287 lines
10 KiB
Go
287 lines
10 KiB
Go
package views
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import (
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"context"
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"encoding/json"
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"errors"
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"fmt"
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"time"
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"github.com/nats-io/nats.go"
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"github.com/nats-io/nats.go/jetstream"
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)
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// Emitter is an owner's process saying each change of its own states on its views family (ADR 0615 §5): it follows
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// each state it is given from the revision its mark says it said up to, publishes one Event per change, and writes the
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// mark once it has said every change the bus had handed it. A part watches only its own state (ADR 0596 §4): an owner
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// follows its own buckets, never another's.
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type Emitter struct {
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// Owner is the owner module, said in every event.
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Owner string
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// Subject is where an event of the given local name lands: the owner's ordinary event (process.Account.EventSubject).
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Subject func(event string) string
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// Publish sends one message to the shared events stream, its id the bus's dedup id (JetStreamPublish).
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Publish func(ctx context.Context, msg *nats.Msg, id string) error
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// Marks is the owner's state MarksState; nil says nothing is marked, and every start says from the bucket's end.
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Marks jetstream.KeyValue
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// TooLarge is told of a value too large for an event (said as a gap): the owner's finding naming the key. Nil
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// only logs it.
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TooLarge func(state, key string, size int)
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// Findings writes and clears the owner's finding of a change not said past UnsaidAfter (UnsaidKind, its own state
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// `findings`); nil says it in the log only.
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Findings FindingWriter
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// UnsaidAfter is how long a change may stay not said before it is the owner's finding; zero is Bound.
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UnsaidAfter time.Duration
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// Wait pauses before a change not said is said again (its attempt so far); it answers false when ctx ended. Nil is
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// a backoff from 250 ms doubling to 30 s.
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Wait func(ctx context.Context, attempt int) bool
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Logf func(string, ...any)
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Now func() time.Time
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}
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// JetStreamPublish is Emitter.Publish through js, with the bus's dedup id.
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func JetStreamPublish(js jetstream.JetStream) func(context.Context, *nats.Msg, string) error {
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return func(ctx context.Context, msg *nats.Msg, id string) error {
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pub, cancel := context.WithTimeout(context.WithoutCancel(ctx), 10*time.Second)
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defer cancel()
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_, err := js.PublishMsg(pub, msg, jetstream.WithMsgID(id))
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return err
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}
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}
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func (e Emitter) now() time.Time {
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if e.Now != nil {
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return e.Now().UTC()
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}
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return time.Now().UTC()
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}
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func (e Emitter) logf(format string, args ...any) {
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if e.Logf != nil {
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e.Logf(format, args...)
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}
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}
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// created is when the bucket's stream was made, and its fill now.
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func created(ctx context.Context, kv jetstream.KeyValue) (time.Time, uint64, Fill, error) {
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st, err := kv.Status(ctx)
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if err != nil {
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return time.Time{}, 0, Fill{}, err
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}
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b, ok := st.(*jetstream.KeyValueBucketStatus)
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if !ok || b.StreamInfo() == nil {
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return time.Time{}, 0, Fill{}, fmt.Errorf("the bus answered no stream behind %s", st.Bucket())
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}
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info := b.StreamInfo()
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return info.Created.UTC(), info.State.LastSeq, Fill{Keys: uint64(info.State.NumSubjects), Bytes: info.State.Bytes, MaxBytes: info.Config.MaxBytes}, nil
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}
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// Start follows state's bucket kv: from the revision after its mark when the mark is of the same bucket (the same
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// Created), otherwise from the bucket's end, writing a mark there first, so a reader's first view taken now misses
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// nothing. It returns once the watch is set; the changes are said on a goroutine until ctx ends, and a watch that ends
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// is sent on errs.
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func (e Emitter) Start(ctx context.Context, state string, kv jetstream.KeyValue, errs chan<- error) error {
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made, last, fill, err := created(ctx, kv)
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if err != nil {
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return fmt.Errorf("the state %s cannot be followed for its views: %w", state, err)
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}
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from := last + 1
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if m, ok := e.mark(ctx, state); ok && m.Created.Equal(made) && m.Revision <= last {
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from = m.Revision + 1
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} else {
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e.writeMark(ctx, state, Mark{State: state, Revision: last, Created: made, Fill: fill})
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}
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w, err := kv.WatchAll(ctx, jetstream.ResumeFromRevision(from))
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if err != nil {
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return fmt.Errorf("the state %s cannot be watched for its views: %w", state, err)
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}
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fillNow := func() (Fill, error) {
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_, _, fill, err := created(ctx, kv)
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return fill, err
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}
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go func() {
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defer w.Stop()
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e.follow(ctx, state, made, w.Updates(), fillNow, errs)
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}()
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return nil
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}
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// follow says each change handed on updates in order, and marks once every change handed so far is said. A change
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// that fails to be said is said again, the same change on a backoff (Wait), until it is said or ctx ends: the mark
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// never moves past a change not said, so no reader misses one (design 25 §12.2).
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func (e Emitter) follow(ctx context.Context, state string, made time.Time, updates <-chan jetstream.KeyValueEntry, fillNow func() (Fill, error), errs chan<- error) {
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said := uint64(0)
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raised := false
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// A finding a run before this one raised is not known to this one: the first change said clears it once, so a
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// restart never leaves it standing (the finding is about the state, its key the same).
