[feature] add paging to AP following / followers endpoints (#2198)

internal/ap/activitystreams.go

@@ -17,6 +17,15 @@
 
 package ap
 
+import (
+	"net/url"
+	"strconv"
+
+	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/activity/streams/vocab"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
+)
+
 // https://www.w3.org/TR/activitystreams-vocabulary
 const (
 	ActivityAccept          = "Accept"          // ActivityStreamsAccept https://www.w3.org/TR/activitystreams-vocabulary/#dfn-accept
@@ -77,3 +86,197 @@
 	// and https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag
 	TagHashtag = "Hashtag"
 )
+
+type CollectionParams struct {
+	// Containing collection
+	// ID (i.e. NOT the page).
+	ID *url.URL
+
+	// Total no. items.
+	Total int
+}
+
+type CollectionPageParams struct {
+	// containing collection.
+	CollectionParams
+
+	// Paging details.
+	Current *paging.Page
+	Next    *paging.Page
+	Prev    *paging.Page
+	Query   url.Values
+
+	// Item appender for each item at index.
+	Append func(int, ItemsPropertyBuilder)
+	Count  int
+}
+
+// CollectionPage is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsCollection
+// vocab.ActivityStreamsOrderedCollection
+type CollectionBuilder interface {
+	SetJSONLDId(vocab.JSONLDIdProperty)
+	SetActivityStreamsFirst(vocab.ActivityStreamsFirstProperty)
+	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
+}
+
+// CollectionPageBuilder is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsCollectionPage
+// vocab.ActivityStreamsOrderedCollectionPage
+type CollectionPageBuilder interface {
+	SetJSONLDId(vocab.JSONLDIdProperty)
+	SetActivityStreamsPartOf(vocab.ActivityStreamsPartOfProperty)
+	SetActivityStreamsNext(vocab.ActivityStreamsNextProperty)
+	SetActivityStreamsPrev(vocab.ActivityStreamsPrevProperty)
+	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
+}
+
+// ItemsPropertyBuilder is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsItemsProperty
+// vocab.ActivityStreamsOrderedItemsProperty
+type ItemsPropertyBuilder interface {
+	AppendIRI(*url.URL)
+
+	// NOTE: add more of the items-property-like interface
+	// functions here as you require them for building pages.
+}
+
+// NewASCollection builds and returns a new ActivityStreams Collection from given parameters.
+func NewASCollection(params CollectionParams) vocab.ActivityStreamsCollection {
+	collection := streams.NewActivityStreamsCollection()
+	buildCollection(collection, params, 40)
+	return collection
+}
+
+// NewASCollectionPage builds and returns a new ActivityStreams CollectionPage from given parameters (including item property appending function).
+func NewASCollectionPage(params CollectionPageParams) vocab.ActivityStreamsCollectionPage {
+	collectionPage := streams.NewActivityStreamsCollectionPage()
+	itemsProp := streams.NewActivityStreamsItemsProperty()
+	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsItems, params)
+	return collectionPage
+}
+
+// NewASOrderedCollection builds and returns a new ActivityStreams OrderedCollection from given parameters.
+func NewASOrderedCollection(params CollectionParams) vocab.ActivityStreamsOrderedCollection {
+	collection := streams.NewActivityStreamsOrderedCollection()
+	buildCollection(collection, params, 40)
+	return collection
+}
+
+// NewASOrderedCollectionPage builds and returns a new ActivityStreams OrderedCollectionPage from given parameters (including item property appending function).
