[feature] serdes for moved/also_known_as (#2600)

* [feature] serdes for moved/also_known_as

* document `alsoKnownAs` and `movedTo` properties

* only implicitly populate AKA uris from DB for local accounts

* don't let remotes store more than 20 AKA uris to avoid shenanigans

4 files changed, 147 insertions, 15 deletions

diff --git a/internal/ap/interfaces.go b/internal/ap/interfaces.go
index 45ddbfba7..811e09125 100644
--- a/internal/ap/interfaces.go
+++ b/internal/ap/interfaces.go
@@ -160,6 +160,8 @@ type Accountable interface {
 	WithFollowing
 	WithFollowers
 	WithFeatured
+	WithMovedTo
+	WithAlsoKnownAs
 	WithManuallyApprovesFollowers
 	WithEndpoints
 	WithTag
@@ -327,7 +329,7 @@ type TypeOrIRI interface {
 }
 
 // Property represents the minimum interface for an ActivityStreams property with IRIs.
-type Property[T TypeOrIRI] interface {
+type Property[T WithIRI] interface {
 	Len() int
 	At(int) T
 
@@ -441,6 +443,18 @@ type WithFeatured interface {
 	SetTootFeatured(vocab.TootFeaturedProperty)
 }
 
+// WithMovedTo represents an Object with ActivityStreamsMovedToProperty.
+type WithMovedTo interface {
+	GetActivityStreamsMovedTo() vocab.ActivityStreamsMovedToProperty
+	SetActivityStreamsMovedTo(vocab.ActivityStreamsMovedToProperty)
+}
+
+// WithAlsoKnownAs represents an Object with ActivityStreamsAlsoKnownAsProperty.
+type WithAlsoKnownAs interface {
+	GetActivityStreamsAlsoKnownAs() vocab.ActivityStreamsAlsoKnownAsProperty
+	SetActivityStreamsAlsoKnownAs(vocab.ActivityStreamsAlsoKnownAsProperty)
+}
+
 // WithAttributedTo represents an activity with ActivityStreamsAttributedToProperty
 type WithAttributedTo interface {
 	GetActivityStreamsAttributedTo() vocab.ActivityStreamsAttributedToProperty
@@ -551,6 +565,12 @@ type WithObject interface {
 	SetActivityStreamsObject(vocab.ActivityStreamsObjectProperty)
 }
 
+// WithTarget represents an activity with ActivityStreamsTargetProperty
+type WithTarget interface {
+	GetActivityStreamsTarget() vocab.ActivityStreamsTargetProperty
+	SetActivityStreamsTarget(vocab.ActivityStreamsTargetProperty)
+}
+
 // WithNext represents an activity with ActivityStreamsNextProperty
 type WithNext interface {
 	GetActivityStreamsNext() vocab.ActivityStreamsNextProperty
diff --git a/internal/ap/normalize.go b/internal/ap/normalize.go
index a27527b84..8e0a022c1 100644
--- a/internal/ap/normalize.go
+++ b/internal/ap/normalize.go
@@ -391,6 +391,36 @@ func NormalizeOutgoingAttachmentProp(item WithAttachment, rawJSON map[string]int
 	rawJSON["attachment"] = []interface{}{attachment}
 }
 
+// NormalizeOutgoingAlsoKnownAsProp replaces single-entry alsoKnownAs values with
+// single-entry arrays, for better compatibility with other AP implementations.
+//
+// Ie:
+//
+//	"alsoKnownAs": "https://example.org/users/some_user"
+//
+// becomes:
+//
+//	"alsoKnownAs": ["https://example.org/users/some_user"]
+//
+// Noop for items with no attachments, or with attachments that are already a slice.
+func NormalizeOutgoingAlsoKnownAsProp(item WithAlsoKnownAs, rawJSON map[string]interface{}) {
+	alsoKnownAs, ok := rawJSON["alsoKnownAs"]
+	if !ok {
+		// No 'alsoKnownAs',
+		// nothing to change.
+		return
+	}
+
+	if _, ok := alsoKnownAs.([]interface{}); ok {
+		// Already slice,
+		// nothing to change.
+		return
+	}
+
+	// Coerce single-object to slice.
+	rawJSON["alsoKnownAs"] = []interface{}{alsoKnownAs}
+}
+
 // NormalizeOutgoingContentProp normalizes go-fed's funky formatting of content and
 // contentMap properties to a format better understood by other AP implementations.
 //
diff --git a/internal/ap/properties.go b/internal/ap/properties.go
index 6103608d6..b77d20a02 100644
--- a/internal/ap/properties.go
+++ b/internal/ap/properties.go
@@ -102,7 +102,7 @@ func AppendTo(with WithTo, to ...*url.URL) {
 // GetCc returns the IRIs contained in the Cc property of 'with'. Panics on entries with missing ID.
 func GetCc(with WithCc) []*url.URL {
 	ccProp := with.GetActivityStreamsCc()
-	return getIRIs[vocab.ActivityStreamsCcPropertyIterator](ccProp)
+	return extractIRIs[vocab.ActivityStreamsCcPropertyIterator](ccProp)
 }
 
