Introduce base plugin

This plugin offers base IMAP/SMTP functionality.

References: https://todo.sr.ht/~sircmpwn/koushin/39

1 files changed, 277 insertions, 0 deletions

diff --git a/plugins/base/imap.go b/plugins/base/imap.go
new file mode 100644
index 0000000..93f3c4e
--- /dev/null
+++ b/plugins/base/imap.go
@@ -0,0 +1,277 @@
+package koushinbase
+
+import (
+	"bufio"
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/emersion/go-imap"
+	imapclient "github.com/emersion/go-imap/client"
+	"github.com/emersion/go-message"
+	"github.com/emersion/go-message/textproto"
+)
+
+func listMailboxes(conn *imapclient.Client) ([]*imap.MailboxInfo, error) {
+	ch := make(chan *imap.MailboxInfo, 10)
+	done := make(chan error, 1)
+	go func() {
+		done <- conn.List("", "*", ch)
+	}()
+
+	var mailboxes []*imap.MailboxInfo
+	for mbox := range ch {
+		mailboxes = append(mailboxes, mbox)
+	}
+
+	if err := <-done; err != nil {
+		return nil, fmt.Errorf("failed to list mailboxes: %v", err)
+	}
+
+	sort.Slice(mailboxes, func(i, j int) bool {
+		return mailboxes[i].Name < mailboxes[j].Name
+	})
+	return mailboxes, nil
+}
+
+func ensureMailboxSelected(conn *imapclient.Client, mboxName string) error {
+	mbox := conn.Mailbox()
+	if mbox == nil || mbox.Name != mboxName {
+		if _, err := conn.Select(mboxName, false); err != nil {
+			return fmt.Errorf("failed to select mailbox: %v", err)
+		}
+	}
+	return nil
+}
+
+type imapMessage struct {
+	*imap.Message
+}
+
+func textPartPath(bs *imap.BodyStructure) ([]int, bool) {
+	if bs.Disposition != "" && !strings.EqualFold(bs.Disposition, "inline") {
+		return nil, false
+	}
+
+	if strings.EqualFold(bs.MIMEType, "text") {
+		return []int{1}, true
+	}
+
+	if !strings.EqualFold(bs.MIMEType, "multipart") {
+		return nil, false
+	}
+
+	textPartNum := -1
+	for i, part := range bs.Parts {
+		num := i + 1
+
+		if strings.EqualFold(part.MIMEType, "multipart") {
+			if subpath, ok := textPartPath(part); ok {
+				return append([]int{num}, subpath...), true
+			}
+		}
+		if !strings.EqualFold(part.MIMEType, "text") {
+			continue
+		}
+
+		var pick bool
+		switch strings.ToLower(part.MIMESubType) {
+		case "plain":
+			pick = true
+		case "html":
+			pick = textPartNum < 0
+		}
+
+		if pick {
+			textPartNum = num
+		}
+	}
+
+	if textPartNum > 0 {
+		return []int{textPartNum}, true
+	}
+	return nil, false
+}
+
+func (msg *imapMessage) TextPartName() string {
+	if msg.BodyStructure == nil {
+		return ""
+	}
+
+	path, ok := textPartPath(msg.BodyStructure)
+	if !ok {
+		return ""
+	}
+
+	l := make([]string, len(path))
+	for i, partNum := range path {
+		l[i] = strconv.Itoa(partNum)
+	}
+
+	return strings.Join(l, ".")
+}
+
+type IMAPPartNode struct {
+	Path     []int
+	MIMEType string
+	Filename string
+	Children []IMAPPartNode
+}
+
+func (node IMAPPartNode) PathString() string {
+	l := make([]string, len(node.Path))
+	for i, partNum := range node.Path {
+		l[i] = strconv.Itoa(partNum)
+	}
+
+	return strings.Join(l, ".")
+}
+
+func (node IMAPPartNode) IsText() bool {
+	return strings.HasPrefix(strings.ToLower(node.MIMEType), "text/")
+}
+
+func (node IMAPPartNode) String() string {
+	if node.Filename != "" {
+		return fmt.Sprintf("%s (%s)", node.Filename, node.MIMEType)
+	} else {
+		return node.MIMEType
+	}
+}
+
+func imapPartTree(bs *imap.BodyStructure, path []int) *IMAPPartNode {
