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

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go.mod

@@ -6,6 +6,7 @@ require modernc.org/sqlite v1.53.0
 
 require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/emersion/go-message v0.18.2 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect

go.sum

@@ -1,5 +1,7 @@
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
+github.com/emersion/go-message v0.18.2 h1:rl55SQdjd9oJcIoQNhubD2Acs1E6IzlZISRTK7x/Lpg=
+github.com/emersion/go-message v0.18.2/go.mod h1:XpJyL70LwRvq2a8rVbHXikPgKj8+aI0kGdHlg16ibYA=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e h1:ijClszYn+mADRFY17kjQEVQ1XRhq2/JR1M3sGqeJoxs=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e/go.mod h1:boTsfXsheKC2y+lKOCMpSfarhxDeIzfZG1jqGcPl3cA=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
@@ -12,15 +14,46 @@ github.com/ncruces/go-strftime v1.0.0 h1:HMFp8mLCTPp341M/ZnA4qaf7ZlsbTc+miZjCLOF
 github.com/ncruces/go-strftime v1.0.0/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
+github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/mod v0.36.0 h1:JJjpVx6myfUsUdAzZuOSTTmRE0PfZeNWzzvKrP7amb4=
 golang.org/x/mod v0.36.0/go.mod h1:moc6ELqsWcOw5Ef3xVprK5ul/MvtVvkIXLziUOICjUQ=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
+golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
 golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.44.0 h1:ildZl3J4uzeKP07r2F++Op7E9B29JRUy+a27EibtBTQ=
 golang.org/x/sys v0.44.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
+golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
+golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
+golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
 golang.org/x/tools v0.45.0 h1:18qN3FAooORvApf5XjCXgsuayZOEtXf6JK18I3+ONa8=
 golang.org/x/tools v0.45.0/go.mod h1:LuUGqqaXcXMEFEruIVJVm5mgDD8vww/z/SR1gQ4uE/0=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 modernc.org/cc/v4 v4.28.4 h1:Hd/4Es+MBj+/7hSdZaisNyu6bv3V0Dp2MdllyfqaH+c=
 modernc.org/cc/v4 v4.28.4/go.mod h1:OnovgIhbbMXMu1aISnJ0wvVD1KnW+cAUJkIrAWh+kVI=
 modernc.org/ccgo/v4 v4.34.4 h1:OVnSOWQjVKOYkFxoHYB+qQmSHK5gqMqARM+K9DpR/Ws=

internal/mail/message.go

@@ -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
+}

internal/mail/message_test.go

@@ -0,0 +1,70 @@
+package mail
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func loadFixture(t *testing.T, name string) []byte {
+	t.Helper()
+	b, err := os.ReadFile(filepath.Join("testdata", name))
+	if err != nil {
+		t.Fatalf("read fixture: %v", err)
+	}
+	return b
+}
+
+func TestParseMessage(t *testing.T) {
+	raw := loadFixture(t, "with_attachment.eml")
+	m, err := ParseMessage(42, raw)
+	if err != nil {
+		t.Fatalf("ParseMessage: %v", err)
+	}
+	if m.Header.UID != 42 {
+		t.Fatalf("uid: %d", m.Header.UID)
+	}
+	if m.Header.Subject != "Your Invoice #5" {
+		t.Fatalf("subject: %q", m.Header.Subject)
+	}
+	if m.Header.From != `"Bob" <bob@trusted.com>` && m.Header.From != "Bob <bob@trusted.com>" {
+		t.Fatalf("from: %q", m.Header.From)
+	}
+	if m.Header.MessageID != "abc123@trusted.com" && m.Header.MessageID != "<abc123@trusted.com>" {
+		t.Fatalf("message-id: %q", m.Header.MessageID)
+	}
+	if want := "Hello, here is your invoice."; !contains(m.BodyText, want) {
+		t.Fatalf("body=%q want contains %q", m.BodyText, want)
+	}
+	if !m.Header.HasAttachments {
+		t.Fatal("HasAttachments should be true")
+	}
+	if len(m.Attachments) != 1 || m.Attachments[0].Name != "invoice.txt" {
+		t.Fatalf("attachments: %+v", m.Attachments)
+	}
+	if !contains(string(m.Attachments[0].Content), "LINE-ITEM 1") {
+		t.Fatalf("attachment content: %q", m.Attachments[0].Content)
+	}
+}
+
+func TestParseHeaderOnly(t *testing.T) {
+	raw := loadFixture(t, "with_attachment.eml")
+	h, err := ParseHeaderOnly(7, raw)
+	if err != nil {
+		t.Fatalf("ParseHeaderOnly: %v", err)
+	}
+	if h.Subject != "Your Invoice #5" || !h.HasAttachments {
+		t.Fatalf("header: %+v", h)
+	}
+}
+
+func contains(s, sub string) bool {
+	return len(s) >= len(sub) && (func() bool {
+		for i := 0; i+len(sub) <= len(s); i++ {
+			if s[i:i+len(sub)] == sub {
+				return true
+			}
+		}
+		return false
+	}())
+}

internal/mail/testdata/with_attachment.eml

@@ -0,0 +1,18 @@
+From: "Bob" <bob@trusted.com>
+To: me@example.com
+Subject: Your Invoice #5
+Date: Sat, 20 Jun 2026 10:00:00 +0000
+Message-ID: <abc123@trusted.com>
+MIME-Version: 1.0
+Content-Type: multipart/mixed; boundary="BOUNDARY"
+
+--BOUNDARY
+Content-Type: text/plain; charset=utf-8
+
+Hello, here is your invoice.
+--BOUNDARY
+Content-Type: text/plain; charset=utf-8
+Content-Disposition: attachment; filename="invoice.txt"
+
+LINE-ITEM 1: 100.00
+--BOUNDARY--