petrbalvin
3a38f00dc0
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Assisted-by: GLM 5.3 Flash
495 lines
18 KiB
Go
495 lines
18 KiB
Go
// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: MIT
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//go:build linux || freebsd
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// Package email handles SMTP message composition and delivery.
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package email
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import (
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"bytes"
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"crypto/rand"
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"crypto/tls"
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"encoding/hex"
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"fmt"
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"html/template"
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"net"
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"net/smtp"
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"strings"
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"time"
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"sourcedock.dev/petrbalvin/nuntius/internal/config"
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"sourcedock.dev/petrbalvin/nuntius/internal/contactform"
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)
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// effectiveTLSConfig returns cfg when set, otherwise a default config that
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// verifies the server certificate against host.
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func effectiveTLSConfig(cfg *tls.Config, host string) *tls.Config {
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if cfg != nil {
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return cfg
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}
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return &tls.Config{ServerName: host}
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}
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// FormSender delivers contact form submissions for a single form
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// using its own SMTP credentials. Each form has its own FormSender
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// so credentials are isolated per tenant.
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type FormSender struct {
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form *config.Form
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// TLSConfig optionally overrides the TLS configuration used for
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// STARTTLS. When nil, a default config with ServerName set to the
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// SMTP host is used.
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TLSConfig *tls.Config
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}
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// NewFormSender returns a new FormSender bound to the given form.
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func NewFormSender(form *config.Form) *FormSender {
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return &FormSender{form: form}
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}
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// Send composes and sends a multi-part email (plain text + HTML)
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// for the given request. Returns an error if composition or the SMTP
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// round-trip fails. The SMTP conversation bound comes from the form's
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// configured smtp.timeout_seconds.
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func (s *FormSender) Send(req contactform.Request) error {
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auth := smtp.PlainAuth("", s.form.SMTP.User, s.form.SMTP.Password, s.form.SMTP.Host)
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msg, err := compose(s.form.From, s.form.To, req, s.form)
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if err != nil {
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return fmt.Errorf("compose message: %w", err)
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}
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return sendMail(s.form.SMTP, auth, s.form.From, []string{s.form.To}, msg, s.form.SMTP.Timeout(), s.TLSConfig)
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}
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// sendMail delivers msg over SMTP with a hard timeout on every network
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// operation. When cfg.Port is 465 the connection speaks TLS from the first
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// byte (implicit TLS); any other port starts plaintext and upgrades via
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// STARTTLS when the server advertises it. With cfg.RequireTLS set, an SMTP
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// server that never offers STARTTLS aborts the delivery instead of sending
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// over plaintext. If tlsConfig is nil, a default config with ServerName set
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// to the target host is used.
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func sendMail(cfg config.SMTPConfig, auth smtp.Auth, from string, to []string, msg []byte, timeout time.Duration, tlsConfig *tls.Config) error {
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addr := cfg.AddrFor()
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implicitTLS := cfg.Port == config.ImplicitTLSPort
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var conn net.Conn
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if implicitTLS {
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dialer := &net.Dialer{Timeout: timeout}
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tconn, err := tls.DialWithDialer(dialer, "tcp", addr, effectiveTLSConfig(tlsConfig, cfg.Host))
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if err != nil {
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return fmt.Errorf("dial smtps %s: %w", addr, err)
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}
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conn = tconn
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} else {
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pconn, err := net.DialTimeout("tcp", addr, timeout)
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if err != nil {
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return fmt.Errorf("dial smtp %s: %w", addr, err)
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}
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conn = pconn
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}
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defer conn.Close()
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if err := conn.SetDeadline(time.Now().Add(timeout)); err != nil {
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return fmt.Errorf("set smtp deadline: %w", err)
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}
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c, err := smtp.NewClient(conn, cfg.Host)
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if err != nil {
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return fmt.Errorf("smtp client: %w", err)
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}
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defer c.Close()
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if !implicitTLS {
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ok, _ := c.Extension("STARTTLS")
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switch {
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case ok:
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if err := c.StartTLS(effectiveTLSConfig(tlsConfig, cfg.Host)); err != nil {
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return fmt.Errorf("starttls: %w", err)
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}
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case cfg.RequireTLS:
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return fmt.Errorf("smtp server %s does not advertise starttls but require_tls is enabled", addr)
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}
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}
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if auth != nil {
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if ok, _ := c.Extension("AUTH"); ok {
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if err := c.Auth(auth); err != nil {
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return fmt.Errorf("smtp auth: %w", err)