+	if !strings.EqualFold(bs.MIMEType, "multipart") && len(path) == 0 {
+		path = []int{1}
+	}
+
+	filename, _ := bs.Filename()
+
+	node := &IMAPPartNode{
+		Path:     path,
+		MIMEType: strings.ToLower(bs.MIMEType + "/" + bs.MIMESubType),
+		Filename: filename,
+		Children: make([]IMAPPartNode, len(bs.Parts)),
+	}
+
+	for i, part := range bs.Parts {
+		num := i + 1
+
+		partPath := append([]int(nil), path...)
+		partPath = append(partPath, num)
+
+		node.Children[i] = *imapPartTree(part, partPath)
+	}
+
+	return node
+}
+
+func (msg *imapMessage) PartTree() *IMAPPartNode {
+	if msg.BodyStructure == nil {
+		return nil
+	}
+
+	return imapPartTree(msg.BodyStructure, nil)
+}
+
+func listMessages(conn *imapclient.Client, mboxName string, page int) ([]imapMessage, error) {
+	if err := ensureMailboxSelected(conn, mboxName); err != nil {
+		return nil, err
+	}
+
+	mbox := conn.Mailbox()
+	to := int(mbox.Messages) - page*messagesPerPage
+	from := to - messagesPerPage + 1
+	if from <= 0 {
+		from = 1
+	}
+	if to <= 0 {
+		return nil, nil
+	}
+
+	seqSet := new(imap.SeqSet)
+	seqSet.AddRange(uint32(from), uint32(to))
+
+	fetch := []imap.FetchItem{imap.FetchEnvelope, imap.FetchUid, imap.FetchBodyStructure}
+
+	ch := make(chan *imap.Message, 10)
+	done := make(chan error, 1)
+	go func() {
+		done <- conn.Fetch(seqSet, fetch, ch)
+	}()
+
+	msgs := make([]imapMessage, 0, to-from)
+	for msg := range ch {
+		msgs = append(msgs, imapMessage{msg})
+	}
+
+	if err := <-done; err != nil {
+		return nil, fmt.Errorf("failed to fetch message list: %v", err)
+	}
+
+	// Reverse list of messages
+	for i := len(msgs)/2 - 1; i >= 0; i-- {
+		opp := len(msgs) - 1 - i
+		msgs[i], msgs[opp] = msgs[opp], msgs[i]
+	}
+
+	return msgs, nil
+}
+
+func getMessagePart(conn *imapclient.Client, mboxName string, uid uint32, partPath []int) (*imapMessage, *message.Entity, error) {
+	if err := ensureMailboxSelected(conn, mboxName); err != nil {
+		return nil, nil, err
+	}
+
+	seqSet := new(imap.SeqSet)
+	seqSet.AddNum(uid)
+
+	var partHeaderSection imap.BodySectionName
+	partHeaderSection.Peek = true
+	if len(partPath) > 0 {
+		partHeaderSection.Specifier = imap.MIMESpecifier
+	} else {
+		partHeaderSection.Specifier = imap.HeaderSpecifier
+	}
+	partHeaderSection.Path = partPath
+
+	var partBodySection imap.BodySectionName
+	partBodySection.Peek = true
+	if len(partPath) > 0 {
+		partBodySection.Specifier = imap.EntireSpecifier
+	} else {
+		partBodySection.Specifier = imap.TextSpecifier
+	}
+	partBodySection.Path = partPath
+
+	fetch := []imap.FetchItem{
+		imap.FetchEnvelope,
+		imap.FetchUid,
+		imap.FetchBodyStructure,
+		partHeaderSection.FetchItem(),
+		partBodySection.FetchItem(),
+	}
+
+	ch := make(chan *imap.Message, 1)
+	if err := conn.UidFetch(seqSet, fetch, ch); err != nil {
+		return nil, nil, fmt.Errorf("failed to fetch message: %v", err)
+	}
+
+	msg := <-ch
+	if msg == nil {
+		return nil, nil, fmt.Errorf("server didn't return message")
+	}
+
+	headerReader := bufio.NewReader(msg.GetBody(&partHeaderSection))
+	h, err := textproto.ReadHeader(headerReader)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to read part header: %v", err)
+	}
+
+	part, err := message.New(message.Header{h}, msg.GetBody(&partBodySection))
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to create message reader: %v", err)
+	}
+
+	return &imapMessage{msg}, part, nil
+}