12 files changed, 935 insertions, 0 deletions
diff --git a/plugins/base/handlers.go b/plugins/base/handlers.go
new file mode 100644
index 0000000..3160026
--- /dev/null
+++ b/plugins/base/handlers.go
@@ -0,0 +1,285 @@
+package koushinbase
+
+import (
+	"fmt"
+	"io/ioutil"
+	"mime"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"git.sr.ht/~emersion/koushin"
+	"github.com/emersion/go-imap"
+	imapclient "github.com/emersion/go-imap/client"
+	"github.com/emersion/go-message"
+	"github.com/labstack/echo/v4"
+)
+
+type MailboxRenderData struct {
+	koushin.RenderData
+	Mailbox            *imap.MailboxStatus
+	Mailboxes          []*imap.MailboxInfo
+	Messages           []imapMessage
+	PrevPage, NextPage int
+}
+
+func handleGetMailbox(ectx echo.Context) error {
+	ctx := ectx.(*koushin.Context)
+
+	mboxName, err := url.PathUnescape(ctx.Param("mbox"))
+	if err != nil {
+		return echo.NewHTTPError(http.StatusBadRequest, err)
+	}
+
+	page := 0
+	if pageStr := ctx.QueryParam("page"); pageStr != "" {
+		var err error
+		if page, err = strconv.Atoi(pageStr); err != nil || page < 0 {
+			return echo.NewHTTPError(http.StatusBadRequest, "invalid page index")
+		}
+	}
+
+	var mailboxes []*imap.MailboxInfo
+	var msgs []imapMessage
+	var mbox *imap.MailboxStatus
+	err = ctx.Session.Do(func(c *imapclient.Client) error {
+		var err error
+		if mailboxes, err = listMailboxes(c); err != nil {
+			return err
+		}
+		if msgs, err = listMessages(c, mboxName, page); err != nil {
+			return err
+		}
+		mbox = c.Mailbox()
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+
+	prevPage, nextPage := -1, -1
+	if page > 0 {
+		prevPage = page - 1
+	}
+	if (page+1)*messagesPerPage < int(mbox.Messages) {
+		nextPage = page + 1
+	}
+
+	return ctx.Render(http.StatusOK, "mailbox.html", &MailboxRenderData{
+		RenderData: *koushin.NewRenderData(ctx),
+		Mailbox:    mbox,
+		Mailboxes:  mailboxes,
+		Messages:   msgs,
+		PrevPage:   prevPage,
+		NextPage:   nextPage,
+	})
+}
+
+func handleLogin(ectx echo.Context) error {
+	ctx := ectx.(*koushin.Context)
+
+	username := ctx.FormValue("username")
+	password := ctx.FormValue("password")
+	if username != "" && password != "" {
+		s, err := ctx.Server.Sessions.Put(username, password)
+		if err != nil {
+			if _, ok := err.(koushin.AuthError); ok {
+				return ctx.Render(http.StatusOK, "login.html", nil)
+			}
+			return fmt.Errorf("failed to put connection in pool: %v", err)
+		}
+		ctx.SetSession(s)
+
+		return ctx.Redirect(http.StatusFound, "/mailbox/INBOX")
+	}
+
+	return ctx.Render(http.StatusOK, "login.html", koushin.NewRenderData(ctx))
+}
+
+func handleLogout(ectx echo.Context) error {
+	ctx := ectx.(*koushin.Context)
+
+	ctx.Session.Close()
+	ctx.SetSession(nil)
+	return ctx.Redirect(http.StatusFound, "/login")
+}
+
+type MessageRenderData struct {
+	koushin.RenderData
+	Mailbox     *imap.MailboxStatus
+	Message     *imapMessage
+	Body        string
+	PartPath    string
+	MailboxPage int
+}
+
+func handleGetPart(ctx *koushin.Context, raw bool) error {
+	mboxName, uid, err := parseMboxAndUid(ctx.Param("mbox"), ctx.Param("uid"))
+	if err != nil {
+		return echo.NewHTTPError(http.StatusBadRequest, err)
+	}
+	partPathString := ctx.QueryParam("part")
+	partPath, err := parsePartPath(partPathString)
+	if err != nil {
+		return echo.NewHTTPError(http.StatusBadRequest, err)
+	}
+
+	var msg *imapMessage
+	var part *message.Entity
+	var mbox *imap.MailboxStatus
+	err = ctx.Session.Do(func(c *imapclient.Client) error {
+		var err error