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}
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}
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}
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if err := c.Mail(from); err != nil {
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return fmt.Errorf("smtp mail from: %w", err)
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}
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for _, rcpt := range to {
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if err := c.Rcpt(rcpt); err != nil {
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return fmt.Errorf("smtp rcpt to: %w", err)
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}
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}
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w, err := c.Data()
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if err != nil {
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return fmt.Errorf("smtp data: %w", err)
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}
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if _, err := w.Write(msg); err != nil {
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return fmt.Errorf("smtp write data: %w", err)
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}
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if err := w.Close(); err != nil {
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return fmt.Errorf("smtp close data: %w", err)
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}
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if err := c.Quit(); err != nil {
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return fmt.Errorf("smtp quit: %w", err)
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}
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return nil
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}
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// randomBoundary returns a MIME boundary that is practically impossible
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// to collide with message content. An error means crypto/rand failed; the
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// message must then not be sent at all, because a predictable delimiter
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// would let crafted content forge MIME part boundaries.
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func randomBoundary() (string, error) {
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var buf [16]byte
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if _, err := rand.Read(buf[:]); err != nil {
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return "", fmt.Errorf("generate mime boundary: %w", err)
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}
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return "nuntius-" + hex.EncodeToString(buf[:]), nil
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}
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// sanitizeHeaderValue makes an interpolated value safe to embed in a
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// single RFC 5322 header line. A CR or LF would terminate the header and
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// let a crafted value inject arbitrary additional headers.
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func sanitizeHeaderValue(v string) string {
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return strings.NewReplacer("\r", " ", "\n", " ").Replace(v)
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}
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// emailTemplateContact is the HTML body template for contact-type forms.
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var emailTemplateContact = template.Must(template.New("contact").Parse(`<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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</head>
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<body style="margin:0;padding:0;background-color:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,-apple-system,sans-serif">
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<table width="100%" cellpadding="0" cellspacing="0" style="background-color:#f3f4f6;padding:32px 0">
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<tr><td align="center">
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<table width="560" cellpadding="0" cellspacing="0" style="background-color:#ffffff;border-radius:12px;overflow:hidden;box-shadow:0 2px 16px rgba(0,0,0,0.06)">
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<!-- Header -->
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<tr>
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<td style="background-color:#1e40af;padding:24px 28px">
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<p style="margin:0;font-size:13px;font-weight:600;color:#93c5fd;text-transform:uppercase;letter-spacing:0.5px">
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Contact Form Submission
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</p>
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<p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#ffffff">
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{{.FormName}}
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</p>
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</td>
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</tr>
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<!-- Body -->
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<tr>
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<td style="padding:28px 28px 12px">
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<!-- Submitter -->
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<table width="100%" cellpadding="0" cellspacing="0" style="margin-bottom:20px">
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<tr>
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<td style="padding-bottom:8px;border-bottom:1px solid #e5e7eb">
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<span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">From</span>
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<br>
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<span style="font-size:15px;font-weight:600;color:#1f2937">{{.Name}}</span>
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<span style="font-size:14px;color:#1e40af;margin-left:8px">{{.Email}}</span>
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</td>
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</tr>
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{{if .Service}}
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<tr>
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<td style="padding:12px 0 8px;border-bottom:1px solid #e5e7eb">
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<span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">Service Interest</span>
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<br>
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<span style="font-size:14px;color:#1f2937">{{.Service}}</span>
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</td>
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</tr>
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{{end}}
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<tr>
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<td style="padding:12px 0 8px;border-bottom:1px solid #e5e7eb">
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<span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">Received</span>
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<br>
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<span style="font-size:13px;color:#9ca3af">{{.Received}}</span>
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</td>
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</tr>
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</table>
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<!-- Message -->
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px;margin:0 0 8px">Message</p>
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<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;padding:6px 0">{{.Message}}</div>
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</td>
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</tr>
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<!-- Footer -->
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{{if .Brand}}
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<tr>
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<td style="padding:16px 28px 28px">
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<p style="margin:0;font-size:11px;color:#9ca3af;border-top:1px solid #e5e7eb;padding-top:16px">
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Delivered by <strong style="color:#6b7280">{{.Brand}}</strong>, a contact form backend for Linux servers.