+func NewASOrderedCollectionPage(params CollectionPageParams) vocab.ActivityStreamsOrderedCollectionPage {
+	collectionPage := streams.NewActivityStreamsOrderedCollectionPage()
+	itemsProp := streams.NewActivityStreamsOrderedItemsProperty()
+	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsOrderedItems, params)
+	return collectionPage
+}
+
+func buildCollection[C CollectionBuilder](collection C, params CollectionParams, pageLimit int) {
+	// Add the collection ID property.
+	idProp := streams.NewJSONLDIdProperty()
+	idProp.SetIRI(params.ID)
+	collection.SetJSONLDId(idProp)
+
+	// Add the collection totalItems count property.
+	totalItems := streams.NewActivityStreamsTotalItemsProperty()
+	totalItems.Set(params.Total)
+	collection.SetActivityStreamsTotalItems(totalItems)
+
+	// Clone the collection ID page
+	// to add first page query data.
+	firstIRI := new(url.URL)
+	*firstIRI = *params.ID
+
+	// Note that simply adding a limit signals to our
+	// endpoint to use paging (which will start at beginning).
+	limit := "limit=" + strconv.Itoa(pageLimit)
+	firstIRI.RawQuery = appendQuery(firstIRI.RawQuery, limit)
+
+	// Add the collection first IRI property.
+	first := streams.NewActivityStreamsFirstProperty()
+	first.SetIRI(firstIRI)
+	collection.SetActivityStreamsFirst(first)
+}
+
+func buildCollectionPage[C CollectionPageBuilder, I ItemsPropertyBuilder](collectionPage C, itemsProp I, setItems func(I), params CollectionPageParams) {
+	// Add the partOf property for its containing collection ID.
+	partOfProp := streams.NewActivityStreamsPartOfProperty()
+	partOfProp.SetIRI(params.ID)
+	collectionPage.SetActivityStreamsPartOf(partOfProp)
+
+	// Build the current page link IRI.
+	currentIRI := params.Current.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	// Add the collection ID property for
+	// the *current* collection page params.
+	idProp := streams.NewJSONLDIdProperty()
+	idProp.SetIRI(currentIRI)
+	collectionPage.SetJSONLDId(idProp)
+
+	// Build the next page link IRI.
+	nextIRI := params.Next.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	if nextIRI != nil {
+		// Add the collection next property for the next page.
+		nextProp := streams.NewActivityStreamsNextProperty()
+		nextProp.SetIRI(nextIRI)
+		collectionPage.SetActivityStreamsNext(nextProp)
+	}
+
+	// Build the prev page link IRI.
+	prevIRI := params.Prev.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	if prevIRI != nil {
+		// Add the collection prev property for the prev page.
+		prevProp := streams.NewActivityStreamsPrevProperty()
+		prevProp.SetIRI(prevIRI)
+		collectionPage.SetActivityStreamsPrev(prevProp)
+	}
+
+	// Add the collection totalItems count property.
+	totalItems := streams.NewActivityStreamsTotalItemsProperty()
+	totalItems.Set(params.Total)
+	collectionPage.SetActivityStreamsTotalItems(totalItems)
+
+	if params.Append == nil {
+		// nil check outside the for loop.
+		panic("nil params.Append function")
+	}
+
+	// Append each of the items to the provided
+	// pre-allocated items property builder type.
+	for i := 0; i < params.Count; i++ {
+		params.Append(i, itemsProp)
+	}
+
+	// Set the collection
+	// page items property.
+	setItems(itemsProp)
+}
+
+// appendQuery appends part to an existing raw
+// query with ampersand, else just returning part.
+func appendQuery(raw, part string) string {
+	if raw != "" {
+		return raw + "&" + part
+	}
+	return part
+}