 // AppendCc appends the given IRIs to the Cc property of 'with'.
@@ -120,7 +120,7 @@ func AppendCc(with WithCc, cc ...*url.URL) {
 // GetBcc returns the IRIs contained in the Bcc property of 'with'. Panics on entries with missing ID.
 func GetBcc(with WithBcc) []*url.URL {
 	bccProp := with.GetActivityStreamsBcc()
-	return getIRIs[vocab.ActivityStreamsBccPropertyIterator](bccProp)
+	return extractIRIs[vocab.ActivityStreamsBccPropertyIterator](bccProp)
 }
 
 // AppendBcc appends the given IRIs to the Bcc property of 'with'.
@@ -170,7 +170,7 @@ func AppendURL(with WithURL, url ...*url.URL) {
 // GetActorIRIs returns the IRIs contained in the Actor property of 'with'.
 func GetActorIRIs(with WithActor) []*url.URL {
 	actorProp := with.GetActivityStreamsActor()
-	return getIRIs[vocab.ActivityStreamsActorPropertyIterator](actorProp)
+	return extractIRIs[vocab.ActivityStreamsActorPropertyIterator](actorProp)
 }
 
 // AppendActorIRIs appends the given IRIs to the Actor property of 'with'.
@@ -188,7 +188,7 @@ func AppendActorIRIs(with WithActor, actor ...*url.URL) {
 // GetObjectIRIs returns the IRIs contained in the Object property of 'with'.
 func GetObjectIRIs(with WithObject) []*url.URL {
 	objectProp := with.GetActivityStreamsObject()
-	return getIRIs[vocab.ActivityStreamsObjectPropertyIterator](objectProp)
+	return extractIRIs[vocab.ActivityStreamsObjectPropertyIterator](objectProp)
 }
 
 // AppendObjectIRIs appends the given IRIs to the Object property of 'with'.
@@ -203,10 +203,28 @@ func AppendObjectIRIs(with WithObject) {
 	})
 }
 
+// GetTargetIRIs returns the IRIs contained in the Target property of 'with'.
+func GetTargetIRIs(with WithTarget) []*url.URL {
+	targetProp := with.GetActivityStreamsTarget()
+	return extractIRIs[vocab.ActivityStreamsTargetPropertyIterator](targetProp)
+}
+
+// AppendTargetIRIs appends the given IRIs to the Target property of 'with'.
+func AppendTargetIRIs(with WithTarget) {
+	appendIRIs(func() Property[vocab.ActivityStreamsTargetPropertyIterator] {
+		targetProp := with.GetActivityStreamsTarget()
+		if targetProp == nil {
+			targetProp = streams.NewActivityStreamsTargetProperty()
+			with.SetActivityStreamsTarget(targetProp)
+		}
+		return targetProp
+	})
+}
+
 // GetAttributedTo returns the IRIs contained in the AttributedTo property of 'with'.
 func GetAttributedTo(with WithAttributedTo) []*url.URL {
 	attribProp := with.GetActivityStreamsAttributedTo()
-	return getIRIs[vocab.ActivityStreamsAttributedToPropertyIterator](attribProp)
+	return extractIRIs[vocab.ActivityStreamsAttributedToPropertyIterator](attribProp)
 }
 
 // AppendAttributedTo appends the given IRIs to the AttributedTo property of 'with'.
@@ -224,7 +242,7 @@ func AppendAttributedTo(with WithAttributedTo, attribTo ...*url.URL) {
 // GetInReplyTo returns the IRIs contained in the InReplyTo property of 'with'.
 func GetInReplyTo(with WithInReplyTo) []*url.URL {
 	replyProp := with.GetActivityStreamsInReplyTo()
-	return getIRIs[vocab.ActivityStreamsInReplyToPropertyIterator](replyProp)
+	return extractIRIs[vocab.ActivityStreamsInReplyToPropertyIterator](replyProp)
 }
 
 // AppendInReplyTo appends the given IRIs to the InReplyTo property of 'with'.
@@ -334,6 +352,43 @@ func SetFeatured(with WithFeatured, featured *url.URL) {
 	featuredProp.SetIRI(featured)
 }
 
