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|
// Package activitypub provides a single-file ActivityPub server that can be
// dropped into any Go project to create ActivityPub-speaking services.
//
// It implements:
// - WebFinger discovery (/.well-known/webfinger)
// - Actor document serving (GET /users/{actor})
// - Inbox (POST /users/{actor}/inbox) with HTTP Signature verification
// - Outbox (GET /users/{actor}/outbox) as a public OrderedCollection
// - Followers / Following collections
// - Server-to-server activity delivery with HTTP Signatures (draft-cavage-12)
// - JSON-file persistence (zero external dependencies, stdlib only)
// - RSA-2048 key generation and persistence
//
// Usage:
//
// cfg := activitypub.Config{
// Domain: "ap.example.com",
// ActorName: "mybot",
// ActorType: "Service",
// Summary: "A helpful bot",
// DataDir: "./data",
// }
// srv, err := activitypub.New(cfg)
// srv.SetHooks(activitypub.Hooks{
// OnFollow: func(actorURL string) activitypub.FollowDecision { return activitypub.AcceptFollow },
// OnDM: func(from, content, noteID, inReplyTo string) { /* handle DM */ },
// })
// srv.Register(http.DefaultServeMux)
// http.ListenAndServe(":8080", nil)
package activitypub
import (
"bytes"
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"io"
"log"
"net"
"net/http"
"net/url"
"os"
"path/filepath"
"slices"
"strings"
"sync"
"syscall"
"time"
)
// ---------------------------------------------------------------------------
// Public types
// ---------------------------------------------------------------------------
// Config holds the configuration for an ActivityPub server instance.
type Config struct {
// Domain is the hostname for this actor, e.g. "ap.example.com".
// All URLs are built as https://{Domain}/...
Domain string
// ActorName is the username part, e.g. "mybot".
// The actor URL will be https://{Domain}/users/{ActorName}.
ActorName string
// ActorType is the ActivityStreams actor type, e.g. "Service" or "Person".
// Defaults to "Service".
ActorType string
// Summary is a short bio shown in the actor document.
Summary string
// DataDir is the directory where JSON state files and the RSA key are stored.
// The directory is created if it does not exist.
DataDir string
// PrivateKey is optional. If nil, a key is loaded from DataDir/key.pem
// or generated and saved there automatically.
PrivateKey *rsa.PrivateKey
}
// FollowDecision is the return type of the OnFollow hook.
type FollowDecision bool
const (
// AcceptFollow instructs the server to accept the incoming Follow activity.
AcceptFollow FollowDecision = true
// RejectFollow instructs the server to reject the incoming Follow activity.
RejectFollow FollowDecision = false
)
// Hooks lets the consuming application react to incoming activities.
type Hooks struct {
// OnFollow is called when a remote actor sends a Follow activity.
// Return AcceptFollow to accept, RejectFollow to reject.
// If nil, all follows are auto-accepted.
OnFollow func(followerActorURL string) FollowDecision
// OnDM is called when a Create{Note} activity is addressed directly to
// this actor (i.e. it is a direct message / mention-only post).
// from is the actor URL of the sender; content is the HTML content of the
// Note; noteID is the URL of the incoming Note (use as inReplyTo when
// replying); inReplyTo is the URL of the note this DM is itself a reply to
// (empty if not a reply).
OnDM func(from string, content string, noteID string, inReplyTo string)
// OnHTML, if non-nil, is called when a browser requests the actor's
// profile page (Accept: text/html). The handler may render whatever HTML
// it likes using w and r. If nil, a 406 Not Acceptable response is
// returned with a JSON body explaining that this is an ActivityPub actor.
OnHTML func(w http.ResponseWriter, r *http.Request)
// ServeNote, if non-nil, is called at the start of GET
// /users/{actor}/notes/{id} before the library's own outbox lookup.
// noteURL is the full canonical URL of the requested note.
// Return true to indicate the request was fully handled; return false to
// fall through to the default outbox-based lookup.
// This hook exists so applications can serve notes that are not yet in
// the outbox (e.g. notes awaiting external authorization before publish).
ServeNote func(w http.ResponseWriter, r *http.Request, noteURL string) bool
// OnAccept, if non-nil, is called when an Accept activity is received.
// The library has already handled Accept{Follow} (updating the following
// list). This hook lets applications handle additional Accept subtypes
// (e.g. Accept{QuoteRequest}).
OnAccept func(activity map[string]any)
// OnReject, if non-nil, is called when a Reject activity is received.
// Applications can use this to handle Reject{QuoteRequest} and similar.
OnReject func(activity map[string]any)
}
// domain groups all actors sharing the same domain for WebFinger lookups.
type domain struct {
mu sync.RWMutex
actors map[string]*Server // keyed by actor name
}
func (d *domain) register(s *Server) {
d.mu.Lock()
d.actors[s.cfg.ActorName] = s
d.mu.Unlock()
}
func (d *domain) lookup(name string) (*Server, bool) {
d.mu.RLock()
s, ok := d.actors[name]
d.mu.RUnlock()
return s, ok
}
// domains is a process-wide map from domain string to domain registry.
var (
domainsMu sync.Mutex
domains = map[string]*domain{}
)
func getDomain(domainName string) *domain {
domainsMu.Lock()
defer domainsMu.Unlock()
if d, ok := domains[domainName]; ok {
return d
}
d := &domain{actors: make(map[string]*Server)}
domains[domainName] = d
return d
}
// Server is an ActivityPub server instance. Create one with New().
type Server struct {
cfg Config
root *os.Root // traversal-resistant handle on cfg.DataDir
privateKey *rsa.PrivateKey
publicKey *rsa.PublicKey
hooks Hooks
dom *domain
mu sync.RWMutex
followers []string // actor URLs
following []string // actor URLs
outbox []map[string]any
inbox []map[string]any
iconURL string // public URL of the actor's avatar image, or ""
iconMu sync.RWMutex
displayName string // actor display name, falls back to ActorName if empty
displayMu sync.RWMutex
// in-process cache of remote actor documents keyed by actor URL
actorCache map[string]map[string]any
actorCacheMu sync.RWMutex
}
// ---------------------------------------------------------------------------
// Constructor
// ---------------------------------------------------------------------------
// New creates a new Server from the given Config, loading or generating keys
// and restoring persisted state from DataDir.
func New(cfg Config) (*Server, error) {
if cfg.Domain == "" {
return nil, errors.New("activitypub: Config.Domain must not be empty")
}
if cfg.ActorName == "" {
return nil, errors.New("activitypub: Config.ActorName must not be empty")
}
if cfg.ActorType == "" {
cfg.ActorType = "Service"
}
if cfg.DataDir == "" {
cfg.DataDir = "."
}
if err := os.MkdirAll(cfg.DataDir, 0o755); err != nil {
return nil, fmt.Errorf("activitypub: create data dir: %w", err)
}
root, err := os.OpenRoot(cfg.DataDir)
if err != nil {
return nil, fmt.Errorf("activitypub: open data dir root: %w", err)
}
s := &Server{
cfg: cfg,
root: root,
dom: getDomain(cfg.Domain),
actorCache: make(map[string]map[string]any),
}
s.dom.register(s)
if cfg.PrivateKey != nil {
s.privateKey = cfg.PrivateKey
} else {
key, err := s.loadOrGenerateKey()
if err != nil {
return nil, err
}
s.privateKey = key
}
s.publicKey = &s.privateKey.PublicKey
// Load persisted state (errors are non-fatal; we start fresh if files are missing)
_ = s.loadJSON("followers.json", &s.followers)
_ = s.loadJSON("following.json", &s.following)
_ = s.loadJSON("outbox.json", &s.outbox)
_ = s.loadJSON("inbox.json", &s.inbox)
return s, nil
}
// SetHooks registers application callbacks. Must be called before Register().
func (s *Server) SetHooks(h Hooks) {
s.hooks = h
}
// ---------------------------------------------------------------------------
// HTTP handler registration
// ---------------------------------------------------------------------------
// Register mounts all ActivityPub and WebFinger routes onto mux.
//
// For single-actor deployments this is all you need. For multi-actor
// deployments, call RegisterActor for each actor and RegisterDomain once:
//
// for _, srv := range servers {
// srv.RegisterActor(mux)
// }
// servers[0].RegisterDomain(mux)
//
// Routes registered by RegisterActor:
//
// GET/POST /users/{actor}/inbox
// GET /users/{actor}/outbox
// GET /users/{actor}/followers
// GET /users/{actor}/following
// GET /users/{actor}
//
// Routes registered by RegisterDomain (domain-wide, register once):
//
// GET /.well-known/webfinger
// POST /inbox (shared inbox)
func (s *Server) Register(mux *http.ServeMux) {
s.RegisterActor(mux)
s.RegisterDomain(mux)
}
// RegisterActor mounts only the per-actor routes for this server's actor.
// Safe to call for each actor in a multi-actor deployment.
func (s *Server) RegisterActor(mux *http.ServeMux) {
mux.HandleFunc("/users/"+s.cfg.ActorName, s.handleActor)
mux.HandleFunc("/users/"+s.cfg.ActorName+"/inbox", s.handleInbox)
mux.HandleFunc("/users/"+s.cfg.ActorName+"/outbox", s.handleOutbox)
mux.HandleFunc("/users/"+s.cfg.ActorName+"/followers", s.handleFollowers)
mux.HandleFunc("/users/"+s.cfg.ActorName+"/following", s.handleFollowing)
mux.HandleFunc("/users/"+s.cfg.ActorName+"/notes/", s.handleNote)
}
// RegisterDomain mounts the domain-wide routes that must only be registered
// once regardless of how many actors share this domain.
