[bugfix] Don't return Account or Status if new and dereferencing failed, other small fixes (#2563)

* tidy up account, status, webfingering logic a wee bit

* go fmt

* invert published check

* alter resp initialization

* get Published from account in typeutils

* don't instantiate error for no darn good reason

* shadow err

* don't repeat error codes in wrapped errors

* don't wrap error unnecessarily

internal/ap/interfaces.go

@@ -163,6 +163,7 @@ type Accountable interface {
 	WithManuallyApprovesFollowers
 	WithEndpoints
 	WithTag
+	WithPublished
 }
 
 // Statusable represents the minimum activitypub interface for representing a 'status'.

internal/federation/dereferencing/account.go

@@ -52,7 +52,7 @@ func accountUpToDate(account *gtsmodel.Account, force bool) bool {
 		return true
 	}
 
-	if !account.CreatedAt.IsZero() && account.IsInstance() {
+	if account.IsInstance() && !account.IsNew() {
 		// Existing instance account. No need for update.
 		return true
 	}
@@ -232,8 +232,8 @@ func (d *Dereferencer) getAccountByUsernameDomain(
 		// Create and pass-through a new bare-bones model for dereferencing.
 		account, accountable, err := d.enrichAccountSafely(ctx, requestUser, nil, &gtsmodel.Account{
 			ID:       id.NewULID(),
-			Username: username,
 			Domain:   domain,
+			Username: username,
 		}, nil)
 		if err != nil {
 			return nil, nil, err
@@ -372,17 +372,18 @@ func (d *Dereferencer) enrichAccountSafely(
 
 	// By default use account.URI
 	// as the per-URI deref lock.
-	uriStr := account.URI
-
-	if uriStr == "" {
+	var lockKey string
+	if account.URI != "" {
+		lockKey = account.URI
+	} else {
 		// No URI is set yet, instead generate a faux-one from user+domain.
-		uriStr = "https://" + account.Domain + "/user/" + account.Username
+		lockKey = "https://" + account.Domain + "/users/" + account.Username
 	}
 
 	// Acquire per-URI deref lock, wraping unlock
 	// to safely defer in case of panic, while still
 	// performing more granular unlocks when needed.
-	unlock := d.state.FedLocks.Lock(uriStr)
+	unlock := d.state.FedLocks.Lock(lockKey)
 	unlock = doOnce(unlock)
 	defer unlock()
 
@@ -394,10 +395,30 @@ func (d *Dereferencer) enrichAccountSafely(
 		accountable,
 	)
 
-	if gtserror.StatusCode(err) >= 400 {
-		// Update fetch-at to slow re-attempts.
+	if code := gtserror.StatusCode(err); code >= 400 {
+		// No matter what, log the error
+		// so instance admins have an idea
+		// why something isn't working.
+		log.Info(ctx, err)
+
+		if account.IsNew() {
+			// This was a new account enrich
+			// attempt which failed before we
+			// got to store it, so we can't
+			// return anything useful.
+			return nil, nil, err
+		}
+
+		// We had this account stored already
+		// before this enrichment attempt.
+		//
+		// Update fetched_at to slow re-attempts
+		// but don't return early. We can still
+		// return the model we had stored already.
 		account.FetchedAt = time.Now()
-		_ = d.state.DB.UpdateAccount(ctx, account, "fetched_at")
+		if err := d.state.DB.UpdateAccount(ctx, account, "fetched_at"); err != nil {
+			log.Errorf(ctx, "error updating account fetched_at: %v", err)
+		}
 	}
 
 	// Unlock now
@@ -414,7 +435,7 @@ func (d *Dereferencer) enrichAccountSafely(
 		// in a call to db.Put(Account). Look again in DB by URI.
 		latest, err = d.state.DB.GetAccountByURI(ctx, account.URI)
 		if err != nil {
-			err = gtserror.Newf("error getting account %s from database after race: %w", uriStr, err)
+			err = gtserror.Newf("error getting account %s from database after race: %w", lockKey, err)
 		}
 	}
 
@@ -440,32 +461,44 @@ func (d *Dereferencer) enrichAccount(
 	if account.Username != "" {
 		// A username was provided so we can attempt a webfinger, this ensures up-to-date accountdomain info.
 		accDomain, accURI, err := d.fingerRemoteAccount(ctx, tsport, account.Username, account.Domain)
-		if err != nil {
-			if account.URI == "" {
-				// this is a new account (to us) with username@domain
+		switch {
+
+		case err != nil && account.URI == "":
+			// This is a new account (to us) with username@domain
 			// but failed webfinger, nothing more we can do.
 			err := gtserror.Newf("error webfingering account: %w", err)
 			return nil, nil, gtserror.SetUnretrievable(err)
-			}
 
-			// Simply log this error and move on, we already have an account URI.
-			log.Errorf(ctx, "error webfingering[1] remote account %s@%s: %v", account.Username, account.Domain, err)
-		}
+		case err != nil:
+			// Simply log this error and move on,
+			// we already have an account URI.
+			log.Errorf(ctx,
+				"error webfingering[1] remote account %s@%s: %v",
+				account.Username, account.Domain, err,
+			)
 
