Added DeserializationOption::Filter (closes #959)

CHANGELOG.md

@@ -1,6 +1,12 @@
 ArduinoJson: change log
 =======================
 
+HEAD
+----
+
+* Added `DeserializationOption::Filter` (issue #959)
+* Added example `JsonFilterExample.ino`
+
 v6.14.1 (2020-01-27)
 -------
 

README.md

@@ -17,6 +17,7 @@ ArduinoJson is a C++ JSON library for Arduino and IoT (Internet Of Things).
     * [Optionally decodes UTF-16 escape sequences to UTF-8](https://arduinojson.org/v6/api/config/decode_unicode/)
     * [Optionally stores links to the input buffer (zero-copy)](https://arduinojson.org/v6/api/json/deserializejson/)
     * [Optionally supports comments in the input](https://arduinojson.org/v6/api/config/enable_comments/)
+    * Optionally filters the input to keep only desired values
     * Supports single quotes as a string delimiter
     * Compatible with NDJSON and JSON Lines
 * [JSON serialization](https://arduinojson.org/v6/api/json/serializejson/)

examples/JsonFilterExample/JsonFilterExample.ino

@@ -0,0 +1,66 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+//
+// This example shows how to use DeserializationOpion::Filter
+//
+// https://arduinojson.org/v6/example/filter/
+
+#include <ArduinoJson.h>
+
+void setup() {
+  // Initialize serial port
+  Serial.begin(9600);
+  while (!Serial) continue;
+
+  // The huge input: an extract from OpenWeatherMap response
+  const __FlashStringHelper* input_json = F(
+      "{\"cod\":\"200\",\"message\":0,\"list\":[{\"dt\":1581498000,\"main\":{"
+      "\"temp\":3.23,\"feels_like\":-3.63,\"temp_min\":3.23,\"temp_max\":4.62,"
+      "\"pressure\":1014,\"sea_level\":1014,\"grnd_level\":1010,\"humidity\":"
+      "58,\"temp_kf\":-1.39},\"weather\":[{\"id\":800,\"main\":\"Clear\","
+      "\"description\":\"clear "
+      "sky\",\"icon\":\"01d\"}],\"clouds\":{\"all\":0},\"wind\":{\"speed\":6."
+      "19,\"deg\":266},\"sys\":{\"pod\":\"d\"},\"dt_txt\":\"2020-02-12 "
+      "09:00:00\"},{\"dt\":1581508800,\"main\":{\"temp\":6.09,\"feels_like\":-"
+      "1.07,\"temp_min\":6.09,\"temp_max\":7.13,\"pressure\":1015,\"sea_"
+      "level\":1015,\"grnd_level\":1011,\"humidity\":48,\"temp_kf\":-1.04},"
+      "\"weather\":[{\"id\":800,\"main\":\"Clear\",\"description\":\"clear "
+      "sky\",\"icon\":\"01d\"}],\"clouds\":{\"all\":9},\"wind\":{\"speed\":6."
+      "64,\"deg\":268},\"sys\":{\"pod\":\"d\"},\"dt_txt\":\"2020-02-12 "
+      "12:00:00\"}],\"city\":{\"id\":2643743,\"name\":\"London\",\"coord\":{"
+      "\"lat\":51.5085,\"lon\":-0.1257},\"country\":\"GB\",\"population\":"
+      "1000000,\"timezone\":0,\"sunrise\":1581492085,\"sunset\":1581527294}}");
+
+  // The filter: it contains "true" for each value we want to keep
+  const __FlashStringHelper* filter_json =
+      F("{\"list\":[{\"dt\":true,\"main\":{\"temp\":true}]}");
+
+  // Create the filter document
+  StaticJsonDocument<200> filter;
+  deserializeJson(filter, filter_json);
+
+  // Deserialize the document
+  StaticJsonDocument<400> doc;
+  deserializeJson(doc, input_json, DeserializationOption::Filter(filter));
+
+  // Print the result
+  serializeJsonPretty(doc, Serial);
+}
+
+void loop() {
+  // not used in this example
+}
+
+// See also
+// --------
+//
+// https://arduinojson.org/ contains the documentation for all the functions
+// used above. It also includes an FAQ that will help you solve any
+// deserialization problem.
+//
+// The book "Mastering ArduinoJson" contains a tutorial on deserialization.
+// It begins with a simple example, like the one above, and then adds more
+// features like deserializing directly from a file or an HTTP request.
+// Learn more at https://arduinojson.org/book/
+// Use the coupon code TWENTY for a 20% discount ❤❤❤❤❤