+		msg, part, err = getMessagePart(c, mboxName, uid, partPath)
+		mbox = c.Mailbox()
+		return err
+	})
+	if err != nil {
+		return err
+	}
+
+	mimeType, _, err := part.Header.ContentType()
+	if err != nil {
+		return fmt.Errorf("failed to parse part Content-Type: %v", err)
+	}
+	if len(partPath) == 0 {
+		mimeType = "message/rfc822"
+	}
+
+	if raw {
+		disp, dispParams, _ := part.Header.ContentDisposition()
+		filename := dispParams["filename"]
+
+		// TODO: set Content-Length if possible
+
+		if !strings.EqualFold(mimeType, "text/plain") || strings.EqualFold(disp, "attachment") {
+			dispParams := make(map[string]string)
+			if filename != "" {
+				dispParams["filename"] = filename
+			}
+			disp := mime.FormatMediaType("attachment", dispParams)
+			ctx.Response().Header().Set("Content-Disposition", disp)
+		}
+		return ctx.Stream(http.StatusOK, mimeType, part.Body)
+	}
+
+	var body string
+	if strings.HasPrefix(strings.ToLower(mimeType), "text/") {
+		b, err := ioutil.ReadAll(part.Body)
+		if err != nil {
+			return fmt.Errorf("failed to read part body: %v", err)
+		}
+		body = string(b)
+	}
+
+	return ctx.Render(http.StatusOK, "message.html", &MessageRenderData{
+		RenderData:  *koushin.NewRenderData(ctx),
+		Mailbox:     mbox,
+		Message:     msg,
+		Body:        body,
+		PartPath:    partPathString,
+		MailboxPage: int(mbox.Messages-msg.SeqNum) / messagesPerPage,
+	})
+}
+
+type ComposeRenderData struct {
+	koushin.RenderData
+	Message *OutgoingMessage
+}
+
+func handleCompose(ectx echo.Context) error {
+	ctx := ectx.(*koushin.Context)
+
+	var msg OutgoingMessage
+	if strings.ContainsRune(ctx.Session.Username(), '@') {
+		msg.From = ctx.Session.Username()
+	}
+
+	if ctx.Request().Method == http.MethodGet && ctx.Param("uid") != "" {
+		// This is a reply
+		mboxName, uid, err := parseMboxAndUid(ctx.Param("mbox"), ctx.Param("uid"))
+		if err != nil {
+			return echo.NewHTTPError(http.StatusBadRequest, err)
+		}
+		partPath, err := parsePartPath(ctx.QueryParam("part"))
+		if err != nil {
+			return echo.NewHTTPError(http.StatusBadRequest, err)
+		}
+
+		var inReplyTo *imapMessage
+		var part *message.Entity
+		err = ctx.Session.Do(func(c *imapclient.Client) error {
+			var err error
+			inReplyTo, part, err = getMessagePart(c, mboxName, uid, partPath)
+			return err
+		})
+		if err != nil {
+			return err
+		}
+
+		mimeType, _, err := part.Header.ContentType()
+		if err != nil {
+			return fmt.Errorf("failed to parse part Content-Type: %v", err)
+		}
+
+		if !strings.HasPrefix(strings.ToLower(mimeType), "text/") {
+			err := fmt.Errorf("cannot reply to \"%v\" part", mimeType)
+			return echo.NewHTTPError(http.StatusBadRequest, err)
+		}
+
+		msg.Text, err = quote(part.Body)
+		if err != nil {
+			return err
+		}
+
+		msg.InReplyTo = inReplyTo.Envelope.MessageId
+		// TODO: populate From from known user addresses and inReplyTo.Envelope.To
+		replyTo := inReplyTo.Envelope.ReplyTo
+		if len(replyTo) == 0 {
+			replyTo = inReplyTo.Envelope.From
+		}
+		if len(replyTo) > 0 {
+			msg.To = make([]string, len(replyTo))
+			for i, to := range replyTo {
+				msg.To[i] = to.Address()
+			}
+		}
+		msg.Subject = inReplyTo.Envelope.Subject
+		if !strings.HasPrefix(strings.ToLower(msg.Subject), "re:") {
+			msg.Subject = "Re: " + msg.Subject
+		}
+	}
+
+	if ctx.Request().Method == http.MethodPost {
+		msg.From = ctx.FormValue("from")
+		msg.To = parseAddressList(ctx.FormValue("to"))
+		msg.Subject = ctx.FormValue("subject")
+		msg.Text = ctx.FormValue("text")
+		msg.InReplyTo = ctx.FormValue("in_reply_to")
