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Merged
butschster merged 2 commits into from
Aug 17, 2026
Merged

feat(smtp): replace CID references in HTML with attachment preview URLs #346

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fe0d3b8
feat(smtp): replace CID references in HTML with attachment preview URLs
Powerhamster Aug 14, 2026
2d414a5
fix(smtp): correct expected ContentID in inline attachment test
Powerhamster Aug 14, 2026
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34 changes: 23 additions & 11 deletions modules/smtp/handler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,8 @@ func (s *session) Data(r io.Reader) error {
// Generate event UUID for attachment storage.
eventUUID := event.GenerateUUID()

// Store attachments.
// Store attachments and collect CID→URL mappings for inline images.
cidMap := make(map[string]string) // cid -> preview URL
if s.backend.attachments != nil && len(attachments) > 0 {
for _, att := range attachments {
path := eventUUID + "/" + att.Filename
Expand All @@ -129,6 +130,17 @@ func (s *session) Data(r io.Reader) error {
attUUID, eventUUID, att.Filename, path, len(att.content), att.Type, att.ContentID,
)
}
if att.ContentID != "" {
cid := strings.Trim(att.ContentID, "<>")
cidMap[cid] = "/api/smtp/attachments/" + eventUUID + "/preview/" + attUUID
}
}
}

// Replace cid: references in HTML with attachment preview URLs.
if parsed.HTML != "" && len(cidMap) > 0 {
for cid, url := range cidMap {
parsed.HTML = strings.ReplaceAll(parsed.HTML, "cid:"+cid, url)
}
}

Expand Down Expand Up @@ -167,16 +179,16 @@ type parsedAttachment struct {
// ParsedEmail is the structure stored as event payload.
// Field names match the original PHP Buggregator Message::jsonSerialize().
type ParsedEmail struct {
ID *string `json:"id"`
Subject string `json:"subject"`
From []EmailAddress `json:"from"`
To []EmailAddress `json:"to"`
Cc []EmailAddress `json:"cc"`
Bcc []string `json:"bcc"`
ReplyTo []EmailAddress `json:"reply_to"`
Text string `json:"text"`
HTML string `json:"html"`
Raw string `json:"raw"`
ID *string `json:"id"`
Subject string `json:"subject"`
From []EmailAddress `json:"from"`
To []EmailAddress `json:"to"`
Cc []EmailAddress `json:"cc"`
Bcc []string `json:"bcc"`
ReplyTo []EmailAddress `json:"reply_to"`
Text string `json:"text"`
HTML string `json:"html"`
Raw string `json:"raw"`
}

func parseEmail(raw []byte, recipients []string) (*ParsedEmail, []parsedAttachment, error) {
Expand Down
72 changes: 72 additions & 0 deletions modules/smtp/handler_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -300,6 +300,78 @@ func TestParseEmail_RFC2047Subject(t *testing.T) {
}
}

func TestParseEmail_InlineAttachmentWithCID(t *testing.T) {
// Build a multipart/related email with an inline image referenced via cid:
raw := []byte("From: sender@example.com\r\nTo: recipient@example.com\r\nSubject: CID Test\r\n" +
"Content-Type: multipart/related; boundary=\"rel\"\r\n\r\n" +
"--rel\r\nContent-Type: text/html\r\n\r\n" +
"<html><body><img src=\"cid:logo123@example.com\"></body></html>\r\n" +
"--rel\r\nContent-Type: image/png\r\nContent-Disposition: inline; filename=\"logo.png\"\r\n" +
"Content-ID: <logo123@example.com>\r\nContent-Transfer-Encoding: base64\r\n\r\n" +
"iVBORw0KGgo=\r\n" +
"--rel--")

parsed, atts, err := parseEmail(raw, []string{"recipient@example.com"})
if err != nil {
t.Fatal(err)
}

// HTML should contain the cid: reference (replacement happens in Data(), not parseEmail).
if !strings.Contains(parsed.HTML, "cid:logo123@example.com") {
t.Errorf("HTML should still contain cid: reference, got %q", parsed.HTML)
}

// Should have one attachment with ContentID set.
if len(atts) != 1 {
t.Fatalf("expected 1 attachment, got %d", len(atts))
}
if atts[0].ContentID != "logo123@example.com" {
t.Errorf("ContentID = %q, want %q", atts[0].ContentID, "logo123@example.com")
}
if atts[0].Filename != "logo.png" {
t.Errorf("Filename = %q, want %q", atts[0].Filename, "logo.png")
}
}

func TestReplaceCIDReferences(t *testing.T) {
// Simulate the CID replacement logic from Data().
html := `<html><body><img src="cid:logo@example.com"><img src="cid:banner@example.com"></body></html>`
cidMap := map[string]string{
"logo@example.com": "/api/smtp/attachments/evt-uuid/preview/att-uuid-1",
"banner@example.com": "/api/smtp/attachments/evt-uuid/preview/att-uuid-2",
}

for cid, url := range cidMap {
html = strings.ReplaceAll(html, "cid:"+cid, url)
}

if strings.Contains(html, "cid:") {
t.Errorf("HTML still contains cid: references: %s", html)
}
if !strings.Contains(html, "/api/smtp/attachments/evt-uuid/preview/att-uuid-1") {
t.Error("missing logo preview URL")
}
if !strings.Contains(html, "/api/smtp/attachments/evt-uuid/preview/att-uuid-2") {
t.Error("missing banner preview URL")
}
}

func TestReplaceCIDReferences_NoCID(t *testing.T) {
// When there are no CID references, HTML should remain unchanged.
html := `<html><body><p>No images</p></body></html>`
cidMap := map[string]string{}

if len(cidMap) > 0 {
for cid, url := range cidMap {
html = strings.ReplaceAll(html, "cid:"+cid, url)
}
}

if html != `<html><body><p>No images</p></body></html>` {
t.Errorf("HTML was modified unexpectedly: %s", html)
}
}

func TestPreviewMapper(t *testing.T) {
m := &previewMapper{}

Expand Down
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