Fix parsing of empty objects in EXT JSON

GODRIVER-630
Co-authored-by: Matthew Chiaravalloti <[email protected]>
Co-authored-by: Divjot Arora <[email protected]>

Change-Id: I718d50c318e45734b8aba7c08cc841ab4dbb81a4

Author: Divjot Arora

bson/bsonrw/extjson_parser.go

@@ -64,6 +64,8 @@ type extJSONParser struct {
 	canonical bool
 	depth     int
 	maxDepth  int
+
+	emptyObject bool
 }
 
 // newExtJSONParser returns a new extended JSON parser, ready to to begin
@@ -107,6 +109,7 @@ func (ejp *extJSONParser) peekType() (bsontype.Type, error) {
 		switch ejp.s {
 		case jpsSawEndObject: // empty embedded document
 			t = bsontype.EmbeddedDocument
+			ejp.emptyObject = true
 		case jpsInvalidState:
 			err = ejp.err
 		case jpsSawKey:
@@ -143,6 +146,11 @@ func (ejp *extJSONParser) peekType() (bsontype.Type, error) {
 
 // readKey parses the next key and its type and returns them
 func (ejp *extJSONParser) readKey() (string, bsontype.Type, error) {
+	if ejp.emptyObject {
+		ejp.emptyObject = false
+		return "", 0, ErrEOD
+	}
+
 	// advance to key (or return with error)
 	switch ejp.s {
 	case jpsStartState:

bson/bsonrw/extjson_parser_test.go

@@ -447,6 +447,7 @@ func TestExtJSONParserAllTypes(t *testing.T) {
 			, "Code"				: { "$code": "function() {}" }
 			, "CodeWithEmptyScope"	: { "$code": "function() {}", "$scope": {} }
 			, "CodeWithScope"		: { "$code": "function() {}", "$scope": { "x": 1 } }
+			, "EmptySubdocument"    : {}
 			, "Subdocument"			: { "foo": "bar", "baz": { "$numberInt": "42" } }
 			, "Array"				: [{"$numberInt": "1"}, {"$numberLong": "2"}, {"$numberDouble": "3"}, 4, 5.0]
 			, "Timestamp"			: { "$timestamp": { "t": 42, "i": 1 } }
@@ -544,6 +545,13 @@ func TestExtJSONParserAllTypes(t *testing.T) {
 				},
 			},
 		},
+		{
+			f: expectSubDocument, p: ejp,
+			k: "EmptySubdocument", t: bsontype.EmbeddedDocument,
+			v: ejpSubDocumentTestValue{
+				ktvs: []ejpKeyTypValTriple{},
+			},
+		},
 		{
 			f: expectSubDocument, p: ejp,
 			k: "Subdocument", t: bsontype.EmbeddedDocument,