mirror of https://github.com/status-im/consul.git
74 lines
2.3 KiB
Go
74 lines
2.3 KiB
Go
// Copyright (c) HashiCorp, Inc.
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// SPDX-License-Identifier: BUSL-1.1
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package submatview
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import (
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"github.com/hashicorp/consul/proto/private/pbsubscribe"
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)
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// eventHandler is a function which performs some operation on the received
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// events, then returns the eventHandler that should be used for the next set
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// of events.
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// If eventHandler fails to handle the events it may return an error. If an
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// error is returned the next eventHandler will be ignored.
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// eventHandler is used to implement a very simple finite-state machine.
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type eventHandler func(state viewState, events *pbsubscribe.Event) (next eventHandler, err error)
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type viewState interface {
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updateView(events []*pbsubscribe.Event, index uint64) error
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reset()
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}
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func initialHandler(index uint64) eventHandler {
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if index == 0 {
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return newSnapshotHandler()
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}
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return resumeStreamHandler
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}
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// snapshotHandler accumulates events. When it receives an EndOfSnapshot event
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// it updates the view, and then returns eventStreamHandler to handle new events.
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type snapshotHandler struct {
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events []*pbsubscribe.Event
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}
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func newSnapshotHandler() eventHandler {
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return (&snapshotHandler{}).handle
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}
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func (h *snapshotHandler) handle(state viewState, event *pbsubscribe.Event) (eventHandler, error) {
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if event.GetEndOfSnapshot() {
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err := state.updateView(h.events, event.Index)
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return eventStreamHandler, err
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}
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h.events = append(h.events, eventsFromEvent(event)...)
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return h.handle, nil
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}
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// eventStreamHandler handles events by updating the view. It always returns
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// itself as the next handler.
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func eventStreamHandler(state viewState, event *pbsubscribe.Event) (eventHandler, error) {
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err := state.updateView(eventsFromEvent(event), event.Index)
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return eventStreamHandler, err
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}
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func eventsFromEvent(event *pbsubscribe.Event) []*pbsubscribe.Event {
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if batch := event.GetEventBatch(); batch != nil {
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return batch.Events
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}
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return []*pbsubscribe.Event{event}
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}
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// resumeStreamHandler checks if the event is a NewSnapshotToFollow event. If it
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// is it resets the view and returns a snapshotHandler to handle the next event.
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// Otherwise it uses eventStreamHandler to handle events.
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func resumeStreamHandler(state viewState, event *pbsubscribe.Event) (eventHandler, error) {
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if event.GetNewSnapshotToFollow() {
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state.reset()
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return newSnapshotHandler(), nil
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}
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return eventStreamHandler(state, event)
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}
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