// The WebFinger handler will respond for all actors registered on this mux
// whose actor name matches the requested resource — call RegisterDomain on
// any one of the actors (typically the first).
func (s *Server) RegisterDomain(mux *http.ServeMux) {
mux.HandleFunc("/.well-known/webfinger", s.handleWebFinger)
mux.HandleFunc("/inbox", s.handleInbox)
}
// ---------------------------------------------------------------------------
// Public ActivityPub operations
// ---------------------------------------------------------------------------
// Announce sends an Announce (boost) activity for the given object URL to all
// followers and saves it to the outbox.
func (s *Server) Announce(objectURL string) error {
return s.AnnounceWithOriginal(objectURL, "")
}
// AnnounceWithOriginal is like Announce but also records the original
// (pre-resolution) URL so that UndoAnnounce can match a Delete activity
// that references the original URL rather than the resolved AP object id.
func (s *Server) AnnounceWithOriginal(objectURL, originalURL string) error {
activity := s.buildAnnounce(objectURL)
if originalURL != "" && originalURL != objectURL {
activity["originalObject"] = originalURL
}
s.mu.Lock()
s.outbox = prependCapped(s.outbox, activity, 500)
s.mu.Unlock()
if err := s.saveOutbox(); err != nil {
log.Printf("activitypub: save outbox: %v", err)
}
return s.deliverToFollowers(activity)
}
// UndoAnnounce sends an Undo{Announce} for any Announce of objectURL in the
// outbox, replaces it with a Tombstone, and delivers the Undo to all followers.
// Matches against both the resolved object URL and the originalObject field.
// Replacing with a Tombstone (rather than deleting) lets remote servers that
// re-fetch the activity id learn that it has been retracted.
func (s *Server) UndoAnnounce(objectURL string) error {
now := time.Now().UTC().Format(time.RFC3339)
s.mu.Lock()
var announce map[string]any
for i, item := range s.outbox {
if item["type"] == "Announce" {
if item["object"] == objectURL || item["originalObject"] == objectURL {
announce = item
// Replace in-place with a Tombstone at the same id
s.outbox[i] = map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": item["id"],
"type": "Tombstone",
"published": item["published"],
"deleted": now,
}
break
}
}
}
s.mu.Unlock()
if err := s.saveOutbox(); err != nil {
log.Printf("activitypub: save outbox after undo: %v", err)
}
if announce == nil {
log.Printf("activitypub: UndoAnnounce: no Announce found for %s", objectURL)
return nil
}
undo := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s#undos/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Undo",
"actor": s.actorURL(),
"object": announce,
"published": now,
"to": []string{"https://www.w3.org/ns/activitystreams#Public"},
"cc": []string{s.actorURL() + "/followers"},
}
return s.deliverToFollowers(undo)
}
// SendDM sends a direct-message Note to toActorURL. The Note is addressed
// only to the recipient (not public, not followers) so it stays out of the
// outbox. inReplyTo may be empty. The Note is delivered to the recipient's
// inbox but never stored in the outbox.
//
// It returns the AP id of the Note it sent. Because DM Notes are not kept in
// the outbox they are not retrievable at that id afterwards, so callers who
// need to recognise replies to their own DMs must remember the id themselves.
// The id is returned even on delivery failure, so it is only meaningful to
// record it when err is nil.
func (s *Server) SendDM(toActorURL, content, inReplyTo string) (noteID string, err error) {
// Use personal inbox, not sharedInbox — DMs are addressed to a specific
// user and sharedInbox delivery may be rejected by the remote server.
actor, err := s.fetchActor(toActorURL)
if err != nil {
return "", fmt.Errorf("fetch actor for DM: %w", err)
}
inbox, _ := actor["inbox"].(string)
if inbox == "" {
return "", fmt.Errorf("actor %s has no inbox", toActorURL)
}
log.Printf("activitypub: SendDM: sending to %s (inbox: %s)", toActorURL, inbox)
now := time.Now().UTC().Format(time.RFC3339)
noteID = fmt.Sprintf("%s/notes/%d", s.actorURL(), time.Now().UnixNano())
note := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": noteID,
"type": "Note",
"attributedTo": s.actorURL(),
"published": now,
"to": []string{toActorURL},
"cc": []string{},
"content": content,
"tag": []map[string]any{
{
"type": "Mention",
"href": toActorURL,
},
},
}
if inReplyTo != "" {
note["inReplyTo"] = inReplyTo
}
create := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s/creates/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Create",
"actor": s.actorURL(),
"published": now,
"to": []string{toActorURL},
"cc": []string{},
"object": note,
}
if err := s.postActivity(inbox, create); err != nil {
return noteID, fmt.Errorf("post DM to %s: %w", inbox, err)
}
log.Printf("activitypub: SendDM: delivered to %s (note %s)", inbox, noteID)
return noteID, nil
}
// DeliverToFollowers signs and POSTs activity to every known follower's inbox.
func (s *Server) DeliverToFollowers(activity map[string]any) error {
return s.deliverToFollowers(activity)
}
// PostToInbox signs and POSTs an activity directly to a specific inbox URL.
// Use this to deliver activities to a single actor rather than all followers.
func (s *Server) PostToInbox(inboxURL string, activity map[string]any) error {
return s.postActivity(inboxURL, activity)
}
// ResolveInbox fetches an actor document and returns the best inbox URL
// (prefers sharedInbox). Useful when delivering to a single target actor.
func (s *Server) ResolveInbox(actorURL string) (string, error) {
return s.resolveInbox(actorURL)
}
// PublishCreate adds a Create{Note} activity to the outbox and delivers it to
// all followers. The activity is saved to disk before delivery.
func (s *Server) PublishCreate(createActivity map[string]any) error {
s.mu.Lock()
s.outbox = prependCapped(s.outbox, createActivity, 500)
s.mu.Unlock()
if err := s.saveOutbox(); err != nil {
log.Printf("activitypub: PublishCreate: save outbox: %v", err)
}
return s.deliverToFollowers(createActivity)
}
// DeleteCreate sends a Delete{Note} for any Create{Note} in the outbox whose
// embedded Note matches objectURL via the "quote", "quoteUri", or "id" fields.
// The Create is replaced in-place with a Tombstone and a Delete activity is
// delivered to all followers.
func (s *Server) DeleteCreate(objectURL string) error {
now := time.Now().UTC().Format(time.RFC3339)
s.mu.Lock()
var note map[string]any
for i, item := range s.outbox {
if item["type"] != "Create" {
continue
}
obj, _ := item["object"].(map[string]any)
if obj == nil {
continue
}
if obj["quote"] == objectURL || obj["quoteUri"] == objectURL || obj["id"] == objectURL {
note = obj
noteID, _ := obj["id"].(string)
s.outbox[i] = map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": noteID,
"type": "Tombstone",
"published": item["published"],
"deleted": now,
}
break
}
}
s.mu.Unlock()
if err := s.saveOutbox(); err != nil {
log.Printf("activitypub: DeleteCreate: save outbox: %v", err)
}
if note == nil {
log.Printf("activitypub: DeleteCreate: no Create{Note} found for %s", objectURL)
return nil
}
noteID, _ := note["id"].(string)
del := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s#deletes/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Delete",
"actor": s.actorURL(),
"object": noteID,
"published": now,
"to": []string{"https://www.w3.org/ns/activitystreams#Public"},
"cc": []string{s.actorURL() + "/followers"},
}
return s.deliverToFollowers(del)
}
// RemoveFollowing removes actorURL from the following list and persists the change.
func (s *Server) RemoveFollowing(actorURL string) {
s.mu.Lock()
s.following = remove(s.following, actorURL)
s.mu.Unlock()
if err := s.saveFollowing(); err != nil {
log.Printf("activitypub: RemoveFollowing: save: %v", err)
}
}
// IsFollowing reports whether this actor is currently following actorURL.
func (s *Server) IsFollowing(actorURL string) bool {
s.mu.RLock()
defer s.mu.RUnlock()
return contains(s.following, actorURL)
}
// buildActorDoc constructs the current actor document as a map.
func (s *Server) buildActorDoc() (map[string]any, error) {
pubKeyPEM, err := s.publicKeyPEM()
if err != nil {
return nil, fmt.Errorf("publicKeyPEM: %w", err)
}
s.iconMu.RLock()
iconURL := s.iconURL
s.iconMu.RUnlock()
actor := map[string]any{
"@context": []any{
"https://www.w3.org/ns/activitystreams",
"https://w3id.org/security/v1",
},
"id": s.actorURL(),
"type": s.cfg.ActorType,
"preferredUsername": s.cfg.ActorName,
"name": s.effectiveName(),
"summary": s.cfg.Summary,
"inbox": s.actorURL() + "/inbox",
"outbox": s.actorURL() + "/outbox",
"followers": s.actorURL() + "/followers",
"following": s.actorURL() + "/following",
"publicKey": map[string]any{
"id": s.actorURL() + "#main-key",
"owner": s.actorURL(),
"publicKeyPem": pubKeyPEM,
},
"endpoints": map[string]any{
"sharedInbox": s.baseURL() + "/inbox",
},
}
if iconURL != "" {
actor["icon"] = map[string]any{
"type": "Image",
"mediaType": "image/jpeg",
"url": iconURL,
}
}
return actor, nil
}
// actorDocFile is where the last delivered actor document is cached inside
// DataDir, for the change comparison in UpdateProfile.
