Introduce base plugin

This plugin offers base IMAP/SMTP functionality.

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

22 files changed, 521 insertions, 450 deletions

diff --git a/.gitignore b/.gitignore
index c7cfe55..b7d2b50 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 /public/themes/*
 !/public/themes/sourcehut
 /plugins/*
+!/plugins/base
diff --git a/README.md b/README.md
index 74706d3..1ca62d5 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ They should be put in `public/themes/<name>/`.
 
 Templates in `public/themes/<name>/*.html` override default templates in
 `public/*.html`. Assets in `public/themes/<name>/assets/*` are served by the
-HTTP server at `themes/<name>/assets/*`.
+HTTP server at `/themes/<name>/assets/*`.
 
 ## Plugins
 
@@ -29,6 +29,8 @@ API:
   called with the HTTP context
 
 Plugins can provide their own templates in `plugins/<name>/public/*.html`.
+Assets in `plugins/<name>/public/assets/*` are served by the HTTP server at
+`/plugins/<name>/assets/*`.
 
 ## Contributing
 
diff --git a/cmd/koushin/main.go b/cmd/koushin/main.go
index e644884..c9df12b 100644
--- a/cmd/koushin/main.go
+++ b/cmd/koushin/main.go
@@ -8,6 +8,8 @@ import (
 	"github.com/labstack/echo/v4"
 	"github.com/labstack/echo/v4/middleware"
 	"github.com/labstack/gommon/log"
+
+	_ "git.sr.ht/~emersion/koushin/plugins/base"
 )
 
 func main() {
diff --git a/imap.go b/imap.go
index 0e0edc1..2a43dd1 100644
--- a/imap.go
+++ b/imap.go
@@ -1,24 +1,18 @@
 package koushin
 
 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/charset"
-	"github.com/emersion/go-message/textproto"
 )
 
 func init() {
 	imap.CharsetReader = charset.Reader
 }
 
-func (s *Server) connectIMAP() (*imapclient.Client, error) {
+func (s *Server) dialIMAP() (*imapclient.Client, error) {
 	var c *imapclient.Client
 	var err error
 	if s.imap.tls {
@@ -41,266 +35,3 @@ func (s *Server) connectIMAP() (*imapclient.Client, error) {
 
 	return c, err
 }
-
-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/plugin_go.go b/plugin_go.go
index 30858b5..1ae0562 100644
--- a/plugin_go.go
+++ b/plugin_go.go
@@ -37,7 +37,7 @@ func (p *goPlugin) SetRoutes(group *echo.Group) {
 		group.Add(r.Method, r.Path, r.Handler)
 	}
 
-	group.Static("/assets", pluginDir + "/" + p.p.Name + "/public/assets")
+	group.Static("/plugins/" + p.p.Name + "/assets", pluginDir + "/" + p.p.Name + "/public/assets")
 }
 
 func (p *goPlugin) Inject(name string, data interface{}) error {
diff --git a/plugin_lua.go b/plugin_lua.go
index 9354de7..55c1d10 100644
--- a/plugin_lua.go
+++ b/plugin_lua.go
@@ -117,6 +117,9 @@ func (p *luaPlugin) SetRoutes(group *echo.Group) {
 			return nil
 		})
 	}
+
+	_, name := filepath.Split(filepath.Dir(p.filename))
+	group.Static("/plugins/" + name + "/assets", filepath.Dir(p.filename) + "/public/assets")
 }
 
 func (p *luaPlugin) Close() error {
diff --git a/handlers.go b/plugins/base/handlers.go
index f53085c..3160026 100644
--- a/handlers.go
+++ b/plugins/base/handlers.go
@@ -1,4 +1,4 @@
-package koushin
+package koushinbase
 
 import (
 	"fmt"
@@ -9,15 +9,15 @@ import (
 	"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/emersion/go-sasl"
 	"github.com/labstack/echo/v4"
 )
 
 type MailboxRenderData struct {
-	RenderData
+	koushin.RenderData
 	Mailbox            *imap.MailboxStatus
 	Mailboxes          []*imap.MailboxInfo
 	Messages           []imapMessage
@@ -25,7 +25,7 @@ type MailboxRenderData struct {
 }
 
 func handleGetMailbox(ectx echo.Context) error {
-	ctx := ectx.(*Context)
+	ctx := ectx.(*koushin.Context)
 
