Antoine,

Nothing in my proposal below precludes introducing a more comprehensive
feature negotiation mechanism at some later date. The only changes I'm
proposing are to Bitcoin Core's policy for how it treats its peer
connections.

> If we don't want to introduce a new message and
> corresponding code changes, it would be wise at least to extract VERSION's
> `fRelay` and how Core handles it in its own BIP.

I believe this is what BIP 60 does, or did you have something else in
mind?

> Explicit addr-relay negotiation will offer more
> flexibility

I agree!

> (and more hygienic code paths rather than triggering data
> structures initialization in few different locations).

Not sure what you mean by hygienic here. This seems like a code style
preference.

> Given inbound connections might be attacker-controlled and tx-relay
opt-out
> signaling is also attacker-controlled, wouldn't this give a bias toward an
> attacker in occupying our inbound slots ? Compared to honest inbound
peers,
> which in average are going to be full-relay.

Sorry - I meant that Bitcoin Core should allow a certain number of
inbound peers that do not relay txs. This would be in addition to the
full-relay inbound peers.

John

On Mon, Mar 1, 2021 at 11:11 PM Antoine Riard <antoine.riard@gmail.com>
wrote:

> Hi John,
>
> > I think a good counter-argument against simply using `fRelay` for this
> > purpose is that we shouldn't reuse a protocol feature designed for one
> > function to achieve a totally different aim. However, we know that nodes
> > on the network have been using `fRelay` to disable transaction relay
> > since Bitcoin Core version 0.12 (when `-blocksonly` was added), and that
> > usage was expanded to _all_ nodes running Bitcoin Core version 0.19 or
> > later (when block-relay-only connections were introduced), so using
> > `fRelay` to disable transaction relay is now de facto part of the p2p
> > protocol.
>
>
> I don't think this is good practice ecosystem-wise. To understand tx-relay
> opt-out from peers correctly, a _non_ Bitcoin Core client has to implement
> the `fRelay` subset of BIP37, but ignore the wider part around FILTER*
> messages. Or implement those messages, only to disconnect peers sending
> them, thus following BIP111 requirements.
>
> Thus, future developers of bitcoin software have the choice between
> implementing a standard in a non-compliant way or implementing p2p messages
> for a light client protocol in a way of deprecation ? Even further, an
> interpretation of BIP 37 ("Being able to opt-out of _inv_ messages until
> the filter is set prevents a client being flooded with traffic in the brief
> window of time") would make it okay to send TX messages to your inbound
> block-relay-only peers. And that your client shouldn't be disconnected for
> such behavior.
>
> On the long-term, IMHO, better to have a well-defined standard with a
> clean negotiation mechanism rather than relying on code specifics of a
> given Bitcoin client. If we don't want to introduce a new message and
> corresponding code changes, it would be wise at least to extract VERSION's
> `fRelay` and how Core handles it in its own BIP.
>
> > I think a better approach would be for Bitcoin Core to only relay addr
> > records to an inbound peer if it has previously received an `addr` or
> > `addrv2` message from that peer, since that indicates definitively that
> > the peer actively gossips `addr` records. This approach was first
> > suggested by AJ in the original block-relay-only PR[15].
>
> If a node is willingly to opt-out from addr-relay from one of its inbound
> peers, how is it supposed to do ? Of course, you can drop such messages on
> the floor, your peer is just going to waste bandwidth for nothing. IIRC
> from past irc p2p meetings, we're really unclear about what a
> good-propagation-and-privacy-preserving addr-relay strategy should look
> like. Note, that distrusting your inbound peers with your addr-relay might
> be a sane direction. Explicit addr-relay negotiation will offer more
> flexibility (and more hygienic code paths rather than triggering data
> structures initialization in few different locations).
>
> > - update the inbound eviction logic to protect more inbound peers which
> > do not have transaction relay data structures.
>
> Given inbound connections might be attacker-controlled and tx-relay
> opt-out signaling is also attacker-controlled, wouldn't this give a bias
> toward an attacker in occupying our inbound slots ? Compared to honest
> inbound peers, which in average are going to be full-relay.
