[bugfix] media.Processor{}.GetFile() returning 404s on first call, correctly loading on 2nd (#3129)

* refactor file handling a tiny bit

* whoops

* make processing media / emoji defers a bit clear to see that it's the "on finished processing" path

* some wording

* add some debug logging

* add mutex locks for processing remote media

* try removing freshness check

* fix derefMedia not being allocated

* fix log format string

* handle case of empty file paths (i.e. not stored)

* remove media / emoji once finished processing from dereferencer maps

* whoops, fix the cached / force checks

* move url parsing outside of 'process___Safely()' funcs to prevalidate url

* use emoji.ShortcodeDomain()

* update RefreshEmoji() to also match RefreshMedia() changes

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

internal/cleaner/cleaner.go

@@ -59,12 +59,19 @@ func (c *Cleaner) Media() *Media {
 
 // haveFiles returns whether all of the provided files exist within current storage.
 func (c *Cleaner) haveFiles(ctx context.Context, files ...string) (bool, error) {
-	for _, file := range files {
+	for _, path := range files {
+		if path == "" {
+			// File not stored.
+			return false, nil
+		}
+
 		// Check whether each file exists in storage.
-		have, err := c.state.Storage.Has(ctx, file)
+		have, err := c.state.Storage.Has(ctx, path)
 		if err != nil {
-			return false, gtserror.Newf("error checking storage for %s: %w", file, err)
+			return false, gtserror.Newf("error checking storage for %s: %w", path, err)
-		} else if !have {
+		}
+
+		if !have {
 			// Missing file(s).
 			return false, nil
 		}
@@ -81,28 +88,33 @@ func (c *Cleaner) removeFiles(ctx context.Context, files ...string) (int, error)
 
 	var (
 		errs  gtserror.MultiError
-		errCount int
+		count int
 	)
 
 	for _, path := range files {
+		if path == "" {
+			// not stored.
+			continue
+		}
+
 		// Remove each provided storage path.
 		log.Debugf(ctx, "removing file: %s", path)
 		err := c.state.Storage.Delete(ctx, path)
 		if err != nil && !storage.IsNotFound(err) {
 			errs.Appendf("error removing %s: %w", path, err)
-			errCount++
+			continue
-		}
 		}
 
-	// Calculate no. files removed.
+		// Incr.
-	diff := len(files) - errCount
+		count++
+	}
 
 	// Wrap the combined error slice.
 	if err := errs.Combine(); err != nil {
-		return diff, gtserror.Newf("error(s) removing files: %w", err)
+		return count, gtserror.Newf("error(s) removing files: %w", err)
 	}
 
-	return diff, nil
+	return count, nil
 }
 
 // ScheduleJobs schedules cleaning

internal/cleaner/media.go

@@ -97,7 +97,7 @@ func (m *Media) PruneOrphaned(ctx context.Context) (int, error) {
 	if err := m.state.Storage.WalkKeys(ctx, func(path string) error {
 		// Check for our expected fileserver path format.
 		if !regexes.FilePath.MatchString(path) {
-			log.Warn(ctx, "unexpected storage item: %s", path)
+			log.Warnf(ctx, "unexpected storage item: %s", path)
 			return nil
 		}
 

internal/federation/dereferencing/dereferencer.go

@@ -85,12 +85,9 @@ type Dereferencer struct {
 	mediaManager        *media.Manager
 	visibility          *visibility.Filter
 
-	// in-progress dereferencing emoji. we already perform
+	// in-progress dereferencing media / emoji
-	// locks per-status and per-account so we don't need
+	derefMedia    map[string]*media.ProcessingMedia
-	// processing maps for other media which won't often
+	derefMediaMu  sync.Mutex
-	// end up being repeated. worst case we run into an
-	// db.ErrAlreadyExists error which then gets handled
-	// appropriately by enrich{Account,Status}Safely().
 	derefEmojis   map[string]*media.ProcessingEmoji
 	derefEmojisMu sync.Mutex
 
@@ -119,6 +116,7 @@ func NewDereferencer(
 		transportController: transportController,
 		mediaManager:        mediaManager,
 		visibility:          visFilter,
+		derefMedia:          make(map[string]*media.ProcessingMedia),
 		derefEmojis:         make(map[string]*media.ProcessingEmoji),
 		handshakes:          make(map[string][]*url.URL),
 	}

internal/federation/dereferencing/emoji.go

@@ -77,6 +77,11 @@ func (d *Dereferencer) GetEmoji(
 	// Generate shortcode domain for locks + logging.
 	shortcodeDomain := shortcode + "@" + domain
 
