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// Package proposal is chapter 12: a change pushed to a ref, numbered by the repository itself.
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package proposal
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import (
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"context"
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"fmt"
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"strconv"
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"strings"
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"github.com/barerepo/server/internal/gitx"
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// CounterRef is a ref, so update-ref makes allocation atomic and the number travels with the repo.
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const CounterRef = "refs/meta/counter"
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// maxRetries bounds the swap, where contention is two simultaneous pushes, not a herd.
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const maxRetries = 20
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// Allocate returns the next number, shared by proposals and threads, which are one object.
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func Allocate(ctx context.Context, dir string) (int, error) {
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for attempt := 0; attempt < maxRetries; attempt++ {
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oldBlob, current, err := readCounter(ctx, dir)
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if err != nil {
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return 0, err
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// Skip what is taken, because chapter 35.5 lets a push leave the counter behind.
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next := current + 1
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for taken(ctx, dir, next) {
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next++
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newBlob, err := gitx.RunStdin(ctx, dir, strconv.Itoa(next)+"\n", "hash-object", "-w", "--stdin")
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if err != nil {
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return 0, err
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newBlob = strings.TrimSpace(newBlob)
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args := []string{"update-ref", CounterRef, newBlob}
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// An empty old value means the ref must not exist, which makes the first allocation safe.
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args = append(args, oldBlob)
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if _, err := gitx.Run(ctx, dir, args...); err == nil {
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return next, nil
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// Somebody else allocated between the read and the write. Read again.
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return 0, fmt.Errorf("could not allocate a number after %d tries; too many pushes at once", maxRetries)
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// readCounter returns the counter blob and value, and a repository with neither starts at zero.
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func readCounter(ctx context.Context, dir string) (blob string, value int, err error) {
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out, err := gitx.Run(ctx, dir, "rev-parse", "--verify", "--quiet", CounterRef)
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if err != nil {
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return "", 0, nil // no counter yet
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blob = strings.TrimSpace(out)
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body, err := gitx.Run(ctx, dir, "cat-file", "blob", blob)
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if err != nil {
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// Refuse rather than restart the numbering, which threads already refer to.
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return "", 0, fmt.Errorf("%s is not readable: %w", CounterRef, err)
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value, err = strconv.Atoi(strings.TrimSpace(body))
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if err != nil {
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return "", 0, fmt.Errorf("%s does not hold a number: %q", CounterRef, strings.TrimSpace(body))
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return blob, value, nil
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func Ref(n int) string { return "refs/proposals/" + strconv.Itoa(n) }
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// RevisionRef retains old tips outside refs/proposals, where a file and directory would collide.
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func RevisionRef(n, k int) string {
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return fmt.Sprintf("refs/revisions/%d/%d", n, k)
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// CurrentRevision is the number the content on screen will take when the next force-push retains it.
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func CurrentRevision(dir string, n int) int {
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refs, err := gitx.ListRefs(dir, RevisionPrefix(n))
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if err != nil {
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return 0
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// The highest kept plus one, because pruning drops the low numbers and a count would reuse them.
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high := 0
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for name := range refs {
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k, err := strconv.Atoi(strings.TrimPrefix(name, RevisionPrefix(n)+"/"))
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if err == nil && k > high {
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high = k
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return high + 1
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// RevisionPrefix is where one proposal's retained tips live, as a ref prefix and not a glob.
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func RevisionPrefix(n int) string {
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return fmt.Sprintf("refs/revisions/%d", n)
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// RevisionGlob matches every retained revision of proposal n.
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func RevisionGlob(n int) string {
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return fmt.Sprintf("refs/revisions/%d/*", n)
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// NewRef is the magic name. It is reserved and never created.
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const NewRef = "refs/proposals/new"
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// Number reads the proposal number out of a ref name, or returns 0.
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func Number(ref string) int {
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rest, ok := strings.CutPrefix(ref, "refs/proposals/")
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if !ok {
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return 0
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}
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// refs/proposals/47 and refs/proposals/47/rev/2 both belong to 47.
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if i := strings.Index(rest, "/"); i >= 0 {
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rest = rest[:i]
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}
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n, err := strconv.Atoi(rest)
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if err != nil || n <= 0 {
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return 0
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}
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return n
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// taken reports whether a number already names a thread or a proposal.
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func taken(ctx context.Context, dir string, n int) bool {
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for _, ref := range []string{Ref(n), "refs/notes/threads/" + strconv.Itoa(n)} {
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if _, err := gitx.Run(ctx, dir, "rev-parse", "--verify", "--quiet", ref); err == nil {
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return true
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}
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}
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return false