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</p>
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</td>
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</tr>
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{{end}}
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</table>
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</td></tr>
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</table>
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</body>
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</html>`))
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// emailTemplateFeedback is the HTML body template for feedback-type forms.
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var emailTemplateFeedback = template.Must(template.New("feedback").Parse(`<!DOCTYPE html>
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<html lang="en">
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<head><meta charset="UTF-8"></head>
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<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
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<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
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<tr><td align="center">
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<table width="560" cellpadding="0" cellspacing="0" style="background:#fff;border-radius:12px;overflow:hidden;box-shadow:0 2px 16px rgba(0,0,0,.06)">
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<tr><td style="background:#0f766e;padding:24px 28px">
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<p style="margin:0;font-size:13px;font-weight:600;color:#5eead4;text-transform:uppercase;letter-spacing:.5px">New Feedback</p>
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<p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}</p>
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</td></tr>
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<tr><td style="padding:28px">
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0">From</p>
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<p style="font-size:15px;font-weight:600;color:#1f2937;margin:2px 0 16px">{{.Name}} <span style="color:#0f766e">{{.Email}}</span></p>
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{{if .Service}}
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Service Interest</p>
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<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;margin:0 0 16px">{{.Service}}</div>
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{{end}}
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Feedback</p>
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<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap">{{.Message}}</div>
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{{if .Brand}}
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<p style="font-size:11px;color:#9ca3af;margin:20px 0 0;border-top:1px solid #e5e7eb;padding-top:16px">Delivered by <strong style="color:#6b7280">{{.Brand}}</strong></p>
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{{end}}
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</td></tr>
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</table>
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</td></tr>
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</table>
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</body>
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</html>`))
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// emailTemplateNewsletter is the HTML body template for newsletter-signup forms.
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var emailTemplateNewsletter = template.Must(template.New("newsletter").Parse(`<!DOCTYPE html>
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<html lang="en">
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<head><meta charset="UTF-8"></head>
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<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
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<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
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<tr><td align="center">
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<table width="460" cellpadding="0" cellspacing="0" style="background:#fff;border-radius:12px;overflow:hidden;box-shadow:0 2px 16px rgba(0,0,0,.06)">
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<tr><td style="background:#1e40af;padding:20px 24px">
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<p style="margin:0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}: new subscriber</p>
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</td></tr>
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<tr><td style="padding:24px">
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 4px">Email</p>
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<p style="font-size:16px;font-weight:600;color:#1e40af;margin:0 0 16px">{{.Email}}</p>
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{{if .Brand}}
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<p style="font-size:11px;color:#9ca3af;margin:16px 0 0;border-top:1px solid #e5e7eb;padding-top:16px">Delivered by <strong style="color:#6b7280">{{.Brand}}</strong></p>
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{{end}}
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</td></tr>
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</table>
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</td></tr>
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</table>
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</body>
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</html>`))
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// emailTemplateGeneric is the HTML body template for generic forms.
