spread

https://git.tonybtw.com/spread.git git://git.tonybtw.com/spread.git
spread / internal / app / mail.go
3,514 bytes raw
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package app
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import (
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	"bytes"
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	"encoding/json"
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	"fmt"
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	"io"
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	"log"
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	"net/http"
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	"net/smtp"
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	"os"
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	"strings"
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)
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// Mailer sends transactional email. Kept deliberately small so backends are
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// swappable and the whole thing can be repointed or removed easily.
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type Mailer interface {
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	Send(to []string, subject, htmlBody, textBody string) error
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}
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// NewMailerFromEnv picks a backend from MAIL_BACKEND (log|smtp|sendgrid),
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// defaulting to log so development needs no email infrastructure.
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func NewMailerFromEnv() Mailer {
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	from := envOr("MAIL_FROM", "Spread <no-reply@spread.local>")
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	switch strings.ToLower(os.Getenv("MAIL_BACKEND")) {
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	case "smtp":
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		return &SMTPMailer{
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			Host: os.Getenv("SMTP_HOST"),
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			Port: envOr("SMTP_PORT", "587"),
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			User: os.Getenv("SMTP_USER"),
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			Pass: os.Getenv("SMTP_PASS"),
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			From: from,
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		}
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	case "sendgrid":
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		return &SendgridMailer{Key: os.Getenv("SENDGRID_API_KEY"), From: from}
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	default:
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		return LogMailer{}
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	}
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}
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func envOr(key, def string) string {
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	if v := os.Getenv(key); v != "" {
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		return v
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	}
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	return def
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}
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// LogMailer writes messages to the server log — the default in development.
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type LogMailer struct{}
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func (LogMailer) Send(to []string, subject, htmlBody, textBody string) error {
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	log.Printf("[mail:log] to=%s subject=%q\n%s", strings.Join(to, ", "), subject, textBody)
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	return nil
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}
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// SMTPMailer sends via any SMTP relay using only the standard library.
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type SMTPMailer struct {
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	Host, Port, User, Pass, From string
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}
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func (m *SMTPMailer) Send(to []string, subject, htmlBody, textBody string) error {
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	const boundary = "spreadalt"
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	var b strings.Builder
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	fmt.Fprintf(&b, "From: %s\r\n", m.From)
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	fmt.Fprintf(&b, "To: %s\r\n", strings.Join(to, ", "))
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	fmt.Fprintf(&b, "Subject: %s\r\n", subject)
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	b.WriteString("MIME-Version: 1.0\r\n")
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	fmt.Fprintf(&b, "Content-Type: multipart/alternative; boundary=%s\r\n\r\n", boundary)
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	fmt.Fprintf(&b, "--%s\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n%s\r\n\r\n", boundary, textBody)
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	fmt.Fprintf(&b, "--%s\r\nContent-Type: text/html; charset=UTF-8\r\n\r\n%s\r\n\r\n", boundary, htmlBody)
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	fmt.Fprintf(&b, "--%s--\r\n", boundary)
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	var auth smtp.Auth
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	if m.User != "" {
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		auth = smtp.PlainAuth("", m.User, m.Pass, m.Host)
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	}
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	return smtp.SendMail(m.Host+":"+m.Port, auth, m.From, to, []byte(b.String()))
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}
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// SendgridMailer posts to SendGrid's v3 API over plain net/http (no SDK).
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type SendgridMailer struct {
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	Key, From string
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}
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func (m *SendgridMailer) Send(to []string, subject, htmlBody, textBody string) error {
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	recips := make([]map[string]string, len(to))
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	for i, addr := range to {
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		recips[i] = map[string]string{"email": addr}
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	}
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	payload := map[string]any{
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		"personalizations": []any{map[string]any{"to": recips}},
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		"from":             map[string]string{"email": m.From},
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		"subject":          subject,
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		"content": []any{
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			map[string]string{"type": "text/plain", "value": textBody},
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			map[string]string{"type": "text/html", "value": htmlBody},
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		},
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	}
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	body, _ := json.Marshal(payload)
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	req, err := http.NewRequest(http.MethodPost, "https://api.sendgrid.com/v3/mail/send", bytes.NewReader(body))
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	if err != nil {
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		return err
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	}
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	req.Header.Set("Authorization", "Bearer "+m.Key)
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	req.Header.Set("Content-Type", "application/json")
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	resp, err := http.DefaultClient.Do(req)
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	if err != nil {
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		return err
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	}
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	defer resp.Body.Close()
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	if resp.StatusCode >= 300 {
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		msg, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
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		return fmt.Errorf("sendgrid: %s: %s", resp.Status, msg)
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	}
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	return nil
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}