feat: contact form backend for linux and freebsd servers

Assisted-by: GLM 5.3 Flash

internal/email/sender.go

@@ -0,0 +1,494 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+//go:build linux || freebsd
+
+// Package email handles SMTP message composition and delivery.
+package email
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/tls"
+	"encoding/hex"
+	"fmt"
+	"html/template"
+	"net"
+	"net/smtp"
+	"strings"
+	"time"
+
+	"sourcedock.dev/petrbalvin/nuntius/internal/config"
+	"sourcedock.dev/petrbalvin/nuntius/internal/contactform"
+)
+
+// effectiveTLSConfig returns cfg when set, otherwise a default config that
+// verifies the server certificate against host.
+func effectiveTLSConfig(cfg *tls.Config, host string) *tls.Config {
+	if cfg != nil {
+		return cfg
+	}
+	return &tls.Config{ServerName: host}
+}
+
+// FormSender delivers contact form submissions for a single form
+// using its own SMTP credentials. Each form has its own FormSender
+// so credentials are isolated per tenant.
+type FormSender struct {
+	form *config.Form
+	// TLSConfig optionally overrides the TLS configuration used for
+	// STARTTLS. When nil, a default config with ServerName set to the
+	// SMTP host is used.
+	TLSConfig *tls.Config
+}
+
+// NewFormSender returns a new FormSender bound to the given form.
+func NewFormSender(form *config.Form) *FormSender {
+	return &FormSender{form: form}
+}
+
+// Send composes and sends a multi-part email (plain text + HTML)
+// for the given request. Returns an error if composition or the SMTP
+// round-trip fails. The SMTP conversation bound comes from the form's
+// configured smtp.timeout_seconds.
+func (s *FormSender) Send(req contactform.Request) error {
+	auth := smtp.PlainAuth("", s.form.SMTP.User, s.form.SMTP.Password, s.form.SMTP.Host)
+	msg, err := compose(s.form.From, s.form.To, req, s.form)
+	if err != nil {
+		return fmt.Errorf("compose message: %w", err)
+	}
+	return sendMail(s.form.SMTP, auth, s.form.From, []string{s.form.To}, msg, s.form.SMTP.Timeout(), s.TLSConfig)
+}
+
+// sendMail delivers msg over SMTP with a hard timeout on every network
+// operation. When cfg.Port is 465 the connection speaks TLS from the first
+// byte (implicit TLS); any other port starts plaintext and upgrades via
+// STARTTLS when the server advertises it. With cfg.RequireTLS set, an SMTP
+// server that never offers STARTTLS aborts the delivery instead of sending
+// over plaintext. If tlsConfig is nil, a default config with ServerName set
+// to the target host is used.
+func sendMail(cfg config.SMTPConfig, auth smtp.Auth, from string, to []string, msg []byte, timeout time.Duration, tlsConfig *tls.Config) error {
+	addr := cfg.AddrFor()
+	implicitTLS := cfg.Port == config.ImplicitTLSPort
+
+	var conn net.Conn
+	if implicitTLS {
+		dialer := &net.Dialer{Timeout: timeout}
+		tconn, err := tls.DialWithDialer(dialer, "tcp", addr, effectiveTLSConfig(tlsConfig, cfg.Host))
+		if err != nil {
+			return fmt.Errorf("dial smtps %s: %w", addr, err)
+		}
+		conn = tconn
+	} else {
+		pconn, err := net.DialTimeout("tcp", addr, timeout)
+		if err != nil {
+			return fmt.Errorf("dial smtp %s: %w", addr, err)
+		}
+		conn = pconn
+	}
+	defer conn.Close()
+
+	if err := conn.SetDeadline(time.Now().Add(timeout)); err != nil {
+		return fmt.Errorf("set smtp deadline: %w", err)
+	}
+
+	c, err := smtp.NewClient(conn, cfg.Host)
+	if err != nil {
+		return fmt.Errorf("smtp client: %w", err)
+	}
+	defer c.Close()
+
+	if !implicitTLS {
+		ok, _ := c.Extension("STARTTLS")
+		switch {
+		case ok:
+			if err := c.StartTLS(effectiveTLSConfig(tlsConfig, cfg.Host)); err != nil {
+				return fmt.Errorf("starttls: %w", err)
+			}
+		case cfg.RequireTLS:
+			return fmt.Errorf("smtp server %s does not advertise starttls but require_tls is enabled", addr)
+		}
+	}
+
+	if auth != nil {
+		if ok, _ := c.Extension("AUTH"); ok {
+			if err := c.Auth(auth); err != nil {
+				return fmt.Errorf("smtp auth: %w", err)
+			}
+		}
+	}
+
+	if err := c.Mail(from); err != nil {
+		return fmt.Errorf("smtp mail from: %w", err)
+	}
+	for _, rcpt := range to {
+		if err := c.Rcpt(rcpt); err != nil {
+			return fmt.Errorf("smtp rcpt to: %w", err)
+		}
+	}
+
+	w, err := c.Data()
+	if err != nil {
+		return fmt.Errorf("smtp data: %w", err)
+	}
+	if _, err := w.Write(msg); err != nil {
+		return fmt.Errorf("smtp write data: %w", err)
+	}
+	if err := w.Close(); err != nil {
+		return fmt.Errorf("smtp close data: %w", err)
+	}
+
+	if err := c.Quit(); err != nil {
+		return fmt.Errorf("smtp quit: %w", err)
+	}
+	return nil
+}
+
+// randomBoundary returns a MIME boundary that is practically impossible
+// to collide with message content. An error means crypto/rand failed; the
+// message must then not be sent at all, because a predictable delimiter
+// would let crafted content forge MIME part boundaries.
