1 // apub is an implementation of the ActivityPub protocol.
2 //
3 // https://www.w3.org/TR/activitypub/
4 // https://www.w3.org/TR/activitystreams-core/
5 // https://www.w3.org/TR/activitystreams-vocabulary/
6 package apub
7 
8 import (
9 	"bytes"
10 	"encoding/json"
11 	"errors"
12 	"fmt"
13 	"io"
14 	"net/mail"
15 	"strings"
16 	"time"
17 )
18 
19 // NormContext is a URL referencing the
20 // normative Activity Streams 2.0 JSON-LD @context definition.
21 // All [Activity] variables should have their AtContext field set to this value.
22 // See [Activity Streams 2.0] section 2.1.
23 //
24 // [Activity Streams 2.0]: https://www.w3.org/TR/activitystreams-core/
25 const NormContext string = "https://www.w3.org/ns/activitystreams"
26 
27 // ContentType is the MIME media type for ActivityPub.
28 const ContentType string = "application/activity+json"
29 
30 // PublicCollection is the ActivityPub ID for the special collection indicating public access.
31 // Any Activity addressed to this collection is meant to be available to all users,
32 // authenticated or not.
33 // See W3C Recommendation ActivityPub Section 5.6.
34 const PublicCollection string = "https://www.w3.org/ns/activitystreams#Public"
35 
36 var ErrNotExist = errors.New("no such activity")
37 
38 // Activity represents the Activity Streams Object core type.
39 // See Activity Streams 2.0, section 4.1.
40 type Activity struct {
41 	AtContext    string     `json:"@context"`
42 	ID           string     `json:"id,omitempty"`
43 	Type         string     `json:"type"`
44 	Name         string     `json:"name,omitempty"`
45 	Actor        string     `json:"actor,omitempty"`
46 	Username     string     `json:"preferredUsername,omitempty"`
47 	Summary      string     `json:"summary,omitempty"`
48 	Inbox        string     `json:"inbox,omitempty"`
49 	Outbox       string     `json:"outbox,omitempty"`
50 	To           []string   `json:"to,omitempty"`
51 	CC           []string   `json:"cc,omitempty"`
52 	Followers    string     `json:"followers,omitempty"`
53 	InReplyTo    string     `json:"inReplyTo,omitempty"`
54 	Published    *time.Time `json:"published,omitempty"`
55 	AttributedTo string     `json:"attributedTo,omitempty"`
56 	Content      string     `json:"content,omitempty"`
57 	MediaType    string     `json:"mediaType,omitempty"`
58 	Source       struct {
59 		Content   string `json:"content,omitempty"`
60 		MediaType string `json:"mediaType,omitempty"`
61 	} `json:"source,omitempty"`
62 	PublicKey *PublicKey `json:"publicKey,omitempty"`
63 	Audience  string     `json:"audience,omitempty"`
64 	Href      string     `json:"href,omitempty"`
65 	Tag       []Activity `json:"tag,omitempty"`
66 	// Contains a JSON-encoded Activity, or a URL as a JSON string
67 	// pointing to an Activity. Use Activity.Unwrap() to access
68 	// the enclosed, decoded value.
69 	Object json.RawMessage `json:"object,omitempty"`
70 }
71 
72 func (act *Activity) UnmarshalJSON(b []byte) error {
73 	type Alias Activity
74 	aux := &struct {
75 		AtContext interface{} `json:"@context"`
76 		Object    interface{}
77 		*Alias
78 	}{
79 		Alias: (*Alias)(act),
80 	}
81 	if err := json.Unmarshal(b, &aux); err != nil {
82 		return err
83 	}
84 	switch v := aux.AtContext.(type) {
85 	case string:
86 		act.AtContext = v
87 	case []interface{}:
88 		if vv, ok := v[0].(string); ok {
89 			act.AtContext = vv
90 		}
91 	}
92 	return nil
93 }
94 
95 // Unwrap returns the JSON-encoded Activity, if any, enclosed in act.
96 // The Activity may be referenced by ID,
97 // in which case the activity is looked up by client or by
98 // apub.defaultClient if client is nil.
99 func (act *Activity) Unwrap(client *Client) (*Activity, error) {
100 	if act.Object == nil {
101 		return nil, errors.New("no wrapped activity")
102 	}
103 
104 	var buf io.Reader
105 	buf = bytes.NewReader(act.Object)
106 	if strings.HasPrefix(string(act.Object), "https") {
107 		if client == nil {
108 			return Lookup(string(act.Object))
109 		}
110 		return client.Lookup(string(act.Object))
111 	}
112 	return Decode(buf)
113 }
114 
115 func Decode(r io.Reader) (*Activity, error) {
116 	var a Activity
117 	if err := json.NewDecoder(r).Decode(&a); err != nil {
118 		return nil, fmt.Errorf("decode activity: %w", err)
119 	}
120 	return &a, nil
121 }
122 
123 func DecodeActor(r io.Reader) (*Actor, error) {
124 	a, err := Decode(r)
125 	if err != nil {
126 		return nil, err
127 	}
128 	return activityToActor(a), nil
129 }
130 
131 type Actor struct {
132 	AtContext string     `json:"@context"`
133 	ID        string     `json:"id"`
134 	Type      string     `json:"type"`
135 	Name      string     `json:"name"`
136 	Username  string     `json:"preferredUsername"`
137 	Summary   string     `json:"summary,omitempty"`
138 	Inbox     string     `json:"inbox"`
139 	Outbox    string     `json:"outbox"`
140 	Followers string     `json:"followers"`
141 	Published *time.Time `json:"published,omitempty"`
142 	PublicKey PublicKey  `json:"publicKey"`
143 }
144 
145 type PublicKey struct {
146 	ID           string `json:"id"`
147 	Owner        string `json:"owner"`
148 	PublicKeyPEM string `json:"publicKeyPem"`
149 }
150 
151 // Address generates the most likely address of the Actor.
152 // The Actor's name (not the username) is used as the address' proper name, if present.
153 // Implementors should verify the address using WebFinger.
154 // For example, the address for the Actor ID
155 // https://hachyderm.io/users/otl is:
156 //
157 //	"Oliver Lowe" <otl@hachyderm.io>
158 func (a *Actor) Address() *mail.Address {
159 	if a.Username == "" && a.Name == "" {
160 		return &mail.Address{"", a.ID}
161 	}
162 	trimmed := strings.TrimPrefix(a.ID, "https://")
163 	host, _, _ := strings.Cut(trimmed, "/")
164 	addr := fmt.Sprintf("%s@%s", a.Username, host)
165 	return &mail.Address{a.Name, addr}
166 }
167 
168 // FollowersAddress generates a non-standard address representing the Actor's followers
169 // using plus addressing.
170 // It is the Actor's address username part with a "+followers" suffix.
171 // The address cannot be resolved using WebFinger.
172 //
173 // For example, the followers address for Actor ID
174 // https://hachyderm.io/users/otl is:
175 //
176 //	"Oliver Lowe (followers)" <otl+followers@hachyderm.io>
177 func (a *Actor) FollowersAddress() *mail.Address {
178 	if a.Followers == "" {
179 		return &mail.Address{"", ""}
180 	}
181 	addr := a.Address()
182 	user, domain, found := strings.Cut(addr.Address, "@")
183 	if !found {
184 		return &mail.Address{"", ""}
185 	}
186 	addr.Address = fmt.Sprintf("%s+followers@%s", user, domain)
187 	if addr.Name != "" {
188 		addr.Name += " (followers)"
189 	}
190 	return addr
191 }