internal/ap/activitystreams_test.go

@@ -0,0 +1,221 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+package ap_test
+
+import (
+	"encoding/json"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/superseriousbusiness/activity/streams/vocab"
+	"github.com/superseriousbusiness/gotosocial/internal/ap"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
+)
+
+func TestASCollection(t *testing.T) {
+	const (
+		proto = "https"
+		host  = "zorg.flabormagorg.xyz"
+		path  = "/users/itsa_me_mario"
+
+		idURI = proto + "://" + host + path
+		total = 10
+	)
+
+	// Create JSON string of expected output.
+	expect := toJSON(map[string]any{
+		"@context":   "https://www.w3.org/ns/activitystreams",
+		"type":       "Collection",
+		"id":         idURI,
+		"first":      idURI + "?limit=40",
+		"totalItems": total,
+	})
+
+	// Create new collection using builder function.
+	c := ap.NewASCollection(ap.CollectionParams{
+		ID:    parseURI(idURI),
+		Total: total,
+	})
+
+	// Serialize collection.
+	s := toJSON(c)
+
+	// Ensure outputs are equal.
+	assert.Equal(t, s, expect)
+}
+
+func TestASCollectionPage(t *testing.T) {
+	const (
+		proto = "https"
+		host  = "zorg.flabormagorg.xyz"
+		path  = "/users/itsa_me_mario"
+
+		idURI = proto + "://" + host + path
+		total = 10
+
+		minID = "minimum"
+		maxID = "maximum"
+		limit = 40
+		count = 2
+	)
+
+	// Create the current page.
+	currPg := &paging.Page{
+		Limit: 40,
+	}
+
+	// Create JSON string of expected output.
+	expect := toJSON(map[string]any{
+		"@context":   "https://www.w3.org/ns/activitystreams",
+		"type":       "CollectionPage",
+		"id":         currPg.ToLink(proto, host, path, nil),
+		"partOf":     idURI,
+		"next":       currPg.Next(minID, maxID).ToLink(proto, host, path, nil),
+		"prev":       currPg.Prev(minID, maxID).ToLink(proto, host, path, nil),
+		"items":      []interface{}{},
+		"totalItems": total,
+	})
+
+	// Create new collection page using builder function.
+	p := ap.NewASCollectionPage(ap.CollectionPageParams{
+		CollectionParams: ap.CollectionParams{
+			ID:    parseURI(idURI),
+			Total: total,
+		},
+
+		Current: currPg,
+		Next:    currPg.Next(minID, maxID),
+		Prev:    currPg.Prev(minID, maxID),
+
+		Append: func(i int, ipb ap.ItemsPropertyBuilder) {},
+		Count:  count,
+	})
+
+	// Serialize page.
+	s := toJSON(p)
+
+	// Ensure outputs are equal.
+	assert.Equal(t, s, expect)
+}
+
+func TestASOrderedCollection(t *testing.T) {
+	const (
+		idURI = "https://zorg.flabormagorg.xyz/users/itsa_me_mario"
+		total = 10
+	)
+
+	// Create JSON string of expected output.
+	expect := toJSON(map[string]any{
+		"@context":   "https://www.w3.org/ns/activitystreams",
+		"type":       "OrderedCollection",
+		"id":         idURI,
+		"first":      idURI + "?limit=40",
+		"totalItems": total,
+	})
+
+	// Create new collection using builder function.
+	c := ap.NewASOrderedCollection(ap.CollectionParams{
+		ID:    parseURI(idURI),
+		Total: total,
+	})
+
+	// Serialize collection.
+	s := toJSON(c)
+
+	// Ensure outputs are equal.
+	assert.Equal(t, s, expect)
+}
+
+func TestASOrderedCollectionPage(t *testing.T) {
+	const (
+		proto = "https"
+		host  = "zorg.flabormagorg.xyz"
+		path  = "/users/itsa_me_mario"
+
+		idURI = proto + "://" + host + path
+		total = 10
+
+		minID = "minimum"
+		maxID = "maximum"
+		limit = 40
+		count = 2
+	)
+
+	// Create the current page.
+	currPg := &paging.Page{
+		Limit: 40,
+	}
+
+	// Create JSON string of expected output.
+	expect := toJSON(map[string]any{
+		"@context":     "https://www.w3.org/ns/activitystreams",
+		"type":         "OrderedCollectionPage",
+		"id":           currPg.ToLink(proto, host, path, nil),
+		"partOf":       idURI,
+		"next":         currPg.Next(minID, maxID).ToLink(proto, host, path, nil),
+		"prev":         currPg.Prev(minID, maxID).ToLink(proto, host, path, nil),
+		"orderedItems": []interface{}{},
+		"totalItems":   total,
+	})
+
+	// Create new collection page using builder function.
+	p := ap.NewASOrderedCollectionPage(ap.CollectionPageParams{
+		CollectionParams: ap.CollectionParams{
+			ID:    parseURI(idURI),
+			Total: total,
+		},
+
+		Current: currPg,
+		Next:    currPg.Next(minID, maxID),
+		Prev:    currPg.Prev(minID, maxID),
+
+		Append: func(i int, ipb ap.ItemsPropertyBuilder) {},
+		Count:  count,
+	})
+
+	// Serialize page.
+	s := toJSON(p)
+
+	// Ensure outputs are equal.
+	assert.Equal(t, s, expect)
+}
+
+func parseURI(s string) *url.URL {
+	u, err := url.Parse(s)
+	if err != nil {
+		panic(err)
+	}
+	return u
+}
+
+// toJSON will return indented JSON serialized form of 'a'.
+func toJSON(a any) string {
+	v, ok := a.(vocab.Type)
+	if ok {
+		m, err := ap.Serialize(v)
+		if err != nil {
+			panic(err)
+		}
+		a = m
+	}
+	b, err := json.MarshalIndent(a, "", "  ")
+	if err != nil {
+		panic(err)
+	}
+	return string(b)
+}