>
> Cheers,
> Antoine
>
>
>
> Le lun. 1 mars 2021 à 16:07, John Newbery via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> a écrit :
>
>> Hi Suhas,
>>
>> Thank you for this proposal. I agree with your aims, but I think a new
>> P2P message isn't necessary to achieve them.
>>
>> # Motivation
>>
>> There are two distinct (but interacting) motivations:
>>
>> 1. Allow a node to accept more incoming connections which will only be
>>    used for block propagation (no transaction relay or addr gossip),
>>    while minimizing resource requirements.
>>
>> 2. Prevent `addr` gossip messages from being sent to peers which will
>>    'black hole' those addrs (i.e. not relay them further).
>>
>> These motivations interact because if we simply increase the number of
>> block-relay-only connections that nodes make without making any
>> allowance for the fact those connections won't gossip addr records, then
>> we'll increase the number of addr black holes and worsen addr gossip.
>>
>> # Using fRelay=false to signal no transaction relay.
>>
>> `fRelay` is an optional field in the `version` message. There are three
>> BIPs concerned with `fRelay`:
>>
>> - BIP 37[1] introduced the `fRelay` field to indicate to the recipient
>>   that they must not relay transactions over the connection until a
>>   `filteradd` message has been received.
>>
>> - BIP 60[2] aimed to make the `fRelay` field mandatory. It is not clear
>>   how widely this BIP has been adopted by implementations.
>>
>> - BIP 111[3] introduced a `NODE_BLOOM` service bit to indicate that
>>   bloom filters are served by this node. According to this BIP, "If a
>>   node does not support bloom filters but receives a "filterload",
>>   "filteradd", or "filterclear" message from a peer the node should
>>   disconnect that peer immediately."
>>
>> Within Bitcoin Core:
>>
>> - PR 1795[4] (merged in January 2013) added support for BIP 37 Bloom
>>   filters.
>>
>> - Since PR 2763[5] (merged in June 2013), Bitcoin Core will _always_
>>   include the `fRelay` flag in `version` messages that it sends. Bitcoin
>>   Core will tolerate the `fRelay` field being present or absent in any
>>   `version` message that it receives[6].
>>
>> - PR 6579[7] (merged in August 2015) implemented BIP 111. From that
>>   point on, a Bitcoin Core node would disconnect peers that sent it
>>   `filter*` messages if it hadn't enabled `NODE_BLOOM`, provided the
>>   peer's version was >= 70011. In PR 7708[8] (merged in March 2016) this
>>   was extended to disconnect any peer that sends a `filter*` message,
>>   regardless of its version (in general, a 'polite disconnect' for any
>>   peer that requests an unsupported service is probably the best
>>   behaviour). In PR 16152[9] (merged in July 2019), serving Bloom
>>   filters was disabled by default, due to potential denial-of-service
>>   attacks being possible against nodes which serve bloom filters on
>>   public connections.
>>
>> - PR 6993[10] (merged in November 2015) started reusing the `fRelay`
>>   field for the new `-blocksonly` mode. If Bitcoin Core is started with
>>   `-blocksonly` configured, then it includes `fRelay=false` in all of
>>   the `version` messages it sends. In PR 15759[11] (merged  in September
>>   2019), this usage of `fRelay` to permanently disable tx relay was
>>   extended for use by the new block-relay only connection type.
>>
>> The net effect is that `fRelay` is already being used to indicate that
>> transactions should not be relayed over a connection. In the motivation
>> for your BIP, you write:
>>
>> > The low-bandwidth / minimal-resource nature of these connections is
>> > currently known only by the initiator of the connection; this is
>> > because the transaction relay field in the version message is not a
>> > permanent setting for the lifetime of the connection.  Consequently, a
>> > node receiving an inbound connection with transaction relay disabled
>> > cannot distinguish between a peer that will never enable transaction
>> > relay (as described in BIP 37) and one that will...