-		if err == nil {
-			if account.Domain != accDomain {
+		case err == nil && account.Domain != accDomain:
 			// After webfinger, we now have correct account domain from which we can do a final DB check.
-				alreadyAccount, err := d.state.DB.GetAccountByUsernameDomain(ctx, account.Username, accDomain)
+			alreadyAcct, err := d.state.DB.GetAccountByUsernameDomain(ctx, account.Username, accDomain)
 			if err != nil && !errors.Is(err, db.ErrNoEntries) {
 				return nil, nil, gtserror.Newf("db err looking for account again after webfinger: %w", err)
 			}
 
-				if alreadyAccount != nil {
-					// Enrich existing account.
-					account = alreadyAccount
-				}
+			if alreadyAcct != nil {
+				// We had this account stored under
+				// the discovered accountDomain.
+				// Proceed with this account.
+				account = alreadyAcct
 			}
 
+			// Whether we had the account or not, we
+			// now have webfinger info relevant to the
+			// account, so fallthrough to set webfinger
+			// info on either the account we just found,
+			// or the stub account we were passed.
+			fallthrough
+
+		case err == nil:
 			// Update account with latest info.
 			account.URI = accURI.String()
 			account.Domain = accDomain
@@ -474,13 +507,31 @@ func (d *Dereferencer) enrichAccount(
 	}
 
 	if uri == nil {
-		// No URI provided / found, must parse from account.
+		// No URI provided / found,
+		// must parse from account.
 		uri, err = url.Parse(account.URI)
 		if err != nil {
-			return nil, nil, gtserror.Newf("invalid uri %q: %w", account.URI, err)
+			return nil, nil, gtserror.Newf(
+				"invalid uri %q: %w",
+				account.URI, gtserror.SetUnretrievable(err),
+			)
+		}
+
+		if uri.Scheme != "http" && uri.Scheme != "https" {
+			err = errors.New("account URI scheme must be http or https")
+			return nil, nil, gtserror.Newf(
+				"invalid uri %q: %w",
+				account.URI, gtserror.SetUnretrievable(err),
+			)
 		}
 	}
 
+	/*
+		BY THIS POINT we must have an account URI set,
+		either provided, pinned to the account, or
+		obtained via webfinger call.
+	*/
+
 	// Check whether this account URI is a blocked domain / subdomain.
 	if blocked, err := d.state.DB.IsDomainBlocked(ctx, uri.Host); err != nil {
 		return nil, nil, gtserror.Newf("error checking blocked domain: %w", err)
@@ -493,27 +544,45 @@ func (d *Dereferencer) enrichAccount(
 	defer d.stopHandshake(requestUser, uri)
 
 	if apubAcc == nil {
+		// We were not given any (partial) ActivityPub
+		// version of this account as a parameter.
 		// Dereference latest version of the account.
 		b, err := tsport.Dereference(ctx, uri)
 		if err != nil {
-			err := gtserror.Newf("error deferencing %s: %w", uri, err)
+			err := gtserror.Newf("error dereferencing %s: %w", uri, err)
 			return nil, nil, gtserror.SetUnretrievable(err)
 		}
 
 		// Attempt to resolve ActivityPub acc from data.
 		apubAcc, err = ap.ResolveAccountable(ctx, b)
 		if err != nil {
-			return nil, nil, gtserror.Newf("error resolving accountable from data for account %s: %w", uri, err)
+			// ResolveAccountable will set Unretrievable/WrongType
+			// on the returned error, so we don't need to do it here.
+			err = gtserror.Newf("error resolving accountable from data for account %s: %w", uri, err)
+			return nil, nil, err
 		}
 	}
 
+	/*
+		BY THIS POINT we must have the ActivityPub
+		representation of the account, either provided,
+		or obtained via a dereference call.
+	*/
+
 	// Convert the dereferenced AP account object to our GTS model.
+	//
+	// We put this in the variable latestAcc because we might want
+	// to compare the provided account model with this fresh version,
+	// in order to check if anything changed since we last saw it.
 	latestAcc, err := d.converter.ASRepresentationToAccount(ctx,
 		apubAcc,
 		account.Domain,
 	)
 	if err != nil {
-		return nil, nil, gtserror.Newf("error converting accountable to gts model for account %s: %w", uri, err)
+		// ASRepresentationToAccount will set Malformed on the
+		// returned error, so we don't need to do it here.
+		err = gtserror.Newf("error converting accountable to gts model for account %s: %w", uri, err)
+		return nil, nil, err
 	}
 
 	if account.Username == "" {
@@ -528,14 +597,15 @@ func (d *Dereferencer) enrichAccount(
 		// from example.org to somewhere.else: we want to take somewhere.else
 		// as the accountDomain then, not the example.org we were redirected from.
 