internal/api/activitypub/users/followers.go

@@ -26,6 +26,7 @@
 	"github.com/gin-gonic/gin"
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
 )
 
 // FollowersGETHandler returns a collection of URIs for followers of the target user, formatted so that other AP servers can understand it.
@@ -51,7 +52,17 @@ func (m *Module) FollowersGETHandler(c *gin.Context) {
 		return
 	}
 
-	resp, errWithCode := m.processor.Fedi().FollowersGet(c.Request.Context(), requestedUsername)
+	page, errWithCode := paging.ParseIDPage(c,
+		1,  // min limit
+		80, // max limit
+		0,  // default = disabled
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	resp, errWithCode := m.processor.Fedi().FollowersGet(c.Request.Context(), requestedUsername, page)
 	if errWithCode != nil {
 		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
 		return

internal/api/activitypub/users/following.go

@@ -26,6 +26,7 @@
 	"github.com/gin-gonic/gin"
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
 )
 
 // FollowingGETHandler returns a collection of URIs for accounts that the target user follows, formatted so that other AP servers can understand it.
@@ -51,7 +52,17 @@ func (m *Module) FollowingGETHandler(c *gin.Context) {
 		return
 	}
 
-	resp, errWithCode := m.processor.Fedi().FollowingGet(c.Request.Context(), requestedUsername)
+	page, errWithCode := paging.ParseIDPage(c,
+		1,  // min limit
+		80, // max limit
+		0,  // default = disabled
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	resp, errWithCode := m.processor.Fedi().FollowingGet(c.Request.Context(), requestedUsername, page)
 	if errWithCode != nil {
 		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
 		return

internal/federation/federatingdb/followers.go

@@ -23,7 +23,7 @@
 	"net/url"
 
 	"github.com/superseriousbusiness/activity/streams/vocab"
-	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
 
 // Followers obtains the Followers Collection for an actor with the
@@ -38,25 +38,19 @@ func (f *federatingDB) Followers(ctx context.Context, actorIRI *url.URL) (follow
 		return nil, err
 	}
 
+	// Fetch followers for account from database.
 	follows, err := f.state.DB.GetAccountFollowers(ctx, acct.ID, nil)
 	if err != nil {
 		return nil, fmt.Errorf("Followers: db error getting followers for account id %s: %s", acct.ID, err)
 	}
 