>>
>> However, as AJ points out in his response [12], the Bitcoin Core node
>> _does_ know whether transaction relay can be supported as soon as the
>> `version` message is received:
>>
>> > [...] you either set m_tx_relay->fRelayTxes to true via the VERSION
>> > message (either explicitly or by not setting fRelay), or you enable it
>> > later with FILTERLOAD or FILTERCLEAR, both of which will cause a
>> > disconnect if bloom filters aren't supported. Bloom filter support is
>> > (optionally?) indicated via a service bit (BIP 111), so you could
>> > assume you know whether they're supported as soon as you receive the
>> > VERSION line.
>>
>> i.e. if Bitcoin Core node is running under normal configuration with
>> bloom filters disabled for public connections (which is both the default
>> setting and highly recommended due to DoS concerns), then as soon as it
>> receives a `version` message with `fRelay=false`, it can be sure that
>> there will never be any transaction relay with that peer. If the peer
>> later tries to enable transaction relay by sending a `filterload`
>> message, then the node will disconnect that peer immediately.
>>
>> In summary, we can continue using the `fRelay` field to indicate that
>> no transaction relay can happen for the entire lifetime of the
>> connection.  Bitcoin Core can postpone allocating resources for
>> transaction relay data structures until after the version message has
>> been received to minimize resource usage for incoming block-relay-only
>> connections. A rough implementation is here[13]. Obviously, a node that
>> has been configured to serve bloom filters on public connections would
>> not be able to take advantage of this and accept additional incoming
>> block-relay-only peers, but I think that's fine - we already discourage
>> that configuration.
>>
>> I think a good counter-argument against simply using `fRelay` for this
>> purpose is that we shouldn't reuse a protocol feature designed for one
>> function to achieve a totally different aim. However, we know that nodes
>> on the network have been using `fRelay` to disable transaction relay
>> since Bitcoin Core version 0.12 (when `-blocksonly` was added), and that
>> usage was expanded to _all_ nodes running Bitcoin Core version 0.19 or
>> later (when block-relay-only connections were introduced), so using
>> `fRelay` to disable transaction relay is now de facto part of the p2p
>> protocol.
>>
>> # Preventing addr black holes
>>
>> Addresses of potential peers are gossiped around the p2p network using
>> `addr` messages. When a Bitcoin Core node learns of a new `addr` record,
>> it will relay that record to one or two of its peers, chosen at
>> random[14]. The idea is that eventually the `addr` record will reach
>> most of the nodes on the network.
>>
>> If there are too many nodes on the network that receive `addr` records
>> and do not relay those records on to their peers (termed _addr black
>> hole_ nodes), then propagation of those `addr` records suffers -- any
>> individual `addr` record is unlikely to reach a large proportion of
>> nodes on the network.
>>
>> Since a motivation for block-relay-only connections is to protect
>> against eclipse attacks and thwart network topology analysis, Bitcoin
>> Core will not relay `addr` records on those connections, and will ignore
>> any `addr` record received over those connections. Therefore, increasing
>> the number of block-relay-only connections without changing the `addr`
>> gossip logic is likely to increase the prevalence of addr black holes,
>> and negatively impact addr propagation. This is why BIP 338 includes:
>>
>> > It is RECOMMENDED that a node that has sent or received a disabletx
>> > message to/from a peer not send any of these messages to the peer:
>> >
>> > - addr/getaddr
>> > - addrv2 (BIP 155)
>>
>> I think a better approach would be for Bitcoin Core to only relay addr
>> records to an inbound peer if it has previously received an `addr` or
>> `addrv2` message from that peer, since that indicates definitively that
>> the peer actively gossips `addr` records. This approach was first
>> suggested by AJ in the original block-relay-only PR[15].
>>
>> An advantage of this approach is that it will improve addr propagation
>> immediately and without any change to the P2P protocol, and will prevent
>> sending `addr` records to all addr black holes (such as light clients),
>> not just incoming block-relay-only connections.
>>
>> # Conclusion
>>
>> We can increase the permitted number of inbound block-relay-only peers
>> while minimizing resource requirement _and_ improving addr record
>> propagation, without any changes to the p2p protocol required.
