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+# Hacking on I2PD
+
+This document contains notes compiled from hacking on i2pd
+
+## prerequisites
+
+This guide assumes:
+
+* a decent understanding of c++ 
+* basic understanding of how i2p works at i2np level and up
+
+## general structure
+
+Notes on multithreading
+
+* every compontent runs in its own thread 
+
+* each component (usually) has a public function `GetService()` which can be used to obtain the `boost::asio::io_service` that it uses.
+
+* when talking between components/threads, **always** use `GetService().post()` and be mindfull of stack allocated memory.
+
+
+### NetDb
+
+#### NetDb.h
+
+The `i2p::data::netdb` is a `i2p::data::NetDb` instance processes and dispatches *inbound* i2np messages passed in from transports.
+
+global singleton at `i2p::data::netdb` as of 2.10.1
+
+#### NetDbRequests.h
+
+For Pending RouterInfo/LeaseSet lookup and store requests
+
+
+### ClientContext 
+
+#### ClientContext.h
+
+`i2p::client::ClientContext` spawns all destinations used by the i2p router including the shared local destination.
+
+global singleton at `i2p::client::context` as of 2.10.1
+
+
+
+### Daemon
+
+File: Daemon.cpp
+
+`i2p::util::Daemon_Singleton_Private` subclasses implement the daemon start-up and tear-down, creates Http Webui and i2p control server.
+
+
+
+
+### Destinations
+
+#### Destination.h
+
+each destination runs in its own thread
+
+##### i2p::client::LeaseSetDestination
+
+Base for `i2p::client::ClientDestination`
+
+##### i2p::client::ClientDestination
+
+Destination capable of creating (tcp/i2p) streams and datagram sessions.
+
+
+#### Streaming.h
+
+##### i2p::stream::StreamingDestination
+
+Does not implement any destination related members, the name is a bit misleading.
+
+Owns a `i2p::client::ClientDestination` and runs in the destination thread.
+
+Anyone creating or using streams outside of the destination thread **MUST** be aware of the consequences of multithreaded c++ :^)
+
+If you use streaming please consider running all code within the destination thread using `ClientDestination::GetService().post()`
+
+
+#### Garlic.h
+
+Provides Inter-Destination routing primatives.
+
+##### i2p::garlic::GarlicDestination
+
+sublcass of `i2p::client::LeaseSetDestination` for sending messages down shared routing paths.
+
+##### i2p::garlic::GarlicRoutingSession
+
+a point to point conversation between us and 1 other destination.
+
+##### i2p::garlic::GarlicRoutingPath
+
+A routing path currently used by a routing session. specifies which outbound tunnel to use and which remote lease set to use for `OBEP` to `IBGW` inter tunnel communication.
+
+members:
+
+* outboundTunnel (OBEP)
+* remoteLease (IBGW)
+* rtt (round trip time)
+* updatedTime (last time this path's IBGW/OBEP was updated)
+* numTimesUsesd (number of times this path was used)
+
+### Transports
+
+each transport runs in its own thread
+
+#### Transports.h
+
+`i2p::transport::Transports` contains NTCP and SSU transport instances