+	// Pass along for safe processing.
+	return d.processEmojiSafely(ctx,
+		shortcodeDomain,
+		func() (*media.ProcessingEmoji, error) {
+
 			// Ensure we have a valid remote URL.
 			url, err := url.Parse(remoteURL)
 			if err != nil {
@@ -99,10 +104,7 @@ func (d *Dereferencer) GetEmoji(
 				return tsport.DereferenceMedia(ctx, url, int64(maxsz))
 			}
 
-	// Pass along for safe processing.
+			// Create new emoji with prepared info.
-	return d.processEmojiSafely(ctx,
-		shortcodeDomain,
-		func() (*media.ProcessingEmoji, error) {
 			return d.mediaManager.CreateEmoji(ctx,
 				shortcode,
 				domain,
@@ -142,24 +144,25 @@ func (d *Dereferencer) RefreshEmoji(
 	switch {
 	case info.URI != nil &&
 		*info.URI != emoji.URI:
+		emoji.URI = *info.URI
 		force = true
 	case info.ImageRemoteURL != nil &&
 		*info.ImageRemoteURL != emoji.ImageRemoteURL:
+		emoji.ImageRemoteURL = *info.ImageRemoteURL
 		force = true
 	case info.ImageStaticRemoteURL != nil &&
 		*info.ImageStaticRemoteURL != emoji.ImageStaticRemoteURL:
+		emoji.ImageStaticRemoteURL = *info.ImageStaticRemoteURL
 		force = true
 	}
 
 	// Check if needs updating.
-	if !force && *emoji.Cached {
+	if *emoji.Cached && !force {
 		return emoji, nil
 	}
 
-	// TODO: more finegrained freshness checks.
+	// Get shortcode domain for locks + logging.
-
+	shortcodeDomain := emoji.ShortcodeDomain()
-	// Generate shortcode domain for locks + logging.
-	shortcodeDomain := emoji.Shortcode + "@" + emoji.Domain
 
 	// Ensure we have a valid image remote URL.
 	url, err := url.Parse(emoji.ImageRemoteURL)
@@ -168,6 +171,11 @@ func (d *Dereferencer) RefreshEmoji(
 		return nil, err
 	}
 
+	// Pass along for safe processing.
+	return d.processEmojiSafely(ctx,
+		shortcodeDomain,
+		func() (*media.ProcessingEmoji, error) {
+
 			// Acquire new instance account transport for emoji dereferencing.
 			tsport, err := d.transportController.NewTransportForUsername(ctx, "")
 			if err != nil {
@@ -183,10 +191,7 @@ func (d *Dereferencer) RefreshEmoji(
 				return tsport.DereferenceMedia(ctx, url, int64(maxsz))
 			}
 
-	// Pass along for safe processing.
+			// Refresh emoji with prepared info.
-	return d.processEmojiSafely(ctx,
-		shortcodeDomain,
-		func() (*media.ProcessingEmoji, error) {
 			return d.mediaManager.RefreshEmoji(ctx,
 				emoji,
 				data,
@@ -226,6 +231,13 @@ func (d *Dereferencer) processEmojiSafely(
 		if err != nil {
 			return nil, err
 		}
+
+		defer func() {
+			// Remove on finish.
+			d.derefEmojisMu.Lock()
+			delete(d.derefEmojis, shortcodeDomain)
+			d.derefEmojisMu.Unlock()
+		}()
 	}
 
 	// Unlock map.
@@ -240,10 +252,7 @@ func (d *Dereferencer) processEmojiSafely(
 		// which can determine if loading error should allow remaining placeholder.
 	}
 
-	// Return a COPY of emoji.
+	return
-	emoji2 := new(gtsmodel.Emoji)
-	*emoji2 = *emoji
-	return emoji2, err
 }
 
 func (d *Dereferencer) fetchEmojis(

internal/federation/dereferencing/media.go

@@ -26,6 +26,7 @@
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/media"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
 )
 