 	mboxName, err := url.PathUnescape(ctx.Param("mbox"))
 	if err != nil {
@@ -67,7 +67,7 @@ func handleGetMailbox(ectx echo.Context) error {
 	}
 
 	return ctx.Render(http.StatusOK, "mailbox.html", &MailboxRenderData{
-		RenderData: *NewRenderData(ctx),
+		RenderData: *koushin.NewRenderData(ctx),
 		Mailbox:    mbox,
 		Mailboxes:  mailboxes,
 		Messages:   msgs,
@@ -77,14 +77,14 @@ func handleGetMailbox(ectx echo.Context) error {
 }
 
 func handleLogin(ectx echo.Context) error {
-	ctx := ectx.(*Context)
+	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.(AuthError); ok {
+			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)
@@ -94,11 +94,11 @@ func handleLogin(ectx echo.Context) error {
 		return ctx.Redirect(http.StatusFound, "/mailbox/INBOX")
 	}
 
-	return ctx.Render(http.StatusOK, "login.html", NewRenderData(ctx))
+	return ctx.Render(http.StatusOK, "login.html", koushin.NewRenderData(ctx))
 }
 
 func handleLogout(ectx echo.Context) error {
-	ctx := ectx.(*Context)
+	ctx := ectx.(*koushin.Context)
 
 	ctx.Session.Close()
 	ctx.SetSession(nil)
@@ -106,7 +106,7 @@ func handleLogout(ectx echo.Context) error {
 }
 
 type MessageRenderData struct {
-	RenderData
+	koushin.RenderData
 	Mailbox     *imap.MailboxStatus
 	Message     *imapMessage
 	Body        string
@@ -114,7 +114,7 @@ type MessageRenderData struct {
 	MailboxPage int
 }
 
-func handleGetPart(ctx *Context, raw bool) error {
+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)
@@ -173,7 +173,7 @@ func handleGetPart(ctx *Context, raw bool) error {
 	}
 
 	return ctx.Render(http.StatusOK, "message.html", &MessageRenderData{
-		RenderData:  *NewRenderData(ctx),
+		RenderData:  *koushin.NewRenderData(ctx),
 		Mailbox:     mbox,
 		Message:     msg,
 		Body:        body,
@@ -183,16 +183,16 @@ func handleGetPart(ctx *Context, raw bool) error {
 }
 
 type ComposeRenderData struct {
-	RenderData
+	koushin.RenderData
 	Message *OutgoingMessage
 }
 
 func handleCompose(ectx echo.Context) error {
-	ctx := ectx.(*Context)
+	ctx := ectx.(*koushin.Context)
 
 	var msg OutgoingMessage
-	if strings.ContainsRune(ctx.Session.username, '@') {
-		msg.From = ctx.Session.username
+	if strings.ContainsRune(ctx.Session.Username(), '@') {
+		msg.From = ctx.Session.Username()
 	}
 
 	if ctx.Request().Method == http.MethodGet && ctx.Param("uid") != "" {
@@ -257,16 +257,13 @@ func handleCompose(ectx echo.Context) error {
 		msg.Text = ctx.FormValue("text")
 		msg.InReplyTo = ctx.FormValue("in_reply_to")
 
-		c, err := ctx.Server.connectSMTP()
+		c, err := ctx.Session.ConnectSMTP()
 		if err != nil {
+			if _, ok := err.(koushin.AuthError); ok {
+				return echo.NewHTTPError(http.StatusForbidden, err)
+			}
 			return err
 		}
-		defer c.Close()
-
-		auth := sasl.NewPlainClient("", ctx.Session.username, ctx.Session.password)
-		if err := c.Auth(auth); err != nil {
-			return echo.NewHTTPError(http.StatusForbidden, err)
-		}
 
 		if err := sendMessage(c, &msg); err != nil {
 			return err
@@ -282,7 +279,7 @@ func handleCompose(ectx echo.Context) error {
 	}
 