extras/tests/IntegrationTests/CMakeLists.txt

@@ -6,6 +6,7 @@ add_executable(IntegrationTests
 	gbathree.cpp
 	issue772.cpp
 	round_trip.cpp
+	openweathermap.cpp
 )
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")

extras/tests/JsonDeserializer/CMakeLists.txt

@@ -6,12 +6,13 @@ add_executable(JsonDeserializerTests
 	array.cpp
 	array_static.cpp
 	DeserializationError.cpp
+	filter.cpp
 	incomplete_input.cpp
 	input_types.cpp
-	number.cpp
 	invalid_input.cpp
 	misc.cpp
 	nestingLimit.cpp
+	number.cpp
 	object.cpp
 	object_static.cpp
 	string.cpp

extras/tests/JsonDeserializer/filter.cpp

@@ -0,0 +1,577 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+#include <sstream>
+#include <string>
+
+TEST_CASE("Filtering") {
+  struct TestCase {
+    const char* input;
+    const char* filter;
+    uint8_t nestingLimit;
+    DeserializationError error;
+    const char* output;
+    size_t memoryUsage;
+  };
+
+  // clang-format off
+  TestCase testCases[] = {
+    {
+      "{\"hello\":\"world\"}",   // 1. input
+      "null",                    // 2. filter
+      10,                        // 3. nestingLimit
+      DeserializationError::Ok,  // 4. error
+      "null",                    // 5. output
+      0                          // 6. memoryUsage
+    },
+    {
+      "{\"hello\":\"world\"}",
+      "false",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      "{\"abcdefg\":\"hijklmn\"}",
+      "true",
+      10,
+      DeserializationError::Ok,
+      "{\"abcdefg\":\"hijklmn\"}",
+      JSON_OBJECT_SIZE(1) + 16
+    },
+    {
+      "{\"hello\":\"world\"}",
+      "{}",
+      10,
+      DeserializationError::Ok,
+      "{}",
+      JSON_OBJECT_SIZE(0)
+    },
+    {
+      // Input in an object, but filter wants an array
+      "{\"hello\":\"world\"}",
+      "[]",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // Input is an array, but filter wants an object
+      "[\"hello\",\"world\"]",
+      "{}",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // Input is a bool, but filter wants an object
+      "true",
+      "{}",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // Input is a string, but filter wants an object
+      "\"hello\"",
+      "{}",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // skip an integer
+      "{\"an_integer\":666,example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // skip a float
+      "{\"a_float\":12.34e-6,example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip a boolean
+      "{\"a_bool\":false,example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip a double-quoted string
+      "{\"a_double_quoted_string\":\"hello\",example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip a single-quoted string
+      "{\"a_single_quoted_string\":'hello',example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an empty array
+      "{\"an_empty_array\":[],example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an empty array with spaces in it
+      "{\"an_empty_array\":[\t],example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an array
+      "{\"an_array\":[1,2,3],example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an array with spaces in it
+      "{\"an_array\": [ 1 , 2 , 3 ] ,example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an empty object
+      "{\"an_empty_object\":{},example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an empty object with spaces in it
+      "{\"an_empty_object\":{    },example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // can skip an object
+      "{\"an_object\":{a:1,'b':2,\"c\":3},example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      // skip an object with spaces in it
+      "{\"an_object\" : { a : 1 , 'b' : 2 , \"c\" : 3 } ,example:42}",
+      "{\"example\":true}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":42}",
+      JSON_OBJECT_SIZE(1) + 8
+    },
+    {
+      "{\"an_integer\": 0,\"example\":{\"type\":\"int\",\"outcome\":42}}",
