Extract message parsing to common worker module

Things like FetchEntityPartReader etc can be reused by most workers
working with raw email files from disk (or any reader for that matter).

This patch extract that common functionality in a separate package.

1 files changed, 240 insertions, 0 deletions

diff --git a/worker/lib/parse.go b/worker/lib/parse.go
new file mode 100644
index 00000000..9f9fa62e
--- /dev/null
+++ b/worker/lib/parse.go
@@ -0,0 +1,240 @@
+package lib
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"mime/quotedprintable"
+	"strings"
+
+	"git.sr.ht/~sircmpwn/aerc/models"
+	"github.com/emersion/go-message"
+	_ "github.com/emersion/go-message/charset"
+	"github.com/emersion/go-message/mail"
+)
+
+func FetchEntityPartReader(e *message.Entity, index []int) (io.Reader, error) {
+	if len(index) < 1 {
+		return nil, fmt.Errorf("no part to read")
+	}
+	if mpr := e.MultipartReader(); mpr != nil {
+		idx := 0
+		for {
+			idx++
+			part, err := mpr.NextPart()
+			if err != nil {
+				return nil, err
+			}
+			if idx == index[0] {
+				rest := index[1:]
+				if len(rest) < 1 {
+					return fetchEntityReader(part)
+				}
+				return FetchEntityPartReader(part, index[1:])
+			}
+		}
+	}
+	if index[0] != 1 {
+		return nil, fmt.Errorf("cannont return non-first part of non-multipart")
+	}
+	return fetchEntityReader(e)
+}
+
+// fetchEntityReader makes an io.Reader for the given entity. Since the
+// go-message package decodes the body for us, and the UI expects to deal with
+// a reader whose bytes are encoded with the part's encoding, we are in the
+// interesting position of needing to re-encode the reader before sending it
+// off to the UI layer.
+//
+// TODO: probably change the UI to expect an already-decoded reader and decode
+// in the IMAP worker.
+func fetchEntityReader(e *message.Entity) (io.Reader, error) {
+	enc := e.Header.Get("content-transfer-encoding")
+	var buf bytes.Buffer
+
+	// base64
+	if strings.EqualFold(enc, "base64") {
+		wc := base64.NewEncoder(base64.StdEncoding, &buf)
+		defer wc.Close()
+		if _, err := io.Copy(wc, e.Body); err != nil {
+			return nil, fmt.Errorf("could not base64 encode: %v", err)
+		}
+		return &buf, nil
+	}
+
+	// quoted-printable
+	if strings.EqualFold(enc, "quoted-printable") {
+		wc := quotedprintable.NewWriter(&buf)
+		defer wc.Close()
+		if _, err := io.Copy(wc, e.Body); err != nil {
+			return nil, fmt.Errorf("could not quoted-printable encode: %v", err)
+		}
+		return &buf, nil
+	}
+
+	// other general encoding
+	if _, err := io.Copy(&buf, e.Body); err != nil {
+		return nil, err
+	}
+
+	return &buf, nil
+}
+
+// split a MIME type into its major and minor parts
+func splitMIME(m string) (string, string) {
+	parts := strings.Split(m, "/")
+	if len(parts) != 2 {
+		return parts[0], ""
+	}
+	return parts[0], parts[1]
+}
+
+func parseEntityStructure(e *message.Entity) (*models.BodyStructure, error) {
+	var body models.BodyStructure
+	contentType, ctParams, err := e.Header.ContentType()
+	if err != nil {
+		return nil, fmt.Errorf("could not parse content type: %v", err)
+	}
+	mimeType, mimeSubType := splitMIME(contentType)
+	body.MIMEType = mimeType
+	body.MIMESubType = mimeSubType
+	body.Params = ctParams
+	body.Description = e.Header.Get("content-description")
+	body.Encoding = e.Header.Get("content-transfer-encoding")
+	if cd := e.Header.Get("content-disposition"); cd != "" {
+		contentDisposition, cdParams, err := e.Header.ContentDisposition()
+		if err != nil {
