feat(mail): RFC822 message parsing (headers, body, attachments)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-06-21 23:51:29 +01:00
parent b9d0b57f84
commit d73aabca96
5 changed files with 220 additions and 0 deletions
@@ -0,0 +1,98 @@
+// Package mail provides IMAP reading and RFC822 message parsing.
+package mail
+
+import (
+	"bytes"
+	"io"
+	"strings"
+
+	"github.com/emersion/go-message/mail"
+)
+
+type Header struct {
+	UID            uint32
+	From           string
+	To             string
+	Subject        string
+	Date           string
+	MessageID      string
+	HasAttachments bool
+}
+
+type Attachment struct {
+	Name    string
+	Size    int
+	MIME    string
+	Content []byte
+}
+
+type Message struct {
+	Header      Header
+	BodyText    string
+	Attachments []Attachment
+}
+
+func readHeader(mr *mail.Reader, uid uint32) Header {
+	h := Header{UID: uid}
+	hd := mr.Header
+	h.Subject, _ = hd.Subject()
+	if addrs, err := hd.AddressList("From"); err == nil && len(addrs) > 0 {
+		h.From = addrs[0].String()
+	}
+	if addrs, err := hd.AddressList("To"); err == nil && len(addrs) > 0 {
+		h.To = addrs[0].String()
+	}
+	if d, err := hd.Date(); err == nil {
+		h.Date = d.UTC().Format("Mon, 02 Jan 2006 15:04:05 -0700")
+	}
+	if msgID, err := hd.MessageID(); err == nil {
+		h.MessageID = msgID
+	} else {
+		h.MessageID = strings.Trim(hd.Get("Message-Id"), "<> ")
+	}
+	return h
+}
+
+// ParseMessage decodes the full message including attachment contents.
+func ParseMessage(uid uint32, raw []byte) (Message, error) {
+	mr, err := mail.CreateReader(bytes.NewReader(raw))
+	if err != nil {
+		return Message{}, err
+	}
+	m := Message{Header: readHeader(mr, uid)}
+	for {
+		part, err := mr.NextPart()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return Message{}, err
+		}
+		switch hdr := part.Header.(type) {
+		case *mail.InlineHeader:
+			ct, _, _ := hdr.ContentType()
+			if strings.HasPrefix(ct, "text/plain") && m.BodyText == "" {
+				b, _ := io.ReadAll(part.Body)
+				m.BodyText = string(b)
+			}
+		case *mail.AttachmentHeader:
+			name, _ := hdr.Filename()
+			ct, _, _ := hdr.ContentType()
+			b, _ := io.ReadAll(part.Body)
+			m.Attachments = append(m.Attachments, Attachment{
+				Name: name, Size: len(b), MIME: ct, Content: b,
+			})
+		}
+	}
+	m.Header.HasAttachments = len(m.Attachments) > 0
+	return m, nil
+}
+
+// ParseHeaderOnly decodes headers and detects attachments without keeping bodies.
+func ParseHeaderOnly(uid uint32, raw []byte) (Header, error) {
+	m, err := ParseMessage(uid, raw)
+	if err != nil {
+		return Header{}, err
+	}
+	return m.Header, nil
+}