+func randomBoundary() (string, error) {
+	var buf [16]byte
+	if _, err := rand.Read(buf[:]); err != nil {
+		return "", fmt.Errorf("generate mime boundary: %w", err)
+	}
+	return "nuntius-" + hex.EncodeToString(buf[:]), nil
+}
+
+// sanitizeHeaderValue makes an interpolated value safe to embed in a
+// single RFC 5322 header line. A CR or LF would terminate the header and
+// let a crafted value inject arbitrary additional headers.
+func sanitizeHeaderValue(v string) string {
+	return strings.NewReplacer("\r", " ", "\n", " ").Replace(v)
+}
+
+// emailTemplateContact is the HTML body template for contact-type forms.
+var emailTemplateContact = template.Must(template.New("contact").Parse(`<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+</head>
+<body style="margin:0;padding:0;background-color:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,-apple-system,sans-serif">
+<table width="100%" cellpadding="0" cellspacing="0" style="background-color:#f3f4f6;padding:32px 0">
+<tr><td align="center">
+<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)">
+
+<!-- Header -->
+<tr>
+<td style="background-color:#1e40af;padding:24px 28px">
+  <p style="margin:0;font-size:13px;font-weight:600;color:#93c5fd;text-transform:uppercase;letter-spacing:0.5px">
+    Contact Form Submission
+  </p>
+  <p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#ffffff">
+    {{.FormName}}
+  </p>
+</td>
+</tr>
+
+<!-- Body -->
+<tr>
+<td style="padding:28px 28px 12px">
+
+  <!-- Submitter -->
+  <table width="100%" cellpadding="0" cellspacing="0" style="margin-bottom:20px">
+  <tr>
+    <td style="padding-bottom:8px;border-bottom:1px solid #e5e7eb">
+      <span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">From</span>
+      <br>
+      <span style="font-size:15px;font-weight:600;color:#1f2937">{{.Name}}</span>
+      <span style="font-size:14px;color:#1e40af;margin-left:8px">{{.Email}}</span>
+    </td>
+  </tr>
+  {{if .Service}}
+  <tr>
+    <td style="padding:12px 0 8px;border-bottom:1px solid #e5e7eb">
+      <span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">Service Interest</span>
+      <br>
+      <span style="font-size:14px;color:#1f2937">{{.Service}}</span>
+    </td>
+  </tr>
+  {{end}}
+  <tr>
+    <td style="padding:12px 0 8px;border-bottom:1px solid #e5e7eb">
+      <span style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px">Received</span>
+      <br>
+      <span style="font-size:13px;color:#9ca3af">{{.Received}}</span>
+    </td>
+  </tr>
+  </table>
+
+  <!-- Message -->
+  <p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:0.5px;margin:0 0 8px">Message</p>
+  <div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;padding:6px 0">{{.Message}}</div>
+
+</td>
+</tr>
+
+<!-- Footer -->
+{{if .Brand}}
+<tr>
+<td style="padding:16px 28px 28px">
+  <p style="margin:0;font-size:11px;color:#9ca3af;border-top:1px solid #e5e7eb;padding-top:16px">
+    Delivered by <strong style="color:#6b7280">{{.Brand}}</strong>, a contact form backend for Linux servers.
+  </p>
+</td>
+</tr>
+{{end}}
+
+</table>
+</td></tr>
+</table>
+</body>
+</html>`))
+
+// emailTemplateFeedback is the HTML body template for feedback-type forms.
+var emailTemplateFeedback = template.Must(template.New("feedback").Parse(`<!DOCTYPE html>
+<html lang="en">
+<head><meta charset="UTF-8"></head>
+<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
+<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
+<tr><td align="center">
+<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)">
+<tr><td style="background:#0f766e;padding:24px 28px">
+<p style="margin:0;font-size:13px;font-weight:600;color:#5eead4;text-transform:uppercase;letter-spacing:.5px">New Feedback</p>
+<p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}</p>
+</td></tr>
+<tr><td style="padding:28px">
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0">From</p>
+<p style="font-size:15px;font-weight:600;color:#1f2937;margin:2px 0 16px">{{.Name}} <span style="color:#0f766e">{{.Email}}</span></p>
+{{if .Service}}
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Service Interest</p>
+<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;margin:0 0 16px">{{.Service}}</div>
+{{end}}
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Feedback</p>
+<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap">{{.Message}}</div>
+{{if .Brand}}
+<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>
+{{end}}
+</td></tr>
+</table>
+</td></tr>
+</table>
+</body>
+</html>`))
+
+// emailTemplateNewsletter is the HTML body template for newsletter-signup forms.
