4.1 KiB
P2P Multiplex Connection
MConnection
MConnection is a multiplex connection that supports multiple independent streams
with distinct quality of service guarantees atop a single TCP connection.
Each stream is known as a Channel and each Channel has a globally unique byte id.
Each Channel also has a relative priority that determines the quality of service
of the Channel compared to other Channels.
The byte id and the relative priorities of each Channel are configured upon
initialization of the connection.
The MConnection supports three packet types:
- Ping
- Pong
- Msg
Ping and Pong
The ping and pong messages consist of writing a single byte to the connection; 0x1 and 0x2, respectively.
When we haven't received any messages on an MConnection in time pingTimeout, we send a ping message.
When a ping is received on the MConnection, a pong is sent in response only if there are no other messages
to send and the peer has not sent us too many pings (TODO).
If a pong or message is not received in sufficient time after a ping, the peer is disconnected from.
Msg
Messages in channels are chopped into smaller msgPackets for multiplexing.
type msgPacket struct {
ChannelID byte
EOF byte // 1 means message ends here.
Bytes []byte
}
The msgPacket is serialized using go-wire and prefixed with 0x3.
The received Bytes of a sequential set of packets are appended together
until a packet with EOF=1 is received, then the complete serialized message
is returned for processing by the onReceive function of the corresponding channel.
Multiplexing
Messages are sent from a single sendRoutine, which loops over a select statement and results in the sending
of a ping, a pong, or a batch of data messages. The batch of data messages may include messages from multiple channels.
Message bytes are queued for sending in their respective channel, with each channel holding one unsent message at a time.
Messages are chosen for a batch one at a time from the channel with the lowest ratio of recently sent bytes to channel priority.
Sending Messages
There are two methods for sending messages:
func (m MConnection) Send(chID byte, msg interface{}) bool {}
func (m MConnection) TrySend(chID byte, msg interface{}) bool {}
Send(chID, msg) is a blocking call that waits until msg is successfully queued
for the channel with the given id byte chID. The message msg is serialized
using the tendermint/wire submodule's WriteBinary() reflection routine.
TrySend(chID, msg) is a nonblocking call that queues the message msg in the channel
with the given id byte chID if the queue is not full; otherwise it returns false immediately.
Send() and TrySend() are also exposed for each Peer.
Peer
Each peer has one MConnection instance, and includes other information such as whether the connection
was outbound, whether the connection should be recreated if it closes, various identity information about the node,
and other higher level thread-safe data used by the reactors.
Switch/Reactor
The Switch handles peer connections and exposes an API to receive incoming messages
on Reactors. Each Reactor is responsible for handling incoming messages of one
or more Channels. So while sending outgoing messages is typically performed on the peer,
incoming messages are received on the reactor.
// Declare a MyReactor reactor that handles messages on MyChannelID.
type MyReactor struct{}
func (reactor MyReactor) GetChannels() []*ChannelDescriptor {
return []*ChannelDescriptor{ChannelDescriptor{ID:MyChannelID, Priority: 1}}
}
func (reactor MyReactor) Receive(chID byte, peer *Peer, msgBytes []byte) {
r, n, err := bytes.NewBuffer(msgBytes), new(int64), new(error)
msgString := ReadString(r, n, err)
fmt.Println(msgString)
}
// Other Reactor methods omitted for brevity
...
switch := NewSwitch([]Reactor{MyReactor{}})
...
// Send a random message to all outbound connections
for _, peer := range switch.Peers().List() {
if peer.IsOutbound() {
peer.Send(MyChannelID, "Here's a random message")
}
}