[bugfix] Tidy up rss feed serving; don't error on empty feed (#1970)

* [bugfix] Tidy up rss feed serving; don't error on empty feed

* fall back to account creation time as rss feed update time

* return feed early when account has no eligible statuses

internal/processing/account/rss.go

@@ -27,82 +27,151 @@
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 )
 
-const rssFeedLength = 20
+const (
+	rssFeedLength = 20
+)
+
+type GetRSSFeed func() (string, gtserror.WithCode)
+
+// GetRSSFeedForUsername returns a function to return the RSS feed of a local account
+// with the given username, and the last-modified time (time that the account last
+// posted a status eligible to be included in the rss feed).
+//
+// To save db calls, callers to this function should only call the returned GetRSSFeed
+// func if the last-modified time is newer than the last-modified time they have cached.
+//
+// If the account has not yet posted an RSS-eligible status, the returned last-modified
+// time will be zero, and the GetRSSFeed func will return a valid RSS xml with no items.
+func (p *Processor) GetRSSFeedForUsername(ctx context.Context, username string) (GetRSSFeed, time.Time, gtserror.WithCode) {
+	var (
+		never = time.Time{}
+	)
 
-// GetRSSFeedForUsername returns RSS feed for the given local username.
-func (p *Processor) GetRSSFeedForUsername(ctx context.Context, username string) (func() (string, gtserror.WithCode), time.Time, gtserror.WithCode) {
 	account, err := p.state.DB.GetAccountByUsernameDomain(ctx, username, "")
 	if err != nil {
-		if err == db.ErrNoEntries {
+		if errors.Is(err, db.ErrNoEntries) {
-			return nil, time.Time{}, gtserror.NewErrorNotFound(errors.New("GetRSSFeedForUsername: account not found"))
+			// Simply no account with this username.
+			err = gtserror.New("account not found")
+			return nil, never, gtserror.NewErrorNotFound(err)
 		}
-		return nil, time.Time{}, gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: db error: %s", err))
+
+		// Real db error.
+		err = gtserror.Newf("db error getting account %s: %w", username, err)
+		return nil, never, gtserror.NewErrorInternalError(err)
 	}
 
+	// Ensure account has rss feed enabled.
 	if !*account.EnableRSS {
-		return nil, time.Time{}, gtserror.NewErrorNotFound(errors.New("GetRSSFeedForUsername: account RSS feed not enabled"))
+		err = gtserror.New("account RSS feed not enabled")
+		return nil, never, gtserror.NewErrorNotFound(err)
 	}
 
-	lastModified, err := p.state.DB.GetAccountLastPosted(ctx, account.ID, true)
+	// LastModified time is needed by callers to check freshness for cacheing.
-	if err != nil {
+	// This might be a zero time.Time if account has never posted a status that's
-		return nil, time.Time{}, gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: db error: %s", err))
+	// eligible to appear in the RSS feed; that's fine.
+	lastPostAt, err := p.state.DB.GetAccountLastPosted(ctx, account.ID, true)
+	if err != nil && !errors.Is(err, db.ErrNoEntries) {
+		err = gtserror.Newf("db error getting account %s last posted: %w", username, err)
+		return nil, never, gtserror.NewErrorInternalError(err)
 	}
 
 	return func() (string, gtserror.WithCode) {
-		statuses, err := p.state.DB.GetAccountWebStatuses(ctx, account.ID, rssFeedLength, "")
+		// Assemble author namestring once only.
-		if err != nil && err != db.ErrNoEntries {
-			return "", gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: db error: %s", err))
-		}
-
 		author := "@" + account.Username + "@" + config.GetAccountDomain()
-		title := "Posts from " + author
-		description := "Posts from " + author
-		link := &feeds.Link{Href: account.URL}
 
-		var image *feeds.Image
+		// Derive image/thumbnail for this account (may be nil).
-		if account.AvatarMediaAttachmentID != "" {
+		image, errWithCode := p.rssImageForAccount(ctx, account, author)
-			if account.AvatarMediaAttachment == nil {
+		if errWithCode != nil {
-				avatar, err := p.state.DB.GetAttachmentByID(ctx, account.AvatarMediaAttachmentID)
+			return "", errWithCode
-				if err != nil {
-					return "", gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: db error fetching avatar attachment: %s", err))
-				}
-				account.AvatarMediaAttachment = avatar
-			}
-			image = &feeds.Image{
-				Url:   account.AvatarMediaAttachment.Thumbnail.URL,
-				Title: "Avatar for " + author,
-				Link:  account.URL,
-			}
 		}
 
 		feed := &feeds.Feed{
-			Title:       title,
+			Title:       "Posts from " + author,
-			Description: description,
+			Description: "Posts from " + author,
-			Link:        link,
+			Link:        &feeds.Link{Href: account.URL},
 			Image:       image,
 		}
 