 // GetMedia fetches the media at given remote URL by
@@ -56,12 +57,17 @@ func (d *Dereferencer) GetMedia(
 	*gtsmodel.MediaAttachment,
 	error,
 ) {
-	// Parse str as valid URL object.
+	// Ensure we have a valid remote URL.
 	url, err := url.Parse(remoteURL)
 	if err != nil {
-		return nil, gtserror.Newf("invalid remote media url %q: %v", remoteURL, err)
+		err := gtserror.Newf("invalid media remote url %s: %w", remoteURL, err)
+		return nil, err
 	}
 
+	return d.processMediaSafeley(ctx,
+		remoteURL,
+		func() (*media.ProcessingMedia, error) {
+
 			// Fetch transport for the provided request user from controller.
 			tsport, err := d.transportController.NewTransportForUsername(ctx,
 				requestUser,
@@ -73,8 +79,8 @@ func (d *Dereferencer) GetMedia(
 			// Get maximum supported remote media size.
 			maxsz := config.GetMediaRemoteMaxSize()
 
-	// Start processing remote attachment at URL.
+			// Create media with prepared info.
-	processing, err := d.mediaManager.CreateMedia(
+			return d.mediaManager.CreateMedia(
 				ctx,
 				accountID,
 				func(ctx context.Context) (io.ReadCloser, error) {
@@ -82,20 +88,8 @@ func(ctx context.Context) (io.ReadCloser, error) {
 				},
 				info,
 			)
-	if err != nil {
+		},
-		return nil, err
+	)
-	}
-
-	// Perform media load operation.
-	media, err := processing.Load(ctx)
-	if err != nil {
-		err = gtserror.Newf("error loading media %s: %w", media.RemoteURL, err)
-
-		// TODO: in time we should return checkable flags by gtserror.Is___()
-		// which can determine if loading error should allow remaining placeholder.
-	}
-
-	return media, err
 }
 
 // RefreshMedia ensures that given media is up-to-date,
@@ -119,7 +113,7 @@ func(ctx context.Context) (io.ReadCloser, error) {
 func (d *Dereferencer) RefreshMedia(
 	ctx context.Context,
 	requestUser string,
-	media *gtsmodel.MediaAttachment,
+	attach *gtsmodel.MediaAttachment,
 	info media.AdditionalMediaInfo,
 	force bool,
 ) (
@@ -127,38 +121,44 @@ func (d *Dereferencer) RefreshMedia(
 	error,
 ) {
 	// Can't refresh local.
-	if media.IsLocal() {
+	if attach.IsLocal() {
-		return media, nil
+		return attach, nil
 	}
 
 	// Check emoji is up-to-date
 	// with provided extra info.
 	switch {
 	case info.Blurhash != nil &&
-		*info.Blurhash != media.Blurhash:
+		*info.Blurhash != attach.Blurhash:
+		attach.Blurhash = *info.Blurhash
 		force = true
 	case info.Description != nil &&
-		*info.Description != media.Description:
+		*info.Description != attach.Description:
+		attach.Description = *info.Description
 		force = true
 	case info.RemoteURL != nil &&
-		*info.RemoteURL != media.RemoteURL:
+		*info.RemoteURL != attach.RemoteURL:
+		attach.RemoteURL = *info.RemoteURL
 		force = true
 	}
 
 	// Check if needs updating.
-	if !force && *media.Cached {
+	if *attach.Cached && !force {
-		return media, nil
+		return attach, nil
 	}
 
-	// TODO: more finegrained freshness checks.
-
 	// Ensure we have a valid remote URL.
-	url, err := url.Parse(media.RemoteURL)
+	url, err := url.Parse(attach.RemoteURL)
 	if err != nil {
-		err := gtserror.Newf("invalid media remote url %s: %w", media.RemoteURL, err)
+		err := gtserror.Newf("invalid media remote url %s: %w", attach.RemoteURL, err)
 		return nil, err
 	}
 
+	// Pass along for safe processing.
+	return d.processMediaSafeley(ctx,
+		attach.RemoteURL,
+		func() (*media.ProcessingMedia, error) {
+
 			// Fetch transport for the provided request user from controller.
 			tsport, err := d.transportController.NewTransportForUsername(ctx,
 				requestUser,
@@ -170,24 +170,16 @@ func (d *Dereferencer) RefreshMedia(
 			// Get maximum supported remote media size.
 			maxsz := config.GetMediaRemoteMaxSize()
 