+
+		c, err := ctx.Session.ConnectSMTP()
+		if err != nil {
+			if _, ok := err.(koushin.AuthError); ok {
+				return echo.NewHTTPError(http.StatusForbidden, err)
+			}
+			return err
+		}
+
+		if err := sendMessage(c, &msg); err != nil {
+			return err
+		}
+
+		if err := c.Quit(); err != nil {
+			return fmt.Errorf("QUIT failed: %v", err)
+		}
+
+		// TODO: append to IMAP Sent mailbox
+
+		return ctx.Redirect(http.StatusFound, "/mailbox/INBOX")
+	}
+
+	return ctx.Render(http.StatusOK, "compose.html", &ComposeRenderData{
+		RenderData: *koushin.NewRenderData(ctx),
+		Message:    &msg,
+	})
+}
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
+}
diff --git a/plugins/base/plugin.go b/plugins/base/plugin.go
new file mode 100644
index 0000000..906730d
--- /dev/null
+++ b/plugins/base/plugin.go
@@ -0,0 +1,48 @@
+package koushinbase
+
+import (
+	"html/template"
+	"net/url"
+
+	"git.sr.ht/~emersion/koushin"
+	"github.com/labstack/echo/v4"
+)
+
+const messagesPerPage = 50
+
+func init() {
+	p := koushin.GoPlugin{Name: "base"}
+
+	p.TemplateFuncs(template.FuncMap{
+		"tuple": func(values ...interface{}) []interface{} {
+			return values
+		},
+		"pathescape": func(s string) string {
+			return url.PathEscape(s)
+		},
+	})
+
+	p.GET("/mailbox/:mbox", handleGetMailbox)
+
+	p.GET("/message/:mbox/:uid", func(ectx echo.Context) error {
+		ctx := ectx.(*koushin.Context)
+		return handleGetPart(ctx, false)
+	})
+	p.GET("/message/:mbox/:uid/raw", func(ectx echo.Context) error {
+		ctx := ectx.(*koushin.Context)
+		return handleGetPart(ctx, true)
+	})
+
+	p.GET("/login", handleLogin)
+	p.POST("/login", handleLogin)
+
+	p.GET("/logout", handleLogout)
+
+	p.GET("/compose", handleCompose)
+	p.POST("/compose", handleCompose)
+
+	p.GET("/message/:mbox/:uid/reply", handleCompose)
+	p.POST("/message/:mbox/:uid/reply", handleCompose)
+
+	koushin.RegisterPlugin(p.Plugin())
+}
diff --git a/plugins/base/public/assets/style.css b/plugins/base/public/assets/style.css
new file mode 100644
index 0000000..8f414f5
--- /dev/null
+++ b/plugins/base/public/assets/style.css
@@ -0,0 +1 @@
+/* TODO */
diff --git a/plugins/base/public/compose.html b/plugins/base/public/compose.html
new file mode 100644
index 0000000..2a52675
--- /dev/null
+++ b/plugins/base/public/compose.html
@@ -0,0 +1,26 @@
+{{template "head.html"}}
+
+<h1>koushin</h1>
+
+<p>
+	<a href="/mailbox/INBOX">Back</a>
+</p>
+
+<h2>Compose new message</h2>
+
+<form method="post" action="">
+	<input type="hidden" name="in_reply_to" value="{{.Message.InReplyTo}}">
+
+	<p>From:</p>
+	<input type="email" name="from" value="{{.Message.From}}">
+	<p>To:</p>
+	<input type="email" name="to" multiple value="{{.Message.ToString}}">
+	<p>Subject:</p>
+	<input type="text" name="subject" value="{{.Message.Subject}}">
+	<p>Body:</p>
+	<textarea name="text" cols="80" rows="20">{{.Message.Text}}</textarea>
+	<br><br>
+	<input type="submit" value="Send">
+</form>
+
+{{template "foot.html"}}
diff --git a/plugins/base/public/foot.html b/plugins/base/public/foot.html
new file mode 100644
index 0000000..b605728
--- /dev/null
+++ b/plugins/base/public/foot.html
@@ -0,0 +1,2 @@
+  </body>
+</html>
diff --git a/plugins/base/public/head.html b/plugins/base/public/head.html
new file mode 100644
index 0000000..bed1bb3
--- /dev/null
+++ b/plugins/base/public/head.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <title>koushin</title>
+    <link rel="stylesheet" href="/plugins/base/assets/style.css">
+  </head>
+  <body>
diff --git a/plugins/base/public/login.html b/plugins/base/public/login.html
