# README
devp2p Simulations
The p2p/simulations package implements a simulation framework which supports
creating a collection of devp2p nodes, connecting them together to form a
simulation network, performing simulation actions in that network and then
extracting useful information.
Nodes
Each node in a simulation network runs multiple services by wrapping a collection
of objects which implement the node.Service interface meaning they:
- can be started and stopped
- run p2p protocols
- expose RPC APIs
This means that any object which implements the node.Service interface can be
used to run a node in the simulation.
Services
Before running a simulation, a set of service initializers must be registered which can then be used to run nodes in the network.
A service initializer is a function with the following signature:
func(ctx *adapters.ServiceContext) (node.Service, error)
These initializers should be registered by calling the adapters.RegisterServices
function in an init() hook:
func init() {
adapters.RegisterServices(adapters.Services{
"service1": initService1,
"service2": initService2,
})
}
Node Adapters
The simulation framework includes multiple "node adapters" which are responsible for creating an environment in which a node runs.
SimAdapter
The SimAdapter runs nodes in-memory, connecting them using an in-memory,
synchronous net.Pipe and connecting to their RPC server using an in-memory
rpc.Client.
ExecAdapter
The ExecAdapter runs nodes as child processes of the running simulation.
It does this by executing the binary which is running the simulation but
setting argv[0] (i.e. the program name) to p2p-node which is then
detected by an init hook in the child process which runs the node.Service
using the devp2p node stack rather than executing main().
The nodes listen for devp2p connections and WebSocket RPC clients on random localhost ports.
DockerAdapter
The DockerAdapter is similar to the ExecAdapter but executes docker run
to run the node in a Docker container using a Docker image containing the
simulation binary at /bin/p2p-node.
The Docker image is built using docker build when the adapter is initialised,
meaning no prior setup is necessary other than having a working Docker client.
Each node listens on the external IP of the container and the default p2p and
RPC ports (30303 and 8546 respectively).
Network
A simulation network is created with an ID and default service (which is used if a node is created without an explicit service), exposes methods for creating, starting, stopping, connecting and disconnecting nodes, and emits events when certain actions occur.
Events
A simulation network emits the following events:
- node event - when nodes are created / started / stopped
- connection event - when nodes are connected / disconnected
- message event - when a protocol message is sent between two nodes
The events have a "control" flag which when set indicates that the event is the outcome of a controlled simulation action (e.g. creating a node or explicitly connecting two nodes together).
This is in contrast to a non-control event, otherwise called a "live" event, which is the outcome of something happening in the network as a result of a control event (e.g. a node actually started up or a connection was actually established between two nodes).
Live events are detected by the simulation network by subscribing to node peer events via RPC when the nodes start up.
Testing Framework
The Simulation type can be used in tests to perform actions in a simulation
network and then wait for expectations to be met.
With a running simulation network, the Simulation.Run method can be called
with a Step which has the following fields:
-
Action- a function which performs some action in the network -
Expect- an expectation function which returns whether or not a given node meets the expectation -
Trigger- a channel which receives node IDs which then trigger a check of the expectation function to be performed against that node
As a concrete example, consider a simulated network of Ethereum nodes. An
Action could be the sending of a transaction, Expect it being included in
a block, and Trigger a check for every block that is mined.
On return, the Simulation.Run method returns a StepResult which can be used
to determine if all nodes met the expectation, how long it took them to meet
the expectation and what network events were emitted during the step run.
HTTP API
The simulation framework includes a HTTP API which can be used to control the simulation.
The API is initialised with a particular node adapter and has the following endpoints:
GET / Get network information
POST /start Start all nodes in the network
POST /stop Stop all nodes in the network
GET /events Stream network events
GET /snapshot Take a network snapshot
POST /snapshot Load a network snapshot
POST /nodes Create a node
GET /nodes Get all nodes in the network
GET /nodes/:nodeid Get node information
POST /nodes/:nodeid/start Start a node
POST /nodes/:nodeid/stop Stop a node
POST /nodes/:nodeid/conn/:peerid Connect two nodes
DELETE /nodes/:nodeid/conn/:peerid Disconnect two nodes
GET /nodes/:nodeid/rpc Make RPC requests to a node via WebSocket
For convenience, nodeid in the URL can be the name of a node rather than its
ID.
Command line client
p2psim is a command line client for the HTTP API, located in
cmd/p2psim.
It provides the following commands:
p2psim show
p2psim events [--current] [--filter=FILTER]
p2psim snapshot
p2psim load
p2psim node create [--name=NAME] [--services=SERVICES] [--key=KEY]
p2psim node list
p2psim node show <node>
p2psim node start <node>
p2psim node stop <node>
p2psim node connect <node> <peer>
p2psim node disconnect <node> <peer>
p2psim node rpc <node> <method> [<args>] [--subscribe]