-	// Start processing remote attachment recache.
+			// Recache media with prepared info,
-	processing := d.mediaManager.RecacheMedia(
+			// this will also update media in db.
-		media,
+			return d.mediaManager.RecacheMedia(
+				attach,
 				func(ctx context.Context) (io.ReadCloser, error) {
 					return tsport.DereferenceMedia(ctx, url, int64(maxsz))
 				},
+			), nil
+		},
 	)
-
-	// Perform media load operation.
-	media, err = processing.Load(ctx)
-	if err != nil {
-		err = gtserror.Newf("error loading media %s: %w", media.RemoteURL, err)
-
-		// TODO: in time we should return checkable flags by gtserror.Is___()
-		// which can determine if loading error should allow remaining placeholder.
-	}
-
-	return media, err
 }
 
 // updateAttachment handles the case of an existing media attachment
@@ -220,3 +212,57 @@ func (d *Dereferencer) updateAttachment(
 		false,
 	)
 }
+
+// processingEmojiSafely provides concurrency-safe processing of
+// an emoji with given shortcode+domain. if a copy of the emoji is
+// not already being processed, the given 'process' callback will
+// be used to generate new *media.ProcessingEmoji{} instance.
+func (d *Dereferencer) processMediaSafeley(
+	ctx context.Context,
+	remoteURL string,
+	process func() (*media.ProcessingMedia, error),
+) (
+	media *gtsmodel.MediaAttachment,
+	err error,
+) {
+
+	// Acquire map lock.
+	d.derefMediaMu.Lock()
+
+	// Ensure unlock only done once.
+	unlock := d.derefMediaMu.Unlock
+	unlock = util.DoOnce(unlock)
+	defer unlock()
+
+	// Look for an existing deref in progress.
+	processing, ok := d.derefMedia[remoteURL]
+
+	if !ok {
+		// Start new processing emoji.
+		processing, err = process()
+		if err != nil {
+			return nil, err
+		}
+
+		defer func() {
+			// Remove on finish.
+			d.derefMediaMu.Lock()
+			delete(d.derefMedia, remoteURL)
+			d.derefMediaMu.Unlock()
+		}()
+	}
+
+	// Unlock map.
+	unlock()
+
+	// Perform media load operation.
+	media, err = processing.Load(ctx)
+	if err != nil {
+		err = gtserror.Newf("error loading media %s: %w", remoteURL, err)
+
+		// TODO: in time we should return checkable flags by gtserror.Is___()
+		// which can determine if loading error should allow remaining placeholder.
+	}
+
+	return
+}

internal/media/processingemoji.go

@@ -22,7 +22,6 @@
 
 	errorsv2 "codeberg.org/gruf/go-errors/v2"
 	"codeberg.org/gruf/go-runners"
-	"github.com/superseriousbusiness/gotosocial/internal/gtscontext"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
@@ -77,22 +76,17 @@ func (p *ProcessingEmoji) load(ctx context.Context) (
 
 		defer func() {
 			// This is only done when ctx NOT cancelled.
-			done = (err == nil || !errorsv2.IsV2(err,
+			if done = (err == nil || !errorsv2.IsV2(err,
 				context.Canceled,
 				context.DeadlineExceeded,
-			))
+			)); done {
-
+				// Processing finished,
-			if !done {
+				// whether error or not!
-				return
-			}
 
 				// Anything from here, we
 				// need to ensure happens
 				// (i.e. no ctx canceled).
-			ctx = gtscontext.WithValues(
+				ctx = context.WithoutCancel(ctx)
-				context.Background(),
-				ctx, // values
-			)
 
 				// On error, clean
 				// downloaded files.
@@ -100,19 +94,16 @@ func (p *ProcessingEmoji) load(ctx context.Context) (
 					p.cleanup(ctx)
 				}
 
-			if !done {
-				return
-			}
-
 				// Update with latest details, whatever happened.
 				e := p.mgr.state.DB.UpdateEmoji(ctx, p.emoji)
 				if e != nil {
 					log.Errorf(ctx, "error updating emoji in db: %v", e)
 				}
 
-			// Store final values.
+				// Store values.
 				p.done = true
 				p.err = err
+			}
 		}()
 
 		// Attempt to store media and calculate
@@ -122,7 +113,10 @@ func (p *ProcessingEmoji) load(ctx context.Context) (
 		err = p.store(ctx)
 		return err
 	})
-	emoji = p.emoji
+
+	// Return a copy of emoji.
+	emoji = new(gtsmodel.Emoji)
+	*emoji = *p.emoji
 	return
 }
 