-		// Assume the host from the returned ActivityPub representation.
-		idProp := apubAcc.GetJSONLDId()
-		if idProp == nil || !idProp.IsIRI() {
+		// Assume the host from the returned
+		// ActivityPub representation.
+		id := ap.GetJSONLDId(apubAcc)
+		if id == nil {
 			return nil, nil, gtserror.New("no id property found on person, or id was not an iri")
 		}
 
 		// Get IRI host value.
-		accHost := idProp.GetIRI().Host
+		accHost := id.Host
 
 		latestAcc.Domain, _, err = d.fingerRemoteAccount(ctx,
 			tsport,
@@ -553,7 +623,7 @@ func (d *Dereferencer) enrichAccount(
 	}
 
 	if latestAcc.Domain == "" {
-		// ensure we have a domain set by this point,
+		// Ensure we have a domain set by this point,
 		// otherwise it gets stored as a local user!
 		//
 		// TODO: there is probably a more granular way
@@ -562,7 +632,16 @@ func (d *Dereferencer) enrichAccount(
 		return nil, nil, gtserror.Newf("empty domain for %s", uri)
 	}
 
-	// Ensure ID is set and update fetch time.
+	/*
+		BY THIS POINT we have more or less a fullly-formed
+		representation of the target account, derived from
+		a combination of webfinger lookups and dereferencing.
+		Further fetching beyond this point is for peripheral
+		things like account avatar, header, emojis.
+	*/
+
+	// Ensure internal db ID is
+	// set and update fetch time.
 	latestAcc.ID = account.ID
 	latestAcc.FetchedAt = time.Now()
 
@@ -581,12 +660,14 @@ func (d *Dereferencer) enrichAccount(
 		log.Errorf(ctx, "error fetching remote emojis for account %s: %v", uri, err)
 	}
 
-	if account.CreatedAt.IsZero() {
-		// CreatedAt will be zero if no local copy was
-		// found in one of the GetAccountBy___() functions.
-		//
-		// Set time of creation from the last-fetched date.
+	if account.IsNew() {
+		// Prefer published/created time from
+		// apubAcc, fall back to FetchedAt value.
+		if latestAcc.CreatedAt.IsZero() {
 			latestAcc.CreatedAt = latestAcc.FetchedAt
+		}
+
+		// Set time of update from the last-fetched date.
 		latestAcc.UpdatedAt = latestAcc.FetchedAt
 
 		// This is new, put it in the database.
@@ -595,11 +676,16 @@ func (d *Dereferencer) enrichAccount(
 			return nil, nil, gtserror.Newf("error putting in database: %w", err)
 		}
 	} else {
+		// Prefer published time from apubAcc,
+		// fall back to previous stored value.
+		if latestAcc.CreatedAt.IsZero() {
+			latestAcc.CreatedAt = account.CreatedAt
+		}
+
 		// Set time of update from the last-fetched date.
 		latestAcc.UpdatedAt = latestAcc.FetchedAt
 
-		// Use existing account values.
-		latestAcc.CreatedAt = account.CreatedAt
+		// Carry over existing account language.
 		latestAcc.Language = account.Language
 
 		// This is an existing account, update the model in the database.

internal/federation/dereferencing/finger.go

@@ -20,54 +20,109 @@
 import (
 	"context"
 	"encoding/json"
-	"errors"
-	"fmt"
 	"net/url"
 	"strings"
 
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
 	"github.com/superseriousbusiness/gotosocial/internal/transport"
 	"github.com/superseriousbusiness/gotosocial/internal/util"
 )
 
-func (d *Dereferencer) fingerRemoteAccount(ctx context.Context, transport transport.Transport, targetUsername string, targetHost string) (accountDomain string, accountURI *url.URL, err error) {
-	b, err := transport.Finger(ctx, targetUsername, targetHost)
+// fingerRemoteAccount performs a webfinger call for the
+// given username and host, using the provided transport.
+//
+// The webfinger response will be parsed, and the subject
+// domain and AP URI will be extracted and returned.
+//
+// In case the response cannot be parsed, or the response
+// does not contain a valid subject string or AP URI, an
+// error will be returned instead.
+func (d *Dereferencer) fingerRemoteAccount(
+	ctx context.Context,
+	transport transport.Transport,
+	username string,
+	host string,
+) (
+	string, // discovered account domain
+	*url.URL, // discovered account URI
+	error,
+) {
+	// Assemble target namestring for logging.
+	var target = "@" + username + "@" + host
+
+	b, err := transport.Finger(ctx, username, host)
 	if err != nil {
-		err = fmt.Errorf("fingerRemoteAccount: error fingering @%s@%s: %s", targetUsername, targetHost, err)
-		return
+		err = gtserror.Newf("error webfingering %s: %w", target, err)
+		return "", nil, err
 	}
 
-	resp := &apimodel.WellKnownResponse{}
-	if err = json.Unmarshal(b, resp); err != nil {
-		err = fmt.Errorf("fingerRemoteAccount: could not unmarshal server response as WebfingerAccountResponse while dereferencing @%s@%s: %s", targetUsername, targetHost, err)
-		return
+	var resp apimodel.WellKnownResponse
+	if err := json.Unmarshal(b, &resp); err != nil {
+		err = gtserror.Newf("error parsing response as JSON for %s: %w", target, err)
+		return "", nil, err
 	}
 
 	if len(resp.Links) == 0 {
-		err = fmt.Errorf("fingerRemoteAccount: no links found in webfinger response %s", string(b))
-		return
+		err = gtserror.Newf("no links found in response for %s", target)
+		return "", nil, err
 	}
 
 	if resp.Subject == "" {
-		err = fmt.Errorf("fingerRemoteAccount: no subject found in webfinger response %s", string(b))
-		return
+		err = gtserror.Newf("no subject found in response for %s", target)
+		return "", nil, err
 	}
 