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leftover := e.Findings != nil
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for {
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select {
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case <-ctx.Done():
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return
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case u, ok := <-updates:
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if !ok {
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if errs != nil {
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errs <- fmt.Errorf("the watch of %s for its views ended", state)
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}
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return
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}
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if u != nil {
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var first time.Time
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for attempt := 1; ; attempt++ {
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err := e.say(ctx, state, made, u)
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if err == nil {
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break
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}
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e.logf("views: %s.%s at %d is not said (try %d): %v; said again before the next change", state, u.Key(), u.Revision(), attempt, err)
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if first.IsZero() {
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first = e.now()
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}
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if !raised && e.now().Sub(first) >= e.unsaidAfter() {
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raised = e.raiseUnsaid(state, u, first, err)
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}
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if !e.wait(ctx, attempt) {
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// Not marked: the next start says it again from the mark, and the bus keeps it once by its id.
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return
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}
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}
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if raised || leftover {
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raised = !e.clearUnsaid(state)
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leftover = false
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}
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said = u.Revision()
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}
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// Marked once every change handed so far is said, so a busy state writes one mark per burst.
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if said > 0 && len(updates) == 0 {
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fill, err := fillNow()
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if err != nil {
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e.logf("views: the fill of %s is not read: %v", state, err)
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}
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e.writeMark(ctx, state, Mark{State: state, Revision: said, Created: made, Fill: fill})
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said = 0
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}
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}
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}
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}
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func (e Emitter) unsaidAfter() time.Duration {
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if e.UnsaidAfter > 0 {
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return e.UnsaidAfter
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}
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return Bound
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}
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// raiseUnsaid writes the owner's finding of u not said since first; it answers whether the finding stands.
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func (e Emitter) raiseUnsaid(state string, u jetstream.KeyValueEntry, first time.Time, cause error) bool {
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e.logf("views: %s.%s at %d is not said since %s: the owner's finding %s", state, u.Key(), u.Revision(), first.Format(time.RFC3339), UnsaidKind)
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if e.Findings == nil {
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return false
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}
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if err := e.Findings.Put(UnsaidFinding(e.Owner, state, u.Key(), u.Revision(), first, cause.Error(), e.now())); err != nil {
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e.logf("views: the finding of %s's change not said could not be written: %v", state, err)
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return false
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}
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return true
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}
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// clearUnsaid clears the finding once the change is said; it answers whether it is cleared.
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func (e Emitter) clearUnsaid(state string) bool {
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if err := e.Findings.Delete(UnsaidFinding(e.Owner, state, "", 0, time.Time{}, "", e.now())); err != nil {
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e.logf("views: the finding of %s's change not said could not be cleared: %v", state, err)
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return false
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}
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return true
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}
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// wait is the pause before the attempt+1'th try of a change not said: Wait when given, else a backoff from 250 ms
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// doubling to 30 s. It answers false once ctx ends.
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func (e Emitter) wait(ctx context.Context, attempt int) bool {
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if e.Wait != nil {
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return e.Wait(ctx, attempt)
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}
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d := 250 * time.Millisecond
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for i := 1; i < attempt && d < 30*time.Second; i++ {
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d *= 2
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}
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d = min(d, 30*time.Second)
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t := time.NewTimer(d)
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defer t.Stop()
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select {
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case <-ctx.Done():
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return false
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case <-t.C:
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return true
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}
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}
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// Event is the event saying u, a change of state made at made.
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func (e Emitter) Event(state string, made time.Time, u jetstream.KeyValueEntry) Event {
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ev := Event{V: Version, Owner: e.Owner, State: state, Key: u.Key(), Revision: u.Revision(), Created: made, At: u.Created().UTC()}
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if u.Operation() != jetstream.KeyValuePut {
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ev.Deleted = true
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return ev
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}
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if n := len(u.Value()); n > MaxValueBytes {
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ev.Gap = true
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e.logf("views: %s.%s at %d holds %d bytes, more than an event carries: said as a gap, so a reader asks its first view", state, u.Key(), u.Revision(), n)
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if e.TooLarge != nil {
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e.TooLarge(state, u.Key(), n)
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}
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return ev
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}
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ev.Value = json.RawMessage(u.Value())
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if !json.Valid(ev.Value) {
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ev.Value, _ = json.Marshal(string(u.Value()))
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}
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return ev
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}
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func (e Emitter) say(ctx context.Context, state string, made time.Time, u jetstream.KeyValueEntry) error {
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ev := e.Event(state, made, u)
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data, err := ev.Encode()
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if err != nil {
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return err
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}
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msg := nats.NewMsg(e.Subject(EventName(state)))
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msg.Header.Set("x-event-id", ev.ID())
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msg.Header.Set("x-source", e.Owner)
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msg.Header.Set("x-time", e.now().Format(time.RFC3339Nano))
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msg.Header.Set("content-type", "application/json")
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msg.Data = data
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return e.Publish(ctx, msg, ev.ID())
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}
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func (e Emitter) mark(ctx context.Context, state string) (Mark, bool) {
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if e.Marks == nil {
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return Mark{}, false
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}
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got, err := e.Marks.Get(ctx, state)
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if err != nil {
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if !errors.Is(err, jetstream.ErrKeyNotFound) {
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e.logf("views: the mark of %s is not read (%v): said from the bucket's end", state, err)
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}
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return Mark{}, false
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}
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m, err := DecodeMark(got.Value())
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if err != nil {
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e.logf("views: the mark of %s is not read (%v): said from the bucket's end", state, err)
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return Mark{}, false
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}
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return m, true
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}
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func (e Emitter) writeMark(ctx context.Context, state string, m Mark) {
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if e.Marks == nil {
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return
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}
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m.V, m.At = Version, e.now()
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data, err := json.Marshal(m)
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if err != nil {
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e.logf("views: the mark of %s is not written: %v", state, err)
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return
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}
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if _, err := e.Marks.Put(ctx, state, data); err != nil {
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e.logf("views: the mark of %s at %d is not written (%v): a first view answers the one before", state, m.Revision, err)
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}
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}
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