 0.18.
>>
>>
>> On 06/03/2019 01.53, Marco Falke via bitcoin-dev wrote:
>>> Bitcoin Core may send "reject" messages as response to "tx", "block" or
>>> "version" messages from a network peer when the message could not be accepted.
>>>
>>> This feature is toggled by the `-enablebip61` command line option and has been
>>> disabled by default since Bitcoin Core version 0.18.0 (not yet released as of
>>> time of writing). Nodes on the network can not generally be trusted to send
>>> valid ("reject") messages, so this should only ever be used when connected to a
>>> trusted node. At this time, I am not aware of any software that requires this
>>> feature, and I would like to remove if from Bitcoin Core to make the codebase
>>> slimmer, easier to understand and maintain. Let us know if your application
>>> relies on this feature and you can not use any of the recommended alternatives:
>>>
>>> * Testing or debugging of implementations of the Bitcoin P2P network protocol
>>>  should be done by inspecting the log messages that are produced by a recent
>>>  version of Bitcoin Core. Bitcoin Core logs debug messages
>>>  (`-debug=<category>`) to a stream (`-printtoconsole`) or to a file
>>>  (`-debuglogfile=<debug.log>`).
>>>
>>> * Testing the validity of a block can be achieved by specific RPCs:
>>>  - `submitblock`
>>>  - `getblocktemplate` with `'mode'` set to `'proposal'` for blocks with
>>>    potentially invalid POW
>>>
>>> * Testing the validity of a transaction can be achieved by specific RPCs:
>>>  - `sendrawtransaction`
>>>  - `testmempoolaccept`
>>>
>>> * Wallets should not use the absence of "reject" messages to indicate a
>>>  transaction has propagated the network, nor should wallets use "reject"
>>>  messages to set transaction fees. Wallets should rather use fee estimation
>>>  to determine transaction fees and set replace-by-fee if desired. Thus, they
>>>  could wait until the transaction has confirmed (taking into account the fee
>>>  target they set (compare the RPC `estimatesmartfee`)) or listen for the
>>>  transaction announcement by other network peers to check for propagation.
>>>
>>> I propose to remove "reject" messages from Bitcoin Core 0.19.0 unless there are
>>> valid concerns about its removal.
>>>
>>> Marco
>>>
>>
>>
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