+      "{\"example\":{\"outcome\":true}}",
+      10,
+      DeserializationError::Ok,
+      "{\"example\":{\"outcome\":42}}",
+      2 * JSON_OBJECT_SIZE(1) + 16
+    },
+    {
+      // only the first element of array counts
+      "[1,2,3]",
+      "[true, false]",
+      10,
+      DeserializationError::Ok,
+      "[1,2,3]",
+      JSON_ARRAY_SIZE(3)
+    },
+    {
+      // only the first element of array counts
+      "[1,2,3]",
+      "[false, true]",
+      10,
+      DeserializationError::Ok,
+      "[]",
+      JSON_ARRAY_SIZE(0)
+    },
+    {
+      // filter members of object in array
+      "[{\"example\":1,\"ignore\":2},{\"example\":3,\"ignore\":4}]",
+      "[{\"example\":true}]",
+      10,
+      DeserializationError::Ok,
+      "[{\"example\":1},{\"example\":3}]",
+      JSON_ARRAY_SIZE(2) + 2 * JSON_OBJECT_SIZE(1) + 16
+    },
+    {
+      "[',2,3]",
+      "[false,true]",
+      10,
+      DeserializationError::IncompleteInput,
+      "[]",
+      JSON_ARRAY_SIZE(0)
+    },
+    {
+      "[\",2,3]",
+      "[false,true]",
+      10,
+      DeserializationError::IncompleteInput,
+      "[]",
+      JSON_ARRAY_SIZE(0)
+    },
+    {
+      // ignore errors in skipped value
+      "[!,2,\\]",
+      "[false]",
+      10,
+      DeserializationError::Ok,
+      "[]",
+      JSON_ARRAY_SIZE(0)
+    },
+    {
+      // detect incomplete string event if it's skipped
+      "\"ABC",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // detect incomplete string event if it's skipped
+      "'ABC",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // handle escaped quotes
+      "'A\\'BC'",
+      "false",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // handle escaped quotes
+      "\"A\\\"BC\"",
+      "false",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // detect incomplete string in presence of escaped quotes
+      "'A\\'BC",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // detect incomplete string in presence of escaped quotes
+      "\"A\\\"BC",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // skip empty array
+      "[]",
+      "false",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // skip empty array with spaces
+      " [ ] ",
+      "false",
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // bubble up element error even if array is skipped 
+      "[1,'2,3]",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // bubble up member error even if object is skipped 
+      "{'hello':'worl}",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // bubble up colon error even if object is skipped 
+      "{'hello','world'}",
+      "false",
+      10,
+      DeserializationError::InvalidInput,
+      "null",
+      0
+    },
+    {
+      // bubble up key error even if object is skipped 
+      "{'hello:1}",
+      "false",
+      10,
+      DeserializationError::IncompleteInput,
+      "null",
+      0
+    },
+    {
+      // ignore invalid value in skipped object
+      "{'hello':!}",
+      "false", 
+      10,
+      DeserializationError::Ok,
+      "null",
+      0
+    },
+    {
+      // ignore invalid value in skipped object
+      "{'hello':\\}",
+      "false", 
+      10,
+      DeserializationError::Ok,
+      "null", 
+      0
+    },
+    {
+      // check nesting limit even for ignored objects
+      "{}",
+      "false", 
+      0,
+      DeserializationError::TooDeep,
+      "null", 
+      0
+    },
+    {
+      // check nesting limit even for ignored objects
+      "{'hello':{}}",
+      "false", 
+      1,
+      DeserializationError::TooDeep,
+      "null", 
+      0
+    },
+    {
+      // check nesting limit even for ignored values in objects
+      "{'hello':{}}",
+      "{}", 
+      1,
+      DeserializationError::TooDeep,
+      "{}", 
+      JSON_OBJECT_SIZE(0)
+    },
+    {
+      // check nesting limit even for ignored arrays
+      "[]",
+      "false", 
+      0,
+      DeserializationError::TooDeep,
+      "null", 