-		for i, s := range statuses {
+		// If the account has never posted anything, just use
-			// take the date of the first (ie., latest) status as feed updated value
+		// account creation time as Updated value for the feed;
-			if i == 0 {
+		// we could use time.Now() here but this would likely
-				feed.Updated = s.UpdatedAt
+		// mess up cacheing; we want something determinate.
-			}
+		//
+		// We can also return early rather than wasting a db call,
+		// since we already know there's no eligible statuses.
+		if lastPostAt.IsZero() {
+			feed.Updated = account.CreatedAt
+			return stringifyFeed(feed)
+		}
 
-			item, err := p.tc.StatusToRSSItem(ctx, s)
+		// Account has posted at least one status that's
+		// eligible to appear in the RSS feed.
+		//
+		// Reuse the lastPostAt value for feed.Updated.
+		feed.Updated = lastPostAt
+
+		// Retrieve latest statuses as they'd be shown on the web view of the account profile.
+		statuses, err := p.state.DB.GetAccountWebStatuses(ctx, account.ID, rssFeedLength, "")
+		if err != nil && !errors.Is(err, db.ErrNoEntries) {
+			err = fmt.Errorf("db error getting account web statuses: %w", err)
+			return "", gtserror.NewErrorInternalError(err)
+		}
+
+		// Add each status to the rss feed.
+		for _, status := range statuses {
+			item, err := p.tc.StatusToRSSItem(ctx, status)
 			if err != nil {
-				return "", gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: error converting status to feed item: %s", err))
+				err = gtserror.Newf("error converting status to feed item: %w", err)
+				return "", gtserror.NewErrorInternalError(err)
 			}
 
 			feed.Add(item)
 		}
 
-		rss, err := feed.ToRss()
+		return stringifyFeed(feed)
-		if err != nil {
+	}, lastPostAt, nil
-			return "", gtserror.NewErrorInternalError(fmt.Errorf("GetRSSFeedForUsername: error converting feed to rss string: %s", err))
+}
-		}
+
-
+func (p *Processor) rssImageForAccount(ctx context.Context, account *gtsmodel.Account, author string) (*feeds.Image, gtserror.WithCode) {
-		return rss, nil
+	if account.AvatarMediaAttachmentID == "" {
-	}, lastModified, nil
+		// No image, no problem!
+		return nil, nil
+	}
+
+	// Ensure account avatar attachment populated.
+	if account.AvatarMediaAttachment == nil {
+		var err error
+		account.AvatarMediaAttachment, err = p.state.DB.GetAttachmentByID(ctx, account.AvatarMediaAttachmentID)
+		if err != nil {
+			if errors.Is(err, db.ErrNoEntries) {
+				// No attachment found with this ID (race condition?).
+				return nil, nil
+			}
+
+			// Real db error.
+			err = gtserror.Newf("db error fetching avatar media attachment: %w", err)
+			return nil, gtserror.NewErrorInternalError(err)
+		}
+	}
+
+	return &feeds.Image{
+		Url:   account.AvatarMediaAttachment.Thumbnail.URL,
+		Title: "Avatar for " + author,
+		Link:  account.URL,
+	}, nil
+}
+
+func stringifyFeed(feed *feeds.Feed) (string, gtserror.WithCode) {
+	// Stringify the feed. Even with no statuses,
+	// this will still produce valid rss xml.
+	rss, err := feed.ToRss()
+	if err != nil {
+		err := gtserror.Newf("error converting feed to rss string: %w", err)
+		return "", gtserror.NewErrorInternalError(err)
+	}
+
+	return rss, nil
 }

