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coordinator.go
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coordinator.go
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package coord
import (
"context"
"errors"
"fmt"
"sync"
"time"
"github.com/benbjohnson/clock"
"github.com/plprobelab/go-kademlia/kad"
"github.com/plprobelab/go-kademlia/kaderr"
"github.com/plprobelab/go-kademlia/key"
"github.com/plprobelab/go-kademlia/network/address"
"github.com/plprobelab/go-kademlia/network/endpoint"
"github.com/plprobelab/go-kademlia/query"
"github.com/plprobelab/go-kademlia/util"
)
// A Coordinator coordinates the state machines that comprise a Kademlia DHT
// Currently this is only queries but will expand to include other state machines such as routing table refresh,
// and reproviding.
type Coordinator[K kad.Key[K], A kad.Address[A]] struct {
// self is the node id of the system the coordinator is running on
self kad.NodeID[K]
// cfg is a copy of the optional configuration supplied to the coordinator
cfg Config
qp *query.Pool[K, A]
// rt is the routing table used to look up nodes by distance
rt kad.RoutingTable[K]
// ep is the message endpoint used to send requests
ep endpoint.Endpoint[K, A]
peerstoreTTL time.Duration
outboundEvents chan KademliaEvent
inboundEvents chan coordinatorInternalEvent
startOnce sync.Once
}
const DefaultChanqueueCapacity = 1024
type Config struct {
// TODO: review if this is needed here
PeerstoreTTL time.Duration // duration for which a peer is kept in the peerstore
Clock clock.Clock // a clock that may replaced by a mock when testing
}
// Validate checks the configuration options and returns an error if any have invalid values.
func (cfg *Config) Validate() error {
if cfg.Clock == nil {
return &kaderr.ConfigurationError{
Component: "CoordinatorConfig",
Err: fmt.Errorf("clock must not be nil"),
}
}
return nil
}
func DefaultConfig() *Config {
return &Config{
Clock: clock.New(), // use standard time
PeerstoreTTL: 10 * time.Minute,
}
}
func NewCoordinator[K kad.Key[K], A kad.Address[A]](self kad.NodeID[K], ep endpoint.Endpoint[K, A], rt kad.RoutingTable[K], cfg *Config) (*Coordinator[K, A], error) {
if cfg == nil {
cfg = DefaultConfig()
} else if err := cfg.Validate(); err != nil {
return nil, err
}
qpCfg := query.DefaultPoolConfig()
qpCfg.Clock = cfg.Clock
qp, err := query.NewPool[K, A](self, qpCfg)
if err != nil {
return nil, fmt.Errorf("query pool: %w", err)
}
return &Coordinator[K, A]{
self: self,
cfg: *cfg,
ep: ep,
rt: rt,
qp: qp,
outboundEvents: make(chan KademliaEvent, 20),
inboundEvents: make(chan coordinatorInternalEvent, 20),
}, nil
}
func (c *Coordinator[K, A]) Start(ctx context.Context) <-chan KademliaEvent {
ctx, span := util.StartSpan(ctx, "Coordinator.Start")
defer span.End()
// ensure there is only ever one mainloop
c.startOnce.Do(func() {
go c.mainloop(ctx)
go c.heartbeat(ctx)
})
return c.outboundEvents
}
func (c *Coordinator[K, A]) mainloop(ctx context.Context) {
ctx, span := util.StartSpan(ctx, "Coordinator.mainloop")
defer span.End()
// once the main loop exits no further events will be sent so clients waiting
// on the event channel should be notified
defer close(c.outboundEvents)
for {
// wait for inbound events to trigger state changes
select {
case <-ctx.Done():
return
case ev := <-c.inboundEvents:
switch tev := ev.(type) {
case *eventUnroutablePeer[K]:
// TODO: remove from routing table
c.dispatchQueryPoolEvent(ctx, nil)
case *eventMessageFailed[K]:
qev := &query.EventPoolMessageFailure[K]{
QueryID: tev.QueryID,
NodeID: tev.NodeID,
Error: tev.Error,
}
c.dispatchQueryPoolEvent(ctx, qev)
case *eventMessageResponse[K, A]:
if tev.Response != nil {