new file mode 100644
index 0000000..6ae1737
--- /dev/null
+++ b/plugins/base/public/login.html
@@ -0,0 +1,14 @@
+{{template "head.html"}}
+
+<h1>koushin</h1>
+
+<form method="post" action="/login">
+	<label for="username">Username:</label>
+	<input type="text" name="username" id="username"/>
+	<label for="password">Password:</label>
+	<input type="password" name="password" id="password"/>
+	<br><br>
+	<input type="submit" value="Login">
+</form>
+
+{{template "foot.html"}}
diff --git a/plugins/base/public/mailbox.html b/plugins/base/public/mailbox.html
new file mode 100644
index 0000000..ddd1260
--- /dev/null
+++ b/plugins/base/public/mailbox.html
@@ -0,0 +1,45 @@
+{{template "head.html"}}
+
+<h1>koushin</h1>
+
+<p>
+	<a href="/logout">Logout</a> · <a href="/compose">Compose</a>
+</p>
+
+<h2>{{.Mailbox.Name}}</h2>
+
+<p>Mailboxes:</p>
+<ul>
+	{{range .Mailboxes}}
+		<li><a href="/mailbox/{{.Name | pathescape}}">{{.Name}}</a></li>
+	{{end}}
+</ul>
+
+{{if .Messages}}
+	<p>Messages:</p>
+	<ul>
+		{{range .Messages}}
+			<li><a href="/message/{{$.Mailbox.Name | pathescape}}/{{.Uid}}?part={{.TextPartName}}">
+				{{if .Envelope.Subject}}
+					{{.Envelope.Subject}}
+				{{else}}
+					(No subject)
+				{{end}}
+			</a></li>
+		{{end}}
+	</ul>
+
+	<p>
+		{{if ge .PrevPage 0}}
+			<a href="?page={{.PrevPage}}">Prev</a>
+		{{end}}
+		{{if and (ge .PrevPage 0) (ge .NextPage 0)}}·{{end}}
+		{{if ge .NextPage 0}}
+			<a href="?page={{.NextPage}}">Next</a>
+		{{end}}
+	</p>
+{{else}}
+	<p>Mailbox is empty.</p>
+{{end}}
+
+{{template "foot.html"}}
diff --git a/plugins/base/public/message.html b/plugins/base/public/message.html
new file mode 100644
index 0000000..729937d
--- /dev/null
+++ b/plugins/base/public/message.html
@@ -0,0 +1,58 @@
+{{template "head.html"}}
+
+<h1>koushin</h1>
+
+<p>
+	<a href="/mailbox/{{.Mailbox.Name | pathescape}}?page={{.MailboxPage}}">
+		Back
+	</a>
+</p>
+
+<h2>
+	{{if .Message.Envelope.Subject}}
+		{{.Message.Envelope.Subject}}
+	{{else}}
+		(No subject)
+	{{end}}
+</h2>
+
+{{define "message-part-tree"}}
+	{{/* nested templates can't access the parent's context */}}
+	{{$ = index . 0}}
+	{{with index . 1}}
+		<a
+			{{if .IsText}}
+				href="{{$.Message.Uid}}?part={{.PathString}}"
+			{{else}}
+				href="{{$.Message.Uid}}/raw?part={{.PathString}}"
+			{{end}}
+		>
+			{{if eq $.PartPath .PathString}}<strong>{{end}}
+			{{.String}}
+			{{if eq $.PartPath .PathString}}</strong>{{end}}
+		</a>
+		{{if gt (len .Children) 0}}
+		<ul>
+			{{range .Children}}
+				<li>{{template "message-part-tree" (tuple $ .)}}</li>
+			{{end}}
+		</ul>
+		{{end}}
+	{{end}}
+{{end}}
+
+<p>Parts:</p>
+
+{{template "message-part-tree" (tuple $ .Message.PartTree)}}
+
+<hr>
+
+{{if .Body}}
+	<p><a href="{{.Message.Uid}}/reply?part={{.PartPath}}">Reply</a></p>
+	<pre>{{.Body}}</pre>
+{{else}}
+	<p>Can't preview this message part.</p>
+	<a href="{{.Message.Uid}}/raw?part={{.PartPath}}">Download</a>
+{{end}}
+
+{{template "foot.html"}}
diff --git a/plugins/base/smtp.go b/plugins/base/smtp.go
new file mode 100644
index 0000000..9ade78f
--- /dev/null
+++ b/plugins/base/smtp.go
@@ -0,0 +1,114 @@
+package koushinbase
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strings"
+	"time"
+
+	"github.com/emersion/go-message/mail"
+	"github.com/emersion/go-smtp"
+)
+
+func quote(r io.Reader) (string, error) {
+	scanner := bufio.NewScanner(r)
+	var builder strings.Builder
+	for scanner.Scan() {
+		builder.WriteString("> ")
+		builder.Write(scanner.Bytes())