-	_, accountDomain, err = util.ExtractWebfingerParts(resp.Subject)
+	_, accountDomain, err := util.ExtractWebfingerParts(resp.Subject)
 	if err != nil {
-		err = fmt.Errorf("fingerRemoteAccount: error extracting webfinger subject parts: %s", err)
+		err = gtserror.Newf("error extracting subject parts for %s: %w", target, err)
+		return "", nil, err
 	}
 
-	// look through the links for the first one that matches what we need
-	for _, l := range resp.Links {
-		if l.Rel == "self" && (strings.EqualFold(l.Type, "application/activity+json") || strings.EqualFold(l.Type, "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"")) {
-			if uri, thiserr := url.Parse(l.Href); thiserr == nil && (uri.Scheme == "http" || uri.Scheme == "https") {
-				// found it!
-				accountURI = uri
-				return
-			}
-		}
+	// Look through links for the first
+	// one that matches what we need:
+	//
+	//   - Must be self link.
+	//   - Must be AP type.
+	//   - Valid https/http URI.
+	for _, link := range resp.Links {
+		if link.Rel != "self" {
+			// Not self link, ignore.
+			continue
 		}
 
-	return "", nil, errors.New("fingerRemoteAccount: no match found in webfinger response")
+		if !strings.EqualFold(link.Type, "application/activity+json") &&
+			!strings.EqualFold(link.Type, "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"") {
+			// Not an AP type, ignore.
+			continue
+		}
+
+		uri, err := url.Parse(link.Href)
+		if err != nil {
+			log.Warnf(ctx,
+				"invalid href for ActivityPub self link %s for %s: %v",
+				link.Href, target, err,
+			)
+
+			// Funky URL, ignore.
+			continue
+		}
+
+		if uri.Scheme != "http" && uri.Scheme != "https" {
+			log.Warnf(ctx,
+				"invalid href for ActivityPub self link %s for %s: schema must be http or https",
+				link.Href, target,
+			)
+
+			// Can't handle this
+			// schema, ignore.
+			continue
+		}
+
+		// All looks good, return happily!
+		return accountDomain, uri, nil
+	}
+
+	return "", nil, gtserror.Newf("no suitable self, AP-type link found in webfinger response for %s", target)
 }

internal/federation/dereferencing/status.go

@@ -294,10 +294,30 @@ func (d *Dereferencer) enrichStatusSafely(
 		apubStatus,
 	)
 
-	if gtserror.StatusCode(err) >= 400 {
-		// Update fetch-at to slow re-attempts.
+	if code := gtserror.StatusCode(err); code >= 400 {
+		// No matter what, log the error
+		// so instance admins have an idea
+		// why something isn't working.
+		log.Info(ctx, err)
+
+		if isNew {
+			// This was a new status enrich
+			// attempt which failed before we
+			// got to store it, so we can't
+			// return anything useful.
+			return nil, nil, isNew, err
+		}
+
+		// We had this status stored already
+		// before this enrichment attempt.
+		//
+		// Update fetched_at to slow re-attempts
+		// but don't return early. We can still
+		// return the model we had stored already.
 		status.FetchedAt = time.Now()
-		_ = d.state.DB.UpdateStatus(ctx, status, "fetched_at")
+		if err := d.state.DB.UpdateStatus(ctx, status, "fetched_at"); err != nil {
+			log.Errorf(ctx, "error updating status fetched_at: %v", err)
+		}
 	}
 
 	// Unlock now
@@ -358,7 +378,7 @@ func (d *Dereferencer) enrichStatus(
 		// Dereference latest version of the status.
 		b, err := tsport.Dereference(ctx, uri)
 		if err != nil {
-			err := gtserror.Newf("error deferencing %s: %w", uri, err)
+			err := gtserror.Newf("error dereferencing %s: %w", uri, err)
 			return nil, nil, gtserror.SetUnretrievable(err)
 		}
 
@@ -388,16 +408,21 @@ func (d *Dereferencer) enrichStatus(
 		return nil, nil, gtserror.Newf("error converting statusable to gts model for status %s: %w", uri, err)
 	}
 
-	// Use existing status ID.
-	latestStatus.ID = status.ID
-	if latestStatus.ID == "" {
-
-		// Generate new status ID from the provided creation date.
+	// Check if we've previously
+	// stored this status in the DB.
+	// If we have, it'll be ID'd.
+	var isNew = (status.ID == "")
+	if isNew {
+		// No ID, we haven't stored this status before.
+		// Generate new status ID from the status publication time.
 		latestStatus.ID, err = id.NewULIDFromTime(latestStatus.CreatedAt)
 		if err != nil {
 			log.Errorf(ctx, "invalid created at date (falling back to 'now'): %v", err)
 			latestStatus.ID = id.NewULID() // just use "now"
 		}
+	} else {
+		// Reuse existing status ID.
+		latestStatus.ID = status.ID
 	}
 
