imapserver: add COMPRESS

imapserver/capability.go

@@ -57,6 +57,9 @@ func (c *Conn) availableCaps() []imap.Cap {
 	} else if c.state == imap.ConnStateNotAuthenticated {
 		caps = append(caps, imap.CapLoginDisabled)
 	}
+	if c.canCompress() {
+		caps = append(caps, imap.Cap("COMPRESS=DEFLATE"))
+	}
 	if c.state == imap.ConnStateAuthenticated || c.state == imap.ConnStateSelected {
 		if available.Has(imap.CapIMAP4rev1) {
 			caps = append(caps, []imap.Cap{

imapserver/compress.go

@@ -0,0 +1,86 @@
+package imapserver
+
+import (
+	"bytes"
+	"compress/flate"
+	"io"
+
+	"github.com/emersion/go-imap/v2"
+	"github.com/emersion/go-imap/v2/internal/imapwire"
+)
+
+func (c *Conn) canCompress() bool {
+	switch c.state {
+	case imap.ConnStateAuthenticated, imap.ConnStateSelected:
+		return true // TODO
+	default:
+		return false
+	}
+}
+
+func (c *Conn) handleCompress(tag string, dec *imapwire.Decoder) error {
+	var algo string
+	if !dec.ExpectSP() || !dec.ExpectAtom(&algo) || !dec.ExpectCRLF() {
+		return dec.Err()
+	}
+
+	if !c.canCompress() {
+		return &imap.Error{
+			Type: imap.StatusResponseTypeBad,
+			Text: "COMPRESS not available",
+		}
+	}
+	if algo != "DEFLATE" {
+		return &imap.Error{
+			Type: imap.StatusResponseTypeNo,
+			Text: "Unsupported compression algorithm",
+		}
+	}
+
+	// Do not allow to write uncompressed data past this point: keep c.encMutex
+	// locked until the end
+	enc := newResponseEncoder(c)
+	defer enc.end()
+
+	err := writeStatusResp(enc.Encoder, tag, &imap.StatusResponse{
+		Type: imap.StatusResponseTypeOK,
+		Text: "Begin compression now",
+	})
+	if err != nil {
+		return err
+	}
+
+	// Drain buffered data from our bufio.Reader
+	var buf bytes.Buffer
+	if _, err := io.CopyN(&buf, c.br, int64(c.br.Buffered())); err != nil {
+		panic(err) // unreachable
+	}
+
+	var r io.Reader
+	if buf.Len() > 0 {
+		r = io.MultiReader(&buf, c.conn)
+	} else {
+		r = c.conn
+	}
+
+	c.mutex.Lock()
+	// TODO
+	c.mutex.Unlock()
+
+	w, err := flate.NewWriter(c.conn, flate.DefaultCompression)
+	if err != nil {
+		panic(err) // can only happen due to bad arguments
+	}
+
+	rw := c.server.options.wrapReadWriter(struct {
+		io.Reader
+		io.Writer
+	}{
+		Reader: flate.NewReader(r),
+		Writer: w,
+	})
+	c.br.Reset(rw)
+	c.bw.Reset(rw)
+
+	return nil
+}

imapserver/conn.go

@@ -266,6 +266,8 @@ func (c *Conn) readCommand(dec *imapwire.Decoder) error {
 		err = c.handleMove(dec, numKind)
 	case "SEARCH", "UID SEARCH":
 		err = c.handleSearch(tag, dec, numKind)
+	case "COMPRESS":
+		err = c.handleCompress(tag, dec)
 	default:
 		if c.state == imap.ConnStateNotAuthenticated {
 			// Don't allow a single unknown command before authentication to