+var emailTemplateNewsletter = template.Must(template.New("newsletter").Parse(`<!DOCTYPE html>
+<html lang="en">
+<head><meta charset="UTF-8"></head>
+<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
+<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
+<tr><td align="center">
+<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)">
+<tr><td style="background:#1e40af;padding:20px 24px">
+<p style="margin:0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}: new subscriber</p>
+</td></tr>
+<tr><td style="padding:24px">
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 4px">Email</p>
+<p style="font-size:16px;font-weight:600;color:#1e40af;margin:0 0 16px">{{.Email}}</p>
+{{if .Brand}}
+<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>
+{{end}}
+</td></tr>
+</table>
+</td></tr>
+</table>
+</body>
+</html>`))
+
+// emailTemplateGeneric is the HTML body template for generic forms.
+var emailTemplateGeneric = template.Must(template.New("generic").Parse(`<!DOCTYPE html>
+<html lang="en">
+<head><meta charset="UTF-8"></head>
+<body style="margin:0;padding:0;background:#f3f4f6;font-family:Inter,ui-sans-serif,system-ui,sans-serif">
+<table width="100%" cellpadding="0" cellspacing="0" style="background:#f3f4f6;padding:32px 0">
+<tr><td align="center">
+<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)">
+<tr><td style="background:#1e40af;padding:24px 28px">
+<p style="margin:0;font-size:13px;font-weight:600;color:#93c5fd;text-transform:uppercase;letter-spacing:.5px">Form Submission</p>
+<p style="margin:4px 0 0;font-size:18px;font-weight:700;color:#fff">{{.FormName}}</p>
+</td></tr>
+<tr><td style="padding:28px">
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0">From</p>
+<p style="font-size:15px;font-weight:600;color:#1f2937;margin:2px 0 16px">{{.Name}} <span style="color:#1e40af">{{.Email}}</span></p>
+{{if .Service}}
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Service Interest</p>
+<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap;margin:0 0 16px">{{.Service}}</div>
+{{end}}
+<p style="font-size:11px;font-weight:600;color:#6b7280;text-transform:uppercase;letter-spacing:.5px;margin:0 0 8px">Message</p>
+<div style="font-size:14px;line-height:1.6;color:#1f2937;white-space:pre-wrap">{{.Message}}</div>
+{{if .Brand}}
+<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>
+{{end}}
+</td></tr>
+</table>
+</td></tr>
+</table>
+</body>
+</html>`))
+
+// compose builds the multipart message for one submission. The subject
+// prefix and the footer brand come from the form's configuration; the
+// defaults reproduce the subjects and footers earlier releases sent.
+func compose(from, to string, req contactform.Request, form *config.Form) ([]byte, error) {
+	received := time.Now().UTC().Format("January 2, 2006 at 15:04 UTC")
+
+	// The service interest only surfaces when the form actually accepts
+	// the field: the contact template has always shown it, and a form
+	// with its own services list has opted the field into validation.
+	service := ""
+	if req.Service != "" && (form.Type == "contact" || form.Services != nil) {
+		service = req.Service
+	}
+
+	// --- HTML part ---
+	var htmlBuf bytes.Buffer
+	tmpl := emailTemplateContact
+	switch form.Type {
+	case "newsletter":
+		tmpl = emailTemplateNewsletter
+	case "feedback":
+		tmpl = emailTemplateFeedback
+	case "generic":
+		tmpl = emailTemplateGeneric
+	}
+	if err := tmpl.Execute(&htmlBuf, map[string]string{
+		"FormName": form.Name,
+		"Name":     req.Name,
+		"Email":    req.Email,
+		"Service":  service,
+		"Message":  req.Message,
+		"Received": received,
+		"Brand":    form.Brand(),
+	}); err != nil {
+		// template.Must guarantees valid templates; this path is
+		// unreachable in normal operation.
+		htmlBuf.Reset()
+		fmt.Fprintf(&htmlBuf, "<p>Email generation error: %v</p>", err)
+	}
+
+	// --- Subject + plain-text body per form type ---
+	var base string
+	switch form.Type {
+	case "newsletter":
+		base = "New newsletter subscriber"
+	case "feedback":
+		base = "New feedback"
+	case "generic":
+		base = "New submission"
+	default: // contact
+		base = "Contact form submission"
+	}
+	subject := base
+	if tag := subjectTag(form, service); tag != "" {
+		subject = tag + " " + base
+	}
+
+	footer := ""
+	if brand := form.Brand(); brand != "" {
+		footer = "Delivered by " + brand + "\r\n"
+	}
+
+	var text string
+	switch form.Type {
+	case "newsletter":
+		text = fmt.Sprintf(
+			"New Newsletter Subscriber: %s\r\n"+
+				"---\r\n"+
+				"Email: %s\r\n"+
+				"Received: %s\r\n"+
+				"\r\n",
+			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)
+}