mirror Discord deletions to X and bluesky

Deleting a message on the watched channel now deletes the posts it
produced. Making that possible reshapes how a message reaches an output:

  - OutputInterface takes an output.Post and returns an output.Ref, the
    identifier the platform gave the new post (tweet ID for X, URI and
    CID for bluesky). It also gained Delete(Ref).
  - The discord package no longer forwards raw MessageCreate values but
    a discord.Event carrying the kind of change, so the MessageDelete
    handler can use the same channel. Deleted messages arrive without an
    author, so only the channel ID can be filtered on.
  - The new store package remembers Discord message ID -> per output Ref.
    Set POST_STORE to a path to keep that mapping across restarts;
    without it the mapping is memory only and a restart makes older
    messages undeletable. It holds the most recent 1000 messages.

main.go grows a distributor type to hold the outputs and the store
rather than threading them through the event loop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

discord/discordread.go

@@ -6,34 +6,69 @@ import (
 	"github.com/bwmarrin/discordgo"
 )
 
-type discord struct {
+// EventKind tells apart the things that can happen to a watched message.
+type EventKind int
+
+const (
+	MessageCreated EventKind = iota
+	MessageDeleted
+)
+
+// Event is a change on the watched channel that the distributor has to mirror.
+type Event struct {
+	Kind        EventKind
+	MessageID   string
+	Content     string
+	Attachments []*discordgo.MessageAttachment
+}
+
+type Client struct {
 	Token     string
 	ChannelID string
 	dgsession *discordgo.Session
 }
 
-func Discord(token string, channelId string) *discord {
+func Discord(token string, channelId string) *Client {
-	return &discord{
+	return &Client{
 		Token:     token,
 		ChannelID: channelId,
 	}
 }
 
-func (d *discord) BeginRead(tweetchannel chan<- *discordgo.MessageCreate) {
+func (d *Client) BeginRead(eventchannel chan<- Event) {
-	d.read(tweetchannel)
+	d.read(eventchannel)
 }
 
-func (d *discord) read(tweetchannel chan<- *discordgo.MessageCreate) {
+func (d *Client) read(eventchannel chan<- Event) {
 	dgsession, err := discordgo.New("Bot " + d.Token)
 	if err != nil {
 		return
 	}
 
 	dgsession.AddHandler(func(s *discordgo.Session, m *discordgo.MessageCreate) {
-		if m.ChannelID == d.ChannelID && m.Author.ID != s.State.User.ID {
+		if m.ChannelID != d.ChannelID || m.Author.ID == s.State.User.ID {
-			tweetchannel <- m
+			return
+		}
+		eventchannel <- Event{
+			Kind:        MessageCreated,
+			MessageID:   m.ID,
+			Content:     m.Content,
+			Attachments: m.Attachments,
 		}
 	})
+
+	// Deleted messages arrive without an author, so the channel is the only
+	// thing to filter on; messages we never distributed are dropped later.
+	dgsession.AddHandler(func(s *discordgo.Session, m *discordgo.MessageDelete) {
+		if m.ChannelID != d.ChannelID {
+			return
+		}
+		eventchannel <- Event{
+			Kind:      MessageDeleted,
+			MessageID: m.ID,
+		}
+	})
+
 	d.dgsession = dgsession
 
 	errOpen := dgsession.Open()
@@ -45,6 +80,6 @@ func Read() string {
 	return "discord"
 }
 
-func (d *discord) Write(str string) {
+func (d *Client) Write(str string) {
 	d.dgsession.ChannelMessageSend(d.ChannelID, str)
 }

go.sum

@@ -0,0 +1,228 @@
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main.go

@@ -14,6 +14,7 @@ import (
 	"strings"
 	"tweetdistributor/discord"
 	"tweetdistributor/output"
+	"tweetdistributor/store"
 	"unicode/utf8"
 
 	"github.com/bwmarrin/discordgo"
@@ -99,11 +100,91 @@ func downloadImages(attachments []*discordgo.MessageAttachment) ([]output.Image,
 	return images, nil
 }
 