>>
>> I propose that for Bitcoin Core version 22.0:
>>
>> - only initialize the transaction relay data structures after the
>>   `version` message is received, and only if fRelay=true and
>>   `NODE_BLOOM` is not offered on this connection.
>> - only initialize the addr data structures for inbound connections when
>>   an `addr`, `addrv2` or `getaddr` message is received on the
>>   connection, and only consider a connection for addr relay if its addr
>>   data structures are initialized.
>> - update the inbound eviction logic to protect more inbound peers which
>>   do not have transaction relay data structures.
>>
>> Then, in version 23.0:
>>
>> - modestly increase the number of outbound block-relay-only connections.
>>
>> John
>>
>> [1] https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki
>> [2] https://github.com/bitcoin/bips/blob/master/bip-0060.mediawiki
>> [3] https://github.com/bitcoin/bips/blob/master/bip-0111.mediawiki
>> [4] https://github.com/bitcoin/bitcoin/pull/1795
>> [5] https://github.com/bitcoin/bitcoin/pull/2763
>> [6]
>> https://github.com/bitcoin/bitcoin/blob/e49117470b77fb7d53be122c6490ba163c6e304d/src/net_processing.cpp#L2582-L2583
>> [7] https://github.com/bitcoin/bitcoin/pull/6579
>> [8] https://github.com/bitcoin/bitcoin/pull/7708
>> [9] https://github.com/bitcoin/bitcoin/pull/16152
>> [10] https://github.com/bitcoin/bitcoin/pull/6993
>> [11] https://github.com/bitcoin/bitcoin/pull/15759
>> [12]
>> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-January/018347.html
>> [13] https://github.com/jnewbery/bitcoin/tree/2021-02-lazy-init-peer
>> [14]
>> https://github.com/bitcoin/bitcoin/blob/e52ce9f2b312b3cf3b0837918e07d7603e241d63/src/net_processing.cpp#L1696-L1700
>> [15] https://github.com/bitcoin/bitcoin/pull/15759#issuecomment-527012757
>>
>> > Hi,
>> >
>> > I'm proposing the addition of a new, optional p2p message to allow
>> peers to communicate that they do not want to send or receive (loose)
>> transactions for the lifetime of a connection.
>> >
>> > The goal of this message is to help facilitate connections on the
>> network over which only block-related data (blocks/headers/compact
>> blocks/etc) are relayed, to create low-resource connections that help
>> protect against partition attacks on the network.  In particular, by adding
>> a network message that communicates that transactions will not be relayed
>> for the life of the connection, we ease the implementation of software that
>> could have increased inbound connection limits for such peers, which in
>> turn will make it easier to add additional persistent block-relay-only
>> connections on the network -- strengthening network security for little
>> additional bandwidth.
>> >
>> > Software has been deployed for over a year now which makes such
>> connections, using the BIP37/BIP60 "fRelay" field in the version message to
>> signal that transactions should not be sent initially.  However, BIP37
>> allows for transaction relay to be enabled later in the connection's
>> lifetime, complicating software that would try to distinguish inbound peers
>> that will never relay transactions from those that might.
>> >
>> > This proposal would add a single new p2p message, "disabletx", which
>> (if used at all) must be sent between version and verack.  I propose that
>> this message is valid for peers advertising protocol version 70017 or
>> higher.  Software is free to implement this BIP or ignore this message and
>> remain compatible with software that does implement it.
>> >
>> > Full text of the proposed BIP is below.
>> >
>> > Thanks,
>> > Suhas
>> >
>> > ---------------------------------------------------
>> >
>> > <pre>
>> >   BIP: XXX
>> >   Layer: Peer Services
>> >   Title: Disable transaction relay message
>> >   Author: Suhas Daftuar <sdaftuar@chaincode.com>
>> >   Comments-Summary: No comments yet.
