Fix filter not working in zero-copy mode (fixes #1697)

CHANGELOG.md

@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Fix crash when adding an object member in a too small `JsonDocument`
+* Fix filter not working in zero-copy mode (issue #1697)
 
 v6.19.0 (2022-01-08)
 -------

extras/tests/JsonDeserializer/filter.cpp

@@ -667,6 +667,20 @@ TEST_CASE("Filtering") {
   }
 }
 
+TEST_CASE("Zero-copy mode") {  // issue #1697
+  char input[] = "{\"include\":42,\"exclude\":666}";
+
+  StaticJsonDocument<256> filter;
+  filter["include"] = true;
+
+  StaticJsonDocument<256> doc;
+  DeserializationError err =
+      deserializeJson(doc, input, DeserializationOption::Filter(filter));
+
+  REQUIRE(err == DeserializationError::Ok);
+  CHECK(doc.as<std::string>() == "{\"include\":42}");
+}
+
 TEST_CASE("Overloads") {
   StaticJsonDocument<256> doc;
   StaticJsonDocument<256> filter;

extras/tests/JsonDeserializer/object.cpp

@@ -279,6 +279,22 @@ TEST_CASE("deserialize JSON object") {
       REQUIRE(err == DeserializationError::Ok);
       REQUIRE(doc["a"] == 2);
     }
+
+    SECTION("Repeated key with zero copy mode") {  // issue #1697
+      char input[] = "{a:{b:{c:1}},a:2}";
+      DeserializationError err = deserializeJson(doc, input);
+
+      REQUIRE(err == DeserializationError::Ok);
+      REQUIRE(doc["a"] == 2);
+    }
+
+    SECTION("NUL in keys") {  // we don't support NULs in keys
+      DeserializationError err =
+          deserializeJson(doc, "{\"x\\u0000a\":1,\"x\\u0000b\":2}");
+
+      REQUIRE(err == DeserializationError::Ok);
+      REQUIRE(doc.as<std::string>() == "{\"x\":2}");
+    }
   }
 
   SECTION("Should clear the JsonObject") {

extras/tests/MsgPackDeserializer/filter.cpp

@@ -1027,6 +1027,20 @@ TEST_CASE("deserializeMsgPack() filter") {
   }
 }
 
+TEST_CASE("Zero-copy mode") {  // issue #1697
+  char input[] = "\x82\xA7include\x01\xA6ignore\x02";
+
+  StaticJsonDocument<256> filter;
+  filter["include"] = true;
+
+  StaticJsonDocument<256> doc;
+  DeserializationError err =
+      deserializeMsgPack(doc, input, 18, DeserializationOption::Filter(filter));
+
+  CHECK(err == DeserializationError::Ok);
+  CHECK(doc.as<std::string>() == "{\"include\":1}");
+}
+
 TEST_CASE("Overloads") {
   StaticJsonDocument<256> doc;
   StaticJsonDocument<256> filter;

src/ArduinoJson/StringStorage/StringMover.hpp

@@ -18,7 +18,6 @@ class StringMover {
   }
 
   FORCE_INLINE String save() {
-    _writePtr[0] = 0;  // terminator
     String s = str();
     _writePtr++;
     return s;
@@ -33,6 +32,7 @@ class StringMover {
   }
 
   String str() const {
+    _writePtr[0] = 0;  // terminator
     return String(_startPtr, size(), true);
   }