 	return ctx.Render(http.StatusOK, "compose.html", &ComposeRenderData{
-		RenderData: *NewRenderData(ctx),
+		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/public/assets/style.css b/plugins/base/public/assets/style.css
index 8f414f5..8f414f5 100644
--- a/public/assets/style.css
+++ b/plugins/base/public/assets/style.css
diff --git a/public/compose.html b/plugins/base/public/compose.html
index 2a52675..2a52675 100644
--- a/public/compose.html
+++ b/plugins/base/public/compose.html
diff --git a/public/foot.html b/plugins/base/public/foot.html
index b605728..b605728 100644
--- a/public/foot.html
+++ b/plugins/base/public/foot.html
diff --git a/public/head.html b/plugins/base/public/head.html
index 35dda42..bed1bb3 100644
--- a/public/head.html
+++ b/plugins/base/public/head.html
@@ -3,6 +3,6 @@
   <head>
     <meta charset="utf-8">
     <title>koushin</title>
-    <link rel="stylesheet" href="/assets/style.css">
+    <link rel="stylesheet" href="/plugins/base/assets/style.css">
   </head>
   <body>
diff --git a/public/login.html b/plugins/base/public/login.html
index 6ae1737..6ae1737 100644
--- a/public/login.html
+++ b/plugins/base/public/login.html
diff --git a/public/mailbox.html b/plugins/base/public/mailbox.html
index ddd1260..ddd1260 100644
--- a/public/mailbox.html
+++ b/plugins/base/public/mailbox.html
diff --git a/public/message.html b/plugins/base/public/message.html
index 729937d..729937d 100644
--- a/public/message.html
+++ b/plugins/base/public/message.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/strconv.go b/plugins/base/strconv.go
index 63cbffc..1a32e75 100644
--- a/strconv.go
+++ b/plugins/base/strconv.go
@@ -1,4 +1,4 @@
-package koushin
+package koushinbase
 
 import (
 	"fmt"
diff --git a/server.go b/server.go
index 98b5fb2..f2d4c11 100644
--- a/server.go
+++ b/server.go
@@ -12,8 +12,6 @@ import (
 
 const cookieName = "koushin_session"
 
-const messagesPerPage = 50
-
 // Server holds all the koushin server state.
 type Server struct {
 	Sessions *SessionManager
@@ -76,7 +74,6 @@ func (s *Server) parseSMTPURL(smtpURL string) error {
 
 func newServer(imapURL, smtpURL string) (*Server, error) {
 	s := &Server{}
-	s.Sessions = newSessionManager(s.connectIMAP)
 
 	if err := s.parseIMAPURL(imapURL); err != nil {
 		return nil, err
@@ -88,6 +85,8 @@ func newServer(imapURL, smtpURL string) (*Server, error) {
 		}
 	}
 
+	s.Sessions = newSessionManager(s.dialIMAP, s.dialSMTP)
+
 	return s, nil
 }
 
@@ -121,8 +120,11 @@ func (ctx *Context) SetSession(s *Session) {
 }
 
 func isPublic(path string) bool {
-	return path == "/login" || strings.HasPrefix(path, "/assets/") ||
-		strings.HasPrefix(path, "/themes/")
+	if strings.HasPrefix(path, "/plugins/") {
+		parts := strings.Split(path, "/")
+		return len(parts) >= 4 && parts[3] == "assets"
+	}
+	return path == "/login" || strings.HasPrefix(path, "/themes/")
 }
 
 type Options struct {
@@ -194,29 +196,6 @@ func New(e *echo.Echo, options *Options) error {
 		}
 	})
 
-	e.GET("/mailbox/:mbox", handleGetMailbox)
-
-	e.GET("/message/:mbox/:uid", func(ectx echo.Context) error {
-		ctx := ectx.(*Context)
-		return handleGetPart(ctx, false)
-	})
-	e.GET("/message/:mbox/:uid/raw", func(ectx echo.Context) error {
-		ctx := ectx.(*Context)
-		return handleGetPart(ctx, true)
-	})
-
-	e.GET("/login", handleLogin)
-	e.POST("/login", handleLogin)
-
-	e.GET("/logout", handleLogout)
-
-	e.GET("/compose", handleCompose)
-	e.POST("/compose", handleCompose)
-
-	e.GET("/message/:mbox/:uid/reply", handleCompose)
-	e.POST("/message/:mbox/:uid/reply", handleCompose)
-
-	e.Static("/assets", "public/assets")
 	e.Static("/themes", "public/themes")
 
 	for _, p := range s.Plugins {
diff --git a/session.go b/session.go
index 8fafd57..8f3f748 100644
--- a/session.go
+++ b/session.go
@@ -9,6 +9,8 @@ import (
 	"time"
 
 	imapclient "github.com/emersion/go-imap/client"
+	"github.com/emersion/go-smtp"
+	"github.com/emersion/go-sasl"
 )
 
 // TODO: make this configurable
@@ -51,6 +53,11 @@ func (s *Session) ping() {
 	s.pings <- struct{}{}
 }
 