>> >   Comments-URI:
>> >   Status: Draft
>> >   Type: Standards Track
>> >   Created: 2020-09-03
>> >   License: BSD-2-Clause
>> > </pre>
>> >
>> > ==Abstract==
>> >
>> > This BIP describes a change to the p2p protocol to allow a node to tell
>> a peer
>> > that a connection will not be used for transaction relay, to support
>> > block-relay-only connections that are currently in use on the network.
>> >
>> > ==Motivation==
>> >
>> > For nearly the past year, software has been deployed[1] which initiates
>> > connections on the Bitcoin network and sets the transaction relay field
>> > (introduced by BIP 37 and also defined in BIP 60) to false, to prevent
>> > transaction relay from occurring on the connection. Additionally, addr
>> messages
>> > received from the peer are ignored by this software.
>> >
>> > The purpose of these connections is two-fold: by making additional
>> > low-bandwidth connections on which blocks can propagate, the robustness
>> of a
>> > node to network partitioning attacks is strengthened.  Additionally, by
>> not
>> > relaying transactions and ignoring received addresses, the ability of an
>> > adversary to learn the complete network graph (or a subgraph) is
>> reduced[2],
>> > which in turn increases the cost or difficulty to an attacker seeking
>> to carry
>> > out a network partitioning attack (when compared with having such
>> knowledge).
>> >
>> > The low-bandwidth / minimal-resource nature of these connections is
>> currently
>> > known only by the initiator of the connection; this is because the
>> transaction
>> > relay field in the version message is not a permanent setting for the
>> lifetime
>> > of the connection.  Consequently, a node receiving an inbound
>> connection with
>> > transaction relay disabled cannot distinguish between a peer that will
>> never
>> > enable transaction relay (as described in BIP 37) and one that will.
>> Moreover,
>> > the node also cannot determine that the incoming connection will ignore
>> relayed
>> > addresses; with that knowledge a node would likely choose other peers to
>> > receive announced addresses instead.
>> >
>> > This proposal adds a new, optional message that a node can send a peer
>> when
>> > initiating a connection to that peer, to indicate that connection
>> should not be
>> > used for transaction-relay for the connection's lifetime. In addition,
>> without
>> > a current mechanism to negotiate whether addresses should be relayed on
>> a
>> > connection, this BIP suggests that address messages not be sent on
>> links where
>> > tx-relay has been disabled.
>> >
>> > ==Specification==
>> >
>> > # A new disabletx message is added, which is defined as an empty
>> message where pchCommand == "disabletx".
>> > # The protocol version of nodes implementing this BIP must be set to
>> 70017 or higher.
>> > # If a node sets the transaction relay field in the version message to
>> a peer to false, then the disabletx message MAY also be sent in response to
>> a version message from that peer if the peer's protocol version is >=
>> 70017. If sent, the disabletx message MUST be sent prior to sending a
>> verack.
>> > # A node that has sent or received a disabletx message to/from a peer
>> MUST NOT send any of these messages to the peer:
>> > ## inv messages for transactions
>> > ## getdata messages for transactions
>> > ## getdata messages for merkleblock (BIP 37)
>> > ## filteradd/filterload/filterclear (BIP 37)
>> > ## mempool (BIP 35)
>> > # It is RECOMMENDED that a node that has sent or received a disabletx
>> message to/from a peer not send any of these messages to the peer:
>> > ## addr/getaddr
>> > ## addrv2 (BIP 155)
>> > # The behavior regarding sending or processing other message types is
>> not specified by this BIP.
>> > # Nodes MAY decide to not remain connected to peers that send this
>> message (for example, if trying to find a peer that will relay
>> transactions).
>> >
>> > ==Compatibility==
>> >
>> > Nodes with protocol version >= 70017 that do not implement this BIP,
>> and nodes
>> > with protocol version < 70017, will continue to remain compatible with
>> > implementing software: transactions would not be relayed to peers
>> sending the
>> > disabletx message (provided that BIP 37 or BIP 60 has been
>> implemented), and while
>> > periodic address relay may still take place, software implementing this
>> BIP
>> > should not be disconnecting such peers solely for that reason.