+      0
+    },
+    {
+      // check nesting limit even for ignored arrays
+      "[[]]",
+      "false", 
+      1,
+      DeserializationError::TooDeep,
+      "null", 
+      0
+    },
+    {
+      // check nesting limit even for ignored values in arrays
+      "[[]]",
+      "[]", 
+      1,
+      DeserializationError::TooDeep,
+      "[]", 
+      JSON_ARRAY_SIZE(0)
+    },
+  };  // clang-format on
+
+  for (size_t i = 0; i < sizeof(testCases) / sizeof(testCases[0]); i++) {
+    CAPTURE(i);
+
+    DynamicJsonDocument filter(256);
+    DynamicJsonDocument doc(256);
+    TestCase& tc = testCases[i];
+
+    CAPTURE(tc.filter);
+    REQUIRE(deserializeJson(filter, tc.filter) == DeserializationError::Ok);
+
+    CAPTURE(tc.input);
+    CAPTURE(tc.nestingLimit);
+    CHECK(deserializeJson(doc, tc.input, DeserializationOption::Filter(filter),
+                          DeserializationOption::NestingLimit(
+                              tc.nestingLimit)) == tc.error);
+
+    CHECK(doc.as<std::string>() == tc.output);
+    CHECK(doc.memoryUsage() == tc.memoryUsage);
+  }
+}
+
+TEST_CASE("Overloads") {
+  StaticJsonDocument<256> doc;
+  StaticJsonDocument<256> filter;
+
+  using namespace DeserializationOption;
+
+  // deserializeJson(..., Filter)
+
+  SECTION("const char*, Filter") {
+    deserializeJson(doc, "{}", Filter(filter));
+  }
+
+  SECTION("const char*, size_t, Filter") {
+    deserializeJson(doc, "{}", 2, Filter(filter));
+  }
+
+  SECTION("const std::string&, Filter") {
+    deserializeJson(doc, std::string("{}"), Filter(filter));
+  }
+
+  SECTION("std::istream&, Filter") {
+    std::stringstream s("{}");
+    deserializeJson(doc, s, Filter(filter));
+  }
+
+#ifdef HAS_VARIABLE_LENGTH_ARRAY
+  SECTION("char[n], Filter") {
+    int i = 4;
+    char vla[i];
+    strcpy(vla, "{}");
+    deserializeJson(doc, vla, Filter(filter));
+  }
+#endif
+
+  // deserializeJson(..., Filter, NestingLimit)
+
+  SECTION("const char*, Filter, NestingLimit") {
+    deserializeJson(doc, "{}", Filter(filter), NestingLimit(5));
+  }
+
+  SECTION("const char*, size_t, Filter, NestingLimit") {
+    deserializeJson(doc, "{}", 2, Filter(filter), NestingLimit(5));
+  }
+
+  SECTION("const std::string&, Filter, NestingLimit") {
+    deserializeJson(doc, std::string("{}"), Filter(filter), NestingLimit(5));
+  }
+
+  SECTION("std::istream&, Filter, NestingLimit") {
+    std::stringstream s("{}");
+    deserializeJson(doc, s, Filter(filter), NestingLimit(5));
+  }
+
+#ifdef HAS_VARIABLE_LENGTH_ARRAY
+  SECTION("char[n], Filter, NestingLimit") {
+    int i = 4;
+    char vla[i];
+    strcpy(vla, "{}");
+    deserializeJson(doc, vla, Filter(filter), NestingLimit(5));
+  }
+#endif
+
+  // deserializeJson(..., NestingLimit, Filter)
+
+  SECTION("const char*, NestingLimit, Filter") {
+    deserializeJson(doc, "{}", NestingLimit(5), Filter(filter));
+  }
+
+  SECTION("const char*, size_t, NestingLimit, Filter") {
+    deserializeJson(doc, "{}", 2, NestingLimit(5), Filter(filter));
+  }
+
+  SECTION("const std::string&, NestingLimit, Filter") {
+    deserializeJson(doc, std::string("{}"), NestingLimit(5), Filter(filter));
+  }
+
+  SECTION("std::istream&, NestingLimit, Filter") {
+    std::stringstream s("{}");
+    deserializeJson(doc, s, NestingLimit(5), Filter(filter));
+  }
+
+#ifdef HAS_VARIABLE_LENGTH_ARRAY
+  SECTION("char[n], NestingLimit, Filter") {
+    int i = 4;
+    char vla[i];
+    strcpy(vla, "{}");
+    deserializeJson(doc, vla, NestingLimit(5), Filter(filter));
+  }
+#endif
+}
+
+TEST_CASE("StringMover::reclaim()") {
+  StaticJsonDocument<200> filter;
+  filter["a"] = true;
+  filter["c"] = true;
+  char input[] = "{\"a\":1,\"b\":2,\"c\":1}";
+
+  StaticJsonDocument<200> doc;
+  deserializeJson(doc, input, DeserializationOption::Filter(filter));
+
+  REQUIRE(doc.as<std::string>() == "{\"a\":1,\"c\":1}");
+
+  CHECK(input[0] == 'a');
+  CHECK(input[1] == 0);
+  CHECK(input[2] == 'c');
+  CHECK(input[3] == 0);
+}

