Restrict source.Filter values to *describedType

client.go

@@ -1167,9 +1167,9 @@ func LinkSelectorFilter(filter string) LinkOption {
 			l.source = new(source)
 		}
 		if l.source.Filter == nil {
-			l.source.Filter = make(map[symbol]interface{})
+			l.source.Filter = make(map[symbol]*describedType)
 		}
-		l.source.Filter[name] = describedType{
+		l.source.Filter[name] = &describedType{
 			descriptor: code,
 			value:      filter,
 		}

encode.go

@@ -479,6 +479,18 @@ func writeMap(wr *buffer, m interface{}) error {
 				return err
 			}
 		}
+	case filter:
+		pairs = len(m) * 2
+		for key, val := range m {
+			err := key.marshal(wr)
+			if err != nil {
+				return err
+			}
+			err = val.marshal(wr)
+			if err != nil {
+				return err
+			}
+		}
 	default:
 		return errorErrorf("unsupported map type %T", m)
 	}

marshal_test.go

@@ -280,8 +280,11 @@ var (
 					"lifetime-policy": deleteOnClose,
 				},
 				DistributionMode: "some-mode",
-				Filter: map[symbol]interface{}{
-					"foo:filter": "bar value",
+				Filter: filter{
+					"foo:filter": &describedType{
+						descriptor: "foo:filter",
+						value:      "bar value",
+					},
 				},
 				Outcomes:     []symbol{"amqp:accepted:list"},
 				Capabilities: []symbol{"barCap"},
@@ -323,8 +326,11 @@ var (
 				"lifetime-policy": deleteOnClose,
 			},
 			DistributionMode: "some-mode",
-			Filter: map[symbol]interface{}{
-				"foo:filter": "bar value",
+			Filter: filter{
+				"foo:filter": &describedType{
+					descriptor: "foo:filter",
+					value:      "bar value",
+				},
 			},
 			Outcomes:     []symbol{"amqp:accepted:list"},
 			Capabilities: []symbol{"barCap"},

types.go

@@ -588,6 +588,35 @@ func (u *unsettled) unmarshal(r *buffer) error {
 	return nil
 }
 
+type filter map[symbol]*describedType
+
+func (f filter) marshal(wr *buffer) error {
+	return writeMap(wr, f)
+}
+
+func (f *filter) unmarshal(r *buffer) error {
+	_, count, err := readMapHeader(r)
+	if err != nil {
+		return err
+	}
+
+	m := make(filter, count/2)
+	for i := uint32(0); i < count; i += 2 {
+		key, err := readString(r)
+		if err != nil {
+			return err
+		}
+		var value describedType
+		err = unmarshal(r, &value)
+		if err != nil {
+			return err
+		}
+		m[symbol(key)] = &value
+	}
+	*f = m
+	return nil
+}
+
 /*
 <type name="source" class="composite" source="list" provides="source">
     <descriptor name="amqp:source:list" code="0x00000000:0x00000028"/>
@@ -696,7 +725,7 @@ type source struct {
 	// actually in place (including any filters defaulted at the node). The receiving
 	// endpoint MUST check that the filter in place meets its needs and take responsibility
 	// for detaching if it does not.
-	Filter map[symbol]interface{} // TODO: implement custom type with validation
+	Filter filter
 
 	// default outcome for unsettled transfers
 	//