>> >
>> > Disabling address relay is suggested but not required by this BIP, to
>> allow for
>> > future protocol extensions that might specify more carefully how
>> address relay
>> > is to be negotiated. This BIP's recommendations for software to not
>> relay
>> > addresses is intended to be interpreted as guidance in the absence of
>> any such
>> > future protocol extension, to accommodate existing software behavior.
>> >
>> > Note that all messages specified in BIP 152, including blocktxn and
>> > getblocktxn, are permitted between peers that have sent/received a
>> disabletx
>> > message, subject to the feature negotiation of BIP 152.
>> >
>> > ==Implementation==
>> >
>> > TBD
>> >
>> > ==References==
>> >
>> > # Bitcoin Core has [https://github.com/bitcoin/bitcoin/pull/15759
>> implemented this functionality] since version 0.19.0.1, released in
>> November 2019.
>> > # For example, see
>> https://www.cs.umd.edu/projects/coinscope/coinscope.pdf and
>> https://arxiv.org/pdf/1812.00942.pdf.
>> >
>> > ==Copyright==
>> >
>> > This BIP is licensed under the 2-clause BSD license.
>>
>> On Wed, Jan 6, 2021 at 4:35 PM Suhas Daftuar via bitcoin-dev <
>> bitcoin-dev@lists.linuxfoundation.org> wrote:
>>
>>> Hi,
>>>
>>> I'm proposing the addition of a new, optional p2p message to allow peers
>>> to communicate that they do not want to send or receive (loose)
>>> transactions for the lifetime of a connection.
>>>
>>> The goal of this message is to help facilitate connections on the
>>> network over which only block-related data (blocks/headers/compact
>>> blocks/etc) are relayed, to create low-resource connections that help
>>> protect against partition attacks on the network.  In particular, by adding
>>> a network message that communicates that transactions will not be relayed
>>> for the life of the connection, we ease the implementation of software that
>>> could have increased inbound connection limits for such peers, which in
>>> turn will make it easier to add additional persistent block-relay-only
>>> connections on the network -- strengthening network security for little
>>> additional bandwidth.
>>>
>>> Software has been deployed for over a year now which makes such
>>> connections, using the BIP37/BIP60 "fRelay" field in the version message to
>>> signal that transactions should not be sent initially.  However, BIP37
>>> allows for transaction relay to be enabled later in the connection's
>>> lifetime, complicating software that would try to distinguish inbound peers
>>> that will never relay transactions from those that might.
>>>
>>> This proposal would add a single new p2p message, "disabletx", which (if
>>> used at all) must be sent between version and verack.  I propose that this
>>> message is valid for peers advertising protocol version 70017 or higher.
>>> Software is free to implement this BIP or ignore this message and remain
>>> compatible with software that does implement it.
>>>
>>> Full text of the proposed BIP is below.
>>>
>>> Thanks,
>>> Suhas
>>>
>>> ---------------------------------------------------
>>>
>>> <pre>
>>>   BIP: XXX
>>>   Layer: Peer Services
>>>   Title: Disable transaction relay message
>>>   Author: Suhas Daftuar <sdaftuar@chaincode.com>
>>>   Comments-Summary: No comments yet.
>>>   Comments-URI:
>>>   Status: Draft
>>>   Type: Standards Track
>>>   Created: 2020-09-03
>>>   License: BSD-2-Clause
>>> </pre>
>>>
>>> ==Abstract==
>>>
>>> This BIP describes a change to the p2p protocol to allow a node to tell a peer
>>> that a connection will not be used for transaction relay, to support
>>> block-relay-only connections that are currently in use on the network.
>>>
>>> ==Motivation==
>>>
>>> For nearly the past year, software has been deployed[1] which initiates
>>> connections on the Bitcoin network and sets the transaction relay field
>>> (introduced by BIP 37 and also defined in BIP 60) to false, to prevent
>>> transaction relay from occurring on the connection. Additionally, addr messages
>>> received from the peer are ignored by this software.