+// distributor mirrors what happens on the Discord channel to every output.
+type distributor struct {
+	d       *discord.Client
+	outputs []output.OutputInterface
+	store   *store.Store
+}
+
+// reportf logs an error and echoes it back into the Discord channel.
+func (dist *distributor) reportf(format string, args ...any) {
+	errstr := fmt.Sprintf(format, args...)
+	fmt.Fprintln(os.Stderr, errstr)
+	dist.d.Write(errstr)
+}
+
+// created posts a new Discord message to every output.
+func (dist *distributor) created(event discord.Event) {
+	if length := utf8.RuneCountInString(event.Content); length > maxTweetLength {
+		dist.reportf("Error: message is %d characters, exceeding the %d character limit; not posted", length, maxTweetLength)
+		return
+	}
+
+	images, err := downloadImages(event.Attachments)
+	if err != nil {
+		dist.reportf("Error: %s; not posted", err)
+		return
+	}
+	if len(images) > maxImagesPerPost {
+		dist.reportf("Error: %d images attached, exceeding the limit of %d; not posted", len(images), maxImagesPerPost)
+		return
+	}
+
+	refs := store.Refs{}
+	for _, out := range dist.outputs {
+		ref, err := out.Write(output.Post{
+			Text:   event.Content,
+			Images: images,
+		})
+		if err != nil {
+			dist.reportf("%s Error: %s", out.GetName(), err)
+			continue
+		}
+		refs[out.GetName()] = ref
+	}
+
+	if len(refs) == 0 {
+		return
+	}
+	if err := dist.store.Put(event.MessageID, refs); err != nil {
+		dist.reportf("Error: could not remember the posts for this message: %s", err)
+	}
+}
+
+// deleted removes the posts that a now deleted Discord message produced.
+func (dist *distributor) deleted(event discord.Event) {
+	refs, ok := dist.store.Get(event.MessageID)
+	if !ok {
+		return
+	}
+
+	for _, out := range dist.outputs {
+		ref, ok := refs[out.GetName()]
+		if !ok {
+			continue
+		}
+		if err := out.Delete(ref); err != nil {
+			dist.reportf("%s Error: could not delete the post: %s", out.GetName(), err)
+		}
+	}
+
+	if err := dist.store.Delete(event.MessageID); err != nil {
+		dist.reportf("Error: could not forget the posts for this message: %s", err)
+	}
+}
+
 func main() {
+	posts, err := store.New(os.Getenv("POST_STORE"))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
 	d := discord.Discord(os.Getenv("DISCORD_TOKEN"), os.Getenv("DISCORD_CHANNEL"))
 
-	tweetchannel := make(chan *discordgo.MessageCreate, 1)
+	eventchannel := make(chan discord.Event, 1)
-	d.BeginRead(tweetchannel)
+	d.BeginRead(eventchannel)
 
 	d.Write("Tweetdistributor Started")
 
@@ -112,35 +193,14 @@ func main() {
 	outputs = append(outputs, output.TwitterOutput(os.Getenv("TW_ACCESS_TOKEN"), os.Getenv("TW_ACCESS_SECRET")))
 	outputs = append(outputs, output.BlueskyOutput(os.Getenv("BSKY_IDENTIFIER"), os.Getenv("BSKY_PASSWORD")))
 
-	for tweet := range tweetchannel {
+	dist := &distributor{d: d, outputs: outputs, store: posts}
-		if length := utf8.RuneCountInString(tweet.Content); length > maxTweetLength {
-			errstr := fmt.Sprintf("Error: message is %d characters, exceeding the %d character limit; not posted", length, maxTweetLength)
-			fmt.Fprintln(os.Stderr, errstr)
-			d.Write(errstr)
-			continue
-		}
 