internal/processing/account/rss_test.go

@@ -55,6 +55,34 @@ func (suite *GetRSSTestSuite) TestGetAccountRSSZork() {
 	suite.Equal("<?xml version=\"1.0\" encoding=\"UTF-8\"?><rss version=\"2.0\" xmlns:content=\"http://purl.org/rss/1.0/modules/content/\">\n  <channel>\n    <title>Posts from @the_mighty_zork@localhost:8080</title>\n    <link>http://localhost:8080/@the_mighty_zork</link>\n    <description>Posts from @the_mighty_zork@localhost:8080</description>\n    <pubDate>Wed, 20 Oct 2021 10:40:37 +0000</pubDate>\n    <lastBuildDate>Wed, 20 Oct 2021 10:40:37 +0000</lastBuildDate>\n    <image>\n      <url>http://localhost:8080/fileserver/01F8MH1H7YV1Z7D2C8K2730QBF/avatar/small/01F8MH58A357CV5K7R7TJMSH6S.jpg</url>\n      <title>Avatar for @the_mighty_zork@localhost:8080</title>\n      <link>http://localhost:8080/@the_mighty_zork</link>\n    </image>\n    <item>\n      <title>introduction post</title>\n      <link>http://localhost:8080/@the_mighty_zork/statuses/01F8MHAMCHF6Y650WCRSCP4WMY</link>\n      <description>@the_mighty_zork@localhost:8080 made a new post: &#34;hello everyone!&#34;</description>\n      <content:encoded><![CDATA[hello everyone!]]></content:encoded>\n      <author>@the_mighty_zork@localhost:8080</author>\n      <guid>http://localhost:8080/@the_mighty_zork/statuses/01F8MHAMCHF6Y650WCRSCP4WMY</guid>\n      <pubDate>Wed, 20 Oct 2021 10:40:37 +0000</pubDate>\n      <source>http://localhost:8080/@the_mighty_zork/feed.rss</source>\n    </item>\n  </channel>\n</rss>", feed)
 }
 
+func (suite *GetRSSTestSuite) TestGetAccountRSSZorkNoPosts() {
+	ctx := context.Background()
+
+	// Get all of zork's posts.
+	statuses, err := suite.db.GetAccountStatuses(ctx, suite.testAccounts["local_account_1"].ID, 0, false, false, "", "", false, false)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	// Now delete them! Hahaha!
+	for _, status := range statuses {
+		if err := suite.db.DeleteStatusByID(ctx, status.ID); err != nil {
+			suite.FailNow(err.Error())
+		}
+	}
+
+	getFeed, lastModified, err := suite.accountProcessor.GetRSSFeedForUsername(ctx, "the_mighty_zork")
+	suite.NoError(err)
+	suite.Empty(lastModified)
+
+	feed, err := getFeed()
+	suite.NoError(err)
+
+	fmt.Println(feed)
+
+	suite.Equal("<?xml version=\"1.0\" encoding=\"UTF-8\"?><rss version=\"2.0\" xmlns:content=\"http://purl.org/rss/1.0/modules/content/\">\n  <channel>\n    <title>Posts from @the_mighty_zork@localhost:8080</title>\n    <link>http://localhost:8080/@the_mighty_zork</link>\n    <description>Posts from @the_mighty_zork@localhost:8080</description>\n    <pubDate>Fri, 20 May 2022 11:09:18 +0000</pubDate>\n    <lastBuildDate>Fri, 20 May 2022 11:09:18 +0000</lastBuildDate>\n    <image>\n      <url>http://localhost:8080/fileserver/01F8MH1H7YV1Z7D2C8K2730QBF/avatar/small/01F8MH58A357CV5K7R7TJMSH6S.jpg</url>\n      <title>Avatar for @the_mighty_zork@localhost:8080</title>\n      <link>http://localhost:8080/@the_mighty_zork</link>\n    </image>\n  </channel>\n</rss>", feed)
+}
+
 func TestGetRSSTestSuite(t *testing.T) {
 	suite.Run(t, new(GetRSSTestSuite))
 }

internal/web/rss.go

@@ -19,8 +19,6 @@
 
 import (
 	"bytes"
-	"errors"
-	"fmt"
 	"net/http"
 	"strings"
 	"time"
@@ -31,86 +29,50 @@
 	"github.com/superseriousbusiness/gotosocial/internal/log"
 )
 