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var emailTemplateGeneric = template.Must(template.New("generic").Parse(`<!DOCTYPE html>
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<html lang="en">
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<head><meta charset="UTF-8"></head>
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<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
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<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
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<tr><td align="center">
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<table width="560" cellpadding="0" cellspacing="0" style="background:#fff;border-radius:12px;overflow:hidden;box-shadow:0 2px 16px rgba(0,0,0,.06)">
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<tr><td style="background:#1e40af;padding:24px 28px">
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<p style="margin:0;font-size:13px;font-weight:600;color:#93c5fd;text-transform:uppercase;letter-spacing:.5px">Form Submission</p>
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<p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}</p>
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</td></tr>
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<tr><td style="padding:28px">
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0">From</p>
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<p style="font-size:15px;font-weight:600;color:#1f2937;margin:2px 0 16px">{{.Name}} <span style="color:#1e40af">{{.Email}}</span></p>
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{{if .Service}}
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Service Interest</p>
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<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;margin:0 0 16px">{{.Service}}</div>
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{{end}}
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<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Message</p>
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<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap">{{.Message}}</div>
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{{if .Brand}}
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<p style="font-size:11px;color:#9ca3af;margin:20px 0 0;border-top:1px solid #e5e7eb;padding-top:16px">Delivered by <strong style="color:#6b7280">{{.Brand}}</strong></p>
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{{end}}
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</td></tr>
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</table>
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</td></tr>
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</table>
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</body>
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</html>`))
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// compose builds the multipart message for one submission. The subject
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// prefix and the footer brand come from the form's configuration; the
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// defaults reproduce the subjects and footers earlier releases sent.
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func compose(from, to string, req contactform.Request, form *config.Form) ([]byte, error) {
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received := time.Now().UTC().Format("January 2, 2006 at 15:04 UTC")
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// The service interest only surfaces when the form actually accepts
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// the field: the contact template has always shown it, and a form
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// with its own services list has opted the field into validation.
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service := ""
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if req.Service != "" && (form.Type == "contact" || form.Services != nil) {
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service = req.Service
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}
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// --- HTML part ---
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var htmlBuf bytes.Buffer
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tmpl := emailTemplateContact
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switch form.Type {
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case "newsletter":
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tmpl = emailTemplateNewsletter
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case "feedback":
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tmpl = emailTemplateFeedback
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case "generic":
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tmpl = emailTemplateGeneric
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}
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if err := tmpl.Execute(&htmlBuf, map[string]string{
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"FormName": form.Name,
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"Name": req.Name,
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"Email": req.Email,
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"Service": service,
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"Message": req.Message,
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"Received": received,
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"Brand": form.Brand(),
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}); err != nil {