//
// It is deliberately NOT called "actor.json": DataDir is chosen by the
// embedding application, which may well keep its own per-actor config in that
// same directory. booster-bot did exactly that, and the two files silently
// overwrote each other — the actor document won, and the application's
// settings (curator allowlist, display name, avatar id) were lost. A name
// carrying the library's own prefix keeps the two apart.
const actorDocFile = "ap-actor-doc.json"
// UpdateProfile sends an Update{Actor} activity to all followers if the actor
// document has changed since the last save. If force is true, the update is
// delivered unconditionally. Safe to call on every startup with force=false.
func (s *Server) UpdateProfile(force bool) error {
actor, err := s.buildActorDoc()
if err != nil {
return err
}
currentJSON, err := json.Marshal(actor)
if err != nil {
return fmt.Errorf("marshal actor: %w", err)
}
if !force {
var saved map[string]any
if err := s.loadJSON(actorDocFile, &saved); err == nil {
savedJSON, err := json.Marshal(saved)
if err == nil && bytes.Equal(currentJSON, savedJSON) {
log.Printf("activitypub: actor doc unchanged, skipping UpdateProfile")
return nil
}
}
log.Printf("activitypub: actor doc changed, sending UpdateProfile")
}
if err := s.saveJSON(actorDocFile, actor); err != nil {
log.Printf("activitypub: save %s: %v", actorDocFile, err)
}
update := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s#updates/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Update",
"actor": s.actorURL(),
"object": actor,
"published": time.Now().UTC().Format(time.RFC3339),
"to": []string{"https://www.w3.org/ns/activitystreams#Public"},
}
return s.deliverToFollowers(update)
}
// SetSummary updates the in-memory summary for this actor. The new value is
// reflected immediately in the actor document served at GET /users/{name}.
// Call UpdateProfile() afterwards to push the change to followers.
func (s *Server) SetSummary(summary string) {
s.cfg.Summary = summary
}
// SetIcon sets the public URL of the actor's avatar image. Pass an empty
// string to remove the icon. The change is reflected immediately in the actor
// document; call UpdateProfile() to push it to followers.
func (s *Server) SetIcon(iconURL string) {
s.iconMu.Lock()
s.iconURL = iconURL
s.iconMu.Unlock()
}
// SetDisplayName sets the actor's display name (the "name" field in the actor
// document). Pass an empty string to fall back to the ActorName. The change
// is reflected immediately; call UpdateProfile() to push it to followers.
func (s *Server) SetDisplayName(name string) {
s.displayMu.Lock()
s.displayName = name
s.displayMu.Unlock()
}
// Close releases the file descriptor held by the server's data directory root.
// It is safe but not required to call Close for servers that live for the
// duration of the process.
func (s *Server) Close() error {
return s.root.Close()
}
// effectiveName returns the display name, falling back to ActorName.
func (s *Server) effectiveName() string {
s.displayMu.RLock()
n := s.displayName
s.displayMu.RUnlock()
if n == "" {
return s.cfg.ActorName
}
return n
}
// SetAnnounceField sets an arbitrary extra field on the first Announce in the
// outbox whose object or originalObject matches objectURL. Useful for storing
// application-level metadata (e.g. a content snippet) alongside the activity.
// Returns true if a matching Announce was found and updated.
func (s *Server) SetAnnounceField(objectURL, key string, value any) bool {
s.mu.Lock()
defer s.mu.Unlock()
for _, item := range s.outbox {
if item["type"] == "Announce" &&
(item["object"] == objectURL || item["originalObject"] == objectURL) {
item[key] = value
go func() { _ = s.saveOutbox() }()
return true
}
}
return false
}
// Outbox returns a snapshot of the outbox containing only live Announce
// activities (Tombstones are excluded). Safe for concurrent use.
func (s *Server) Outbox() []map[string]any {
s.mu.RLock()
defer s.mu.RUnlock()
var result []map[string]any
for _, item := range s.outbox {
t, _ := item["type"].(string)
if t == "Announce" || t == "Create" {
cp := make(map[string]any, len(item))
for k, v := range item {
cp[k] = v
}
result = append(result, cp)
}
}
return result
}
// ---------------------------------------------------------------------------
// WebFinger handler
// ---------------------------------------------------------------------------
func (s *Server) handleWebFinger(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
resource := r.URL.Query().Get("resource")
if resource == "" {
http.Error(w, "missing resource parameter", http.StatusBadRequest)
return
}
// Resolve the resource to an actor name on this domain.
var name string
if after, ok := strings.CutPrefix(resource, "acct:"); ok {
parts := strings.SplitN(after, "@", 2)
if len(parts) != 2 || parts[1] != s.cfg.Domain {
http.Error(w, "not found", http.StatusNotFound)
return
}
name = parts[0]
} else {
// resource is an actor URL — extract name from path /users/{name}
prefix := "https://" + s.cfg.Domain + "/users/"
if !strings.HasPrefix(resource, prefix) {
http.Error(w, "not found", http.StatusNotFound)
return
}
name = strings.TrimPrefix(resource, prefix)
}
// Look up the actor in the domain registry (covers all actors on this domain)
actor, ok := s.dom.lookup(name)
if !ok {
http.Error(w, "not found", http.StatusNotFound)
return
}
resp := map[string]any{
"subject": fmt.Sprintf("acct:%s@%s", actor.cfg.ActorName, actor.cfg.Domain),
"aliases": []string{actor.actorURL()},
"links": []map[string]any{
{
"rel": "self",
"type": "application/activity+json",
"href": actor.actorURL(),
},
{
"rel": "http://webfinger.net/rel/profile-page",
"type": "text/html",
"href": actor.actorURL(),
},
},
}
w.Header().Set("Content-Type", "application/jrd+json")
writeJSONRaw(w, resp)
}
// ---------------------------------------------------------------------------
// Actor handler
// ---------------------------------------------------------------------------
func (s *Server) handleActor(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
// Content-negotiate: browsers get HTML (or 406), AP clients get JSON.
accept := r.Header.Get("Accept")
wantsHTML := strings.Contains(accept, "text/html") &&
!strings.Contains(accept, "application/activity+json") &&
!strings.Contains(accept, "application/ld+json")
if wantsHTML {
if s.hooks.OnHTML != nil {
s.hooks.OnHTML(w, r)
} else {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusNotAcceptable)
writeJSONRaw(w, map[string]any{
"error": "Not Acceptable",
"message": "This is an ActivityPub actor. Request with Accept: application/activity+json to get the actor document.",
"actor": s.actorURL(),
})
}
return
}
actor, err := s.buildActorDoc()
if err != nil {
http.Error(w, "internal error", http.StatusInternalServerError)
return
}
w.Header().Set("Content-Type", "application/activity+json")
writeJSON(w, actor)
}
// ---------------------------------------------------------------------------
// Inbox handler
// ---------------------------------------------------------------------------
func (s *Server) handleInbox(w http.ResponseWriter, r *http.Request) {
switch r.Method {
case http.MethodGet:
s.serveOrderedCollection(w, s.inbox, s.actorURL()+"/inbox")
case http.MethodPost:
s.receiveInbox(w, r)
default:
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
}
}
// ---------------------------------------------------------------------------
// SSRF-safe HTTP client
// ---------------------------------------------------------------------------
//
// All outbound HTTP requests use newSafeClient, which hooks into the TCP
// dialer after DNS resolution to block connections to private/loopback/
// link-local addresses and to restrict to HTTPS (port 443) only.
// This prevents Server-Side Request Forgery via attacker-controlled URLs
// (inbox URLs from actor documents, object URLs from DM content, etc.)
// and also prevents DNS-rebinding attacks because the check happens after
// the OS has resolved the hostname to an IP address.
//
// IP blocklist and structure adapted from Andrew Ayer's public-domain article
// "Preventing Server Side Request Forgery in Golang" (2019).
func ipv4Net(a, b, c, d byte, prefixLen int) net.IPNet {
return net.IPNet{
IP: net.IPv4(a, b, c, d),
Mask: net.CIDRMask(96+prefixLen, 128),
}
}
// reservedIPv4Nets lists every IPv4 range that must not be reached.
var reservedIPv4Nets = []net.IPNet{
ipv4Net(0, 0, 0, 0, 8), // "This" network
ipv4Net(10, 0, 0, 0, 8), // Private
ipv4Net(100, 64, 0, 0, 10), // Shared address space (RFC 6598)
ipv4Net(127, 0, 0, 0, 8), // Loopback
ipv4Net(169, 254, 0, 0, 16), // Link-local (includes AWS metadata 169.254.169.254)
ipv4Net(172, 16, 0, 0, 12), // Private
ipv4Net(192, 0, 0, 0, 24), // IETF protocol assignments (RFC 6890)
ipv4Net(192, 0, 2, 0, 24), // Documentation (TEST-NET-1)
ipv4Net(192, 88, 99, 0, 24), // 6to4 relay anycast (deprecated)
ipv4Net(192, 168, 0, 0, 16), // Private
ipv4Net(198, 18, 0, 0, 15), // Benchmarking (RFC 2544)
ipv4Net(198, 51, 100, 0, 24), // Documentation (TEST-NET-2)
ipv4Net(203, 0, 113, 0, 24), // Documentation (TEST-NET-3)
ipv4Net(224, 0, 0, 0, 4), // Multicast
ipv4Net(240, 0, 0, 0, 4), // Reserved (broadcast)
}
// globalUnicastIPv6Net is 2000::/3, the only IPv6 range considered public.
var globalUnicastIPv6Net = net.IPNet{
IP: net.IP{0x20, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
Mask: net.CIDRMask(3, 128),
}
// isPublicIPAddress returns true if ip is a globally routable address.
func isPublicIPAddress(ip net.IP) bool {
if ip.To4() != nil {
for _, reserved := range reservedIPv4Nets {
if reserved.Contains(ip) {
return false
}
}
return true
}
return globalUnicastIPv6Net.Contains(ip)
}
// safeSocketControl is a net.Dialer.Control function that aborts the dial if
// the resolved address is not a public IP on port 443 (HTTPS only).
func safeSocketControl(network, address string, _ syscall.RawConn) error {
if network != "tcp4" && network != "tcp6" {
return fmt.Errorf("activitypub: network %q is not allowed", network)
}
host, port, err := net.SplitHostPort(address)
if err != nil {
return fmt.Errorf("activitypub: invalid address %q: %w", address, err)
}
if port != "443" {
return fmt.Errorf("activitypub: port %s is not allowed (only 443/HTTPS)", port)
}
ip := net.ParseIP(host)
if ip == nil {
return fmt.Errorf("activitypub: %q is not a valid IP address", host)
}
if !isPublicIPAddress(ip) {
return fmt.Errorf("activitypub: %s is not a public IP address", ip)
}
return nil
}
// newSafeClient returns an *http.Client that enforces SSRF protection via
// safeSocketControl. All outbound requests in this package must use this
// client rather than http.DefaultClient or a bare &http.Client{}.
