feat: contact form backend for linux and freebsd servers

Assisted-by: GLM 5.3 Flash

internal/email/acknowledgement_test.go

@@ -0,0 +1,92 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+//go:build linux || freebsd
+
+package email
+
+import (
+	"strings"
+	"testing"
+
+	"sourcedock.dev/petrbalvin/nuntius/internal/config"
+)
+
+func ackForm() *config.Form {
+	return &config.Form{
+		Name:          "contact",
+		Type:          "contact",
+		To:            "owner@example.com",
+		From:          "noreply@example.com",
+		SubjectPrefix: new("nuntius"),
+		EmailBrand:    new("nuntius"),
+	}
+}
+
+func TestComposeAcknowledgement(t *testing.T) {
+	msg, err := composeAcknowledgement(ackForm(), "jane@example.com")
+	if err != nil {
+		t.Fatalf("compose: %v", err)
+	}
+	raw := string(msg)
+
+	for _, want := range []string{
+		"From: noreply@example.com\r\n",
+		"To: jane@example.com\r\n",
+		"Subject: [nuntius/contact] Message received\r\n",
+		// The reply lands in the owner's inbox, not in the void.
+		"Reply-To: owner@example.com\r\n",
+		"Content-Type: multipart/alternative; boundary=nuntius-",
+		"your message to contact was received",
+		"Delivered by nuntius",
+	} {
+		if !strings.Contains(raw, want) {
+			t.Errorf("message missing %q", want)
+		}
+	}
+	// The submitted values are deliberately never echoed back.
+	if strings.Contains(raw, "jane@example.com\r\n\r\n") && strings.Count(raw, "jane@example.com") != 1 {
+		t.Errorf("message echoes the submitter context beyond the To header")
+	}
+}
+
+func TestComposeAcknowledgementHeaderInjection(t *testing.T) {
+	msg, err := composeAcknowledgement(ackForm(), "jane@example.com\r\nBcc: victim@example.com")
+	if err != nil {
+		t.Fatalf("compose: %v", err)
+	}
+	raw := string(msg)
+	// The whole string collapses into one To header line: no line starts
+	// with the injected header name.
+	for line := range strings.SplitSeq(raw, "\r\n") {
+		if strings.HasPrefix(line, "Bcc:") {
+			t.Errorf("a CR/LF in the recipient injected a header line %q", line)
+		}
+	}
+	if !strings.Contains(raw, "To: jane@example.com  Bcc: victim@example.com\r\n") {
+		t.Errorf("the CR/LF was not neutralised into spaces")
+	}
+}
+
+func TestComposeAcknowledgementSubjectWithoutPrefix(t *testing.T) {
+	form := ackForm()
+	form.SubjectPrefix = new("")
+	msg, err := composeAcknowledgement(form, "jane@example.com")
+	if err != nil {
+		t.Fatalf("compose: %v", err)
+	}
+	if !strings.Contains(string(msg), "Subject: Message received\r\n") {
+		t.Errorf("subject with an empty prefix = %q, want the bare subject", subjectOf(t, string(msg)))
+	}
+}
+
+func subjectOf(t *testing.T, raw string) string {
+	t.Helper()
+	for line := range strings.SplitSeq(raw, "\r\n") {
+		if after, ok := strings.CutPrefix(line, "Subject: "); ok {
+			return after
+		}
+	}
+	t.Fatalf("no subject line in message")
+	return ""
+}