@@ -265,11 +259,11 @@ func (p *ProcessingEmoji) store(ctx context.Context) error {
 // cleanup will remove any traces of processing emoji from storage,
 // and perform any other necessary cleanup steps after failure.
 func (p *ProcessingEmoji) cleanup(ctx context.Context) {
-	var err error
+	log.Debugf(ctx, "running cleanup of emoji %s", p.emoji.ID)
 
 	if p.emoji.ImagePath != "" {
 		// Ensure emoji file at path is deleted from storage.
-		err = p.mgr.state.Storage.Delete(ctx, p.emoji.ImagePath)
+		err := p.mgr.state.Storage.Delete(ctx, p.emoji.ImagePath)
 		if err != nil && !storage.IsNotFound(err) {
 			log.Errorf(ctx, "error deleting %s: %v", p.emoji.ImagePath, err)
 		}
@@ -277,7 +271,7 @@ func (p *ProcessingEmoji) cleanup(ctx context.Context) {
 
 	if p.emoji.ImageStaticPath != "" {
 		// Ensure emoji static file at path is deleted from storage.
-		err = p.mgr.state.Storage.Delete(ctx, p.emoji.ImageStaticPath)
+		err := p.mgr.state.Storage.Delete(ctx, p.emoji.ImageStaticPath)
 		if err != nil && !storage.IsNotFound(err) {
 			log.Errorf(ctx, "error deleting %s: %v", p.emoji.ImageStaticPath, err)
 		}

internal/media/processingmedia.go

@@ -19,12 +19,10 @@
 
 import (
 	"context"
-	"time"
 
 	errorsv2 "codeberg.org/gruf/go-errors/v2"
 	"codeberg.org/gruf/go-runners"
 
-	"github.com/superseriousbusiness/gotosocial/internal/gtscontext"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
@@ -63,6 +61,7 @@ func (p *ProcessingMedia) Load(ctx context.Context) (*gtsmodel.MediaAttachment,
 	media, done, err := p.load(ctx)
 	if !done {
 		// On a context-canceled error (marked as !done), requeue for loading.
+		log.Warnf(ctx, "reprocessing media %s after canceled ctx", p.media.ID)
 		p.mgr.state.Workers.Dereference.Queue.Push(func(ctx context.Context) {
 			if _, _, err := p.load(ctx); err != nil {
 				log.Errorf(ctx, "error loading media: %v", err)
@@ -86,22 +85,17 @@ func (p *ProcessingMedia) load(ctx context.Context) (
 
 		defer func() {
 			// This is only done when ctx NOT cancelled.
-			done = (err == nil || !errorsv2.IsV2(err,
+			if done = (err == nil || !errorsv2.IsV2(err,
 				context.Canceled,
 				context.DeadlineExceeded,
-			))
+			)); done {
-
+				// Processing finished,
-			if !done {
+				// whether error or not!
-				return
-			}
 
 				// Anything from here, we
 				// need to ensure happens
 				// (i.e. no ctx canceled).
-			ctx = gtscontext.WithValues(
+				ctx = context.WithoutCancel(ctx)
-				context.Background(),
-				ctx, // values
-			)
 
 				// On error or unknown media types, perform error cleanup.
 				if err != nil || p.media.Type == gtsmodel.FileTypeUnknown {
@@ -114,26 +108,11 @@ func (p *ProcessingMedia) load(ctx context.Context) (
 					log.Errorf(ctx, "error updating media in db: %v", e)
 				}
 
-			// Store final values.
+				// Store values.
 				p.done = true
 				p.err = err
-		}()
-
-		// TODO: in time update this
-		// to perhaps follow a similar
-		// freshness window to statuses
-		// / accounts? But that's a big
-		// maybe, media don't change in
-		// the same way so this is largely
-		// just to slow down fail retries.
-		const maxfreq = 6 * time.Hour
-
-		// Check whether media is uncached but repeatedly failing,
-		// specifically limit the frequency at which we allow this.
-		if !p.media.UpdatedAt.Equal(p.media.CreatedAt) && // i.e. not new
-			p.media.UpdatedAt.Add(maxfreq).Before(time.Now()) {
-			return nil
 			}
+		}()
 