+	// Convert the followers to a slice of account URIs.
 	iris := make([]*url.URL, 0, len(follows))
 	for _, follow := range follows {
-		if follow.Account == nil {
-			// Follow account no longer exists,
-			// for some reason. Skip this one.
-			log.WithContext(ctx).WithField("follow", follow).Warnf("follow missing account %s", follow.AccountID)
-			continue
-		}
-
 		u, err := url.Parse(follow.Account.URI)
 		if err != nil {
-			return nil, err
+			return nil, gtserror.Newf("invalid account uri: %v", err)
 		}
-
 		iris = append(iris, u)
 	}
 

internal/federation/federatingdb/following.go

@@ -19,11 +19,10 @@
 
 import (
 	"context"
-	"fmt"
 	"net/url"
 
 	"github.com/superseriousbusiness/activity/streams/vocab"
-	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
 
 // Following obtains the Following Collection for an actor with the
@@ -38,23 +37,18 @@ func (f *federatingDB) Following(ctx context.Context, actorIRI *url.URL) (follow
 		return nil, err
 	}
 
+	// Fetch follows for account from database.
 	follows, err := f.state.DB.GetAccountFollows(ctx, acct.ID, nil)
 	if err != nil {
-		return nil, fmt.Errorf("Following: db error getting following for account id %s: %w", acct.ID, err)
+		return nil, gtserror.Newf("db error getting following for account id %s: %w", acct.ID, err)
 	}
 
+	// Convert the follows to a slice of account URIs.
 	iris := make([]*url.URL, 0, len(follows))
 	for _, follow := range follows {
-		if follow.TargetAccount == nil {
-			// Follow target account no longer exists,
-			// for some reason. Skip this one.
-			log.WithContext(ctx).WithField("follow", follow).Warnf("follow missing target account %s", follow.TargetAccountID)
-			continue
-		}
-
 		u, err := url.Parse(follow.TargetAccount.URI)
 		if err != nil {
-			return nil, err
+			return nil, gtserror.Newf("invalid account uri: %v", err)
 		}
 		iris = append(iris, u)
 	}

internal/paging/page.go

@@ -205,12 +205,21 @@ func (p *Page) Prev(lo, hi string) *Page {
 	return p2
 }
 
+// ToLink performs ToLinkURL() and calls .String() on the resulting URL.
+func (p *Page) ToLink(proto, host, path string, queryParams url.Values) string {
+	u := p.ToLinkURL(proto, host, path, queryParams)
+	if u == nil {
+		return ""
+	}
+	return u.String()
+}
+
 // ToLink builds a URL link for given endpoint information and extra query parameters,
 // appending this Page's minimum / maximum boundaries and available limit (if any).
-func (p *Page) ToLink(proto, host, path string, queryParams url.Values) string {
+func (p *Page) ToLinkURL(proto, host, path string, queryParams url.Values) *url.URL {
 	if p == nil {
 		// no paging.
-		return ""
+		return nil
 	}
 
 	if queryParams == nil {
@@ -234,10 +243,10 @@ func (p *Page) ToLink(proto, host, path string, queryParams url.Values) string {
 	}
 
 	// Build URL string.
-	return (&url.URL{
+	return &url.URL{
 		Scheme:   proto,
 		Host:     host,
 		Path:     path,
 		RawQuery: queryParams.Encode(),
-	}).String()
+	}
 }

internal/processing/fedi/collections.go

@@ -20,13 +20,15 @@
 import (
 	"context"
 	"errors"
-	"fmt"
 	"net/http"
 	"net/url"
 
+	"github.com/superseriousbusiness/activity/streams/vocab"
 	"github.com/superseriousbusiness/gotosocial/internal/ap"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
 )
 
 // InboxPost handles POST requests to a user's inbox for new activitypub messages.
@@ -102,24 +104,90 @@ func (p *Processor) OutboxGet(ctx context.Context, requestedUsername string, pag
 