+// Username returns the session's username.
+func (s *Session) Username() string {
+	return s.username
+}
+
 // Do executes an IMAP operation on this session. The IMAP client can only be
 // used from inside f.
 func (s *Session) Do(f func(*imapclient.Client) error) error {
@@ -69,6 +76,23 @@ func (s *Session) Do(f func(*imapclient.Client) error) error {
 	return f(s.imapConn)
 }
 
+// ConnectSMTP connects to the upstream SMTP server and authenticates this
+// session.
+func (s *Session) ConnectSMTP() (*smtp.Client, error) {
+	c, err := s.manager.dialSMTP()
+	if err != nil {
+		return nil, err
+	}
+
+	auth := sasl.NewPlainClient("", s.username, s.password)
+	if err := c.Auth(auth); err != nil {
+		c.Close()
+		return nil, AuthError{err}
+	}
+
+	return c, nil
+}
+
 // Close destroys the session. This can be used to log the user out.
 func (s *Session) Close() {
 	select {
@@ -79,24 +103,33 @@ func (s *Session) Close() {
 	}
 }
 
+type (
+	// DialIMAPFunc connects to the upstream IMAP server.
+	DialIMAPFunc func() (*imapclient.Client, error)
+	// DialSMTPFunc connects to the upstream SMTP server.
+	DialSMTPFunc func() (*smtp.Client, error)
+)
+
 // SessionManager keeps track of active sessions. It connects and re-connects
 // to the upstream IMAP server as necessary. It prunes expired sessions.
 type SessionManager struct {
-	newIMAPClient func() (*imapclient.Client, error)
+	dialIMAP DialIMAPFunc
+	dialSMTP DialSMTPFunc
 
 	locker   sync.Mutex
 	sessions map[string]*Session // protected by locker
 }
 
-func newSessionManager(newIMAPClient func() (*imapclient.Client, error)) *SessionManager {
+func newSessionManager(dialIMAP DialIMAPFunc, dialSMTP DialSMTPFunc) *SessionManager {
 	return &SessionManager{
 		sessions:      make(map[string]*Session),
-		newIMAPClient: newIMAPClient,
+		dialIMAP: dialIMAP,
+		dialSMTP: dialSMTP,
 	}
 }
 
 func (sm *SessionManager) connect(username, password string) (*imapclient.Client, error) {
-	c, err := sm.newIMAPClient()
+	c, err := sm.dialIMAP()
 	if err != nil {
 		return nil, err
 	}
diff --git a/smtp.go b/smtp.go
index b9d77b2..0eabf4d 100644
--- a/smtp.go
+++ b/smtp.go
@@ -1,31 +1,16 @@
 package koushin
 
 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")
+func (s *Server) dialSMTP() (*smtp.Client, error) {
+	if s.smtp.host == "" {
+		return nil, fmt.Errorf("SMTP is disabled")
 	}
-	if err := scanner.Err(); err != nil {
-		return "", fmt.Errorf("quote: failed to read original message: %s", err)
-	}
-	return builder.String(), nil
-}
 
-func (s *Server) connectSMTP() (*smtp.Client, error) {
 	var c *smtp.Client
 	var err error
 	if s.smtp.tls {
@@ -48,91 +33,3 @@ func (s *Server) connectSMTP() (*smtp.Client, error) {
 
 	return c, err
 }
-
-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/template.go b/template.go
index cdcbf66..e5078c5 100644
--- a/template.go
+++ b/template.go
@@ -5,7 +5,6 @@ import (
 	"html/template"
 	"io"
 	"io/ioutil"
-	"net/url"
 	"os"
 
 	"github.com/labstack/echo/v4"
@@ -86,19 +85,7 @@ func loadTheme(name string, base *template.Template) (*template.Template, error)
 }
 
 func loadTemplates(logger echo.Logger, defaultTheme string, plugins []Plugin) (*renderer, error) {
-	base := template.New("").Funcs(template.FuncMap{
-		"tuple": func(values ...interface{}) []interface{} {
-			return values
-		},
-		"pathescape": func(s string) string {
-			return url.PathEscape(s)
-		},
-	})
-
-	base, err := base.ParseGlob("public/*.html")
-	if err != nil {
-		return nil, err
-	}
+	base := template.New("")
 
 	for _, p := range plugins {
 		if err := p.LoadTemplate(base); err != nil {