 		// Attempt to store media and calculate
 		// full-size media attachment details.
@@ -142,7 +121,10 @@ func (p *ProcessingMedia) load(ctx context.Context) (
 		err = p.store(ctx)
 		return err
 	})
-	media = p.media
+
+	// Return a copy of media attachment.
+	media = new(gtsmodel.MediaAttachment)
+	*media = *p.media
 	return
 }
 
@@ -331,11 +313,9 @@ func (p *ProcessingMedia) store(ctx context.Context) error {
 // cleanup will remove any traces of processing media from storage.
 // and perform any other necessary cleanup steps after failure.
 func (p *ProcessingMedia) cleanup(ctx context.Context) {
-	var err error
-
 	if p.media.File.Path != "" {
 		// Ensure media file at path is deleted from storage.
-		err = p.mgr.state.Storage.Delete(ctx, p.media.File.Path)
+		err := p.mgr.state.Storage.Delete(ctx, p.media.File.Path)
 		if err != nil && !storage.IsNotFound(err) {
 			log.Errorf(ctx, "error deleting %s: %v", p.media.File.Path, err)
 		}
@@ -343,7 +323,7 @@ func (p *ProcessingMedia) cleanup(ctx context.Context) {
 
 	if p.media.Thumbnail.Path != "" {
 		// Ensure media thumbnail at path is deleted from storage.
-		err = p.mgr.state.Storage.Delete(ctx, p.media.Thumbnail.Path)
+		err := p.mgr.state.Storage.Delete(ctx, p.media.Thumbnail.Path)
 		if err != nil && !storage.IsNotFound(err) {
 			log.Errorf(ctx, "error deleting %s: %v", p.media.Thumbnail.Path, err)
 		}

internal/processing/media/getfile.go

@@ -30,6 +30,7 @@
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/media"
+	"github.com/superseriousbusiness/gotosocial/internal/regexes"
 	"github.com/superseriousbusiness/gotosocial/internal/storage"
 	"github.com/superseriousbusiness/gotosocial/internal/uris"
 )
@@ -41,79 +42,97 @@ func (p *Processor) GetFile(
 	requester *gtsmodel.Account,
 	form *apimodel.GetContentRequestForm,
 ) (*apimodel.Content, gtserror.WithCode) {
-	// parse the form fields
+	// Parse media size (small, static, original).
 	mediaSize, err := parseSize(form.MediaSize)
 	if err != nil {
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media size %s not valid", form.MediaSize))
+		err := gtserror.Newf("media size %s not valid", form.MediaSize)
+		return nil, gtserror.NewErrorNotFound(err)
 	}
 
+	// Parse media type (emoji, header, avatar, attachment).
 	mediaType, err := parseType(form.MediaType)
 	if err != nil {
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media type %s not valid", form.MediaType))
+		err := gtserror.Newf("media type %s not valid", form.MediaType)
+		return nil, gtserror.NewErrorNotFound(err)
 	}
 
-	spl := strings.Split(form.FileName, ".")
+	// Parse media ID from file name.
-	if len(spl) != 2 || spl[0] == "" || spl[1] == "" {
+	mediaID, _, err := parseFileName(form.FileName)
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("file name %s not parseable", form.FileName))
-	}
-	wantedMediaID := spl[0]
-	owningAccountID := form.AccountID
-
-	// get the account that owns the media and make sure it's not suspended
-	owningAccount, err := p.state.DB.GetAccountByID(ctx, owningAccountID)
 	if err != nil {
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("account with id %s could not be selected from the db: %s", owningAccountID, err))
+		err := gtserror.Newf("media file name %s not valid", form.FileName)
-	}
+		return nil, gtserror.NewErrorNotFound(err)
-	if !owningAccount.SuspendedAt.IsZero() {
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("account with id %s is suspended", owningAccountID))
 	}
 
