P2P - Add qfcommit message (no hexdump example)

DIP6 quorum final commitment (dashpay/dash#2477)

_autocrossref.yaml

@@ -170,6 +170,9 @@ protocol version 70012: section protocol versions
 protocol version 70013: section protocol versions
 protocol version 70014: section protocol versions
 public key infrastructure: pki
+'Quorum Commitment': quorum commitment special tx
+'`qfcommit` message': qfcommit message
+'`qfcommit` messages': qfcommit message
 '`r`': r
 receipt: DO NOT AUTOCROSSREF
 recurrent rebilling:

_config.yml

@@ -572,6 +572,7 @@ devsearches:
     - "mnw": "/en/developer-reference#mnw"
     - "mnwb": "/en/developer-reference#mnwb"
     - "ssc": "/en/developer-reference#ssc"
+    - "qfcommit": "/en/developer-reference#qfcommit"
 
     # Dash - governance
     - "govobj": "/en/developer-reference#govobj"

_includes/devdoc/ref_p2p_networking.md

@@ -3057,6 +3057,49 @@ bf110000 ................................... Count: 4543
 
 {% endautocrossref %}
 
+#### qfcommit
+{% include helpers/subhead-links.md %}
+
+{% autocrossref %}
+
+The `qfcommit` message is used to finalize a long-living masternode quorum setup
+by aggregating the information necessary to mine the on-chain Quorum Commitment
+special transaction. The message contains all the necessary information required
+to validate the long-living masternode quorum's signing results.
+
+It is possible to receive multiple valide final commitments for the same DKG
+session. These should only differ in the number of signers, which can be ignored
+as long as there are at least `quorumThreshold` number of signers. The set of
+valid members for these final commitments should always be the same, as each
+member only creates a single premature commitment. This means that only one set
+of valid members (and thus only one quorum verification vector and quorum public
+key) can gain a majority. If the threshold is not reached, there will be no
+valid final commitment.
+
+| Bytes | Name | Data type | Description |
+| --- | --- | --- | --- |
+| 2 | version | uint16_t | Version of the final commitment message
+| 1 | llmqType | uint8_t | Version of the final commitment message
+| 32 | quorumHash | uint256 | The quorum identifier
+| 1-9 | signersSize | compactSize uint | Bit size of the signers bitvector
+| (bitSize + 7) / 8 | signers | byte[] | Bitset representing the aggregated signers of this final commitment
+| 1-9 | validMembersSize | compactSize uint | Bit size of the `validMembers` bitvector
+| (bitSize + 7) / 8 | validMembers | byte[] | Bitset of valid members in this commitment
+| 48 | quorumPublicKey | BLSPubKey | The quorum public key
+| 32 | quorumVvecHash | uint256 | The hash of the quorum verification vector
+| 96 | quorumSig | BLSSig | Recovered threshold signature
+| 96 | sig | BLSSig | Aggregated BLS signatures from all included commitments
+
+<!--
+The following annotated hexdump shows a `qfcommit` message. (The
+message header has been omitted.)
+
+{% highlight text %}
+
+{% endhighlight %}
+
+-->
+{% endautocrossref %}
 
 ### Governance Messages
 {% include helpers/subhead-links.md %}

_includes/references.md

@@ -251,6 +251,7 @@ http://opensource.org/licenses/MIT.
 [notfound message]: /en/developer-reference#notfound "A P2P protocol message sent to indicate that the requested data was not available"
 [ping message]: /en/developer-reference#ping "A P2P network message used to see if the remote host is still connected"
 [pong message]: /en/developer-reference#pong "A P2P network message used to reply to a P2P network ping message"
+[qfcommit message]: /en/developer-reference#qfcommit "A P2P network message used to finalize the members of a long-living masternode quorum (LLMQ)"
 [reject message]: /en/developer-reference#reject "A P2P network message used to indicate a previously-received message was rejected for some reason"
 [sendcmpct message]: /en/developer-reference#sendcmpct "A P2P network message used to request new blocks be announced as compact blocks"
 [sendheaders message]: /en/developer-reference#sendheaders "A P2P network message used to request new blocks be announced through headers messages rather than inv messages"
@@ -458,6 +459,7 @@ http://opensource.org/licenses/MIT.
 [proupservtx special tx]: /en/developer-reference#proupservtx
 [python-bitcoinlib]: https://github.com/petertodd/python-bitcoinlib
 [python-blkmaker]: https://gitorious.org/bitcoin/python-blkmaker
+[quorum commitment special tx]: /en/developer-reference#quorum-commitment
 [Satoshi Nakamoto]: https://en.bitcoin.it/wiki/Satoshi_Nakamoto
 [setup tor]: https://www.torproject.org/
 [SHA256]: https://en.wikipedia.org/wiki/SHA-2