-		images, err := downloadImages(tweet.Attachments)
+	for event := range eventchannel {
-		if err != nil {
+		switch event.Kind {
-			errstr := fmt.Sprintf("Error: %s; not posted", err)
+		case discord.MessageCreated:
-			fmt.Fprintln(os.Stderr, errstr)
+			dist.created(event)
-			d.Write(errstr)
+		case discord.MessageDeleted:
-			continue
+			dist.deleted(event)
-		}
-		if len(images) > maxImagesPerPost {
-			errstr := fmt.Sprintf("Error: %d images attached, exceeding the limit of %d; not posted", len(images), maxImagesPerPost)
-			fmt.Fprintln(os.Stderr, errstr)
-			d.Write(errstr)
-			continue
-		}
-
-		for _, output := range outputs {
-			err := output.Write(tweet.Content, images)
-			if err != nil {
-				errstr := fmt.Sprintf("%s Error: %s", output.GetName(), err)
-				fmt.Fprintln(os.Stderr, errstr)
-				d.Write(errstr)
-			}
 		}
 	}
 }

main_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"math/rand"
+	"testing"
+	"tweetdistributor/output"
+)
+
+// noiseJPEG returns a JPEG image of random noise, which compresses poorly
+// and reliably exceeds maxImageBytes at large dimensions.
+func noiseJPEG(t *testing.T, width, height int) []byte {
+	t.Helper()
+	rng := rand.New(rand.NewSource(1))
+	img := image.NewRGBA(image.Rect(0, 0, width, height))
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			img.Set(x, y, color.RGBA{uint8(rng.Intn(256)), uint8(rng.Intn(256)), uint8(rng.Intn(256)), 255})
+		}
+	}
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: 95}); err != nil {
+		t.Fatal(err)
+	}
+	return buf.Bytes()
+}
+
+func TestShrinkImageLarge(t *testing.T) {
+	data := noiseJPEG(t, 3000, 3000)
+	if len(data) <= maxImageBytes {
+		t.Fatalf("test image should exceed maxImageBytes, got %d", len(data))
+	}
+
+	shrunk, err := shrinkImage(output.Image{Data: data, ContentType: "image/jpeg", Filename: "DSC_7277.jpg"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(shrunk.Data) > maxImageBytes {
+		t.Errorf("shrunk image is %d bytes, want <= %d", len(shrunk.Data), maxImageBytes)
+	}
+	if shrunk.ContentType != "image/jpeg" {
+		t.Errorf("ContentType = %q, want image/jpeg", shrunk.ContentType)
+	}
+	if shrunk.Filename != "DSC_7277.jpg" {
+		t.Errorf("Filename = %q, want DSC_7277.jpg", shrunk.Filename)
+	}
+	if _, _, err := image.Decode(bytes.NewReader(shrunk.Data)); err != nil {
+		t.Errorf("shrunk image is not decodable: %s", err)
+	}
+}
+
+func TestShrinkImageSmallPassthrough(t *testing.T) {
+	data := noiseJPEG(t, 100, 100)
+	img := output.Image{Data: data, ContentType: "image/png", Filename: "small.png"}
+	shrunk, err := shrinkImage(img)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(shrunk.Data, img.Data) || shrunk.ContentType != img.ContentType || shrunk.Filename != img.Filename {
+		t.Error("small image should pass through unchanged")
+	}
+}

output/bluesky.go

@@ -3,7 +3,9 @@ package output
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/bluesky-social/indigo/api/atproto"
@@ -13,6 +15,8 @@ import (
 	"github.com/bluesky-social/indigo/xrpc"
 )
 
+const blueskyCollection = "app.bsky.feed.post"
+
 type blueskyoutput struct {
 	identifier string
 	password   string
@@ -27,7 +31,8 @@ func BlueskyOutput(identifier string, password string) *blueskyoutput {
 	return blueskyoutput
 }
 
-func (bo *blueskyoutput) Write(str string, images []Image) error {
+// session logs in and returns a client authenticated as the configured account.
+func (bo *blueskyoutput) session() (*xrpc.Client, error) {
 	cli := &xrpc.Client{
 		Host: "https://bsky.social",
 	}
@@ -39,7 +44,7 @@ func (bo *blueskyoutput) Write(str string, images []Image) error {
 
 	output, err := atproto.ServerCreateSession(context.TODO(), cli, input)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	cli.Auth = &xrpc.AuthInfo{
 		AccessJwt:  output.AccessJwt,
@@ -47,26 +52,34 @@ func (bo *blueskyoutput) Write(str string, images []Image) error {
 		Handle:     output.Handle,
 		Did:        output.Did,
 	}
+	return cli, nil
+}
 