 // FollowersGet handles the getting of a fedi/activitypub representation of a user/account's followers, performing appropriate
 // authentication before returning a JSON serializable interface to the caller.
-func (p *Processor) FollowersGet(ctx context.Context, requestedUsername string) (interface{}, gtserror.WithCode) {
+func (p *Processor) FollowersGet(ctx context.Context, requestedUsername string, page *paging.Page) (interface{}, gtserror.WithCode) {
 	requestedAccount, _, errWithCode := p.authenticate(ctx, requestedUsername)
 	if errWithCode != nil {
 		return nil, errWithCode
 	}
 
-	requestedAccountURI, err := url.Parse(requestedAccount.URI)
+	// Parse the collection ID object from account's followers URI.
+	collectionID, err := url.Parse(requestedAccount.FollowersURI)
 	if err != nil {
-		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error parsing url %s: %s", requestedAccount.URI, err))
+		err := gtserror.Newf("error parsing account followers uri %s: %w", requestedAccount.FollowersURI, err)
+		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	requestedFollowers, err := p.federator.FederatingDB().Followers(ctx, requestedAccountURI)
+	// Calculate total number of followers available for account.
+	total, err := p.state.DB.CountAccountFollowers(ctx, requestedAccount.ID)
 	if err != nil {
-		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error fetching followers for uri %s: %s", requestedAccountURI.String(), err))
+		err := gtserror.Newf("error counting followers: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	data, err := ap.Serialize(requestedFollowers)
+	var obj vocab.Type
+
+	// Start building AS collection params.
+	var params ap.CollectionParams
+	params.ID = collectionID
+	params.Total = total
+
+	if page == nil {
+		// i.e. paging disabled, the simplest case.
+		//
+		// Just build collection object from params.
+		obj = ap.NewASOrderedCollection(params)
+	} else {
+		// i.e. paging enabled
+
+		// Get the request page of full follower objects with attached accounts.
+		followers, err := p.state.DB.GetAccountFollowers(ctx, requestedAccount.ID, page)
+		if err != nil {
+			err := gtserror.Newf("error getting followers: %w", err)
+			return nil, gtserror.NewErrorInternalError(err)
+		}
+
+		// Get the lowest and highest
+		// ID values, used for paging.
+		lo := followers[len(followers)-1].ID
+		hi := followers[0].ID
+
+		// Start building AS collection page params.
+		var pageParams ap.CollectionPageParams
+		pageParams.CollectionParams = params
+
+		// Current page details.
+		pageParams.Current = page
+		pageParams.Count = len(followers)
+
+		// Set linked next/prev parameters.
+		pageParams.Next = page.Next(lo, hi)
+		pageParams.Prev = page.Prev(lo, hi)
+
+		// Set the collection item property builder function.
+		pageParams.Append = func(i int, itemsProp ap.ItemsPropertyBuilder) {
+			// Get follower URI at index.
+			follow := followers[i]
+			accURI := follow.Account.URI
+
+			// Parse URL object from URI.
+			iri, err := url.Parse(accURI)
+			if err != nil {
+				log.Errorf(ctx, "error parsing account uri %s: %v", accURI, err)
+				return
+			}
+
+			// Add to item property.
+			itemsProp.AppendIRI(iri)
+		}
+
+		// Build AS collection page object from params.
+		obj = ap.NewASOrderedCollectionPage(pageParams)
+	}
+
+	// Serialized the prepared object.
+	data, err := ap.Serialize(obj)
 	if err != nil {
+		err := gtserror.Newf("error serializing: %w", err)
 		return nil, gtserror.NewErrorInternalError(err)
 	}
 
@@ -128,24 +196,90 @@ func (p *Processor) FollowersGet(ctx context.Context, requestedUsername string)
 