src/ArduinoJson.hpp

@@ -65,6 +65,7 @@ using ARDUINOJSON_NAMESPACE::serializeMsgPack;
 using ARDUINOJSON_NAMESPACE::StaticJsonDocument;
 
 namespace DeserializationOption {
+using ARDUINOJSON_NAMESPACE::Filter;
 using ARDUINOJSON_NAMESPACE::NestingLimit;
-}
+}  // namespace DeserializationOption
 }  // namespace ArduinoJson

src/ArduinoJson/Deserialization/Filter.hpp

@@ -0,0 +1,66 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+class Filter {
+ public:
+  explicit Filter(VariantConstRef v) : _variant(v) {}
+
+  bool allow() const {
+    return _variant;
+  }
+
+  bool allowArray() const {
+    return _variant == true || _variant.is<ArrayRef>();
+  }
+
+  bool allowObject() const {
+    return _variant == true || _variant.is<ObjectRef>();
+  }
+
+  bool allowValue() const {
+    return _variant == true;
+  }
+
+  template <typename TKey>
+  Filter operator[](const TKey& key) const {
+    if (_variant == true)  // "true" means "allow recursively"
+      return *this;
+    else
+      return Filter(_variant[key]);
+  }
+
+ private:
+  VariantConstRef _variant;
+};
+
+struct AllowAllFilter {
+  bool allow() const {
+    return true;
+  }
+
+  bool allowArray() const {
+    return true;
+  }
+
+  bool allowObject() const {
+    return true;
+  }
+
+  bool allowValue() const {
+    return true;
+  }
+
+  template <typename TKey>
+  AllowAllFilter operator[](const TKey&) const {
+    return AllowAllFilter();
+  }
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Deserialization/deserialize.hpp

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Deserialization/DeserializationError.hpp>
+#include <ArduinoJson/Deserialization/Filter.hpp>
 #include <ArduinoJson/Deserialization/NestingLimit.hpp>
 #include <ArduinoJson/Deserialization/Reader.hpp>
 #include <ArduinoJson/StringStorage/StringStorage.hpp>
@@ -19,47 +20,52 @@ TDeserializer<TReader, TWriter> makeDeserializer(MemoryPool &pool,
   return TDeserializer<TReader, TWriter>(pool, reader, writer, nestingLimit);
 }
 
