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 // @context
20 const AtContext string = "https://www.w3.org/ns/activitystreams"
21 
22 const ContentType string = "application/activity+json"
23 
24 const AcceptMediaType string = `application/activity+json; profile="https://www.w3.org/ns/activitystreams"`
25 
26 // Activities addressed to this collection indicates the activity
27 // is available to all users, authenticated or not.
28 // See W3C Recommendation ActivityPub Section 5.6.
29 const PublicCollection string = "https://www.w3.org/ns/activitystreams#Public"
30 
31 var ErrNotExist = errors.New("no such activity")
32 
33 type Activity struct {
34 	AtContext    string     `json:"@context"`
35 	ID           string     `json:"id"`
36 	Type         string     `json:"type"`
37 	Name         string     `json:"name,omitempty"`
38 	Actor        string     `json:"actor,omitempty"`
39 	Username     string     `json:"preferredUsername,omitempty"`
40 	Summary      string     `json:"summary,omitempty"`
41 	Inbox        string     `json:"inbox,omitempty"`
42 	Outbox       string     `json:"outbox,omitempty"`
43 	To           []string   `json:"to,omitempty"`
44 	CC           []string   `json:"cc,omitempty"`
45 	Followers    string     `json:"followers,omitempty"`
46 	InReplyTo    string     `json:"inReplyTo,omitempty"`
47 	Published    *time.Time `json:"published,omitempty"`
48 	AttributedTo string     `json:"attributedTo,omitempty"`
49 	Content      string     `json:"content,omitempty"`
50 	MediaType    string     `json:"mediaType,omitempty"`
51 	Source       struct {
52 		Content   string `json:"content,omitempty"`
53 		MediaType string `json:"mediaType,omitempty"`
54 	} `json:"source,omitempty"`
55 	PublicKey *PublicKey      `json:"publicKey,omitempty"`
56 	Audience  string          `json:"audience,omitempty"`
57 	Object    json.RawMessage `json:"object,omitempty"`
58 }
59 
60 func (act *Activity) UnmarshalJSON(b []byte) error {
61 	type Alias Activity
62 	aux := &struct {
63 		AtContext interface{} `json:"@context"`
64 		Object    interface{}
65 		*Alias
66 	}{
67 		Alias: (*Alias)(act),
68 	}
69 	if err := json.Unmarshal(b, &aux); err != nil {
70 		return err
71 	}
72 	switch v := aux.AtContext.(type) {
73 	case string:
74 		act.AtContext = v
75 	case []interface{}:
76 		if vv, ok := v[0].(string); ok {
77 			act.AtContext = vv
78 		}
79 	}
80 	return nil
81 }
82 
83 func (act *Activity) Unwrap(client *Client) (*Activity, error) {
84 	if act.Object == nil {
85 		return nil, errors.New("no wrapped activity")
86 	}
87 
88 	var buf io.Reader
89 	buf = bytes.NewReader(act.Object)
90 	if strings.HasPrefix(string(act.Object), "https") {
91 		if client == nil {
92 			return Lookup(string(act.Object))
93 		}
94 		return client.Lookup(string(act.Object))
95 	}
96 	return Decode(buf)
97 }
98 
99 func Decode(r io.Reader) (*Activity, error) {
100 	var a Activity
101 	if err := json.NewDecoder(r).Decode(&a); err != nil {
102 		return nil, fmt.Errorf("decode activity: %w", err)
103 	}
104 	return &a, nil
105 }
106 
107 func DecodeActor(r io.Reader) (*Actor, error) {
108 	a, err := Decode(r)
109 	if err != nil {
110 		return nil, err
111 	}
112 	return activityToActor(a), nil
113 }
114 
115 type Actor struct {
116 	AtContext string     `json:"@context"`
117 	ID        string     `json:"id"`
118 	Type      string     `json:"type"`
119 	Name      string     `json:"name"`
120 	Username  string     `json:"preferredUsername"`
121 	Summary   string     `json:"summary,omitempty"`
122 	Inbox     string     `json:"inbox"`
123 	Outbox    string     `json:"outbox"`
124 	Followers string     `json:"followers"`
125 	Published *time.Time `json:"published,omitempty"`
126 	PublicKey PublicKey  `json:"publicKey"`
127 }
128 
129 type PublicKey struct {
130 	ID           string `json:"id"`
131 	Owner        string `json:"owner"`
132 	PublicKeyPEM string `json:"publicKeyPem"`
133 }
134 
135 func (a *Actor) Address() *mail.Address {
136 	if a.Username == "" && a.Name == "" {
137 		return &mail.Address{"", a.ID}
138 	}
139 	trimmed := strings.TrimPrefix(a.ID, "https://")
140 	host, _, _ := strings.Cut(trimmed, "/")
141 	addr := fmt.Sprintf("%s@%s", a.Username, host)
142 	return &mail.Address{a.Name, addr}
143 }
144 
145 func (a *Actor) FollowersAddress() *mail.Address {
146 	if a.Followers == "" {
147 		return &mail.Address{"", ""}
148 	}
149 	addr := a.Address()
150 	user, domain, found := strings.Cut(addr.Address, "@")
151 	if !found {
152 		return &mail.Address{"", ""}
153 	}
154 	addr.Address = fmt.Sprintf("%s+followers@%s", user, domain)
155 	if addr.Name != "" {
156 		addr.Name += " (followers)"
157 	}
158 	return addr
159 }