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authorJames O'Beirne <james.obeirne@gmail.com>2019-09-10 13:09:12 -0400
committerJames O'Beirne <james.obeirne@gmail.com>2019-09-11 10:24:44 -0400
commit82e53f37e1bfa6e34eac16b33329d70c3c0127da (patch)
treef65e290eca64080b3e33370f37b26eebcff4c031 /src/net.h
parent1985c4efda56b48f6f9c04f39d69268ee8f0b40a (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/net.h')
-rw-r--r--src/net.h37
1 files changed, 35 insertions, 2 deletions
diff --git a/src/net.h b/src/net.h
index e9ea0162c9..f33147155a 100644
--- a/src/net.h
+++ b/src/net.h
@@ -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 };