//
// Redirects are capped at 3. Each redirect target is validated by the safe
// dialer, so a chain cannot escape to a private address mid-redirect.
// Go's default of 10 redirects is intentionally overridden here.
func newSafeClient(timeout time.Duration) *http.Client {
dialer := &net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
Control: safeSocketControl,
}
transport := &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: dialer.DialContext,
ForceAttemptHTTP2: true,
MaxIdleConns: 100,
IdleConnTimeout: 90 * time.Second,
TLSHandshakeTimeout: 10 * time.Second,
ExpectContinueTimeout: 1 * time.Second,
}
return &http.Client{
Timeout: timeout,
Transport: transport,
CheckRedirect: func(req *http.Request, via []*http.Request) error {
if len(via) >= 3 {
return fmt.Errorf("too many redirects (max 3)")
}
return nil
},
}
}
// errActorGone is returned when a remote actor's URL responds with 410 Gone,
// indicating the account has been deleted.
var errActorGone = errors.New("actor has been deleted (410 Gone)")
func (s *Server) receiveInbox(w http.ResponseWriter, r *http.Request) {
body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20)) // 1 MiB max
if err != nil {
http.Error(w, "read error", http.StatusBadRequest)
return
}
// Verify HTTP Signature (cavage-12 / draft profile)
actorURL, err := s.verifyHTTPSignature(r, body)
if err != nil {
if errors.Is(err, errActorGone) {
// Signing key belongs to a deleted actor — silently discard
log.Printf("activitypub: inbox: discarding request from deleted actor (%v)", err)
w.WriteHeader(http.StatusAccepted)
return
}
log.Printf("activitypub: inbox signature verification failed: %v", err)
http.Error(w, "signature verification failed", http.StatusUnauthorized)
return
}
var activity map[string]any
if err := json.Unmarshal(body, &activity); err != nil {
http.Error(w, "invalid JSON", http.StatusBadRequest)
return
}
// Basic plausibility check
if _, ok := activity["type"]; !ok {
http.Error(w, "missing type", http.StatusBadRequest)
return
}
// Verify that the activity's actor is the same owner as the signing key.
//
// FEP-fe34 §Signatures:
// "In order to minimize damage in the event of a key compromise or
// insufficient validation, consumers MUST verify that the signing key
// has the same owner as the signed object."
// FEP-fe34 §Ownership:
// "Activities have an actor property … This actor is considered to be
// the owner of the activity."
// FEP-fe34 §Comparing owners:
// "Owners are the same if their identifiers are identical after
// conversion of their schemes and hosts to lowercase."
//
// actorURL is derived from keyId (fragment stripped). The activity's
// declared actor must be the same owner — exact URL equality (with
// case-folded scheme and host) rather than same-origin. This prevents
// a compromised server from injecting activities on behalf of a different
// actor on the same server.
//
// Note: relay forwarding (a relay signing with its own key for an actor
// on a different server) is intentionally not supported and will be
// rejected by this check.
activityActor, _ := activity["actor"].(string)
if activityActor == "" {
http.Error(w, "missing actor field", http.StatusBadRequest)
return
}
if !sameOwner(actorURL, activityActor) {
log.Printf("activitypub: inbox: actor owner mismatch: keyId actor %q vs activity actor %q", actorURL, activityActor)
http.Error(w, "activity actor does not match signing key owner", http.StatusUnauthorized)
return
}
activityType, _ := activity["type"].(string)
log.Printf("inbox: received %s from %s", activityType, actorURL)
bodyJSON, _ := json.MarshalIndent(activity, " ", " ")
log.Printf("inbox body:\n %s", bodyJSON)
// Store a copy in our in-memory / persisted inbox (capped at 200)
s.mu.Lock()
s.inbox = prependCapped(s.inbox, activity, 200)
s.mu.Unlock()
go func() { _ = s.saveInbox() }()
switch activityType {
case "Follow":
s.handleFollow(w, activity, actorURL)
case "Undo":
s.handleUndo(w, activity)
case "Accept":
s.handleAccept(w, activity)
case "Reject":
s.handleReject(w, activity)
case "Create":
s.handleCreate(w, activity, actorURL)
case "Delete":
s.handleDelete(w, activity)
default:
// Accept unknown activity types gracefully
w.WriteHeader(http.StatusAccepted)
}
}
// verifyEmbeddedObject checks that an object embedded inside a trusted activity
// satisfies FEP-fe34 §Embedding. The actorURL argument is the verified signing
// actor (from the HTTP signature). The embedded obj must:
//
// 1. Have a same-origin `id` as actorURL, if it has an id at all.
// Anonymous objects (no id) are unconditionally trusted.
// 2. Have a same-origin owner as actorURL.
// The owner field is `attributedTo` for Object/Note types and `actor`
// for Activity types (Follow, Undo, etc.). If neither field is present
// the object is anonymous with respect to ownership and is accepted.
//
// Returns a non-nil error string suitable for an HTTP 401 response body if
// either check fails. The caller should reject the enclosing activity.
func verifyEmbeddedObject(actorURL string, obj map[string]any) error {
// Check 1: if the embedded object has an id, it must be same-origin.
if id := stringField(obj, "id"); id != "" {
if !sameOrigin(actorURL, id) {
return fmt.Errorf("embedded object id %q has different origin from signing actor %q", id, actorURL)
}
}
// Check 2: the owner of the embedded object must be the same owner.
// Owner is `actor` for Activity subtypes, `attributedTo` for Objects.
// We use sameOwner (exact equality with case-folded scheme+host) rather
// than sameOrigin, per silverpill's recommendation: if the origin server
// does poor C2S validation, an attacker could craft an embedded object
// with attributedTo pointing to a different actor on the same server.
// Exact owner equality catches this.
owner := stringField(obj, "actor")
if owner == "" {
owner = stringField(obj, "attributedTo")
}
if owner != "" && !sameOwner(actorURL, owner) {
return fmt.Errorf("embedded object owner %q differs from signing actor %q", owner, actorURL)
}
return nil
}
// handleFollow processes an incoming Follow activity.
func (s *Server) handleFollow(w http.ResponseWriter, activity map[string]any, senderActorURL string) {
followerURL := stringField(activity, "actor")
if followerURL == "" {
http.Error(w, "missing actor", http.StatusBadRequest)
return
}
// Ask application whether to accept
decision := AcceptFollow
if s.hooks.OnFollow != nil {
decision = s.hooks.OnFollow(followerURL)
}
if decision == AcceptFollow {
// Add to followers
s.mu.Lock()
if !contains(s.followers, followerURL) {
s.followers = append(s.followers, followerURL)
}
s.mu.Unlock()
go func() { _ = s.saveFollowers() }()
// Send Accept{Follow} back to the follower's inbox
go s.sendAcceptFollow(followerURL, activity)
} else {
go s.sendRejectFollow(followerURL, activity)
}
w.WriteHeader(http.StatusAccepted)
}
// handleUndo processes Undo{Follow} (unfollow).
func (s *Server) handleUndo(w http.ResponseWriter, activity map[string]any) {
actorURL := stringField(activity, "actor")
obj, ok := activity["object"].(map[string]any)
if !ok {
w.WriteHeader(http.StatusAccepted)
return
}
if err := verifyEmbeddedObject(actorURL, obj); err != nil {
log.Printf("handleUndo: embedded object failed origin check: %v", err)
http.Error(w, "embedded object origin mismatch", http.StatusUnauthorized)
return
}
if objType, _ := obj["type"].(string); objType == "Follow" {
followerURL := stringField(activity, "actor")
s.mu.Lock()
s.followers = remove(s.followers, followerURL)
s.mu.Unlock()
go func() { _ = s.saveFollowers() }()
}
w.WriteHeader(http.StatusAccepted)
}
// handleAccept processes Accept{Follow} and notifies the application via OnAccept.
func (s *Server) handleAccept(w http.ResponseWriter, activity map[string]any) {
obj, ok := activity["object"].(map[string]any)
if !ok {
w.WriteHeader(http.StatusAccepted)
return
}
if objType, _ := obj["type"].(string); objType == "Follow" {
remoteActorURL := stringField(activity, "actor")
s.mu.Lock()
if !contains(s.following, remoteActorURL) {
s.following = append(s.following, remoteActorURL)
}
s.mu.Unlock()
go func() { _ = s.saveFollowing() }()
}
if s.hooks.OnAccept != nil {
go s.hooks.OnAccept(activity)
}
w.WriteHeader(http.StatusAccepted)
}
// handleReject notifies the application via OnReject.
func (s *Server) handleReject(w http.ResponseWriter, activity map[string]any) {
log.Printf("activitypub: inbox: Reject from %s", stringField(activity, "actor"))
if s.hooks.OnReject != nil {
go s.hooks.OnReject(activity)
}
w.WriteHeader(http.StatusAccepted)
}
// handleDelete processes a Delete activity. If the deleted object matches an
// Announce in our outbox, we send an Undo{Announce} to our followers.
func (s *Server) handleDelete(w http.ResponseWriter, activity map[string]any) {
actorURL := stringField(activity, "actor")
// The object field may be a string ID or an embedded object with an id.
var objectID string
switch v := activity["object"].(type) {
case string:
// A bare string ID — verify it is same-origin as the signing actor.