-	post := &bsky.FeedPost{
+func (bo *blueskyoutput) Write(post Post) (Ref, error) {
-		Text:      str,
+	cli, err := bo.session()
+	if err != nil {
+		return Ref{}, err
+	}
+
+	feedpost := &bsky.FeedPost{
+		Text:      post.Text,
 		CreatedAt: time.Now().Format(util.ISO8601),
 		Langs:     []string{"ja"},
 	}
 
-	if len(images) > 0 {
+	if len(post.Images) > 0 {
-		embedimages := make([]*bsky.EmbedImages_Image, 0, len(images))
+		embedimages := make([]*bsky.EmbedImages_Image, 0, len(post.Images))
-		for _, img := range images {
+		for _, img := range post.Images {
 			blob, err := atproto.RepoUploadBlob(context.TODO(), cli, bytes.NewReader(img.Data))
 			if err != nil {
-				return fmt.Errorf("uploading %s: %w", img.Filename, err)
+				return Ref{}, fmt.Errorf("uploading %s: %w", img.Filename, err)
 			}
 			embedimages = append(embedimages, &bsky.EmbedImages_Image{
 				Alt:   img.Filename,
 				Image: blob.Blob,
 			})
 		}
-		post.Embed = &bsky.FeedPost_Embed{
+		feedpost.Embed = &bsky.FeedPost_Embed{
 			EmbedImages: &bsky.EmbedImages{
 				Images: embedimages,
 			},
@@ -74,13 +87,47 @@ func (bo *blueskyoutput) Write(str string, images []Image) error {
 	}
 
 	Recordinput := &atproto.RepoCreateRecord_Input{
-		Collection: "app.bsky.feed.post",
+		Collection: blueskyCollection,
 		Repo:       cli.Auth.Did, // "matope.bsky.social" のDID
-		Record:     &lexutil.LexiconTypeDecoder{Val: post},
+		Record:     &lexutil.LexiconTypeDecoder{Val: feedpost},
+	}
+	record, recerr := atproto.RepoCreateRecord(context.TODO(), cli, Recordinput)
+	if recerr != nil {
+		return Ref{}, recerr
 	}
-	_, recerr := atproto.RepoCreateRecord(context.TODO(), cli, Recordinput)
 
-	return recerr
+	return Ref{URI: record.Uri, CID: record.Cid}, nil
+}
+
+func (bo *blueskyoutput) Delete(ref Ref) error {
+	rkey, err := recordKey(ref.URI)
+	if err != nil {
+		return err
+	}
+
+	cli, err := bo.session()
+	if err != nil {
+		return err
+	}
+
+	_, err = atproto.RepoDeleteRecord(context.TODO(), cli, &atproto.RepoDeleteRecord_Input{
+		Collection: blueskyCollection,
+		Repo:       cli.Auth.Did,
+		Rkey:       rkey,
+	})
+	return err
+}
+
+// recordKey pulls the rkey out of an at://did/collection/rkey URI.
+func recordKey(uri string) (string, error) {
+	if uri == "" {
+		return "", errors.New("no record URI to delete")
+	}
+	idx := strings.LastIndex(uri, "/")
+	if idx < 0 || idx == len(uri)-1 {
+		return "", fmt.Errorf("malformed record URI %q", uri)
+	}
+	return uri[idx+1:], nil
 }
 
 func (bo *blueskyoutput) GetName() string {

output/bluesky_test.go

@@ -0,0 +1,19 @@
+package output
+
+import "testing"
+
+func TestRecordKey(t *testing.T) {
+	rkey, err := recordKey("at://did:plc:abc123/app.bsky.feed.post/3kqz7xyz")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rkey != "3kqz7xyz" {
+		t.Errorf("recordKey = %q, want 3kqz7xyz", rkey)
+	}
+
+	for _, uri := range []string{"", "at://did:plc:abc123/app.bsky.feed.post/", "nonsense"} {
+		if _, err := recordKey(uri); err == nil {
+			t.Errorf("recordKey(%q) returned no error", uri)
+		}
+	}
+}