 // FollowingGet handles the getting of a fedi/activitypub representation of a user/account's following, performing appropriate
 // authentication before returning a JSON serializable interface to the caller.
-func (p *Processor) FollowingGet(ctx context.Context, requestedUsername string) (interface{}, gtserror.WithCode) {
+func (p *Processor) FollowingGet(ctx context.Context, requestedUsername string, page *paging.Page) (interface{}, gtserror.WithCode) {
 	requestedAccount, _, errWithCode := p.authenticate(ctx, requestedUsername)
 	if errWithCode != nil {
 		return nil, errWithCode
 	}
 
-	requestedAccountURI, err := url.Parse(requestedAccount.URI)
+	// Parse the collection ID object from account's following URI.
+	collectionID, err := url.Parse(requestedAccount.FollowingURI)
 	if err != nil {
-		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error parsing url %s: %s", requestedAccount.URI, err))
+		err := gtserror.Newf("error parsing account following uri %s: %w", requestedAccount.FollowingURI, err)
+		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	requestedFollowing, err := p.federator.FederatingDB().Following(ctx, requestedAccountURI)
+	// Calculate total number of following available for account.
+	total, err := p.state.DB.CountAccountFollows(ctx, requestedAccount.ID)
 	if err != nil {
-		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error fetching following for uri %s: %s", requestedAccountURI.String(), err))
+		err := gtserror.Newf("error counting follows: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	data, err := ap.Serialize(requestedFollowing)
+	var obj vocab.Type
+
+	// Start building AS collection params.
+	var params ap.CollectionParams
+	params.ID = collectionID
+	params.Total = total
+
+	if page == nil {
+		// i.e. paging disabled, the simplest case.
+		//
+		// Just build collection object from params.
+		obj = ap.NewASOrderedCollection(params)
+	} else {
+		// i.e. paging enabled
+
+		// Get the request page of full follower objects with attached accounts.
+		follows, err := p.state.DB.GetAccountFollows(ctx, requestedAccount.ID, page)
+		if err != nil {
+			err := gtserror.Newf("error getting follows: %w", err)
+			return nil, gtserror.NewErrorInternalError(err)
+		}
+
+		// Get the lowest and highest
+		// ID values, used for paging.
+		lo := follows[len(follows)-1].ID
+		hi := follows[0].ID
+
+		// Start building AS collection page params.
+		var pageParams ap.CollectionPageParams
+		pageParams.CollectionParams = params
+
+		// Current page details.
+		pageParams.Current = page
+		pageParams.Count = len(follows)
+
+		// Set linked next/prev parameters.
+		pageParams.Next = page.Next(lo, hi)
+		pageParams.Prev = page.Prev(lo, hi)
+
+		// Set the collection item property builder function.
+		pageParams.Append = func(i int, itemsProp ap.ItemsPropertyBuilder) {
+			// Get follower URI at index.
+			follow := follows[i]
+			accURI := follow.Account.URI
+
+			// Parse URL object from URI.
+			iri, err := url.Parse(accURI)
+			if err != nil {
+				log.Errorf(ctx, "error parsing account uri %s: %v", accURI, err)
+				return
+			}
+
+			// Add to item property.
+			itemsProp.AppendIRI(iri)
+		}
+
+		// Build AS collection page object from params.
+		obj = ap.NewASOrderedCollectionPage(pageParams)
+	}
+
+	// Serialized the prepared object.
+	data, err := ap.Serialize(obj)
 	if err != nil {
+		err := gtserror.Newf("error serializing: %w", err)
 		return nil, gtserror.NewErrorInternalError(err)
 	}
 

internal/typeutils/internaltoas.go

@@ -729,7 +729,7 @@ func (c *converter) StatusToASDelete(ctx context.Context, s *gtsmodel.Status) (v
 
 	// For direct messages, add URI
 	// to To, else just add to CC.
-	var f func(v *url.URL)
+	var f func(*url.URL)
 	if s.Visibility == gtsmodel.VisibilityDirect {
 		f = toProp.AppendIRI
 	} else {