// The sender is asserting they own the object at that URL.
if !sameOrigin(actorURL, v) {
log.Printf("handleDelete: object id %q has different origin from actor %q", v, actorURL)
http.Error(w, "object origin mismatch", http.StatusUnauthorized)
return
}
objectID = v
case map[string]any:
if err := verifyEmbeddedObject(actorURL, v); err != nil {
log.Printf("handleDelete: embedded object failed origin check: %v", err)
http.Error(w, "embedded object origin mismatch", http.StatusUnauthorized)
return
}
objectID, _ = v["id"].(string)
}
if objectID == "" {
log.Printf("handleDelete: no object id found, ignoring")
w.WriteHeader(http.StatusAccepted)
return
}
log.Printf("handleDelete: object %s deleted, checking outbox for matching Announce", objectID)
if err := s.UndoAnnounce(objectID); err != nil {
log.Printf("handleDelete: UndoAnnounce failed: %v", err)
}
w.WriteHeader(http.StatusAccepted)
}
// handleCreate processes Create{Note} activities — i.e. incoming posts/DMs.
func (s *Server) handleCreate(w http.ResponseWriter, activity map[string]any, senderActorURL string) {
if s.hooks.OnDM == nil {
log.Printf("handleCreate: no OnDM hook set, ignoring")
w.WriteHeader(http.StatusAccepted)
return
}
obj, ok := activity["object"].(map[string]any)
if !ok {
log.Printf("handleCreate: object is not a map (type %T), ignoring", activity["object"])
w.WriteHeader(http.StatusAccepted)
return
}
objType, _ := obj["type"].(string)
if objType != "Note" {
log.Printf("handleCreate: object type is %q, not Note, ignoring", objType)
w.WriteHeader(http.StatusAccepted)
return
}
if err := verifyEmbeddedObject(senderActorURL, obj); err != nil {
log.Printf("handleCreate: embedded Note failed origin check: %v", err)
http.Error(w, "embedded object origin mismatch", http.StatusUnauthorized)
return
}
to := toStringSlice(obj["to"])
cc := toStringSlice(obj["cc"])
log.Printf("handleCreate: Note to=%v cc=%v", to, cc)
// Check all actors on this domain — the shared inbox receives DMs for any
// of them, not just the actor that happens to have registered /inbox last.
from := stringField(activity, "actor")
if from == "" {
from = senderActorURL
}
inReplyTo := stringField(obj, "inReplyTo")
content, _ := obj["content"].(string)
dispatched := false
s.dom.mu.RLock()
actors := make([]*Server, 0, len(s.dom.actors))
for _, a := range s.dom.actors {
actors = append(actors, a)
}
s.dom.mu.RUnlock()
for _, a := range actors {
if a.hooks.OnDM == nil {
continue
}
if isDM(obj, a.actorURL()) {
noteID := stringField(obj, "id")
log.Printf("handleCreate: DM for %s from %s noteID=%q inReplyTo=%q content: %s", a.actorURL(), from, noteID, inReplyTo, content)
hook := a.hooks.OnDM
go hook(from, content, noteID, inReplyTo)
dispatched = true
}
}
if !dispatched {
log.Printf("handleCreate: Note is not a DM to any of our actors, ignoring")
}
w.WriteHeader(http.StatusAccepted)
}
// isDM returns true if the Note is addressed directly to actorURL but NOT to Public.
func isDM(note map[string]any, actorURL string) bool {
const public = "https://www.w3.org/ns/activitystreams#Public"
to := toStringSlice(note["to"])
cc := toStringSlice(note["cc"])
all := append(to, cc...)
addressed := false
for _, r := range all {
if r == public || r == "as:Public" || r == "Public" {
return false // public post, not a DM
}
if r == actorURL {
addressed = true
}
}
return addressed
}
// ---------------------------------------------------------------------------
// Outbox handler
// ---------------------------------------------------------------------------
// handleNote serves an individual Note by its ID.
// If the ServeNote hook is set, it is called first; if it returns true the
// request is considered handled. Otherwise the outbox is searched for a
// Create{Note} whose embedded Note id matches the requested URL.
func (s *Server) handleNote(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
noteURL := "https://" + s.cfg.Domain + r.URL.Path
// Give the application a chance to serve notes not yet in the outbox.
if s.hooks.ServeNote != nil {
if s.hooks.ServeNote(w, r, noteURL) {
return
}
}
// Fall through to outbox lookup.
var note map[string]any
s.mu.RLock()
for _, item := range s.outbox {
if obj, ok := item["object"].(map[string]any); ok {
if obj["id"] == noteURL {
note = obj
break
}
}
}
s.mu.RUnlock()
if note == nil {
http.NotFound(w, r)
return
}
w.Header().Set("Content-Type", "application/activity+json")
writeJSON(w, note)
}
func (s *Server) handleOutbox(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
s.mu.RLock()
all := make([]map[string]any, len(s.outbox))
copy(all, s.outbox)
s.mu.RUnlock()
// Serve the full outbox including Tombstones so remote servers can
// discover retractions. Filtering happens only in the HTML profile view
// and the Outbox() getter used by the backend UI.
s.serveOrderedCollection(w, all, s.actorURL()+"/outbox")
}
// ---------------------------------------------------------------------------
// Followers / Following handlers
// ---------------------------------------------------------------------------
func (s *Server) handleFollowers(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
s.mu.RLock()
items := make([]string, len(s.followers))
copy(items, s.followers)
s.mu.RUnlock()
// Convert []string to []map[string]any for the collection helper
var objs []map[string]any
for _, u := range items {
objs = append(objs, map[string]any{"id": u, "type": "Person"})
}
s.serveOrderedCollection(w, objs, s.actorURL()+"/followers")
}
func (s *Server) handleFollowing(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodGet {
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
return
}
s.mu.RLock()
items := make([]string, len(s.following))
copy(items, s.following)
s.mu.RUnlock()
var objs []map[string]any
for _, u := range items {
objs = append(objs, map[string]any{"id": u, "type": "Person"})
}
s.serveOrderedCollection(w, objs, s.actorURL()+"/following")
}
// ---------------------------------------------------------------------------
// Activity delivery (server-to-server)
// ---------------------------------------------------------------------------
// deliverToFollowers fans out an activity to all known followers' inboxes.
func (s *Server) deliverToFollowers(activity map[string]any) error {
s.mu.RLock()
followers := make([]string, len(s.followers))
copy(followers, s.followers)
s.mu.RUnlock()
// Collapse to one inbox per hostname (use sharedInbox where available).
inboxes := map[string]struct{}{}
for _, followerActorURL := range followers {
inbox, err := s.resolveInbox(followerActorURL)
if err != nil {
log.Printf("activitypub: resolve inbox for %s: %v", followerActorURL, err)
continue
}
inboxes[inbox] = struct{}{}
}
var lastErr error
for inbox := range inboxes {
if err := s.postActivity(inbox, activity); err != nil {
log.Printf("activitypub: deliver to %s: %v", inbox, err)
lastErr = err
}
}
return lastErr
}
// sendAcceptFollow sends an Accept{Follow} to the follower's inbox.
func (s *Server) sendAcceptFollow(followerActorURL string, followActivity map[string]any) {
inbox, err := s.resolveInbox(followerActorURL)
if err != nil {
log.Printf("activitypub: resolve inbox for accept: %v", err)
return
}
accept := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s#accepts/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Accept",
"actor": s.actorURL(),
"object": followActivity,
}
if err := s.postActivity(inbox, accept); err != nil {
log.Printf("activitypub: send Accept: %v", err)
}
}
// sendRejectFollow sends a Reject{Follow} to the follower's inbox.
func (s *Server) sendRejectFollow(followerActorURL string, followActivity map[string]any) {
inbox, err := s.resolveInbox(followerActorURL)
if err != nil {
log.Printf("activitypub: resolve inbox for reject: %v", err)
return
}
reject := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": fmt.Sprintf("%s#rejects/%d", s.actorURL(), time.Now().UnixNano()),
"type": "Reject",
"actor": s.actorURL(),
"object": followActivity,
}
if err := s.postActivity(inbox, reject); err != nil {
log.Printf("activitypub: send Reject: %v", err)
}
}
// resolveInbox fetches an actor document and returns the inbox URL.