output/output.go

@@ -6,7 +6,23 @@ type Image struct {
 	Filename    string
 }
 
+// Ref identifies a post an output has already published so it can later be
+// deleted. The fields are output specific; only the ones the publishing
+// output filled in are meaningful to it.
+type Ref struct {
+	ID  string `json:"id,omitempty"`  // twitter: tweet ID
+	URI string `json:"uri,omitempty"` // bluesky: at:// URI of the record
+	CID string `json:"cid,omitempty"` // bluesky: record CID
+}
+
+// Post is a single message to distribute.
+type Post struct {
+	Text   string
+	Images []Image
+}
+
 type OutputInterface interface {
-	Write(string, []Image) error
+	Write(Post) (Ref, error)
+	Delete(Ref) error
 	GetName() string
 }

output/stdout.go

@@ -11,11 +11,16 @@ func StdOutput() *stdoutput {
 	return &stdoutput{}
 }
 
-func (so *stdoutput) Write(str string, images []Image) error {
+func (so *stdoutput) Write(post Post) (Ref, error) {
-	fmt.Println(str)
+	fmt.Println(post.Text)
-	for _, img := range images {
+	for _, img := range post.Images {
 		fmt.Printf("[image: %s (%s, %d bytes)]\n", img.Filename, img.ContentType, len(img.Data))
 	}
+	return Ref{ID: post.Text}, nil
+}
+
+func (so *stdoutput) Delete(ref Ref) error {
+	fmt.Printf("[deleted: %s]\n", ref.ID)
 	return nil
 }
 

output/twitter.go

@@ -3,6 +3,7 @@ package output
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"os"
 
@@ -44,26 +45,39 @@ func (to *twitteroutput) newOAuth1Client(accessToken, accessSecret string) error
 	return err
 }
 
-func (to *twitteroutput) Write(str string, images []Image) error {
+func (to *twitteroutput) Write(post Post) (Ref, error) {
-	mediaIDs := make([]string, 0, len(images))
+	mediaIDs := make([]string, 0, len(post.Images))
-	for _, img := range images {
+	for _, img := range post.Images {
 		mediaID, err := to.uploadImage(img)
 		if err != nil {
-			return fmt.Errorf("uploading %s: %w", img.Filename, err)
+			return Ref{}, fmt.Errorf("uploading %s: %w", img.Filename, err)
 		}
 		mediaIDs = append(mediaIDs, mediaID)
 	}
 
 	p := &types.CreateInput{
-		Text: gotwi.String(str),
+		Text: gotwi.String(post.Text),
 	}
 	if len(mediaIDs) > 0 {
 		p.Media = &types.CreateInputMedia{
 			MediaIDs: mediaIDs,
 		}
 	}
+	out, err := managetweet.Create(context.Background(), to.client, p)
+	if err != nil {
+		return Ref{}, err
+	}
+	if out.Data.ID == nil {
+		return Ref{}, errors.New("created tweet has no ID")
+	}
+	return Ref{ID: *out.Data.ID}, nil
+}
 
-	_, err := managetweet.Create(context.Background(), to.client, p)
+func (to *twitteroutput) Delete(ref Ref) error {
+	if ref.ID == "" {
+		return errors.New("no tweet ID to delete")
+	}
+	_, err := managetweet.Delete(context.Background(), to.client, &types.DeleteInput{ID: ref.ID})
 	return err
 }
 