-	// make sure the requesting account and the media account don't block each other
+	// Get the account that owns the media
+	// and make sure it's not suspended.
+	acctID := form.AccountID
+	acct, err := p.state.DB.GetAccountByID(ctx, acctID)
+	if err != nil {
+		err := gtserror.Newf("db error getting account %s: %w", acctID, err)
+		return nil, gtserror.NewErrorNotFound(err)
+	}
+
+	if acct.IsSuspended() {
+		err := gtserror.Newf("account %s is suspended", acctID)
+		return nil, gtserror.NewErrorNotFound(err)
+	}
+
+	// If requester was authenticated, ensure media
+	// owner and requester don't block each other.
 	if requester != nil {
-		blocked, err := p.state.DB.IsEitherBlocked(ctx, requester.ID, owningAccountID)
+		blocked, err := p.state.DB.IsEitherBlocked(ctx, requester.ID, acctID)
 		if err != nil {
-			return nil, gtserror.NewErrorNotFound(fmt.Errorf("block status could not be established between accounts %s and %s: %s", owningAccountID, requester.ID, err))
+			err := gtserror.Newf("db error checking block between %s and %s: %w", acctID, requester.ID, err)
+			return nil, gtserror.NewErrorNotFound(err)
 		}
+
 		if blocked {
-			return nil, gtserror.NewErrorNotFound(fmt.Errorf("block exists between accounts %s and %s", owningAccountID, requester.ID))
+			err := gtserror.Newf("block exists between %s and %s", acctID, requester.ID)
+			return nil, gtserror.NewErrorNotFound(err)
 		}
 	}
 
-	// the way we store emojis is a little different from the way we store other attachments,
+	// The way we store emojis is a bit different
-	// so we need to take different steps depending on the media type being requested
+	// from the way we store other attachments,
+	// so we need to take different steps depending
+	// on the media type being requested.
 	switch mediaType {
+
 	case media.TypeEmoji:
 		return p.getEmojiContent(ctx,
-			owningAccountID,
+			acctID,
-			wantedMediaID,
 			mediaSize,
+			mediaID,
 		)
+
 	case media.TypeAttachment, media.TypeHeader, media.TypeAvatar:
 		return p.getAttachmentContent(ctx,
 			requester,
-			owningAccountID,
+			acctID,
-			wantedMediaID,
 			mediaSize,
+			mediaID,
 		)
+
 	default:
-		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media type %s not recognized", mediaType))
+		err := gtserror.Newf("media type %s not recognized", mediaType)
+		return nil, gtserror.NewErrorNotFound(err)
 	}
 }
 
 func (p *Processor) getAttachmentContent(
 	ctx context.Context,
 	requester *gtsmodel.Account,
-	ownerID string,
+	acctID string,
-	mediaID string,
 	sizeStr media.Size,
+	mediaID string,
 ) (
 	*apimodel.Content,
 	gtserror.WithCode,
 ) {
-	// Search for media with given ID in the database.
+	// Get attachment with given ID from the database.
 	attach, err := p.state.DB.GetAttachmentByID(ctx, mediaID)
 	if err != nil && !errors.Is(err, db.ErrNoEntries) {
-		err := gtserror.Newf("error fetching media from database: %w", err)
+		err := gtserror.Newf("db error getting attachment %s: %w", mediaID, err)
 		return nil, gtserror.NewErrorInternalError(err)
 	}
 
@@ -122,51 +141,24 @@ func (p *Processor) getAttachmentContent(
 		return nil, gtserror.NewErrorNotFound(errors.New(text), text)
 	}
 
-	// Ensure the 'owner' owns media.
+	// Ensure the account
-	if attach.AccountID != ownerID {
+	// actually owns the media.
+	if attach.AccountID != acctID {
 		const text = "media was not owned by passed account id"
 		return nil, gtserror.NewErrorNotFound(errors.New(text) /* no help text! */)
 	}
 
-	var remoteURL *url.URL
+	// Unknown file types indicate no *locally*
-	if attach.RemoteURL != "" {
-
-		// Parse media remote URL to valid URL object.
-		remoteURL, err = url.Parse(attach.RemoteURL)
-		if err != nil {
-			err := gtserror.Newf("invalid media remote url %s: %w", attach.RemoteURL, err)
-			return nil, gtserror.NewErrorInternalError(err)
-		}
-	}
-
-	// Uknown file types indicate no *locally*
 	// stored data we can serve. Handle separately.
 	if attach.Type == gtsmodel.FileTypeUnknown {
-		if remoteURL == nil {
+		return handleUnknown(attach)
-			err := gtserror.Newf("missing remote url for unknown type media %s: %w", attach.ID, err)
-			return nil, gtserror.NewErrorInternalError(err)
-		}
-
-		// If this is an "Unknown" file type, ie., one we
-		// tried to process and couldn't, or one we refused
-		// to process because it wasn't supported, then we
-		// can skip a lot of steps here by simply forwarding
-		// the request to the remote URL.
-		url := &storage.PresignedURL{
-			URL: remoteURL,
-
-			// We might manage to cache the media
-			// at some point, so set a low-ish expiry.
-			Expiry: time.Now().Add(2 * time.Hour),
-		}
-
-		return &apimodel.Content{URL: url}, nil
 	}
 
