json: fix raw json string decoding crash when expected key is missing (#7206)

vlib/builtin/string.v

@@ -111,6 +111,22 @@ pub fn tos3(s charptr) string {
 	}
 }
 
+// Same as `tos2`, but returns empty string on nil ptr
+pub fn tos4(s byteptr) string {
+	if s == 0 {
+		return ""
+	}
+	return tos2(s)
+}
+
+// Same as `tos4`, but for char*, to avoid warnings
+pub fn tos5(s charptr) string {
+	if s == 0 {
+		return ""
+	}
+	return tos3(s)
+}
+
 [deprecated]
 pub fn tos_lit(s charptr) string {
 	eprintln('warning: `tos_lit` has been deprecated, use `_SLIT` instead')

vlib/json/json_test.v

@@ -111,6 +111,15 @@ fn test_raw_json_field() {
 	assert color.space == 'YCbCr'
 }
 
+fn test_bad_raw_json_field() {
+	color := json.decode(Color, '{"space": "YCbCr"}') or {
+		println('text')
+		return
+	}
+	assert color.point == ''
+	assert color.space == 'YCbCr'
+}
+
 struct City {
 	name string
 }
@@ -310,3 +319,35 @@ fn test_encode_alias_struct() {
 	out := json.encode(msg)
 	assert out == expected
 }
+
+struct List {
+	id int
+	items []string
+}
+
+fn test_list() {
+	list := json.decode(List, '{"id": 1, "items": ["1", "2"]}') or {
+		println('error')
+		return
+	}
+	assert list.id == 1
+	assert list.items == ["1", "2"]
+}
+
+fn test_list_no_id() {
+	list := json.decode(List, '{"items": ["1", "2"]}') or {
+		println('error')
+		return
+	}
+	assert list.id == 0
+	assert list.items == ["1", "2"]
+}
+
+fn test_list_no_items() {
+	list := json.decode(List, '{"id": 1}') or {
+		println('error')
+		return
+	}
+	assert list.id == 1
+	assert list.items == []
+}

vlib/v/gen/json.v

@@ -127,7 +127,7 @@ fn (mut g Gen) gen_struct_enc_dec(type_info table.TypeInfo, styp string, mut enc
 		field_type := g.typ(field.typ)
 		field_sym := g.table.get_type_symbol(field.typ)
 		if field.attrs.contains('raw') {
-			dec.writeln('\tres.${c_name(field.name)} = tos2(cJSON_PrintUnformatted(' + 'js_get(root, "$name")));')
+			dec.writeln('\tres.${c_name(field.name)} = tos4(cJSON_PrintUnformatted(' + 'js_get(root, "$name")));')
 		} else {
 			// Now generate decoders for all field types in this struct
 			// need to do it here so that these functions are generated first
@@ -211,7 +211,7 @@ fn (mut g Gen) decode_array(value_type table.Type) string {
 '
 	}
 	return '
-	if(!cJSON_IsArray(root)) {
+	if(root && !cJSON_IsArray(root)) {
 		Option err = v_error( string_add(_SLIT("Json element is not an array: "), tos2(cJSON_PrintUnformatted(root))) );
 		return *(Option_array_$styp *)&err;
 	}