Merge support for APPENDLIMIT extension

Author: foxcpp

README.md

@@ -139,6 +139,7 @@ includes:
 * [CHILDREN](https://tools.ietf.org/html/rfc3348)
 * [UNSELECT](https://tools.ietf.org/html/rfc3691)
 * [COMPRESS](https://tools.ietf.org/html/rfc4978)
+* [APPENDLIMIT](https://tools.ietf.org/html/rfc7889)
 
 Support for other extensions is provided via separate packages. See below.
 
@@ -150,7 +151,6 @@ 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)
 * [ENABLE](https://github.com/emersion/go-imap-enable)
 * [ID](https://github.com/ProtonMail/go-imap-id)
 * [IDLE](https://github.com/emersion/go-imap-idle)

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

@@ -216,6 +216,10 @@ 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.
@@ -258,6 +262,8 @@ 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
 			}
@@ -285,6 +291,8 @@ 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", "COMPRESS=DEFLATE"}
 
+	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")