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// template.Must guarantees valid templates; this path is
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// unreachable in normal operation.
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htmlBuf.Reset()
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fmt.Fprintf(&htmlBuf, "<p>Email generation error: %v</p>", err)
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}
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// --- Subject + plain-text body per form type ---
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var base string
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switch form.Type {
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case "newsletter":
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base = "New newsletter subscriber"
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case "feedback":
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base = "New feedback"
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case "generic":
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base = "New submission"
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default: // contact
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base = "Contact form submission"
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}
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subject := base
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if tag := subjectTag(form, service); tag != "" {
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subject = tag + " " + base
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}
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footer := ""
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if brand := form.Brand(); brand != "" {
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footer = "Delivered by " + brand + "\r\n"
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}
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var text string
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switch form.Type {
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case "newsletter":
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text = fmt.Sprintf(
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"New Newsletter Subscriber: %s\r\n"+
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"---\r\n"+
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"Email: %s\r\n"+
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"Received: %s\r\n"+
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"\r\n",
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form.Name, req.Email, received,
|
|
)
|
|
case "feedback":
|
|
text = fmt.Sprintf(
|
|
"New Feedback: %s\r\n"+
|
|
"---\r\n"+
|
|
"From: %s <%s>\r\n"+
|
|
"%s"+
|
|
"Received: %s\r\n"+
|
|
"\r\n"+
|
|
"%s\r\n\r\n",
|
|
form.Name, req.Name, req.Email, serviceLine(service), received, req.Message,
|
|
)
|
|
case "generic":
|
|
text = fmt.Sprintf(
|
|
"New Submission: %s\r\n"+
|
|
"---\r\n"+
|
|
"From: %s <%s>\r\n"+
|
|
"%s"+
|
|
"Received: %s\r\n"+
|
|
"\r\n"+
|
|
"%s\r\n\r\n",
|
|
form.Name, req.Name, req.Email, serviceLine(service), received, req.Message,
|
|
)
|
|
default: // contact; the line is printed even when empty, as always
|
|
text = fmt.Sprintf(
|
|
"Contact Form Submission: %s\r\n"+
|
|
"---\r\n"+
|
|
"From: %s <%s>\r\n"+
|
|
"Service interest: %s\r\n"+
|
|
"Received: %s\r\n"+
|
|
"\r\n"+
|
|
"%s\r\n\r\n",
|
|
form.Name, req.Name, req.Email, req.Service, received, req.Message,
|
|
)
|
|
}
|
|
text += footer
|
|
|
|
// Assemble multipart/alternative message. The boundary comes first so
|
|
// that randomness failure aborts the message before anything is built.
|
|
boundary, err := randomBoundary()
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
var msg bytes.Buffer
|
|
msg.WriteString(fmt.Sprintf("From: %s\r\n", sanitizeHeaderValue(from)))
|
|
msg.WriteString(fmt.Sprintf("To: %s\r\n", sanitizeHeaderValue(to)))
|
|
msg.WriteString(fmt.Sprintf("Subject: %s\r\n", sanitizeHeaderValue(subject)))
|
|
msg.WriteString(fmt.Sprintf("Date: %s\r\n", time.Now().UTC().Format(time.RFC1123Z)))
|
|
msg.WriteString(fmt.Sprintf("Reply-To: %s\r\n", sanitizeHeaderValue(req.Email)))
|
|
msg.WriteString("MIME-Version: 1.0\r\n")
|
|
msg.WriteString(fmt.Sprintf("Content-Type: multipart/alternative; boundary=%s\r\n", boundary))
|
|
msg.WriteString("\r\n")
|
|
|
|
msg.WriteString(fmt.Sprintf("--%s\r\n", boundary))
|
|
msg.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
|
|
msg.WriteString("\r\n")
|
|
msg.WriteString(text)
|
|
msg.WriteString("\r\n")
|
|
|
|
msg.WriteString(fmt.Sprintf("--%s\r\n", boundary))
|
|
msg.WriteString("Content-Type: text/html; charset=UTF-8\r\n")
|
|
msg.WriteString("\r\n")
|
|
msg.WriteString(htmlBuf.String())
|
|
msg.WriteString("\r\n")
|
|
|
|
msg.WriteString(fmt.Sprintf("--%s--\r\n", boundary))
|
|
return msg.Bytes(), nil
|
|
}
|
|
|
|
// subjectTag renders the bracket segments of a subject line: the
|
|
// configurable "[<prefix>/<form name>]" segment when a prefix is set,
|
|
// plus the "[<service>]" segment when a service value surfaced.
|
|
func subjectTag(form *config.Form, service string) string {
|
|
tag := ""
|
|
if prefix := form.EmailSubjectPrefix(); prefix != "" {
|
|
tag = "[" + prefix + "/" + form.Name + "]"
|
|
}
|
|
if service != "" {
|
|
tag += "[" + service + "]"
|
|
}
|
|
return tag
|
|
}
|
|
|
|
// serviceLine renders the optional plain-text service row for the form
|
|
// types whose body has no fixed service field.
|
|
func serviceLine(service string) string {
|
|
if service == "" {
|
|
return ""
|
|
}
|
|
return fmt.Sprintf("Service interest: %s\r\n", service)
|
|
}
|