diff options
author | James O'Beirne <james.obeirne@gmail.com> | 2019-09-10 13:09:12 -0400 |
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committer | James O'Beirne <james.obeirne@gmail.com> | 2019-09-11 10:24:44 -0400 |
commit | 82e53f37e1bfa6e34eac16b33329d70c3c0127da (patch) | |
tree | f65e290eca64080b3e33370f37b26eebcff4c031 /src | |
parent | 1985c4efda56b48f6f9c04f39d69268ee8f0b40a (diff) |
doc: add comments clarifying how local services are advertised
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.
Diffstat (limited to 'src')
-rw-r--r-- | src/net.h | 37 | ||||
-rw-r--r-- | src/net_processing.cpp | 3 |
2 files changed, 38 insertions, 2 deletions
@@ -282,6 +282,12 @@ public: bool DisconnectNode(const CNetAddr& addr); bool DisconnectNode(NodeId id); + //! Used to convey which local services we are offering peers during node + //! connection. + //! + //! The data returned by this is used in CNode construction, + //! which is used to advertise which services we are offering + //! that peer during `net_processing.cpp:PushNodeVersion()`. ServiceFlags GetLocalServices() const; //!set the max outbound target in bytes @@ -413,7 +419,18 @@ private: std::atomic<NodeId> nLastNodeId{0}; unsigned int nPrevNodeCount{0}; - /** Services this instance offers */ + /** + * Services this instance offers. + * + * This data is replicated in each CNode instance we create during peer + * connection (in ConnectNode()) under a member also called + * nLocalServices. + * + * This data is not marked const, but after being set it should not + * change. See the note in CNode::nLocalServices documentation. + * + * \sa CNode::nLocalServices + */ ServiceFlags nLocalServices; std::unique_ptr<CSemaphore> semOutbound; @@ -786,8 +803,24 @@ public: private: const NodeId id; const uint64_t nLocalHostNonce; - // Services offered to this peer + + //! Services offered to this peer. + //! + //! This is supplied by the parent CConnman during peer connection + //! (CConnman::ConnectNode()) from its attribute of the same name. + //! + //! This is const because there is no protocol defined for renegotiating + //! services initially offered to a peer. The set of local services we + //! offer should not change after initialization. + //! + //! An interesting example of this is NODE_NETWORK and initial block + //! download: a node which starts up from scratch doesn't have any blocks + //! to serve, but still advertises NODE_NETWORK because it will eventually + //! fulfill this role after IBD completes. P2P code is written in such a + //! way that it can gracefully handle peers who don't make good on their + //! service advertisements. const ServiceFlags nLocalServices; + const int nMyStartingHeight; int nSendVersion{0}; NetPermissionFlags m_permissionFlags{ PF_NONE }; diff --git a/src/net_processing.cpp b/src/net_processing.cpp index 7f2fea5584..93a98974eb 100644 --- a/src/net_processing.cpp +++ b/src/net_processing.cpp @@ -415,6 +415,9 @@ static void UpdatePreferredDownload(CNode* node, CNodeState* state) EXCLUSIVE_LO static void PushNodeVersion(CNode *pnode, CConnman* connman, int64_t nTime) { + // Note that pnode->GetLocalServices() is a reflection of the local + // services we were offering when the CNode object was created for this + // peer. ServiceFlags nLocalNodeServices = pnode->GetLocalServices(); uint64_t nonce = pnode->GetLocalNonce(); int nNodeStartingHeight = pnode->GetMyStartingHeight(); |