Merge #16847: doc: add comments clarifying how local services are advertised
82e53f37e1
doc: add comments clarifying how local services are advertised (James O'Beirne) Pull request description: Recent questions have come up regarding dynamic service registration (see https://github.com/bitcoin/bitcoin/pull/16442#discussion_r308702676 and the assumeutxo project ~~which needs to dynamically flip NODE_NETWORK~~). While investigating how dynamic service registration might work, I was confused about how we convey local services to peers. This adds some documentation that hopefully clarifies this process. ACKs for top commit: laanwj: ACK82e53f37e1
darosior: ACK82e53f37e1
Tree-SHA512: a30c1020387d7a75b5b3cdde45f8b7f2ae46293da97e6227b2ee17e290b93deb5b16c0bbc2b1676972300e5c3c2ad74eb8b3910d6b93e028dac1ae2700468ef9
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eb812257a3
2 changed files with 38 additions and 2 deletions
37
src/net.h
37
src/net.h
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@ -282,6 +282,12 @@ public:
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bool DisconnectNode(const CNetAddr& addr);
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bool DisconnectNode(const CNetAddr& addr);
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bool DisconnectNode(NodeId id);
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bool DisconnectNode(NodeId id);
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//! Used to convey which local services we are offering peers during node
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//! connection.
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//!
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//! The data returned by this is used in CNode construction,
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//! which is used to advertise which services we are offering
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//! that peer during `net_processing.cpp:PushNodeVersion()`.
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ServiceFlags GetLocalServices() const;
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ServiceFlags GetLocalServices() const;
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//!set the max outbound target in bytes
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//!set the max outbound target in bytes
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@ -413,7 +419,18 @@ private:
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std::atomic<NodeId> nLastNodeId{0};
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std::atomic<NodeId> nLastNodeId{0};
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unsigned int nPrevNodeCount{0};
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unsigned int nPrevNodeCount{0};
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/** Services this instance offers */
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/**
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* Services this instance offers.
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*
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* This data is replicated in each CNode instance we create during peer
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* connection (in ConnectNode()) under a member also called
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* nLocalServices.
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*
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* This data is not marked const, but after being set it should not
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* change. See the note in CNode::nLocalServices documentation.
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*
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* \sa CNode::nLocalServices
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*/
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ServiceFlags nLocalServices;
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ServiceFlags nLocalServices;
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std::unique_ptr<CSemaphore> semOutbound;
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std::unique_ptr<CSemaphore> semOutbound;
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@ -786,8 +803,24 @@ public:
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private:
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private:
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const NodeId id;
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const NodeId id;
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const uint64_t nLocalHostNonce;
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const uint64_t nLocalHostNonce;
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// Services offered to this peer
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//! Services offered to this peer.
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//!
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//! This is supplied by the parent CConnman during peer connection
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//! (CConnman::ConnectNode()) from its attribute of the same name.
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//!
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//! This is const because there is no protocol defined for renegotiating
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//! services initially offered to a peer. The set of local services we
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//! offer should not change after initialization.
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//!
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//! An interesting example of this is NODE_NETWORK and initial block
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//! download: a node which starts up from scratch doesn't have any blocks
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//! to serve, but still advertises NODE_NETWORK because it will eventually
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//! fulfill this role after IBD completes. P2P code is written in such a
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//! way that it can gracefully handle peers who don't make good on their
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//! service advertisements.
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const ServiceFlags nLocalServices;
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const ServiceFlags nLocalServices;
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const int nMyStartingHeight;
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const int nMyStartingHeight;
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int nSendVersion{0};
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int nSendVersion{0};
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NetPermissionFlags m_permissionFlags{ PF_NONE };
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NetPermissionFlags m_permissionFlags{ PF_NONE };
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@ -415,6 +415,9 @@ static void UpdatePreferredDownload(CNode* node, CNodeState* state) EXCLUSIVE_LO
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static void PushNodeVersion(CNode *pnode, CConnman* connman, int64_t nTime)
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static void PushNodeVersion(CNode *pnode, CConnman* connman, int64_t nTime)
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{
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{
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// Note that pnode->GetLocalServices() is a reflection of the local
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// services we were offering when the CNode object was created for this
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// peer.
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ServiceFlags nLocalNodeServices = pnode->GetLocalServices();
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ServiceFlags nLocalNodeServices = pnode->GetLocalServices();
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uint64_t nonce = pnode->GetLocalNonce();
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uint64_t nonce = pnode->GetLocalNonce();
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int nNodeStartingHeight = pnode->GetMyStartingHeight();
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int nNodeStartingHeight = pnode->GetMyStartingHeight();
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