1 package apub
2 
3 import (
4 	"bytes"
5 	"fmt"
6 	"io"
7 	"mime/quotedprintable"
8 	"net/mail"
9 	"net/smtp"
10 	"strings"
11 	"time"
12 )
13 
14 func MarshalMail(activity *Activity, client *Client) ([]byte, error) {
15 	msg, err := marshalMail(activity, client)
16 	if err != nil {
17 		return nil, err
18 	}
19 	return encodeMsg(msg), nil
20 }
21 
22 func marshalMail(activity *Activity, client *Client) (*mail.Message, error) {
23 	if client == nil {
24 		client = &DefaultClient
25 	}
26 
27 	msg := new(mail.Message)
28 	msg.Header = make(mail.Header)
29 	var actors []Actor
30 	from, err := client.LookupActor(activity.AttributedTo)
31 	if err != nil {
32 		return nil, fmt.Errorf("build From: lookup actor %s: %w", activity.AttributedTo, err)
33 	}
34 	actors = append(actors, *from)
35 	msg.Header["From"] = []string{from.Address().String()}
36 
37 	var addrs, collections []string
38 	for _, id := range activity.To {
39 		if id == PublicCollection {
40 			continue
41 		}
42 
43 		a, err := client.LookupActor(id)
44 		if err != nil {
45 			return nil, fmt.Errorf("build To: lookup actor %s: %w", id, err)
46 		}
47 		if a.Type == "Collection" || a.Type == "OrderedCollection" {
48 			collections = append(collections, a.ID)
49 		} else {
50 			addrs = append(addrs, a.Address().String())
51 			actors = append(actors, *a)
52 		}
53 	}
54 	for _, id := range collections {
55 		if i := indexFollowers(actors, id); i >= 0 {
56 			addrs = append(addrs, actors[i].FollowersAddress().String())
57 		}
58 	}
59 	msg.Header["To"] = addrs
60 
61 	addrs, collections = []string{}, []string{}
62 	for _, id := range activity.CC {
63 		if id == PublicCollection {
64 			continue
65 		}
66 
67 		a, err := client.LookupActor(id)
68 		if err != nil {
69 			return nil, fmt.Errorf("build CC: lookup actor %s: %w", id, err)
70 		}
71 		if a.Type == "Collection" || a.Type == "OrderedCollection" {
72 			collections = append(collections, a.ID)
73 			continue
74 		}
75 		addrs = append(addrs, a.Address().String())
76 		actors = append(actors, *a)
77 	}
78 	for _, id := range collections {
79 		if i := indexFollowers(actors, id); i >= 0 {
80 			addrs = append(addrs, actors[i].FollowersAddress().String())
81 		}
82 	}
83 	msg.Header["CC"] = addrs
84 
85 	msg.Header["Date"] = []string{activity.Published.Format(time.RFC1123Z)}
86 	msg.Header["Message-ID"] = []string{"<" + activity.ID + ">"}
87 	msg.Header["Subject"] = []string{activity.Name}
88 	if activity.Audience != "" {
89 		msg.Header["List-ID"] = []string{"<" + activity.Audience + ">"}
90 	}
91 	if activity.InReplyTo != "" {
92 		msg.Header["In-Reply-To"] = []string{"<" + activity.InReplyTo + ">"}
93 	}
94 
95 	msg.Body = strings.NewReader(activity.Content)
96 	msg.Header["Content-Type"] = []string{"text/html; charset=utf-8"}
97 	if activity.Source.Content != "" && activity.Source.MediaType == "text/markdown" {
98 		msg.Body = strings.NewReader(activity.Source.Content)
99 		msg.Header["Content-Type"] = []string{"text/plain; charset=utf-8"}
100 	} else if activity.MediaType == "text/markdown" {
101 		msg.Header["Content-Type"] = []string{"text/plain; charset=utf-8"}
102 	}
103 	return msg, nil
104 }
105 
106 func indexFollowers(actors []Actor, id string) int {
107 	for i := range actors {
108 		if actors[i].Followers == id {
109 			return i
110 		}
111 	}
112 	return -1
113 }
114 
115 func UnmarshalMail(msg *mail.Message, client *Client) (*Activity, error) {
116 	if client == nil {
117 		client = &DefaultClient
118 	}
119 	ct := msg.Header.Get("Content-Type")
120 	if strings.HasPrefix(ct, "multipart") {
121 		return nil, fmt.Errorf("cannot unmarshal from multipart message")
122 	}
123 
124 	date, err := msg.Header.Date()
125 	if err != nil {
126 		return nil, fmt.Errorf("parse message date: %w", err)
127 	}
128 	from, err := msg.Header.AddressList("From")
129 	if err != nil {
130 		return nil, fmt.Errorf("parse From: %w", err)
131 	}
132 	wfrom, err := client.Finger(from[0].Address)
133 	if err != nil {
134 		return nil, fmt.Errorf("webfinger From: %w", err)
135 	}
136 
137 	var wto, wcc []string
138 	var tags []Activity
139 	if msg.Header.Get("To") != "" {
140 		to, err := msg.Header.AddressList("To")
141 		// ignore missing To line. Some ActivityPub servers only have the
142 		// PublicCollection listed, which we don't care about.