candidates := tev.Response.CloserNodes()
if len(candidates) > 0 {
// ignore error here
c.AddNodes(ctx, candidates)
}
}
// notify caller so they have chance to stop query
c.outboundEvents <- &KademliaOutboundQueryProgressedEvent[K, A]{
NodeID: tev.NodeID,
QueryID: tev.QueryID,
Response: tev.Response,
Stats: tev.Stats,
}
qev := &query.EventPoolMessageResponse[K, A]{
QueryID: tev.QueryID,
NodeID: tev.NodeID,
Response: tev.Response,
}
c.dispatchQueryPoolEvent(ctx, qev)
case *eventAddQuery[K, A]:
qev := &query.EventPoolAddQuery[K, A]{
QueryID: tev.QueryID,
Target: tev.Target,
ProtocolID: tev.ProtocolID,
Message: tev.Message,
KnownClosestNodes: tev.KnownClosestPeers,
}
c.dispatchQueryPoolEvent(ctx, qev)
case *eventStopQuery[K]:
qev := &query.EventPoolStopQuery{
QueryID: tev.QueryID,
}
c.dispatchQueryPoolEvent(ctx, qev)
case *eventPoll:
c.dispatchQueryPoolEvent(ctx, nil)
default:
panic(fmt.Sprintf("unexpected event: %T", tev))
}
}
}
}
func (c *Coordinator[K, A]) heartbeat(ctx context.Context) {
ticker := c.cfg.Clock.Ticker(5 * time.Millisecond)
for {
// wait for inbound events to trigger state changes
select {
case <-ctx.Done():
return
case <-ticker.C:
c.inboundEvents <- &eventPoll{}
}
}
}
func (c *Coordinator[K, A]) dispatchQueryPoolEvent(ctx context.Context, ev query.PoolEvent) {
ctx, span := util.StartSpan(ctx, "Coordinator.dispatchQueryPoolEvent")
defer span.End()
// attempt to advance the query state machine
state := c.qp.Advance(ctx, ev)
switch st := state.(type) {
case *query.StatePoolQueryMessage[K, A]:
c.attemptSendMessage(ctx, st.ProtocolID, st.NodeID, st.Message, st.QueryID, st.Stats)
case *query.StatePoolWaitingAtCapacity:
// TODO
case *query.StatePoolWaitingWithCapacity:
// TODO
case *query.StatePoolQueryFinished:
c.outboundEvents <- &KademliaOutboundQueryFinishedEvent{
QueryID: st.QueryID,
Stats: st.Stats,
}
// TODO
case *query.StatePoolQueryTimeout:
// TODO
case *query.StatePoolIdle:
// TODO
default:
panic(fmt.Sprintf("unexpected state: %T", st))
}
}
func (c *Coordinator[K, A]) attemptSendMessage(ctx context.Context, protoID address.ProtocolID, to kad.NodeID[K], msg kad.Request[K, A], queryID query.QueryID, stats query.QueryStats) {
ctx, span := util.StartSpan(ctx, "Coordinator.attemptSendMessage")
defer span.End()
onSendError := func(ctx context.Context, err error) {
if errors.Is(err, endpoint.ErrCannotConnect) {
// here we can notify that the peer is unroutable, which would feed into peerstore and routing table
c.inboundEvents <- &eventUnroutablePeer[K]{
NodeID: to,
}
return
}
c.inboundEvents <- &eventMessageFailed[K]{
NodeID: to,
QueryID: queryID,
Stats: stats,
Error: err,
}
}
onMessageResponse := func(ctx context.Context, resp kad.Response[K, A], err error) {
if err != nil {
onSendError(ctx, err)
return
}
c.inboundEvents <- &eventMessageResponse[K, A]{
NodeID: to,
QueryID: queryID,
Response: resp,
Stats: stats,
}
}
err := c.ep.SendRequestHandleResponse(ctx, protoID, to, msg, msg.EmptyResponse(), 0, onMessageResponse)
if err != nil {
onSendError(ctx, err)
}
}
func (c *Coordinator[K, A]) StartQuery(ctx context.Context, queryID query.QueryID, protocolID address.ProtocolID, msg kad.Request[K, A]) error {
knownClosestPeers := c.rt.NearestNodes(msg.Target(), 20)
ev := &eventAddQuery[K, A]{
QueryID: queryID,
Target: msg.Target(),
ProtocolID: protocolID,
Message: msg,
KnownClosestPeers: knownClosestPeers,
}
// c.queue.Enqueue(ctx, ev)
c.inboundEvents <- ev
return nil
}
func (c *Coordinator[K, A]) StopQuery(ctx context.Context, queryID query.QueryID) error {
ev := &eventStopQuery[K]{
QueryID: queryID,
}
c.inboundEvents <- ev
return nil
}
// AddNodes suggests new DHT nodes and their associated addresses to be added to the routing table.