 	// Carry-over values and set fetch time.
@@ -436,10 +461,7 @@ func (d *Dereferencer) enrichStatus(
 		return nil, nil, gtserror.Newf("error populating emojis for status %s: %w", uri, err)
 	}
 
-	if status.CreatedAt.IsZero() {
-		// CreatedAt will be zero if no local copy was
-		// found in one of the GetStatusBy___() functions.
-		//
+	if isNew {
 		// This is new, put the status in the database.
 		err := d.state.DB.PutStatus(ctx, latestStatus)
 		if err != nil {

internal/gtsmodel/account.go

@@ -94,6 +94,12 @@ func (a *Account) IsRemote() bool {
 	return !a.IsLocal()
 }
 
+// IsNew returns whether an account is "new" in the sense
+// that it has not been previously stored in the database.
+func (a *Account) IsNew() bool {
+	return a.CreatedAt.IsZero()
+}
+
 // IsInstance returns whether account is an instance internal actor account.
 func (a *Account) IsInstance() bool {
 	if a.IsLocal() {

internal/regexes/regexes.go

@@ -59,6 +59,8 @@
 
 	userPathPrefix    = `^/?` + users + `/(` + usernameRelaxed + `)`
 	userPath          = userPathPrefix + `$`
+	userWebPathPrefix = `^/?` + `@(` + usernameRelaxed + `)`
+	userWebPath       = userWebPathPrefix + `$`
 	publicKeyPath     = userPathPrefix + `/` + publicKey + `$`
 	inboxPath         = userPathPrefix + `/` + inbox + `$`
 	outboxPath        = userPathPrefix + `/` + outbox + `$`
@@ -110,6 +112,9 @@
 	// UserPath validates and captures the username part from eg /users/example_username.
 	UserPath = regexp.MustCompile(userPath)
 
+	// UserWebPath validates and captures the username part from eg /@example_username.
+	UserWebPath = regexp.MustCompile(userWebPath)
+
 	// PublicKeyPath parses a path that validates and captures the username part from eg /users/example_username/main-key
 	PublicKeyPath = regexp.MustCompile(publicKeyPath)
 

internal/typeutils/astointernal.go

@@ -77,6 +77,18 @@ func (c *Converter) ASRepresentationToAccount(ctx context.Context, accountable a
 		return nil, gtserror.SetMalformed(err)
 	}
 
+	// Extract published time if possible.
+	//
+	// This denotes original creation time
+	// of the account on the remote instance.
+	//
+	// Not every implementation uses this property;
+	// so don't bother warning if we can't find it.
+	if pub := ap.GetPublished(accountable); !pub.IsZero() {
+		acct.CreatedAt = pub
+		acct.UpdatedAt = pub
+	}
+
 	// Extract a preferred name (display name), fallback to username.
 	if displayName := ap.ExtractName(accountable); displayName != "" {
 		acct.DisplayName = displayName
@@ -314,7 +326,7 @@ func (c *Converter) ASStatusToStatus(ctx context.Context, statusable ap.Statusab
 
 	// status.Published
 	//
-	// Extract published time for the boost,
+	// Extract published time for the status,
 	// zero-time will fall back to db defaults.
 	if pub := ap.GetPublished(statusable); !pub.IsZero() {
 		status.CreatedAt = pub

internal/typeutils/astointernal_test.go

@@ -138,6 +138,7 @@ func (suite *ASToInternalTestSuite) TestParseGargron() {
 	acct, err := suite.typeconverter.ASRepresentationToAccount(context.Background(), rep, "")
 	suite.NoError(err)
 	suite.Equal("https://mastodon.social/inbox", *acct.SharedInboxURI)
+	suite.Equal(int64(1458086400), acct.CreatedAt.Unix())
 }
 
 func (suite *ASToInternalTestSuite) TestParseReplyWithMention() {

internal/typeutils/converter_test.go

@@ -279,6 +279,8 @@
 		"url": "https://mastodon.social/@Gargron",
 		"manuallyApprovesFollowers": false,
 		"discoverable": true,
+		"indexable": true,
+		"published": "2016-03-16T00:00:00Z",
 		"devices": "https://mastodon.social/users/Gargron/collections/devices",
 		"alsoKnownAs": [
 		  "https://tooting.ai/users/Gargron"

internal/uris/uri.go

@@ -248,6 +248,11 @@ func IsUserPath(id *url.URL) bool {
 	return regexes.UserPath.MatchString(id.Path)
 }
 
+// IsUserWebPath returns true if the given URL path corresponds to eg /@example_username
+func IsUserWebPath(id *url.URL) bool {
+	return regexes.UserWebPath.MatchString(id.Path)
+}
+
 // IsInboxPath returns true if the given URL path corresponds to eg /users/example_username/inbox
 func IsInboxPath(id *url.URL) bool {
 	return regexes.InboxPath.MatchString(id.Path)
@@ -326,6 +331,17 @@ func ParseUserPath(id *url.URL) (username string, err error) {
 	return
 }
 
