Merge support for APPENDLIMIT extension

Author: foxcpp

README.md

@@ -134,6 +134,7 @@ includes:
 * [SPECIAL-USE](https://tools.ietf.org/html/rfc6154)
 * [CHILDREN](https://tools.ietf.org/html/rfc3348)
 * [UNSELECT](https://tools.ietf.org/html/rfc3691)
+* [APPENDLIMIT](https://tools.ietf.org/html/rfc7889)
 
 Support for other extensions is provided via separate packages. See below.
 
@@ -145,7 +146,6 @@ Commands defined in IMAP extensions are available in other packages. See [the
 wiki](https://github.com/emersion/go-imap/wiki/Using-extensions#using-client-extensions)
 to learn how to use them.
 
-* [APPENDLIMIT](https://github.com/emersion/go-imap-appendlimit)
 * [COMPRESS](https://github.com/emersion/go-imap-compress)
 * [ENABLE](https://github.com/emersion/go-imap-enable)
 * [ID](https://github.com/ProtonMail/go-imap-id)

backend/appendlimit.go

@@ -0,0 +1,29 @@
+package backend
+
+import (
+"errors"
+)
+
+// An error that should be returned by User.CreateMessage when the message size
+// is too big.
+var ErrTooBig = errors.New("Message size exceeding limit")
+
+// A backend that supports retrieving per-user message size limits.
+type AppendLimitBackend interface {
+Backend
+
+// Get the fixed maximum message size in octets that the backend will accept
+// when creating a new message. If there is no limit, return nil.
+CreateMessageLimit() *uint32
+}
+
+// A user that supports retrieving per-user message size limits.
+type AppendLimitUser interface {
+User
+
+// Get the fixed maximum message size in octets that the backend will accept
+// when creating a new message. If there is no limit, return nil.
+//
+// This overrides the global backend limit.
+CreateMessageLimit() *uint32
+}

imap.go

@@ -17,6 +17,8 @@ const (
 StatusUidNext StatusItem = "UIDNEXT"
 StatusUidValidity StatusItem = "UIDVALIDITY"
 StatusUnseen StatusItem = "UNSEEN"
+
+StatusAppendLimit StatusItem = "APPENDLIMIT"
 )
 
 // A FetchItem is a message data item that can be fetched.

mailbox.go

@@ -221,6 +221,10 @@ type MailboxStatus struct {
 // Together with a UID, it is a unique identifier for a message.
 // Must be greater than or equal to 1.
 UidValidity uint32
+
+// Per-mailbox limit of message size. Set only if server supports the
+// APPENDLIMIT extension.
+AppendLimit uint32
 }
 
 // Create a new mailbox status that will contain the specified items.
@@ -263,6 +267,8 @@ func (status *MailboxStatus) Parse(fields []interface{}) error {
 status.UidNext, err = ParseNumber(f)
 case StatusUidValidity:
 status.UidValidity, err = ParseNumber(f)
+case StatusAppendLimit:
+status.AppendLimit, err = ParseNumber(f)
 default:
 status.Items[k] = f
 }
@@ -290,6 +296,8 @@ func (status *MailboxStatus) Format() []interface{} {
 v = status.UidNext
 case StatusUidValidity:
 v = status.UidValidity
+case StatusAppendLimit:
+v = status.AppendLimit
 }
 
 fields = append(fields, RawString(k), v)

server/cmd_auth.go

@@ -253,6 +253,13 @@ func (cmd *Append) Handle(conn Conn) error {
 }
 
 if err := mbox.CreateMessage(cmd.Flags, cmd.Date, cmd.Message); err != nil {
+if err == backend.ErrTooBig {
+return ErrStatusResp(&imap.StatusResp{
+Type: imap.StatusRespNo,
+Code: "TOOBIG",
+Info: "Message size exceeding limit",
+})
+}
 return err
 }
 

server/conn.go

@@ -165,6 +165,24 @@ func (c *conn) Close() error {
 func (c *conn) Capabilities() []string {
 caps := []string{"IMAP4rev1", "LITERAL+", "SASL-IR", "CHILDREN", "UNSELECT"}
 
+appendLimitSet := false
+if c.ctx.State == imap.AuthenticatedState {
+if u, ok := c.ctx.User.(backend.AppendLimitUser); ok {
+if limit := u.CreateMessageLimit(); limit != nil {
+caps = append(caps, fmt.Sprintf("APPENDLIMIT=%v", *limit))
+appendLimitSet = true
+}
+}
+} else if be, ok := c.Server().Backend.(backend.AppendLimitBackend); ok {
+if limit := be.CreateMessageLimit(); limit != nil {
+caps = append(caps, fmt.Sprintf("APPENDLIMIT=%v", *limit))
+appendLimitSet = true
+}
+}
+if !appendLimitSet {
+caps = append(caps, "APPENDLIMIT")
+}
+
 if c.ctx.State == imap.NotAuthenticatedState {
 if !c.IsTLS() && c.s.TLSConfig != nil {
 caps = append(caps, "STARTTLS")

server/server_test.go

@@ -10,7 +10,7 @@ import (
 )
 
 // Extnesions that are always advertised by go-imap server.
-const builtinExtensions = "LITERAL+ SASL-IR CHILDREN UNSELECT"
+const builtinExtensions = "LITERAL+ SASL-IR CHILDREN UNSELECT APPENDLIMIT"
 
 func testServer(t *testing.T) (s *server.Server, conn net.Conn) {
 bkd := memory.New()