-const appRSSUTF8 = string(apiutil.AppRSSXML + "; charset=utf-8")
+const appRSSUTF8 = string(apiutil.AppRSSXML) + "; charset=utf-8"
-
-func (m *Module) GetRSSETag(urlPath string, lastModified time.Time, getRSSFeed func() (string, gtserror.WithCode)) (string, error) {
-	if cachedETag, ok := m.eTagCache.Get(urlPath); ok && !lastModified.After(cachedETag.lastModified) {
-		// only return our cached etag if the file wasn't
-		// modified since last time, otherwise generate a
-		// new one; eat fresh!
-		return cachedETag.eTag, nil
-	}
-
-	rssFeed, errWithCode := getRSSFeed()
-	if errWithCode != nil {
-		return "", fmt.Errorf("error getting rss feed: %s", errWithCode)
-	}
-
-	eTag, err := generateEtag(bytes.NewReader([]byte(rssFeed)))
-	if err != nil {
-		return "", fmt.Errorf("error generating etag: %s", err)
-	}
-
-	// put new entry in cache before we return
-	m.eTagCache.Set(urlPath, eTagCacheEntry{
-		eTag:         eTag,
-		lastModified: lastModified,
-	})
-
-	return eTag, nil
-}
-
-func extractIfModifiedSince(r *http.Request) time.Time {
-	hdr := r.Header.Get(ifModifiedSinceHeader)
-
-	if hdr == "" {
-		return time.Time{}
-	}
-
-	t, err := http.ParseTime(hdr)
-	if err != nil {
-		log.Errorf(r.Context(), "couldn't parse if-modified-since %s: %s", hdr, err)
-		return time.Time{}
-	}
-
-	return t
-}
 
 func (m *Module) rssFeedGETHandler(c *gin.Context) {
-	// set this Cache-Control header to instruct clients to validate the response with us
-	// before each reuse (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control)
-	c.Header(cacheControlHeader, cacheControlNoCache)
-	ctx := c.Request.Context()
-
 	if _, err := apiutil.NegotiateAccept(c, apiutil.AppRSSXML); err != nil {
 		apiutil.WebErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
 		return
 	}
 
-	// usernames on our instance will always be lowercase
+	// Fetch + normalize username from URL.
-	username := strings.ToLower(c.Param(usernameKey))
+	username, errWithCode := apiutil.ParseWebUsername(c.Param(apiutil.WebUsernameKey))
-	if username == "" {
-		err := errors.New("no account username specified")
-		apiutil.WebErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGetV1)
-		return
-	}
-
-	ifNoneMatch := c.Request.Header.Get(ifNoneMatchHeader)
-	ifModifiedSince := extractIfModifiedSince(c.Request)
-
-	getRssFeed, accountLastPostedPublic, errWithCode := m.processor.Account().GetRSSFeedForUsername(ctx, username)
 	if errWithCode != nil {
 		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
 		return
 	}
 
-	var rssFeed string
+	// Usernames on our instance will always be lowercase.
-	cacheKey := c.Request.URL.Path
+	//
-	cacheEntry, ok := m.eTagCache.Get(cacheKey)
+	// todo: https://github.com/superseriousbusiness/gotosocial/issues/1813
+	username = strings.ToLower(username)
 
-	if !ok || cacheEntry.lastModified.Before(accountLastPostedPublic) {
+	// Retrieve the getRSSFeed function from the processor.
-		// we either have no cache entry for this, or we have an expired cache entry; generate a new one
+	// We'll only call the function if we need to, to save db calls.
-		rssFeed, errWithCode = getRssFeed()
+	// lastPostAt may be a zero time if account has never posted.
+	getRSSFeed, lastPostAt, errWithCode := m.processor.Account().GetRSSFeedForUsername(c.Request.Context(), username)
+	if errWithCode != nil {
+		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	var (
+		rssFeed string // Stringified rss feed.
+
+		cacheKey              = c.Request.URL.Path
+		cacheEntry, wasCached = m.eTagCache.Get(cacheKey)
+	)
+
+	if !wasCached || unixAfter(lastPostAt, cacheEntry.lastModified) {
+		// We either have no ETag cache entry for this account's feed,
+		// or we have an expired cache entry (account has posted since
+		// the cache entry was last generated).
+		//
+		// As such, we need to generate a new ETag, and for that we need
+		// the string representation of the RSS feed.
+		rssFeed, errWithCode = getRSSFeed()
 		if errWithCode != nil {
 			apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
 			return
@@ -122,29 +84,73 @@ func (m *Module) rssFeedGETHandler(c *gin.Context) {
 			return
 		}
 