// If the routing table is been updated as a result of this operation a KademliaRoutingUpdatedEvent event is emitted.
func (c *Coordinator[K, A]) AddNodes(ctx context.Context, infos []kad.NodeInfo[K, A]) error {
for _, info := range infos {
if key.Equal(info.ID().Key(), c.self.Key()) {
continue
}
isNew := c.rt.AddNode(info.ID())
c.ep.MaybeAddToPeerstore(ctx, info, c.peerstoreTTL)
if isNew {
c.outboundEvents <- &KademliaRoutingUpdatedEvent[K, A]{
NodeInfo: info,
}
}
}
return nil
}
// Kademlia events emitted by the Coordinator, intended for consumption by clients of the package
type KademliaEvent interface {
kademliaEvent()
}
// KademliaOutboundQueryProgressedEvent is emitted by the coordinator when a query has received a
// response from a node.
type KademliaOutboundQueryProgressedEvent[K kad.Key[K], A kad.Address[A]] struct {
QueryID query.QueryID
NodeID kad.NodeID[K]
Response kad.Response[K, A]
Stats query.QueryStats
}
// KademliaOutboundQueryFinishedEvent is emitted by the coordinator when a query has finished, either through
// running to completion or by being canceled.
type KademliaOutboundQueryFinishedEvent struct {
QueryID query.QueryID
Stats query.QueryStats
}
// KademliaRoutingUpdatedEvent is emitted by the coordinator when a new node has been added to the routing table.
type KademliaRoutingUpdatedEvent[K kad.Key[K], A kad.Address[A]] struct {
NodeInfo kad.NodeInfo[K, A]
}
type KademliaUnroutablePeerEvent[K kad.Key[K]] struct{}
type KademliaRoutablePeerEvent[K kad.Key[K]] struct{}
// kademliaEvent() ensures that only Kademlia events can be assigned to a KademliaEvent.
func (*KademliaRoutingUpdatedEvent[K, A]) kademliaEvent() {}
func (*KademliaOutboundQueryProgressedEvent[K, A]) kademliaEvent() {}
func (*KademliaUnroutablePeerEvent[K]) kademliaEvent() {}
func (*KademliaRoutablePeerEvent[K]) kademliaEvent() {}
func (*KademliaOutboundQueryFinishedEvent) kademliaEvent() {}
// Internal events for the Coordiinator
type coordinatorInternalEvent interface {
coordinatorInternalEvent()
}
type eventUnroutablePeer[K kad.Key[K]] struct {
NodeID kad.NodeID[K]
}
type eventMessageFailed[K kad.Key[K]] struct {
NodeID kad.NodeID[K] // the node the message was sent to
QueryID query.QueryID // the id of the query that sent the message
Stats query.QueryStats // stats for the query sending the message
Error error // the error that caused the failure, if any
}
type eventMessageResponse[K kad.Key[K], A kad.Address[A]] struct {
NodeID kad.NodeID[K] // the node the message was sent to
QueryID query.QueryID // the id of the query that sent the message
Response kad.Response[K, A] // the message response sent by the node
Stats query.QueryStats // stats for the query sending the message
}
type eventAddQuery[K kad.Key[K], A kad.Address[A]] struct {
QueryID query.QueryID
Target K
ProtocolID address.ProtocolID
Message kad.Request[K, A]
KnownClosestPeers []kad.NodeID[K]
}
type eventStopQuery[K kad.Key[K]] struct {
QueryID query.QueryID
}
type eventPoll struct{}
// coordinatorInternalEvent() ensures that only an internal coordinator event can be assigned to the coordinatorInternalEvent interface.
func (*eventUnroutablePeer[K]) coordinatorInternalEvent() {}
func (*eventMessageFailed[K]) coordinatorInternalEvent() {}
func (*eventMessageResponse[K, A]) coordinatorInternalEvent() {}
func (*eventAddQuery[K, A]) coordinatorInternalEvent() {}
func (*eventStopQuery[K]) coordinatorInternalEvent() {}
func (*eventPoll) coordinatorInternalEvent() {}