+	// If requester was provided, use their username
+	// to create a transport to potentially re-fetch
+	// the media. Else falls back to instance account.
 	var requestUser string
-
 	if requester != nil {
-		// Set requesting acc username.
 		requestUser = requester.Username
 	}
 
@@ -217,10 +209,9 @@ func (p *Processor) getAttachmentContent(
 
 func (p *Processor) getEmojiContent(
 	ctx context.Context,
-
+	acctID string,
-	ownerID string,
-	emojiID string,
 	sizeStr media.Size,
+	emojiID string,
 ) (
 	*apimodel.Content,
 	gtserror.WithCode,
@@ -229,7 +220,7 @@ func (p *Processor) getEmojiContent(
 	// As refreshed emojis use a newly generated path ID to
 	// differentiate them (cache-wise) from the original.
 	staticURL := uris.URIForAttachment(
-		ownerID,
+		acctID,
 		string(media.TypeEmoji),
 		string(media.SizeStatic),
 		emojiID,
@@ -323,8 +314,9 @@ func (p *Processor) getContent(
 
 	// Ensure found.
 	if rc == nil {
+		err := gtserror.Newf("file not found at %s", path)
 		const text = "file not found"
-		return nil, gtserror.NewErrorNotFound(errors.New(text), text)
+		return nil, gtserror.NewErrorNotFound(err, text)
 	}
 
 	// Return with stream.
@@ -332,6 +324,41 @@ func (p *Processor) getContent(
 	return content, nil
 }
 
+// handles serving Content for "unknown" file
+// type, ie., a file we couldn't cache (this time).
+func handleUnknown(
+	attach *gtsmodel.MediaAttachment,
+) (*apimodel.Content, gtserror.WithCode) {
+	if attach.RemoteURL == "" {
+		err := gtserror.Newf("empty remote url for %s", attach.ID)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	// Parse media remote URL to valid URL object.
+	remoteURL, err := url.Parse(attach.RemoteURL)
+	if err != nil {
+		err := gtserror.Newf("invalid remote url for %s: %w", attach.ID, err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	if remoteURL == nil {
+		err := gtserror.Newf("nil remote url for %s", attach.ID)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	// Just forward the request to the remote URL,
+	// since this is a type we couldn't process.
+	url := &storage.PresignedURL{
+		URL: remoteURL,
+
+		// We might manage to cache the media
+		// at some point, so set a low-ish expiry.
+		Expiry: time.Now().Add(2 * time.Hour),
+	}
+
+	return &apimodel.Content{URL: url}, nil
+}
+
 func parseType(s string) (media.Type, error) {
 	switch s {
 	case string(media.TypeAttachment):
@@ -357,3 +384,23 @@ func parseSize(s string) (media.Size, error) {
 	}
 	return "", fmt.Errorf("%s not a recognized media.Size", s)
 }
+
+// Extract the mediaID and file extension from
+// a string like "01J3CTH8CZ6ATDNMG6CPRC36XE.gif"
+func parseFileName(s string) (string, string, error) {
+	spl := strings.Split(s, ".")
+	if len(spl) != 2 || spl[0] == "" || spl[1] == "" {
+		return "", "", errors.New("file name not splittable on '.'")
+	}
+
+	var (
+		mediaID  = spl[0]
+		mediaExt = spl[1]
+	)
+
+	if !regexes.ULID.MatchString(mediaID) {
+		return "", "", fmt.Errorf("%s not a valid ULID", mediaID)
+	}
+
+	return mediaID, mediaExt, nil
+}

internal/storage/storage.go

@@ -52,6 +52,12 @@ type PresignedURL struct {
 	Expiry time.Time // link expires at this time
 }
 
+// IsInvalidKey returns whether error is an invalid-key
+// type error returned by the underlying storage library.
+func IsInvalidKey(err error) bool {
+	return errors.Is(err, storage.ErrInvalidKey)
+}
+
 // IsAlreadyExist returns whether error is an already-exists
 // type error returned by the underlying storage library.
 func IsAlreadyExist(err error) bool {