// It prefers sharedInbox where available, and caches actor documents.
func (s *Server) resolveInbox(actorURL string) (string, error) {
actor, err := s.fetchActor(actorURL)
if err != nil {
return "", err
}
// Prefer sharedInbox
if ep, ok := actor["endpoints"].(map[string]any); ok {
if si, ok := ep["sharedInbox"].(string); ok && si != "" {
return si, nil
}
}
if inbox, ok := actor["inbox"].(string); ok && inbox != "" {
return inbox, nil
}
// Fallback: guess /inbox on the same host
u, err := url.Parse(actorURL)
if err != nil {
return "", fmt.Errorf("invalid actor URL: %w", err)
}
return fmt.Sprintf("%s://%s/inbox", u.Scheme, u.Host), nil
}
// fetchActor retrieves and caches a remote actor document.
func (s *Server) fetchActor(actorURL string) (map[string]any, error) {
s.actorCacheMu.RLock()
if actor, ok := s.actorCache[actorURL]; ok {
s.actorCacheMu.RUnlock()
return actor, nil
}
s.actorCacheMu.RUnlock()
req, err := http.NewRequest(http.MethodGet, actorURL, nil)
if err != nil {
return nil, err
}
req.Header.Set("Accept", "application/activity+json, application/ld+json")
if err := s.signRequest(req, nil); err != nil {
return nil, fmt.Errorf("sign actor fetch: %w", err)
}
resp, err := newSafeClient(10 * time.Second).Do(req)
if err != nil {
return nil, err
}
defer resp.Body.Close()
if resp.StatusCode == http.StatusGone {
return nil, errActorGone
}
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("actor fetch returned %d", resp.StatusCode)
}
var actor map[string]any
if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&actor); err != nil {
return nil, fmt.Errorf("decode actor: %w", err)
}
s.actorCacheMu.Lock()
s.actorCache[actorURL] = actor
s.actorCacheMu.Unlock()
return actor, nil
}
// RedirectPolicy controls whether FetchObject resolves redirects before
// signing. Use FollowRedirects when the URL may be a local alias pointing
// to a post on a different instance; use NoRedirects when the URL is
// already canonical.
type RedirectPolicy bool
const (
// FollowRedirects resolves any redirect first with an unsigned request,
// then performs a fresh signed GET to the final URL.
FollowRedirects RedirectPolicy = true
// NoRedirects sends a single signed GET directly to the given URL.
NoRedirects RedirectPolicy = false
)
// FetchObject performs a signed GET for an arbitrary AP object URL, returning
// the parsed JSON. Unlike fetchActor it does not cache.
//
// If policy is FollowRedirects, redirects are resolved first with an unsigned
// request and the final URL is then fetched with a fresh signature.
// This is needed when the input URL may be a local alias (e.g. a mastodon.xyz
// permalink for a post on merveilles.town) — the signature must be computed
// for the destination host, not the redirect source.
//
// If policy is NoRedirects, the request goes directly to objectURL with no
// redirect following; use this when objectURL is already canonical.
func (s *Server) FetchObject(objectURL string, policy RedirectPolicy) (map[string]any, error) {
finalURL := objectURL
if policy == FollowRedirects {
// Resolve redirects with a no-follow client to find the canonical URL.
// The safe client blocks private IPs even on the redirect target.
noFollow := newSafeClient(10 * time.Second)
noFollow.CheckRedirect = func(req *http.Request, via []*http.Request) error {
return http.ErrUseLastResponse
}
resolveReq, err := http.NewRequest(http.MethodGet, objectURL, nil)
if err != nil {
return nil, err
}
resolveReq.Header.Set("Accept", "application/activity+json, application/ld+json")
resolveResp, err := noFollow.Do(resolveReq)
if err != nil {
return nil, fmt.Errorf("resolve redirect: %w", err)
}
resolveResp.Body.Close()
if loc := resolveResp.Header.Get("Location"); loc != "" {
finalURL = loc
log.Printf("activitypub: FetchObject: redirect %s -> %s", objectURL, finalURL)
}
}
req, err := http.NewRequest(http.MethodGet, finalURL, nil)
if err != nil {
return nil, err
}
req.Header.Set("Accept", "application/activity+json, application/ld+json")
if err := s.signRequest(req, nil); err != nil {
return nil, fmt.Errorf("sign object fetch: %w", err)
}
// No-redirect safe client: the signed request must go exactly to finalURL.
fetchClient := newSafeClient(10 * time.Second)
fetchClient.CheckRedirect = func(req *http.Request, via []*http.Request) error {
return http.ErrUseLastResponse
}
resp, err := fetchClient.Do(req)
if err != nil {
return nil, err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("object fetch returned %d", resp.StatusCode)
}
ct := resp.Header.Get("Content-Type")
if !strings.Contains(ct, "activity+json") && !strings.Contains(ct, "ld+json") {
return nil, fmt.Errorf("object fetch returned non-AP content-type %q", ct)
}
var obj map[string]any
if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&obj); err != nil {
return nil, fmt.Errorf("decode object: %w", err)
}
return obj, nil
}
// postActivity JSON-encodes an activity and POSTs it to the given inbox URL,
// signed with this server's private key.
func (s *Server) postActivity(inboxURL string, activity map[string]any) error {
body, err := json.Marshal(activity)
if err != nil {
return fmt.Errorf("marshal activity: %w", err)
}
req, err := http.NewRequest(http.MethodPost, inboxURL, bytes.NewReader(body))
if err != nil {
return err
}
req.Header.Set("Content-Type", "application/activity+json")
req.Header.Set("Accept", "application/activity+json")
if err := s.signRequest(req, body); err != nil {
return fmt.Errorf("sign request: %w", err)
}
// ap-next guide §Network — Delivering activities:
// "Do not follow redirects."
// A redirect on inbox delivery would invalidate the HTTP signature
// (the signed (request-target) and Host headers no longer match).
deliverClient := newSafeClient(15 * time.Second)
deliverClient.CheckRedirect = func(_ *http.Request, _ []*http.Request) error {
return http.ErrUseLastResponse
}
resp, err := deliverClient.Do(req)
if err != nil {
return err
}
defer resp.Body.Close()
if resp.StatusCode < 200 || resp.StatusCode >= 300 {
return fmt.Errorf("inbox returned HTTP %d", resp.StatusCode)
}
return nil
}
// ---------------------------------------------------------------------------
// HTTP Signatures — signing (draft-cavage-12 profile)
// ---------------------------------------------------------------------------
//
// Signed headers: (request-target) host date digest content-type (if present)
// Algorithm: hs2019 (rsa-sha256 in practice)
//
// Signature header format (all on one line):
//
// Signature: keyId="...",algorithm="hs2019",headers="...",signature="..."
func (s *Server) signRequest(req *http.Request, body []byte) error {
now := time.Now().UTC()
req.Header.Set("Date", now.Format(http.TimeFormat))
req.Header.Set("Host", req.URL.Host)
// ap-next guide §Network: "Add User-Agent header."
req.Header.Set("User-Agent", "activitypub-go/1.0 (https://"+s.cfg.Domain+")")
// Build (request-target) pseudo-header value
requestTarget := strings.ToLower(req.Method) + " " + req.URL.RequestURI()
// Compute body digest (required for POST; included for GET too for consistency)
digestHeader := ""
if body != nil {
sum := sha256.Sum256(body)
digestHeader = "SHA-256=" + base64.StdEncoding.EncodeToString(sum[:])
req.Header.Set("Digest", digestHeader)
}
// Determine which headers to sign and build the signing string
type headerPair struct{ name, value string }
var pairs []headerPair
pairs = append(pairs, headerPair{"(request-target)", requestTarget})
pairs = append(pairs, headerPair{"host", req.Header.Get("Host")})
pairs = append(pairs, headerPair{"date", req.Header.Get("Date")})
if digestHeader != "" {
pairs = append(pairs, headerPair{"digest", digestHeader})
}
if ct := req.Header.Get("Content-Type"); ct != "" {
pairs = append(pairs, headerPair{"content-type", ct})
}
var signingLines []string
var headerNames []string
for _, p := range pairs {
signingLines = append(signingLines, p.name+": "+p.value)
headerNames = append(headerNames, p.name)
}
signingString := strings.Join(signingLines, "\n")
// RSA-SHA256 signature over the signing string
hash := sha256.Sum256([]byte(signingString))
sig, err := rsa.SignPKCS1v15(rand.Reader, s.privateKey, crypto.SHA256, hash[:])
if err != nil {
return fmt.Errorf("sign: %w", err)
}
sigB64 := base64.StdEncoding.EncodeToString(sig)
keyID := s.actorURL() + "#main-key"
headerList := strings.Join(headerNames, " ")
req.Header.Set("Signature", fmt.Sprintf(
`keyId="%s",algorithm="hs2019",headers="%s",signature="%s"`,
keyID, headerList, sigB64,
))
return nil
}
// ---------------------------------------------------------------------------
// HTTP Signatures — verification (draft-cavage-12 profile)
// ---------------------------------------------------------------------------
// verifyHTTPSignature verifies the HTTP Signature on an incoming request.
// Returns the actor URL (keyId without fragment) on success.
// Only GET and POST requests are supported; any other method is rejected.
func (s *Server) verifyHTTPSignature(r *http.Request, body []byte) (string, error) {
if r.Method != http.MethodGet && r.Method != http.MethodPost {
return "", fmt.Errorf("HTTP method %q not supported for signature verification", r.Method)
}
sigHeader := r.Header.Get("Signature")
if sigHeader == "" {
return "", errors.New("missing Signature header")
}
// Parse the Signature header into key-value pairs
sigParams := parseSignatureHeader(sigHeader)
keyID, ok := sigParams["keyId"]
if !ok {
return "", errors.New("missing keyId in Signature header")
}
headersParam, ok := sigParams["headers"]
if !ok {
return "", errors.New("missing headers in Signature header")
}
sigB64, ok := sigParams["signature"]
if !ok {
return "", errors.New("missing signature value in Signature header")
}
// Validate the optional algorithm parameter against our key type.
//
// draft-cavage-http-signatures-12 §2.1.3:
// "Implementers SHOULD derive the digital signature algorithm used by
// an implementation from the key metadata identified by the keyId
// rather than from this field. If algorithm is provided and differs
// from the key metadata identified by the keyId … then an
// implementation MUST produce an error."
//
// All keys in this implementation are RSA, so the only acceptable
// declared algorithms are "hs2019" (the generic placeholder from
// cavage-12 that defers algorithm selection to key metadata) and
// "rsa-sha256" (explicitly RSA-SHA256, consistent with our keys).