143 		if err != nil {
144 			return nil, fmt.Errorf("parse To address list: %w", err)
145 		}
146 		actors, err := client.fingerAll(to)
147 		if err != nil {
148 			return nil, fmt.Errorf("webfinger To addresses: %w", err)
149 		}
150 		wto = make([]string, len(actors))
151 		for i, a := range actors {
152 			addr := strings.Trim(to[i].Address, "<>")
153 			if strings.Contains(addr, "+followers") {
154 				wto[i] = a.Followers
155 				continue
156 			}
157 			tags = append(tags, Activity{Type: "Mention", Href: a.ID, Name: "@" + addr})
158 			wto[i] = a.ID
159 		}
160 	}
161 	if msg.Header.Get("CC") != "" {
162 		cc, err := msg.Header.AddressList("CC")
163 		if err != nil {
164 			return nil, fmt.Errorf("parse CC address list: %w", err)
165 		}
166 		actors, err := client.fingerAll(cc)
167 		if err != nil {
168 			return nil, fmt.Errorf("webfinger CC addresses: %w", err)
169 		}
170 		wcc = make([]string, len(actors))
171 		for i, a := range actors {
172 			if strings.Contains(cc[i].Address, "+followers") {
173 				wcc[i] = a.Followers
174 				continue
175 			}
176 			wcc[i] = a.ID
177 		}
178 	}
179 
180 	buf := &bytes.Buffer{}
181 	if msg.Header.Get("Content-Transfer-Encoding") == "quoted-printable" {
182 		_, err = io.Copy(buf, quotedprintable.NewReader(msg.Body))
183 	} else {
184 		_, err = io.Copy(buf, msg.Body)
185 	}
186 	if err != nil {
187 		return nil, fmt.Errorf("read message body: %v", err)
188 	}
189 	content := strings.TrimSpace(strings.ReplaceAll(buf.String(), "\r", ""))
190 
191 	return &Activity{
192 		AtContext:    NormContext,
193 		Type:         "Note",
194 		AttributedTo: wfrom.ID,
195 		To:           wto,
196 		CC:           wcc,
197 		MediaType:    "text/markdown",
198 		Name:         strings.TrimSpace(msg.Header.Get("Subject")),
199 		Content:      content,
200 		InReplyTo:    strings.Trim(msg.Header.Get("In-Reply-To"), "<>"),
201 		Published:    &date,
202 		Tag:          tags,
203 	}, nil
204 }
205 
206 func SendMail(addr string, auth smtp.Auth, from string, to []string, activity *Activity) error {
207 	msg, err := MarshalMail(activity, nil)
208 	if err != nil {
209 		return fmt.Errorf("marshal to mail message: %w", err)
210 	}
211 	return smtp.SendMail(addr, auth, from, to, msg)
212 }
213 
214 func encodeMsg(msg *mail.Message) []byte {
215 	buf := &bytes.Buffer{}
216 	// Lead with "From", end with "Subject" to make some mail clients happy.
217 	fmt.Fprintln(buf, "From:", msg.Header.Get("From"))
218 	for k, v := range msg.Header {
219 		switch k {
220 		case "Subject", "From":
221 			continue
222 		default:
223 			fmt.Fprintf(buf, "%s: %s\n", k, strings.Join(v, ", "))
224 		}
225 	}
226 	fmt.Fprintln(buf, "Subject:", msg.Header.Get("Subject"))
227 	fmt.Fprintln(buf)
228 	io.Copy(buf, msg.Body)
229 	return buf.Bytes()
230 }