store/store.go

@@ -0,0 +1,125 @@
+// Package store remembers which post each output produced for a given Discord
+// message, so a later delete or reply on Discord can be mirrored.
+package store
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"sync"
+
+	"tweetdistributor/output"
+)
+
+// maxEntries bounds how far back a delete or reply can reach; the oldest
+// message is forgotten once the limit is passed.
+const maxEntries = 1000
+
+// Refs maps an output name to the post that output published.
+type Refs map[string]output.Ref
+
+type Store struct {
+	mu    sync.Mutex
+	path  string
+	refs  map[string]Refs
+	order []string
+}
+
+// New returns a store backed by the JSON file at path, loading it if it
+// already exists. An empty path keeps everything in memory only, in which
+// case the mapping is lost on restart.
+func New(path string) (*Store, error) {
+	s := &Store{
+		path: path,
+		refs: map[string]Refs{},
+	}
+	if path == "" {
+		return s, nil
+	}
+
+	data, err := os.ReadFile(path)
+	if os.IsNotExist(err) {
+		return s, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("reading %s: %w", path, err)
+	}
+
+	var saved struct {
+		Order []string        `json:"order"`
+		Refs  map[string]Refs `json:"refs"`
+	}
+	if err := json.Unmarshal(data, &saved); err != nil {
+		return nil, fmt.Errorf("parsing %s: %w", path, err)
+	}
+	if saved.Refs != nil {
+		s.refs = saved.Refs
+	}
+	s.order = saved.Order
+	return s, nil
+}
+
+func (s *Store) Put(messageID string, refs Refs) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if _, exists := s.refs[messageID]; !exists {
+		s.order = append(s.order, messageID)
+	}
+	s.refs[messageID] = refs
+
+	for len(s.order) > maxEntries {
+		delete(s.refs, s.order[0])
+		s.order = s.order[1:]
+	}
+	return s.save()
+}
+
+func (s *Store) Get(messageID string) (Refs, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	refs, ok := s.refs[messageID]
+	return refs, ok
+}
+
+func (s *Store) Delete(messageID string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if _, ok := s.refs[messageID]; !ok {
+		return nil
+	}
+	delete(s.refs, messageID)
+	for i, id := range s.order {
+		if id == messageID {
+			s.order = append(s.order[:i], s.order[i+1:]...)
+			break
+		}
+	}
+	return s.save()
+}
+
+// save writes the whole store out; the caller must hold the lock.
+func (s *Store) save() error {
+	if s.path == "" {
+		return nil
+	}
+
+	data, err := json.Marshal(struct {
+		Order []string        `json:"order"`
+		Refs  map[string]Refs `json:"refs"`
+	}{Order: s.order, Refs: s.refs})
+	if err != nil {
+		return err
+	}
+
+	tmp := s.path + ".tmp"
+	if err := os.WriteFile(tmp, data, 0o600); err != nil {
+		return fmt.Errorf("writing %s: %w", tmp, err)
+	}
+	if err := os.Rename(tmp, s.path); err != nil {
+		return fmt.Errorf("replacing %s: %w", s.path, err)
+	}
+	return nil
+}

store/store_test.go

@@ -0,0 +1,77 @@
+package store
+
+import (
+	"path/filepath"
+	"testing"
+
+	"tweetdistributor/output"
+)
+
+func TestStoreRoundTripThroughFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "posts.json")
+
+	s, err := New(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	refs := Refs{
+		"twitter": {ID: "123"},
+		"bluesky": {URI: "at://did:plc:xyz/app.bsky.feed.post/abc", CID: "bafy"},
+	}
+	if err := s.Put("discord-1", refs); err != nil {
+		t.Fatal(err)
+	}
+
+	reopened, err := New(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, ok := reopened.Get("discord-1")
+	if !ok {
+		t.Fatal("stored message was not found after reopening")
+	}
+	if got["twitter"] != (output.Ref{ID: "123"}) {
+		t.Errorf("twitter ref = %+v, want ID 123", got["twitter"])
+	}
+	if got["bluesky"].URI != refs["bluesky"].URI {
+		t.Errorf("bluesky URI = %q, want %q", got["bluesky"].URI, refs["bluesky"].URI)
+	}
+
+	if err := reopened.Delete("discord-1"); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := reopened.Get("discord-1"); ok {
+		t.Error("message is still present after Delete")
+	}
+}
+
+func TestStoreMissingMessage(t *testing.T) {
+	s, err := New("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := s.Get("nope"); ok {
+		t.Error("Get returned a ref for a message that was never stored")
+	}
+	if err := s.Delete("nope"); err != nil {
+		t.Errorf("deleting an unknown message returned %s", err)
+	}
+}
+
+func TestStoreEvictsOldest(t *testing.T) {
+	s, err := New("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < maxEntries+10; i++ {
+		if err := s.Put(string(rune('a'+i%26))+string(rune(i)), Refs{"stdout": {ID: "x"}}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if len(s.refs) > maxEntries {
+		t.Errorf("store holds %d entries, want at most %d", len(s.refs), maxEntries)
+	}
+	if len(s.order) != len(s.refs) {
+		t.Errorf("order has %d entries but refs has %d", len(s.order), len(s.refs))
+	}
+}