imapserver: add support for APPENDLIMIT

Co-authored-by: Simon Ser <[email protected]>

Author: mercata

imapserver/append.go

@@ -10,10 +10,8 @@ import (
 	"github.com/emersion/go-imap/v2/internal/imapwire"
 )
 
-// appendLimit is the maximum size of an APPEND payload.
-//
-// TODO: make configurable
-const appendLimit = 100 * 1024 * 1024 // 100MiB
+// defaultAppendLimit is the default maximum size of an APPEND payload.
+const defaultAppendLimit = 100 * 1024 * 1024 // 100MiB
 
 func (c *Conn) handleAppend(tag string, dec *imapwire.Decoder) error {
 	var (
@@ -66,6 +64,11 @@ func (c *Conn) handleAppend(tag string, dec *imapwire.Decoder) error {
 		return err
 	}
 
+	appendLimit := int64(defaultAppendLimit)
+	if appendLimitSession, ok := c.session.(SessionAppendLimit); ok {
+		appendLimit = int64(appendLimitSession.AppendLimit())
+	}
+
 	if lit.Size() > appendLimit {
 		return &imap.Error{
 			Type: imap.StatusResponseTypeNo,

imapserver/capability.go

@@ -1,6 +1,8 @@
 package imapserver
 
 import (
+	"fmt"
+
 	"github.com/emersion/go-imap/v2"
 	"github.com/emersion/go-imap/v2/internal/imapwire"
 )
@@ -92,6 +94,13 @@ func (c *Conn) availableCaps() []imap.Cap {
 			imap.CapLiteralPlus,
 			imap.CapUnauthenticate,
 		})
+
+		if appendLimitSession, ok := c.session.(SessionAppendLimit); ok {
+			limit := appendLimitSession.AppendLimit()
+			caps = append(caps, imap.Cap(fmt.Sprintf("APPENDLIMIT=%d", limit)))
+		} else {
+			addAvailableCaps(&caps, available, []imap.Cap{imap.CapAppendLimit})
+		}
 	}
 	return caps
 }

imapserver/session.go

@@ -114,3 +114,13 @@ type SessionUnauthenticate interface {
 	// Authenticated state
 	Unauthenticate() error
 }
+
+// SessionAppendLimit is an IMAP session which has the same APPEND limit for
+// all mailboxes.
+type SessionAppendLimit interface {
+	Session
+
+	// AppendLimit returns the maximum size in bytes that can be uploaded to
+	// this server in an APPEND command.
+	AppendLimit() uint32
+}