+// ParseUserPath returns the username from a path such as /@example_username
+func ParseUserWebPath(id *url.URL) (username string, err error) {
+	matches := regexes.UserWebPath.FindStringSubmatch(id.Path)
+	if len(matches) != 2 {
+		err = fmt.Errorf("expected 2 matches but matches length was %d", len(matches))
+		return
+	}
+	username = matches[1]
+	return
+}
+
 // ParseInboxPath returns the username from a path such as /users/example_username/inbox
 func ParseInboxPath(id *url.URL) (username string, err error) {
 	matches := regexes.InboxPath.FindStringSubmatch(id.Path)

internal/util/namestring.go

@@ -23,101 +23,168 @@
 	"strings"
 
 	"github.com/superseriousbusiness/gotosocial/internal/regexes"
+	"github.com/superseriousbusiness/gotosocial/internal/uris"
 )
 
 // ExtractNamestringParts extracts the username test_user and
 // the domain example.org from a string like @test_user@example.org.
 //
 // If nothing is matched, it will return an error.
-func ExtractNamestringParts(mention string) (username, host string, err error) {
-	matches := regexes.MentionName.FindStringSubmatch(mention)
+func ExtractNamestringParts(namestring string) (username, host string, err error) {
+	matches := regexes.MentionName.FindStringSubmatch(namestring)
 	switch len(matches) {
 	case 2:
 		return matches[1], "", nil
 	case 3:
 		return matches[1], matches[2], nil
 	default:
-		return "", "", fmt.Errorf("couldn't match mention %s", mention)
+		return "", "", fmt.Errorf("couldn't match namestring %s", namestring)
 	}
 }
 
-// ExtractWebfingerParts returns the username and domain from either an
-// account query or an actor URI.
+// ExtractWebfingerParts returns the username and domain from the "subject"
+// part of a webfinger response: either an account namestring or an actor URI.
 //
-// All implementations in the wild generate webfinger account resource
+// All AP implementations in the wild perform webfinger account resource
 // queries with the "acct" scheme and without a leading "@"" on the username.
 // This is also the format the "subject" in a webfinger response adheres to.
 //
-// Despite this fact, we're being permissive about a single leading @. This
-// makes a query for acct:user@domain.tld and acct:@user@domain.tld
-// equivalent. But a query for acct:@@user@domain.tld will have its username
-// returned with the @ prefix.
+// Despite this fact, we're permissive about a single leading @. This makes
+// a query for "acct:user@domain.tld" and "acct:@user@domain.tld" equivalent.
 //
-// We also permit a resource of user@domain.tld or @user@domain.tld, without
-// a scheme. In that case it gets interpreted as if it was using the "acct"
-// scheme.
+// We also permit a resource of "user@domain.tld" or "@user@domain.tld", without
+// a scheme. In that case it gets interpreted as if it was using "acct:".
 //
-// When parsing fails, an error is returned.
-func ExtractWebfingerParts(webfinger string) (username, host string, err error) {
-	orig := webfinger
-
-	u, oerr := url.ParseRequestURI(webfinger)
-	if oerr != nil {
-		// Most likely reason for failing to parse is if the "acct" scheme was
-		// missing but a :port was included. So try an extra time with the scheme.
-		u, err = url.ParseRequestURI("acct:" + webfinger)
+// Will error if parsing fails, or if the extracted username or domain are empty.
+func ExtractWebfingerParts(subject string) (
+	string, // username
+	string, // domain
+	error,
+) {
+	u, err := url.ParseRequestURI(subject)
 	if err != nil {
-			return "", "", fmt.Errorf("failed to parse %s with acct sheme: %w", orig, oerr)
+		// Most likely reason for failing to parse is if
+		// the "acct" scheme was missing but a :port was
+		// included. So try an extra time with the scheme.
+		u, err = url.ParseRequestURI("acct:" + subject)
 	}
+	if err != nil {
+		return "", "", fmt.Errorf("failed to parse %s: %w", subject, err)
 	}
 
-	if u.Scheme == "http" || u.Scheme == "https" {
-		return ExtractWebfingerPartsFromURI(u)
+	switch u.Scheme {
+
+	// Subject looks like
+	// "https://example.org/users/whatever"
+	// or "https://example.org/@whatever".
+	case "http", "https":
+		return partsFromURI(u)
+
+	// Subject looks like
+	// "acct:whatever@example.org"
+	// or "acct:@whatever@example.org".
+	case "acct":
+		// Pass string without "acct:" prefix.
+		return partsFromNamestring(u.Opaque)
+
+	// Subject was probably a relative URL.
+	// Fail since we need the domain.
+	case "":
+		return "", "", fmt.Errorf("no scheme for resource %s", subject)
 	}
 
-	if u.Scheme != "acct" {
-		return "", "", fmt.Errorf("unsupported scheme: %s for resource: %s", u.Scheme, orig)
+	return "", "", fmt.Errorf("unsupported scheme %s for resource %s", u.Scheme, subject)
 }
 