+			return nil, fmt.Errorf("could not parse content disposition: %v", err)
+		}
+		body.Disposition = contentDisposition
+		body.DispositionParams = cdParams
+	}
+	body.Parts = []*models.BodyStructure{}
+	if mpr := e.MultipartReader(); mpr != nil {
+		for {
+			part, err := mpr.NextPart()
+			if err == io.EOF {
+				return &body, nil
+			} else if err != nil {
+				return nil, err
+			}
+			ps, err := parseEntityStructure(part)
+			if err != nil {
+				return nil, fmt.Errorf("could not parse child entity structure: %v", err)
+			}
+			body.Parts = append(body.Parts, ps)
+		}
+	}
+	return &body, nil
+}
+
+func parseEnvelope(h *mail.Header) (*models.Envelope, error) {
+	date, err := h.Date()
+	if err != nil {
+		return nil, fmt.Errorf("could not parse date header: %v", err)
+	}
+	from, err := parseAddressList(h, "from")
+	if err != nil {
+		return nil, fmt.Errorf("could not read from address: %v", err)
+	}
+	to, err := parseAddressList(h, "to")
+	if err != nil {
+		return nil, fmt.Errorf("could not read to address: %v", err)
+	}
+	cc, err := parseAddressList(h, "cc")
+	if err != nil {
+		return nil, fmt.Errorf("could not read cc address: %v", err)
+	}
+	bcc, err := parseAddressList(h, "bcc")
+	if err != nil {
+		return nil, fmt.Errorf("could not read bcc address: %v", err)
+	}
+	subj, err := h.Subject()
+	if err != nil {
+		return nil, fmt.Errorf("could not read subject: %v", err)
+	}
+	msgID, err := h.Text("message-id")
+	if err != nil {
+		return nil, fmt.Errorf("could not read message id: %v", err)
+	}
+	return &models.Envelope{
+		Date:      date,
+		Subject:   subj,
+		MessageId: msgID,
+		From:      from,
+		To:        to,
+		Cc:        cc,
+		Bcc:       bcc,
+	}, nil
+}
+
+func parseAddressList(h *mail.Header, key string) ([]*models.Address, error) {
+	var converted []*models.Address
+	addrs, err := h.AddressList(key)
+	if err != nil {
+		if hdr, err := h.Text(key); err != nil && strings.Index(hdr, "@") < 0 {
+			return []*models.Address{&models.Address{
+				Name: hdr,
+			}}, nil
+		}
+		return nil, err
+	}
+	for _, addr := range addrs {
+		parts := strings.Split(addr.Address, "@")
+		var mbox, host string
+		if len(parts) > 1 {
+			mbox = strings.Join(parts[0:len(parts)-1], "@")
+			host = parts[len(parts)-1]
+		} else {
+			mbox = addr.Address
+		}
+		converted = append(converted, &models.Address{
+			Name:    addr.Name,
+			Mailbox: mbox,
+			Host:    host,
+		})
+	}
+	return converted, nil
+}
+
+// RawMessage is an interface that describes a raw message
+type RawMessage interface {
+	NewReader() (io.Reader, error)
+	ModelFlags() ([]models.Flag, error)
+	UID() uint32
+}
+
+// MessageInfo populates a models.MessageInfo struct for the message.
+// based on the reader returned by NewReader
+func MessageInfo(raw RawMessage) (*models.MessageInfo, error) {
+	r, err := raw.NewReader()
+	if err != nil {
+		return nil, err
+	}
+	msg, err := message.Read(r)
+	if err != nil {
+		return nil, fmt.Errorf("could not read message: %v", err)
+	}
+	bs, err := parseEntityStructure(msg)
+	if err != nil {
+		return nil, fmt.Errorf("could not get structure: %v", err)
+	}
+	env, err := parseEnvelope(&mail.Header{msg.Header})
+	if err != nil {
+		return nil, fmt.Errorf("could not get envelope: %v", err)
+	}
+	flags, err := raw.ModelFlags()
+	if err != nil {
+		return nil, err
+	}
+	return &models.MessageInfo{
+		BodyStructure: bs,
+		Envelope:      env,
+		Flags:         flags,
+		InternalDate:  env.Date,
+		RFC822Headers: &mail.Header{msg.Header},
+		Size:          0,
+		Uid:           raw.UID(),
+	}, nil
+}