+		builder.WriteString("\n")
+	}
+	if err := scanner.Err(); err != nil {
+		return "", fmt.Errorf("quote: failed to read original message: %s", err)
+	}
+	return builder.String(), nil
+}
+
+type OutgoingMessage struct {
+	From      string
+	To        []string
+	Subject   string
+	InReplyTo string
+	Text      string
+}
+
+func (msg *OutgoingMessage) ToString() string {
+	return strings.Join(msg.To, ", ")
+}
+
+func (msg *OutgoingMessage) WriteTo(w io.Writer) error {
+	from := []*mail.Address{{"", msg.From}}
+
+	to := make([]*mail.Address, len(msg.To))
+	for i, addr := range msg.To {
+		to[i] = &mail.Address{"", addr}
+	}
+
+	var h mail.Header
+	h.SetDate(time.Now())
+	h.SetAddressList("From", from)
+	h.SetAddressList("To", to)
+	if msg.Subject != "" {
+		h.SetText("Subject", msg.Subject)
+	}
+	if msg.InReplyTo != "" {
+		h.Set("In-Reply-To", msg.InReplyTo)
+	}
+
+	mw, err := mail.CreateWriter(w, h)
+	if err != nil {
+		return fmt.Errorf("failed to create mail writer: %v", err)
+	}
+
+	var th mail.InlineHeader
+	th.Set("Content-Type", "text/plain; charset=utf-8")
+
+	tw, err := mw.CreateSingleInline(th)
+	if err != nil {
+		return fmt.Errorf("failed to create text part: %v", err)
+	}
+	defer tw.Close()
+
+	if _, err := io.WriteString(tw, msg.Text); err != nil {
+		return fmt.Errorf("failed to write text part: %v", err)
+	}
+
+	if err := tw.Close(); err != nil {
+		return fmt.Errorf("failed to close text part: %v", err)
+	}
+
+	if err := mw.Close(); err != nil {
+		return fmt.Errorf("failed to close mail writer: %v", err)
+	}
+
+	return nil
+}
+
+func sendMessage(c *smtp.Client, msg *OutgoingMessage) error {
+	if err := c.Mail(msg.From, nil); err != nil {
+		return fmt.Errorf("MAIL FROM failed: %v", err)
+	}
+
+	for _, to := range msg.To {
+		if err := c.Rcpt(to); err != nil {
+			return fmt.Errorf("RCPT TO failed: %v", err)
+		}
+	}
+
+	w, err := c.Data()
+	if err != nil {
+		return fmt.Errorf("DATA failed: %v", err)
+	}
+	defer w.Close()
+
+	if err := msg.WriteTo(w); err != nil {
+		return fmt.Errorf("failed to write outgoing message: %v", err)
+	}
+
+	if err := w.Close(); err != nil {
+		return fmt.Errorf("failed to close SMTP data writer: %v", err)
+	}
+
+	return nil
+}
diff --git a/plugins/base/strconv.go b/plugins/base/strconv.go
new file mode 100644
index 0000000..1a32e75
--- /dev/null
+++ b/plugins/base/strconv.go
@@ -0,0 +1,57 @@
+package koushinbase
+
+import (
+	"fmt"
+	"net/url"
+	"strconv"
+	"strings"
+)
+
+func parseUid(s string) (uint32, error) {
+	uid, err := strconv.ParseUint(s, 10, 32)
+	if err != nil {
+		return 0, fmt.Errorf("invalid UID: %v", err)
+	}
+	if uid == 0 {
+		return 0, fmt.Errorf("UID must be non-zero")
+	}
+	return uint32(uid), nil
+}
+
+func parseMboxAndUid(mboxString, uidString string) (string, uint32, error) {
+	mboxName, err := url.PathUnescape(mboxString)
+	if err != nil {
+		return "", 0, fmt.Errorf("invalid mailbox name: %v", err)
+	}
+	uid, err := parseUid(uidString)
+	return mboxName, uid, err
+}
+
+func parsePartPath(s string) ([]int, error) {
+	if s == "" {
+		return nil, nil
+	}
+
+	l := strings.Split(s, ".")
+	path := make([]int, len(l))
+	for i, s := range l {
+		var err error
+		path[i], err = strconv.Atoi(s)
+		if err != nil {
+			return nil, err
+		}
+
+		if path[i] <= 0 {
+			return nil, fmt.Errorf("part num must be strictly positive")
+		}
+	}
+	return path, nil
+}
+
+func parseAddressList(s string) []string {
+	l := strings.Split(s, ",")
+	for i, addr := range l {
+		l[i] = strings.TrimSpace(addr)
+	}
+	return l
+}