-	stripped := strings.TrimPrefix(u.Opaque, "@")
-	userDomain := strings.Split(stripped, "@")
-	if len(userDomain) != 2 {
-		return "", "", fmt.Errorf("failed to extract user and domain from: %s", orig)
-	}
-	return userDomain[0], userDomain[1], nil
-}
-
-// ExtractWebfingerPartsFromURI returns the user and domain extracted from
-// the passed in URI. The URI should be an actor URI.
+// partsFromNamestring returns the username
+// and host parts extracted from a passed-in actor
+// namestring of the format "whatever@example.org".
 //
-// The domain returned is the hostname, and the user will be extracted
-// from either /@test_user or /users/test_user. These two paths match the
-// "aliasses" we include in our webfinger response and are also present in
-// our "links".
-//
-// Like with ExtractWebfingerParts, we're being permissive about a single
-// leading @.
-//
-// Errors are returned in case we end up with an empty domain or username.
-func ExtractWebfingerPartsFromURI(uri *url.URL) (username, host string, err error) {
-	host = uri.Host
+// The function returns an error if username or
+// host cannot be extracted.
+func partsFromNamestring(namestring string) (
+	string, // username
+	string, // host
+	error,
+) {
+	// Trim all leading "@" symbols,
+	// and then inject just one "@".
+	namestring = strings.TrimLeft(namestring, "@")
+	namestring = "@" + namestring
+
+	username, host, err := ExtractNamestringParts(namestring)
+	if err != nil {
+		return "", "", err
+	}
+
+	if username == "" {
+		err := fmt.Errorf("failed to extract username from: %s", namestring)
+		return "", "", err
+	}
+
 	if host == "" {
-		return "", "", fmt.Errorf("failed to extract domain from: %s", uri)
+		err := fmt.Errorf("failed to extract domain from: %s", namestring)
+		return "", "", err
 	}
 
-	// strip any leading slashes
-	path := strings.TrimLeft(uri.Path, "/")
-	segs := strings.Split(path, "/")
+	return username, host, nil
+}
+
+// partsFromURI returns the username and host
+// extracted from the passed in actor URI.
+//
+// The username will be extracted from one of
+// the patterns "/@whatever" or "/users/whatever".
+// These paths match the "aliases" and "links"
+// we include in our own webfinger responses.
+//
+// This function tries to be permissive with
+// regard to leading "@" symbols. Nevertheless,
+// an error will be returned if username or host
+// cannot be extracted.
+func partsFromURI(uri *url.URL) (
+	string, // username
+	string, // host
+	error,
+) {
+	host := uri.Host
+	if host == "" {
+		err := fmt.Errorf("failed to extract domain from: %s", uri)
+		return "", "", err
+	}
+
+	// Copy the URL, taking
+	// only the parts we need.
+	short := &url.URL{
+		Path: uri.Path,
+	}
+
+	// Try "/users/whatever".
+	username, err := uris.ParseUserPath(short)
+	if err == nil && username != "" {
+		return username, host, nil
+	}
+
+	// Try "/@whatever"
+	username, err = uris.ParseUserWebPath(short)
+	if err == nil && username != "" {
+		return username, host, nil
+	}
+
+	// Try some exotic fallbacks like
+	// "/users/@whatever", "/@@whatever", etc.
+	short.Path = strings.TrimLeft(short.Path, "/")
+	segs := strings.Split(short.Path, "/")
 	if segs[0] == "users" {
 		username = segs[1]
 	} else {
 		username = segs[0]
 	}
 
-	username = strings.TrimPrefix(username, "@")
-	if username == "" {
-		return "", "", fmt.Errorf("failed to extract username from: %s", uri)
+	username = strings.TrimLeft(username, "@")
+	if username != "" {
+		return username, host, nil
 	}
 
-	return
+	return "", "", fmt.Errorf("failed to extract username from: %s", uri)
 }

internal/util/namestring_test.go

@@ -18,7 +18,6 @@
 package util_test
 
 import (
-	"net/url"
 	"testing"
 