+// GetMovedTo returns the IRI contained in the movedTo property of 'with'.
+func GetMovedTo(with WithMovedTo) *url.URL {
+	movedToProp := with.GetActivityStreamsMovedTo()
+	if movedToProp == nil || !movedToProp.IsIRI() {
+		return nil
+	}
+	return movedToProp.GetIRI()
+}
+
+// SetMovedTo sets the given IRI on the movedTo property of 'with'.
+func SetMovedTo(with WithMovedTo, movedTo *url.URL) {
+	movedToProp := with.GetActivityStreamsMovedTo()
+	if movedToProp == nil {
+		movedToProp = streams.NewActivityStreamsMovedToProperty()
+		with.SetActivityStreamsMovedTo(movedToProp)
+	}
+	movedToProp.SetIRI(movedTo)
+}
+
+// GetAlsoKnownAs returns the IRI contained in the alsoKnownAs property of 'with'.
+func GetAlsoKnownAs(with WithAlsoKnownAs) []*url.URL {
+	alsoKnownAsProp := with.GetActivityStreamsAlsoKnownAs()
+	return getIRIs[vocab.ActivityStreamsAlsoKnownAsPropertyIterator](alsoKnownAsProp)
+}
+
+// SetAlsoKnownAs sets the given IRIs on the alsoKnownAs property of 'with'.
+func SetAlsoKnownAs(with WithAlsoKnownAs, alsoKnownAs []*url.URL) {
+	appendIRIs(func() Property[vocab.ActivityStreamsAlsoKnownAsPropertyIterator] {
+		alsoKnownAsProp := with.GetActivityStreamsAlsoKnownAs()
+		if alsoKnownAsProp == nil {
+			alsoKnownAsProp = streams.NewActivityStreamsAlsoKnownAsProperty()
+			with.SetActivityStreamsAlsoKnownAs(alsoKnownAsProp)
+		}
+		return alsoKnownAsProp
+	}, alsoKnownAs...)
+}
+
 // GetPublished returns the time contained in the Published property of 'with'.
 func GetPublished(with WithPublished) time.Time {
 	publishProp := with.GetActivityStreamsPublished()
@@ -465,7 +520,12 @@ func SetManuallyApprovesFollowers(with WithManuallyApprovesFollowers, manuallyAp
 	mafProp.Set(manuallyApprovesFollowers)
 }
 
-func getIRIs[T TypeOrIRI](prop Property[T]) []*url.URL {
+// extractIRIs extracts just the AP IRIs from an iterable
+// property that may contain types (with IRIs) or just IRIs.
+//
+// If you know the property contains only IRIs and no types,
+// then use getIRIs instead, since it's slightly faster.
+func extractIRIs[T TypeOrIRI](prop Property[T]) []*url.URL {
 	if prop == nil || prop.Len() == 0 {
 		return nil
 	}
@@ -490,7 +550,29 @@ func getIRIs[T TypeOrIRI](prop Property[T]) []*url.URL {
 	return ids
 }
 
-func appendIRIs[T TypeOrIRI](getProp func() Property[T], iri ...*url.URL) {
+// getIRIs gets AP IRIs from an iterable property of IRIs.
+//
+// Types will be ignored; to extract IRIs from an iterable
+// that may contain types too, use extractIRIs.
+func getIRIs[T WithIRI](prop Property[T]) []*url.URL {
+	if prop == nil || prop.Len() == 0 {
+		return nil
+	}
+	ids := make([]*url.URL, 0, prop.Len())
+	for i := 0; i < prop.Len(); i++ {
+		at := prop.At(i)
+		if at.IsIRI() {
+			id := at.GetIRI()
+			if id != nil {
+				ids = append(ids, id)
+				continue
+			}
+		}
+	}
+	return ids
+}
+
+func appendIRIs[T WithIRI](getProp func() Property[T], iri ...*url.URL) {
 	if len(iri) == 0 {
 		return
 	}
diff --git a/internal/ap/serialize.go b/internal/ap/serialize.go
index 774e95f2d..b13ebb340 100644
--- a/internal/ap/serialize.go
+++ b/internal/ap/serialize.go
@@ -90,13 +90,12 @@ func serializeWithOrderedItems(t vocab.Type) (map[string]interface{}, error) {
 }
 
 // SerializeAccountable is a custom serializer for any Accountable type.
-// This serializer rewrites the 'attachment' value of the Accountable, if
-// present, to always be an array/slice.
+// This serializer rewrites certain values of the Accountable, if present,
+// to always be an array/slice.
 //
-// While this is not strictly necessary in json-ld terms, most other fedi
-// implementations look for attachment to be an array of PropertyValue (field)
-// entries, and will not parse single-entry, non-array attachments on accounts
-// properly.
+// While this may not always be strictly necessary in json-ld terms, most other
+// fedi implementations look for certain fields to be an array and will not parse
+// single-entry, non-array fields on accounts properly.
 //
 // If the accountable is being serialized as a top-level object (eg., for serving
 // in response to an account dereference request), then includeContext should be
@@ -126,6 +125,7 @@ func serializeAccountable(t vocab.Type, includeContext bool) (map[string]interfa
 	}
 
 	NormalizeOutgoingAttachmentProp(accountable, data)
+	NormalizeOutgoingAlsoKnownAsProp(accountable, data)
 
 	return data, nil
 }