Add maildir backend worker

Add the initial implementation of a backend for Maildir accounts. Much
of the functionality required is implemented in the go-message and
go-maildir libraries, so we use them as much as possible.

The maildir worker hooks into a new maildir:// URL scheme in the
accounts.conf file which points to a container of several maildir
directories. From there, the OpenDirectory, FetchDirectoryContents, etc
messages work on subdirectories. This is implemented as a Container
struct which handles mapping between the symbolic email folder names and
UIDs to the concrete directories and file names.

1 files changed, 322 insertions, 0 deletions

diff --git a/worker/maildir/message.go b/worker/maildir/message.go
new file mode 100644
index 00000000..b95ec987
--- /dev/null
+++ b/worker/maildir/message.go
@@ -0,0 +1,322 @@
+package maildir
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"mime/quotedprintable"
+	gomail "net/mail"
+	"strings"
+
+	"github.com/emersion/go-maildir"
+	"github.com/emersion/go-message"
+	_ "github.com/emersion/go-message/charset"
+	"github.com/emersion/go-message/mail"
+
+	"git.sr.ht/~sircmpwn/aerc/models"
+)
+
+// A Message is an individual email inside of a maildir.Dir.
+type Message struct {
+	dir maildir.Dir
+	uid uint32
+	key string
+}
+
+// NewReader reads a message into memory and returns an io.Reader for it.
+func (m Message) NewReader() (io.Reader, error) {
+	f, err := m.dir.Open(m.key)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	b, err := ioutil.ReadAll(f)
+	if err != nil {
+		return nil, err
+	}
+	return bytes.NewReader(b), nil
+}
+
+// Flags fetches the set of flags currently applied to the message.
+func (m Message) Flags() ([]maildir.Flag, error) {
+	return m.dir.Flags(m.key)
+}
+
+// SetFlags replaces the message's flags with a new set.
+func (m Message) SetFlags(flags []maildir.Flag) error {
+	return m.dir.SetFlags(m.key, flags)
+}
+
+// MarkRead either adds or removes the maildir.FlagSeen flag from the message.
+func (m Message) MarkRead(seen bool) error {
+	flags, err := m.Flags()
+	if err != nil {
+		return fmt.Errorf("could not read previous flags: %v", err)
+	}
+	if seen {
+		flags = append(flags, maildir.FlagSeen)
+		return m.SetFlags(flags)
+	}
+	var newFlags []maildir.Flag
+	for _, flag := range flags {
+		if flag != maildir.FlagSeen {
+			newFlags = append(newFlags, flag)
+		}
+	}
+	return m.SetFlags(newFlags)
+}
+
+// Remove deletes the email immediately.
+func (m Message) Remove() error {
+	return m.dir.Remove(m.key)
+}
+
+// MessageInfo populates a models.MessageInfo struct for the message.
+func (m Message) MessageInfo() (*models.MessageInfo, error) {
+	f, err := m.dir.Open(m.key)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	msg, err := message.Read(f)
+	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(&msg.Header)
+	if err != nil {
+		return nil, fmt.Errorf("could not get envelope: %v", err)
+	}
+	flags, err := m.Flags()
+	if err != nil {
+		return nil, fmt.Errorf("could not read flags: %v", err)
+	}
+	return &models.MessageInfo{
+		BodyStructure: bs,
+		Envelope:      env,
+		Flags:         translateFlags(flags),
+		InternalDate:  env.Date,
+		RFC822Headers: &mail.Header{msg.Header},
+		Size:          0,
+		Uid:           m.uid,
+	}, nil
+}
+
+// NewBodyPartReader creates a new io.Reader for the requested body part(s) of
+// the message.
+func (m Message) NewBodyPartReader(requestedParts []int) (io.Reader, error) {
+	f, err := m.dir.Open(m.key)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	msg, err := message.Read(f)
+	if err != nil {
+		return nil, fmt.Errorf("could not read message: %v", err)
+	}
+	return fetchEntityPartReader(msg, requestedParts)
+}
+
+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 *message.Header) (*models.Envelope, error) {
+	date, err := gomail.ParseDate(h.Get("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)
+	}
+	return &models.Envelope{
+		Date:      date,
+		Subject:   h.Get("subject"),
+		MessageId: h.Get("message-id"),
+		From:      from,
+		To:        to,
+		Cc:        cc,
+		Bcc:       bcc,
+	}, nil
+}
+
+func parseAddressList(h *message.Header, key string) ([]*models.Address, error) {
+	var converted []*models.Address
+	hdr := h.Get(key)
+	if strings.TrimSpace(hdr) == "" {
+		return converted, nil
+	}
+	addrs, err := gomail.ParseAddressList(hdr)
+	if err != nil {
+		if 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
+}
+
+var flagMap = map[maildir.Flag]models.Flag{
+	maildir.FlagReplied: models.AnsweredFlag,
+	maildir.FlagSeen:    models.SeenFlag,
+	maildir.FlagTrashed: models.DeletedFlag,
+	maildir.FlagFlagged: models.FlaggedFlag,
+	// maildir.FlagDraft Flag = 'D'
+	// maildir.FlagPassed Flag = 'P'
+}
+
+func translateFlags(maildirFlags []maildir.Flag) []models.Flag {
+	var flags []models.Flag
+	for _, maildirFlag := range maildirFlags {
+		if flag, ok := flagMap[maildirFlag]; ok {
+			flags = append(flags, flag)
+		}
+	}
+	return flags
+}