 	"github.com/stretchr/testify/suite"
@@ -39,11 +38,26 @@ func (suite *NamestringSuite) TestExtractWebfingerParts() {
 		{in: "stonerkitty.monster@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
 		{in: "stonerkitty.monster@stonerkitty.monster:8080", username: "stonerkitty.monster", domain: "stonerkitty.monster:8080"},
 		{in: "@stonerkitty.monster@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "acct:@@stonerkitty.monster@stonerkitty.monster", err: "failed to extract user and domain from: acct:@@stonerkitty.monster@stonerkitty.monster"},
-		{in: "acct:@stonerkitty.monster@@stonerkitty.monster", err: "failed to extract user and domain from: acct:@stonerkitty.monster@@stonerkitty.monster"},
-		{in: "@@stonerkitty.monster@stonerkitty.monster", err: "failed to extract user and domain from: @@stonerkitty.monster@stonerkitty.monster"},
-		{in: "@stonerkitty.monster@@stonerkitty.monster", err: "failed to extract user and domain from: @stonerkitty.monster@@stonerkitty.monster"},
-		{in: "s3:stonerkitty.monster@stonerkitty.monster", err: "unsupported scheme: s3 for resource: s3:stonerkitty.monster@stonerkitty.monster"},
+		{in: "acct:@@stonerkitty.monster@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "acct:@stonerkitty.monster@@stonerkitty.monster", err: "couldn't match namestring @stonerkitty.monster@@stonerkitty.monster"},
+		{in: "@@stonerkitty.monster@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "@stonerkitty.monster@@stonerkitty.monster", err: "couldn't match namestring @stonerkitty.monster@@stonerkitty.monster"},
+		{in: "s3:stonerkitty.monster@stonerkitty.monster", err: "unsupported scheme s3 for resource s3:stonerkitty.monster@stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/users/stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/users/@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/@@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "https://stonerkitty.monster:8080/users/stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster:8080"},
+		{in: "https://stonerkitty.monster/users/stonerkitty.monster/evil", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/@stonerkitty.monster/evil", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
+		{in: "/@stonerkitty.monster", err: "no scheme for resource /@stonerkitty.monster"},
+		{in: "/users/stonerkitty.monster", err: "no scheme for resource /users/stonerkitty.monster"},
+		{in: "@stonerkitty.monster", err: "failed to extract domain from: @stonerkitty.monster"},
+		{in: "users/stonerkitty.monster", err: "couldn't match namestring @users/stonerkitty.monster"},
+		{in: "https://stonerkitty.monster/users/", err: "failed to extract username from: https://stonerkitty.monster/users/"},
+		{in: "https://stonerkitty.monster/users/@", err: "failed to extract username from: https://stonerkitty.monster/users/@"},
+		{in: "https://stonerkitty.monster/@", err: "failed to extract username from: https://stonerkitty.monster/@"},
+		{in: "https://stonerkitty.monster/", err: "failed to extract username from: https://stonerkitty.monster/"},
 	}
 
 	for _, tt := range tests {
@@ -56,45 +70,9 @@ func (suite *NamestringSuite) TestExtractWebfingerParts() {
 				suite.Equal(tt.username, username)
 				suite.Equal(tt.domain, domain)
 			} else {
-				suite.EqualError(err, tt.err)
+				if !suite.EqualError(err, tt.err) {
+					suite.T().Logf("expected error %s", tt.err)
 				}
-		})
-	}
-}
-
-func (suite *NamestringSuite) TestExtractWebfingerPartsFromURI() {
-	tests := []struct {
-		in, username, domain, err string
-	}{
-		{in: "https://stonerkitty.monster/users/stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "https://stonerkitty.monster/users/@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "https://stonerkitty.monster/@stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "https://stonerkitty.monster/@@stonerkitty.monster", username: "@stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "https://stonerkitty.monster:8080/users/stonerkitty.monster", username: "stonerkitty.monster", domain: "stonerkitty.monster:8080"},
-		{in: "https://stonerkitty.monster/users/stonerkitty.monster/evil", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "https://stonerkitty.monster/@stonerkitty.monster/evil", username: "stonerkitty.monster", domain: "stonerkitty.monster"},
-		{in: "/@stonerkitty.monster", err: "failed to extract domain from: /@stonerkitty.monster"},
-		{in: "/users/stonerkitty.monster", err: "failed to extract domain from: /users/stonerkitty.monster"},
-		{in: "@stonerkitty.monster", err: "failed to extract domain from: @stonerkitty.monster"},
-		{in: "users/stonerkitty.monster", err: "failed to extract domain from: users/stonerkitty.monster"},
-		{in: "https://stonerkitty.monster/users/", err: "failed to extract username from: https://stonerkitty.monster/users/"},
-		{in: "https://stonerkitty.monster/users/@", err: "failed to extract username from: https://stonerkitty.monster/users/@"},
-		{in: "https://stonerkitty.monster/@", err: "failed to extract username from: https://stonerkitty.monster/@"},
-		{in: "https://stonerkitty.monster/", err: "failed to extract username from: https://stonerkitty.monster/"},
-	}
-
-	for _, tt := range tests {
-		tt := tt
-		suite.Run(tt.in, func() {
-			suite.T().Parallel()
-			uri, _ := url.Parse(tt.in)
-			username, domain, err := util.ExtractWebfingerPartsFromURI(uri)
-			if tt.err == "" {
-				suite.NoError(err)
-				suite.Equal(tt.username, username)
-				suite.Equal(tt.domain, domain)
-			} else {
-				suite.EqualError(err, tt.err)
 			}
 		})
 	}
@@ -107,7 +85,7 @@ func (suite *NamestringSuite) TestExtractNamestring() {
 		{in: "@stonerkitty.monster@stonerkitty.monster", username: "stonerkitty.monster", host: "stonerkitty.monster"},
 		{in: "@stonerkitty.monster", username: "stonerkitty.monster"},
 		{in: "@someone@somewhere", username: "someone", host: "somewhere"},
-		{in: "", err: "couldn't match mention "},
+		{in: "", err: "couldn't match namestring "},
 	}
 
 	for _, tt := range tests {