// Anything else — "hmac-sha256", "ecdsa-sha256", "rsa-sha1", etc. —
// is inconsistent with an RSA key and must be rejected.
if algo, hasAlgo := sigParams["algorithm"]; hasAlgo {
if algo != "hs2019" && algo != "rsa-sha256" {
return "", fmt.Errorf("signature algorithm %q is incompatible with RSA key", algo)
}
}
signedHeaders := strings.Fields(headersParam)
// Enforce a minimum set of signed headers to prevent replay attacks.
//
// https://swicg.github.io/activitypub-http-signature/#how-to-verify-a-signature
// "Most fediverse software will reject GET requests without signed
// (request-target), and POST requests without signed Digest, in order
// to prevent replay attacks."
requiredSigned := []string{"(request-target)", "host", "date"}
if r.Method == http.MethodPost {
requiredSigned = append(requiredSigned, "digest")
}
signedSet := make(map[string]bool, len(signedHeaders))
for _, h := range signedHeaders {
signedSet[h] = true
}
for _, required := range requiredSigned {
if !signedSet[required] {
return "", fmt.Errorf("required header %q not covered by signature", required)
}
}
// Validate Date header is within ±1 hour (plus a few minutes buffer)
dateStr := r.Header.Get("Date")
if dateStr == "" {
return "", errors.New("missing Date header")
}
reqTime, err := http.ParseTime(dateStr)
if err != nil {
return "", fmt.Errorf("parse Date header: %w", err)
}
diff := time.Since(reqTime)
if diff < 0 {
diff = -diff
}
if diff > 70*time.Minute {
return "", fmt.Errorf("Date header too far from current time (%v)", diff)
}
// For POST requests the Digest header is required and must be present in
// the request (it must also be covered by the signature, enforced above).
// For other methods verify it if present but don't require it.
//
// https://swicg.github.io/activitypub-http-signature/#how-to-verify-a-signature
// "If the request has a body, compare it to the Digest header. If they
// don't match, the signature is invalid, and most fediverse software
// will reject it in order to prevent replay attacks."
digestHeader := r.Header.Get("Digest")
if r.Method == http.MethodPost && digestHeader == "" {
return "", errors.New("POST request missing required Digest header")
}
if digestHeader != "" {
if err := verifyDigest(body, digestHeader); err != nil {
return "", fmt.Errorf("body digest mismatch: %w", err)
}
}
// Reconstruct the signing string.
// NOTE: Go's net/http moves the Host header out of r.Header into r.Host,
// so we must read it from r.Host directly.
var signingLines []string
for _, hdr := range signedHeaders {
var val string
switch hdr {
case "(request-target)":
val = strings.ToLower(r.Method) + " " + r.URL.RequestURI()
case "host":
// r.Host holds the Host header value; r.Header["Host"] is empty
val = r.Host
default:
val = r.Header.Get(http.CanonicalHeaderKey(hdr))
}
line := hdr + ": " + val
signingLines = append(signingLines, line)
}
signingString := strings.Join(signingLines, "\n")
// Obtain the public key for this keyId
pubKey, actorURL, err := s.obtainPublicKey(keyID)
if err != nil {
return "", fmt.Errorf("obtain public key for %s: %w", keyID, err)
}
// Verify RSA-SHA256 signature
sigBytes, err := base64.StdEncoding.DecodeString(sigB64)
if err != nil {
return "", fmt.Errorf("decode signature base64: %w", err)
}
hash := sha256.Sum256([]byte(signingString))
if err := rsa.VerifyPKCS1v15(pubKey, crypto.SHA256, hash[:], sigBytes); err != nil {
log.Printf("activitypub: RSA verify failed with cached key, re-fetching: %v", err)
// Key may have rotated — evict cache and retry once
s.actorCacheMu.Lock()
delete(s.actorCache, actorURL)
s.actorCacheMu.Unlock()
pubKey2, _, err2 := s.obtainPublicKey(keyID)
if err2 != nil {
return "", fmt.Errorf("signature verification failed (and key re-fetch failed: %v)", err2)
}
if err3 := rsa.VerifyPKCS1v15(pubKey2, crypto.SHA256, hash[:], sigBytes); err3 != nil {
return "", fmt.Errorf("signature verification failed: %w", err3)
}
}
return actorURL, nil
}
// obtainPublicKey fetches the actor document for the given keyId and extracts
// the RSA public key from publicKey.publicKeyPem.
// Returns (publicKey, actorURL, error).
func (s *Server) obtainPublicKey(keyID string) (*rsa.PublicKey, string, error) {
// Strip the #fragment to get the actor URL
actorURL := keyID
if before, _, ok := strings.Cut(keyID, "#"); ok {
actorURL = before
}
actor, err := s.fetchActor(actorURL)
if err != nil {
return nil, actorURL, fmt.Errorf("fetch actor: %w", err)
}
pkObj, ok := actor["publicKey"]
if !ok {
return nil, actorURL, errors.New("actor has no publicKey")
}
// publicKey may be a map or a list; handle both
var pkMap map[string]any
switch v := pkObj.(type) {
case map[string]any:
pkMap = v
case []any:
// Find the key whose id matches our keyId
for _, item := range v {
if m, ok := item.(map[string]any); ok {
if id, _ := m["id"].(string); id == keyID {
pkMap = m
break
}
}
}
}
if pkMap == nil {
return nil, actorURL, fmt.Errorf("could not find publicKey with id %s", keyID)
}
// Verify key id matches
if pkID, _ := pkMap["id"].(string); pkID != keyID {
return nil, actorURL, fmt.Errorf("publicKey id %q does not match keyId %q", pkID, keyID)
}
pemStr, ok := pkMap["publicKeyPem"].(string)
if !ok || pemStr == "" {
return nil, actorURL, errors.New("publicKeyPem missing or empty")
}
pub, err := parsePublicKeyPEM(pemStr)
if err != nil {
return nil, actorURL, fmt.Errorf("parse publicKeyPem: %w", err)
}
return pub, actorURL, nil
}
// sameOrigin reports whether two URL strings share the same origin.
//
// Origin is defined as the (scheme, host, port) triple per RFC 6454 §3.2 and
// FEP-fe34 §Origin. url.Parse stores host and port together in the Host field,
// so comparing Host directly covers both. Schemes are compared
// case-insensitively. Returns false if either URL cannot be parsed.
func sameOrigin(a, b string) bool {
ua, err := url.Parse(a)
if err != nil {
return false
}
ub, err := url.Parse(b)
if err != nil {
return false
}
// url.Parse stores host:port together in Host; scheme is already lowercase.
return strings.ToLower(ua.Scheme) == strings.ToLower(ub.Scheme) &&
strings.ToLower(ua.Host) == strings.ToLower(ub.Host)
}
// sameOwner reports whether two actor URL strings refer to the same owner.
//
// FEP-fe34 §Comparing owners:
//
// "Owners are the same if their identifiers are identical after conversion
// of their schemes and hosts to lowercase."
//
// Scheme and host are case-folded; the path, query, and fragment are compared
// exactly (actor paths like /users/Alice and /users/alice are distinct).
// Returns false if either URL cannot be parsed.
func sameOwner(a, b string) bool {
ua, err := url.Parse(a)
if err != nil {
return false
}
ub, err := url.Parse(b)
if err != nil {
return false
}
return strings.ToLower(ua.Scheme) == strings.ToLower(ub.Scheme) &&
strings.ToLower(ua.Host) == strings.ToLower(ub.Host) &&
ua.Path == ub.Path &&
ua.RawQuery == ub.RawQuery
}
// verifyDigest checks the SHA-256 body digest against the Digest header value.
func verifyDigest(body []byte, digestHeader string) error {
if !strings.HasPrefix(digestHeader, "SHA-256=") {
return fmt.Errorf("unsupported digest algorithm in %q", digestHeader)
}
expected := strings.TrimPrefix(digestHeader, "SHA-256=")
sum := sha256.Sum256(body)
actual := base64.StdEncoding.EncodeToString(sum[:])
if actual != expected {
return fmt.Errorf("expected %s, got %s", expected, actual)
}
return nil
}
// parseSignatureHeader parses a cavage-12 Signature header value into a map.
// Example input:
//
// keyId="https://example.com/users/alice#main-key",algorithm="hs2019",headers="...",signature="..."