>>>
>>> The purpose of these connections is two-fold: by making additional
>>> low-bandwidth connections on which blocks can propagate, the robustness of a
>>> node to network partitioning attacks is strengthened.  Additionally, by not
>>> relaying transactions and ignoring received addresses, the ability of an
>>> adversary to learn the complete network graph (or a subgraph) is reduced[2],
>>> which in turn increases the cost or difficulty to an attacker seeking to carry
>>> out a network partitioning attack (when compared with having such knowledge).
>>>
>>> The low-bandwidth / minimal-resource nature of these connections is currently
>>> known only by the initiator of the connection; this is because the transaction
>>> relay field in the version message is not a permanent setting for the lifetime
>>> of the connection.  Consequently, a node receiving an inbound connection with
>>> transaction relay disabled cannot distinguish between a peer that will never
>>> enable transaction relay (as described in BIP 37) and one that will.  Moreover,
>>> the node also cannot determine that the incoming connection will ignore relayed
>>> addresses; with that knowledge a node would likely choose other peers to
>>> receive announced addresses instead.
>>>
>>> This proposal adds a new, optional message that a node can send a peer when
>>> initiating a connection to that peer, to indicate that connection should not be
>>> used for transaction-relay for the connection's lifetime. In addition, without
>>> a current mechanism to negotiate whether addresses should be relayed on a
>>> connection, this BIP suggests that address messages not be sent on links where
>>> tx-relay has been disabled.
>>>
>>> ==Specification==
>>>
>>> # A new disabletx message is added, which is defined as an empty message where pchCommand == "disabletx".
>>> # The protocol version of nodes implementing this BIP must be set to 70017 or higher.
>>> # If a node sets the transaction relay field in the version message to a peer to false, then the disabletx message MAY also be sent in response to a version message from that peer if the peer's protocol version is >= 70017. If sent, the disabletx message MUST be sent prior to sending a verack.
>>> # A node that has sent or received a disabletx message to/from a peer MUST NOT send any of these messages to the peer:
>>> ## inv messages for transactions
>>> ## getdata messages for transactions
>>> ## getdata messages for merkleblock (BIP 37)
>>> ## filteradd/filterload/filterclear (BIP 37)
>>> ## mempool (BIP 35)
>>> # It is RECOMMENDED that a node that has sent or received a disabletx message to/from a peer not send any of these messages to the peer:
>>> ## addr/getaddr
>>> ## addrv2 (BIP 155)
>>> # The behavior regarding sending or processing other message types is not specified by this BIP.
>>> # Nodes MAY decide to not remain connected to peers that send this message (for example, if trying to find a peer that will relay transactions).
>>>
>>> ==Compatibility==
>>>
>>> Nodes with protocol version >= 70017 that do not implement this BIP, and nodes
>>> with protocol version < 70017, will continue to remain compatible with
>>> implementing software: transactions would not be relayed to peers sending the
>>> disabletx message (provided that BIP 37 or BIP 60 has been implemented), and while
>>> periodic address relay may still take place, software implementing this BIP
>>> should not be disconnecting such peers solely for that reason.
>>>
>>> Disabling address relay is suggested but not required by this BIP, to allow for
>>> future protocol extensions that might specify more carefully how address relay
>>> is to be negotiated. This BIP's recommendations for software to not relay
>>> addresses is intended to be interpreted as guidance in the absence of any such
>>> future protocol extension, to accommodate existing software behavior.
>>>
>>> Note that all messages specified in BIP 152, including blocktxn and
>>> getblocktxn, are permitted between peers that have sent/received a disabletx
>>> message, subject to the feature negotiation of BIP 152.
>>>
>>> ==Implementation==
>>>
>>> TBD
>>>
>>> ==References==
>>>
>>> # Bitcoin Core has [https://github.com/bitcoin/bitcoin/pull/15759 implemented this functionality] since version 0.19.0.1, released in November 2019.
>>> # For example, see https://www.cs.umd.edu/projects/coinscope/coinscope.pdf and https://arxiv.org/pdf/1812.00942.pdf.
>>>
>>> ==Copyright==
>>>
>>> This BIP is licensed under the 2-clause BSD license.
>>>
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>>>
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