-		cacheEntry.lastModified = accountLastPostedPublic
+		// We never want lastModified to be zero, so if account
-		cacheEntry.eTag = eTag
+		// has never actually posted anything, just use Now as
+		// the lastModified time instead for cache control.
+		var lastModified time.Time
+		if lastPostAt.IsZero() {
+			lastModified = time.Now()
+		} else {
+			lastModified = lastPostAt
+		}
+
+		// Store the new cache entry.
+		cacheEntry = eTagCacheEntry{
+			eTag:         eTag,
+			lastModified: lastModified,
+		}
 		m.eTagCache.Set(cacheKey, cacheEntry)
 	}
 
+	// Set 'ETag' and 'Last-Modified' headers no matter what;
+	// even if we return 304 in the next checks, caller may
+	// want to cache these header values.
 	c.Header(eTagHeader, cacheEntry.eTag)
-	c.Header(lastModifiedHeader, accountLastPostedPublic.Format(http.TimeFormat))
+	c.Header(lastModifiedHeader, cacheEntry.lastModified.Format(http.TimeFormat))
 
+	// Instruct caller to validate the response with us before
+	// each reuse, so that the 'ETag' and 'Last-Modified' headers
+	// actually take effect.
+	//
+	// "The no-cache response directive indicates that the response
+	// can be stored in caches, but the response must be validated
+	// with the origin server before each reuse, even when the cache
+	// is disconnected from the origin server."
+	//
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
+	c.Header(cacheControlHeader, cacheControlNoCache)
+
+	// Check if caller submitted an ETag via 'If-None-Match'.
+	// If they did + it matches what we have, that means they've
+	// already seen the latest version of this feed, so just bail.
+	ifNoneMatch := c.Request.Header.Get(ifNoneMatchHeader)
 	if ifNoneMatch == cacheEntry.eTag {
 		c.AbortWithStatus(http.StatusNotModified)
 		return
 	}
 
-	lmUnix := cacheEntry.lastModified.Unix()
+	// Check if the caller submitted a time via 'If-Modified-Since'.
-	imsUnix := ifModifiedSince.Unix()
+	// If they did, and our cached ETag entry is not newer than the
-	if lmUnix <= imsUnix {
+	// given time, this means the caller has already seen the latest
+	// version of this feed, so just bail.
+	ifModifiedSince := extractIfModifiedSince(c.Request)
+	if !ifModifiedSince.IsZero() &&
+		!unixAfter(cacheEntry.lastModified, ifModifiedSince) {
 		c.AbortWithStatus(http.StatusNotModified)
 		return
 	}
 
+	// At this point we know that the client wants the newest
+	// representation of the RSS feed, either because they didn't
+	// submit any 'If-None-Match' / 'If-Modified-Since' cache headers,
+	// or because they did but the account has posted more recently
+	// than the values of the submitted headers would suggest.
+	//
+	// If we had a cache hit earlier, we may not have called the
+	// getRSSFeed function yet; if that's the case then do call it
+	// now because we definitely need it.
 	if rssFeed == "" {
-		// we had a cache entry already so we didn't call to get the rss feed yet
+		rssFeed, errWithCode = getRSSFeed()
-		rssFeed, errWithCode = getRssFeed()
 		if errWithCode != nil {
 			apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
 			return
@@ -153,3 +159,41 @@ func (m *Module) rssFeedGETHandler(c *gin.Context) {
 
 	c.Data(http.StatusOK, appRSSUTF8, []byte(rssFeed))
 }
+
+// unixAfter returns true if the unix value of t1
+// is greater than (ie., after) the unix value of t2.
+func unixAfter(t1 time.Time, t2 time.Time) bool {
+	if t1.IsZero() {
+		// if t1 is zero then it cannot
+		// possibly be greater than t2.
+		return false
+	}
+
+	if t2.IsZero() {
+		// t1 is not zero but t2 is,
+		// so t1 is necessarily greater.
+		return true
+	}
+
+	return t1.Unix() > t2.Unix()
+}
+
+// extractIfModifiedSince parses a time.Time from the
+// 'If-Modified-Since' header of the given request.
+//
+// If no time was provided, or the provided time was
+// not parseable, it will return a zero time.
+func extractIfModifiedSince(r *http.Request) time.Time {
+	imsStr := r.Header.Get(ifModifiedSinceHeader)
+	if imsStr == "" {
+		return time.Time{} // Nothing set.
+	}
+
+	ifModifiedSince, err := http.ParseTime(imsStr)
+	if err != nil {
+		log.Errorf(r.Context(), "couldn't parse %s value '%s' as time: %q", ifModifiedSinceHeader, imsStr, err)
+		return time.Time{}
+	}
+
+	return ifModifiedSince
+}