//
// Values are quoted strings per RFC 7235 §4.1. We split on ',' only outside
// quoted strings (tracked with a simple bool toggle), then strip the surrounding
// quotes from each value. This correctly handles commas and '=' characters
// inside quoted values (e.g. base64 signatures with padding, URLs with query
// strings).
func parseSignatureHeader(header string) map[string]string {
result := map[string]string{}
// Split on ',' outside quoted strings.
var parts []string
inQuote := false
start := 0
for i, ch := range header {
switch ch {
case '"':
inQuote = !inQuote
case ',':
if !inQuote {
parts = append(parts, header[start:i])
start = i + 1
}
}
}
parts = append(parts, header[start:])
for _, part := range parts {
part = strings.TrimSpace(part)
// Split on the first '=' only; values may contain '=' (base64 padding).
before, after, ok := strings.Cut(part, "=")
if !ok {
continue
}
key := strings.TrimSpace(before)
val := strings.TrimSpace(after)
// Strip surrounding double-quotes from the value.
val = strings.Trim(val, `"`)
result[key] = val
}
return result
}
// ---------------------------------------------------------------------------
// Activity construction helpers
// ---------------------------------------------------------------------------
func (s *Server) buildAnnounce(objectURL string) map[string]any {
id := fmt.Sprintf("%s/announces/%d", s.actorURL(), time.Now().UnixNano())
return map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": id,
"type": "Announce",
"actor": s.actorURL(),
"object": objectURL,
"published": time.Now().UTC().Format(time.RFC3339),
"to": []string{"https://www.w3.org/ns/activitystreams#Public"},
"cc": []string{s.actorURL() + "/followers"},
}
}
// ---------------------------------------------------------------------------
// OrderedCollection serialisation
// ---------------------------------------------------------------------------
func (s *Server) serveOrderedCollection(w http.ResponseWriter, items []map[string]any, id string) {
col := map[string]any{
"@context": "https://www.w3.org/ns/activitystreams",
"id": id,
"type": "OrderedCollection",
"totalItems": len(items),
"orderedItems": items,
}
w.Header().Set("Content-Type", "application/activity+json")
writeJSON(w, col)
}
// ---------------------------------------------------------------------------
// Key management
// ---------------------------------------------------------------------------
func (s *Server) loadOrGenerateKey() (*rsa.PrivateKey, error) {
f, err := s.root.Open("key.pem")
if err == nil {
// File exists — parse it
data, readErr := io.ReadAll(f)
f.Close()
if readErr != nil {
return nil, fmt.Errorf("activitypub: read key file: %w", readErr)
}
block, _ := pem.Decode(data)
if block == nil {
return nil, fmt.Errorf("activitypub: failed to decode PEM block from key.pem")
}
key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("activitypub: parse private key: %w", err)
}
log.Printf("activitypub: loaded RSA key from %s/key.pem", s.cfg.DataDir)
return key, nil
}
if !errors.Is(err, os.ErrNotExist) {
return nil, fmt.Errorf("activitypub: read key file: %w", err)
}
// Generate a new 2048-bit RSA key
log.Printf("activitypub: generating new RSA-2048 key, saving to %s/key.pem", s.cfg.DataDir)
key, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
return nil, fmt.Errorf("activitypub: generate key: %w", err)
}
pemData := pem.EncodeToMemory(&pem.Block{
Type: "RSA PRIVATE KEY",
Bytes: x509.MarshalPKCS1PrivateKey(key),
})
wf, err := s.root.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
return nil, fmt.Errorf("activitypub: create key file: %w", err)
}
_, werr := wf.Write(pemData)
cerr := wf.Close()
if werr != nil {
return nil, fmt.Errorf("activitypub: save key: %w", werr)
}
if cerr != nil {
return nil, fmt.Errorf("activitypub: close key file: %w", cerr)
}
return key, nil
}
// publicKeyPEM returns the PEM-encoded public key for the actor document.
// Uses PKIX/SPKI encoding ("BEGIN PUBLIC KEY") which is what Mastodon and
// most fediverse servers expect. PKCS#1 ("BEGIN RSA PUBLIC KEY") is not
// widely recognised by AP implementations.
func (s *Server) publicKeyPEM() (string, error) {
pub, err := x509.MarshalPKIXPublicKey(s.publicKey)
if err != nil {
return "", err
}
block := &pem.Block{
Type: "PUBLIC KEY",
Bytes: pub,
}
return string(pem.EncodeToMemory(block)), nil
}
// parsePublicKeyPEM parses a PEM-encoded RSA public key (PKCS#1 or SPKI/X.509).
func parsePublicKeyPEM(pemStr string) (*rsa.PublicKey, error) {
block, _ := pem.Decode([]byte(pemStr))
if block == nil {
return nil, errors.New("failed to decode PEM block")
}
// Try PKCS#1 first
if key, err := x509.ParsePKCS1PublicKey(block.Bytes); err == nil {
return key, nil
}
// Try X.509 SPKI (used by most fediverse servers)
pub, err := x509.ParsePKIXPublicKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("parse public key: %w", err)
}
rsaKey, ok := pub.(*rsa.PublicKey)
if !ok {
return nil, errors.New("public key is not RSA")
}
return rsaKey, nil
}
// ---------------------------------------------------------------------------
// WebFinger client — handle resolution
// ---------------------------------------------------------------------------
// ResolveHandle resolves a fediverse handle to an actor URL via WebFinger.
// Accepts "@alice@example.com" or "alice@example.com".
// Signs the WebFinger GET with this server's key (supports authorized fetch).
func (s *Server) ResolveHandle(handle string) (string, error) {
// Normalise: strip a single leading @ if present
handle = strings.TrimPrefix(handle, "@")
parts := strings.SplitN(handle, "@", 2)
if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
return "", fmt.Errorf("invalid fediverse handle %q: expected user@host", handle)
}
user, host := parts[0], parts[1]
wfURL := fmt.Sprintf("https://%s/.well-known/webfinger?resource=acct:%s@%s",
host, url.QueryEscape(user), host)
req, err := http.NewRequest(http.MethodGet, wfURL, nil)
if err != nil {
return "", fmt.Errorf("build webfinger request: %w", err)
}
req.Header.Set("Accept", "application/jrd+json, application/json")
// Sign so servers with authorized fetch enabled will respond
if err := s.signRequest(req, nil); err != nil {
return "", fmt.Errorf("sign webfinger request: %w", err)
}
resp, err := newSafeClient(10 * time.Second).Do(req)
if err != nil {
return "", fmt.Errorf("webfinger request: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return "", fmt.Errorf("webfinger returned HTTP %d", resp.StatusCode)
}
var wf struct {
Links []struct {
Rel string `json:"rel"`
Type string `json:"type"`
Href string `json:"href"`
} `json:"links"`
}
if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&wf); err != nil {
return "", fmt.Errorf("decode webfinger response: %w", err)
}
for _, link := range wf.Links {
if link.Rel == "self" &&
(link.Type == "application/activity+json" ||
link.Type == "application/ld+json") &&
link.Href != "" {
return link.Href, nil
}
}
return "", fmt.Errorf("no ActivityPub actor link found in WebFinger response for %s@%s", user, host)
}
// ---------------------------------------------------------------------------
// URL helpers
// ---------------------------------------------------------------------------
// Domain returns the configured domain for this server.
func (s *Server) Domain() string {
return s.cfg.Domain
}
// ActorName returns the actor's username (the name component of its URL).
func (s *Server) ActorName() string {
return s.cfg.ActorName
}
// ActorURL returns the canonical actor URL for this server.
func (s *Server) ActorURL() string {
return s.actorURL()
}
func (s *Server) baseURL() string {
return "https://" + s.cfg.Domain
}
func (s *Server) actorURL() string {
return s.baseURL() + "/users/" + s.cfg.ActorName
}
// ---------------------------------------------------------------------------
// JSON persistence
// ---------------------------------------------------------------------------
func (s *Server) loadJSON(filename string, v any) error {
f, err := s.root.Open(filename)
if err != nil {
return err
}
defer f.Close()
data, err := io.ReadAll(f)
if err != nil {
return err
}
return json.Unmarshal(data, v)
}
func (s *Server) saveJSON(filename string, v any) error {
data, err := json.MarshalIndent(v, "", " ")
if err != nil {
return err
}
// Atomic write via temp file + rename.
// os.Root does not yet have Rename, so we use os.Rename with full paths.
// Both paths are constructed from cfg.DataDir which is already validated
// by the os.Root we hold.
tmp := filename + ".tmp"
wf, err := s.root.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
if err != nil {
return err
}
_, werr := wf.Write(data)
cerr := wf.Close()
if werr != nil {
return werr
}
if cerr != nil {
return cerr
}
return os.Rename(
filepath.Join(s.cfg.DataDir, tmp),
filepath.Join(s.cfg.DataDir, filename),
)
}
func (s *Server) saveFollowers() error {
s.mu.RLock()
defer s.mu.RUnlock()
return s.saveJSON("followers.json", s.followers)
}
func (s *Server) saveFollowing() error {
s.mu.RLock()
defer s.mu.RUnlock()
return s.saveJSON("following.json", s.following)
}
func (s *Server) saveOutbox() error {
s.mu.RLock()
defer s.mu.RUnlock()
return s.saveJSON("outbox.json", s.outbox)
}
func (s *Server) saveInbox() error {
s.mu.RLock()
defer s.mu.RUnlock()
return s.saveJSON("inbox.json", s.inbox)
}
// ---------------------------------------------------------------------------
// Generic helpers
// ---------------------------------------------------------------------------
func writeJSON(w http.ResponseWriter, v any) {
w.Header().Set("Content-Type", "application/activity+json")
writeJSONRaw(w, v)
}
// writeJSONRaw encodes v as indented JSON without setting Content-Type,
// allowing the caller to set it beforehand.
func writeJSONRaw(w http.ResponseWriter, v any) {
enc := json.NewEncoder(w)
enc.SetIndent("", " ")
if err := enc.Encode(v); err != nil {
log.Printf("activitypub: write JSON: %v", err)
}
}
// stringField safely extracts a string field from a map.
func stringField(m map[string]any, key string) string {
v, _ := m[key].(string)
return v
}
// toStringSlice converts an any that may be a string or []any of strings
// into a []string.
func toStringSlice(v any) []string {
switch t := v.(type) {
case string:
return []string{t}
case []any:
var result []string
for _, item := range t {
if s, ok := item.(string); ok {
result = append(result, s)
}
}
return result
default:
return nil
}
}
// contains returns true if s is in slice.
func contains(slice []string, s string) bool {
return slices.Contains(slice, s)
}
// remove returns a new slice with all occurrences of s removed.
func remove(slice []string, s string) []string {
var result []string
for _, v := range slice {
if v != s {
result = append(result, v)
}
}
return result
}
// prependCapped inserts item at the front of slice and caps its length at max.
func prependCapped(slice []map[string]any, item map[string]any, max int) []map[string]any {
result := make([]map[string]any, 0, len(slice)+1)
result = append(result, item)
result = append(result, slice...)
if len(result) > max {
result = result[:max]
}
return result
}
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