Ask mesh-delivery whether a merge's group still assembles (hq issue 525)
A merge from any head waited for the window because the controller could not see a group's members, so the window skip changed nothing in production and unrelated merges walked one after another. The controller now asks mesh-delivery's groups, within 3 s and before the plans are held: a merge waits only when its head's group has another member whose pull request is open and whose merge it does not keep yet (ADR 0306 §2). No answer means it waits, and its batch says why. A headed merge in no waiting group and related to no batch is cut at once, as one from no head is (ADR 0304 §1, ADR 0306 §3). The controller's grant names mesh-delivery.groups. The installer's first user list in mesh-host must carry it too before the genesis test can pass.
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package main
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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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"strings"
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"time"
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"github.com/novox/mesh-controller/internal/catalogue"
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"github.com/novox/mesh-controller/internal/inventory"
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"github.com/novox/mesh-controller/internal/link"
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)
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// **A delivery group still assembles** (novox/hq ADR 0306 decision 2): a merge whose delivery group has a member
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// not yet merged waits for the merge window, whether or not a batch is assembling, so the group's members walk in
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// one batch, in their order (ADR 0276 decision 5). Which groups exist and where each member stands is
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// mesh-delivery's record (ADR 0239): a group is the pull requests of two repositories or more sharing a head
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// branch name, which is its id. The controller asks it, through its `groups` verb, when a merge from a head is
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// heard; a member whose pull request is open (proposed, checked, ready or rejected) is still to merge. When
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// mesh-delivery does not answer within groupAskWithin, or answers something unreadable, the merge waits: the safe
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// error is to wait, and its batch says why.
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// groupAskWithin is how long mesh-delivery is given to say a merge's group, while the merge is being heard.
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var groupAskWithin = 3 * time.Second
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// openPullStates are the states of a delivery whose pull request is open and not merged (mesh-delivery's table):
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// a member in one of them is still to merge. Closed unmerged is stopped, final, and waits for nothing.
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var openPullStates = map[string]bool{"proposed": true, "checked": true, "ready": true, "rejected": true}
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// groupMember is one member of a delivery group as mesh-delivery's `groups` says it: `<owner/repo>@<commit> (state)`.
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type groupMember struct {
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Repository, State string
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}
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// deliveryGroupOf is what mesh-delivery says of the group a head names: its members, and whether the head names a
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// group at all; an error when it cannot be asked or did not answer. A seam a test replaces.
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var deliveryGroupOf = func(ctx context.Context, held bool, head string) ([]groupMember, bool, error) {
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if !held {
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return nil, false, fmt.Errorf("no holder of %s is on record to say it", catalogue.DeliverySeat)
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}
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serving := servingBus.Load()
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if serving == nil {
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return nil, false, errors.New("this controller is not on the bus")
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}
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asking, cancel := context.WithTimeout(ctx, groupAskWithin)
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defer cancel()
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raw, err := askDeliveryOwner(asking, serving.Conn(), "groups", map[string]any{})
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if err != nil {
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if errors.Is(err, link.ErrNothingServes) {
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return nil, false, fmt.Errorf("nothing serves %s.groups", catalogue.DeliverySeat)
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}
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return nil, false, err
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}
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var lines []struct {
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ID string `json:"id"`
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Members []string `json:"members"`
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}
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if err := json.Unmarshal(raw, &lines); err != nil {
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return nil, false, fmt.Errorf("%s.groups answered something unreadable: %w", catalogue.DeliverySeat, err)
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}
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for _, l := range lines {
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if l.ID != head {
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continue
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}
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var members []groupMember
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for _, s := range l.Members {
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members = append(members, memberOf(s))
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}
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return members, true, nil
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}
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return nil, false, nil
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}
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// memberOf reads one member as `groups` says it: `novox/mesh-sdk@d41d255f28ad (held)`.
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func memberOf(s string) groupMember {
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id, state := strings.TrimSpace(s), ""
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if i := strings.LastIndex(id, " ("); i >= 0 && strings.HasSuffix(id, ")") {
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id, state = id[:i], id[i+2:len(id)-1]
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}
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repository, _, _ := strings.Cut(id, "@")
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return groupMember{Repository: repository, State: state}
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}
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// groupWait says whether a merge heard now waits for the window for its delivery group, and why in words; nothing
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// when it names no head, its head names no group, or every other member is merged or closed. A member of another
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// repository whose merge this controller already keeps in a batch not yet cut is merged, whatever mesh-delivery
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// says yet (it marks a member merged once its walk opened). Asked before the plans are held: a slow answer holds
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// up no walk.
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func groupWait(ctx context.Context, inv *inventory.Inventory, m link.SourceMoved, held bool) (string, error) {
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if m.Head == "" {
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return "", nil
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}
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members, isGroup, err := deliveryGroupOf(ctx, held, m.Head)
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if err != nil {
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return fmt.Sprintf("%s did not say whether group %s has a member still to merge (%v): it waits for the "+
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"window, the safe side", catalogue.DeliverySeat, m.Head, err), nil
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}
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if !isGroup {
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return "", nil
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}
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kept, err := keptFromHead(ctx, inv, m.Head)
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if err != nil {
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return "", err
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}
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var open []string
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for _, g := range members {
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if strings.EqualFold(g.Repository, m.Owner+"/"+m.Repo) || kept[strings.ToLower(g.Repository)] ||
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!openPullStates[g.State] {
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continue
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}
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open = append(open, g.Repository+" ("+g.State+")")
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}
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if len(open) == 0 {
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return "", nil
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}
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return "group " + m.Head + " has a member still to merge: " + strings.Join(open, ", "), nil
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}
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// keptFromHead are the repositories (lower case) of the merges from a head that batches not yet cut hold.
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func keptFromHead(ctx context.Context, inv *inventory.Inventory, head string) (map[string]bool, error) {
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batches, err := inv.Batches(ctx)
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if err != nil {
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return nil, err
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}
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out := map[string]bool{}
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for _, b := range batches {
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merges, err := inv.MergesOf(ctx, b.ID)
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if err != nil {
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return nil, err
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}
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for _, k := range merges {
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if announcedOf(k).Head == head {
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out[strings.ToLower(k.Repository)] = true
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}
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}
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}
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return out, nil
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}
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