-// deserialize(JsonDocument&, const std::string&);
-// deserialize(JsonDocument&, const String&);
-// deserialize(JsonDocument&, char*);
-// deserialize(JsonDocument&, const char*);
-// deserialize(JsonDocument&, const __FlashStringHelper*);
-template <template <typename, typename> class TDeserializer, typename TString>
+// deserialize(JsonDocument&, const std::string&, NestingLimit, Filter);
+// deserialize(JsonDocument&, const String&, NestingLimit, Filter);
+// deserialize(JsonDocument&, char*, NestingLimit, Filter);
+// deserialize(JsonDocument&, const char*, NestingLimit, Filter);
+// deserialize(JsonDocument&, const __FlashStringHelper*, NestingLimit, Filter);
+template <template <typename, typename> class TDeserializer, typename TString,
+          typename TFilter>
 typename enable_if<!is_array<TString>::value, DeserializationError>::type
-deserialize(JsonDocument &doc, const TString &input,
-            NestingLimit nestingLimit) {
+deserialize(JsonDocument &doc, const TString &input, NestingLimit nestingLimit,
+            TFilter filter) {
   Reader<TString> reader(input);
   doc.clear();
   return makeDeserializer<TDeserializer>(
              doc.memoryPool(), reader,
              makeStringStorage(doc.memoryPool(), input), nestingLimit.value)
-      .parse(doc.data());
+      .parse(doc.data(), filter);
 }
 //
-// deserialize(JsonDocument&, char*, size_t);
-// deserialize(JsonDocument&, const char*, size_t);
-// deserialize(JsonDocument&, const __FlashStringHelper*, size_t);
-template <template <typename, typename> class TDeserializer, typename TChar>
+// deserialize(JsonDocument&, char*, size_t, NestingLimit, Filter);
+// deserialize(JsonDocument&, const char*, size_t, NestingLimit, Filter);
+// deserialize(JsonDocument&, const __FlashStringHelper*, size_t, NL, Filter);
+template <template <typename, typename> class TDeserializer, typename TChar,
+          typename TFilter>
 DeserializationError deserialize(JsonDocument &doc, TChar *input,
-                                 size_t inputSize, NestingLimit nestingLimit) {
+                                 size_t inputSize, NestingLimit nestingLimit,
+                                 TFilter filter) {
   BoundedReader<TChar *> reader(input, inputSize);
   doc.clear();
   return makeDeserializer<TDeserializer>(
              doc.memoryPool(), reader,
              makeStringStorage(doc.memoryPool(), input), nestingLimit.value)
-      .parse(doc.data());
+      .parse(doc.data(), filter);
 }
 //
-// deserialize(JsonDocument&, std::istream&);
-// deserialize(JsonDocument&, Stream&);
-template <template <typename, typename> class TDeserializer, typename TStream>
+// deserialize(JsonDocument&, std::istream&, NestingLimit, Filter);
+// deserialize(JsonDocument&, Stream&, NestingLimit, Filter);
+template <template <typename, typename> class TDeserializer, typename TStream,
+          typename TFilter>
 DeserializationError deserialize(JsonDocument &doc, TStream &input,
-                                 NestingLimit nestingLimit) {
+                                 NestingLimit nestingLimit, TFilter filter) {
   Reader<TStream> reader(input);
   doc.clear();
   return makeDeserializer<TDeserializer>(
              doc.memoryPool(), reader,
              makeStringStorage(doc.memoryPool(), input), nestingLimit.value)
-      .parse(doc.data());
+      .parse(doc.data(), filter);
 }
+
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Json/JsonDeserializer.hpp

@@ -27,9 +27,15 @@ class JsonDeserializer {
         _reader(reader),
         _stringStorage(stringStorage),
         _nestingLimit(nestingLimit),
-        _loaded(false) {}
-  DeserializationError parse(VariantData &variant) {
-    DeserializationError err = parseVariant(variant);
+        _loaded(false) {
+#ifdef ARDUINOJSON_DEBUG
+    _ended = false;
+#endif
+  }
+
+  template <typename TFilter>
+  DeserializationError parse(VariantData &variant, TFilter filter) {
+    DeserializationError err = parseVariant(variant, filter);
 
     if (!err && _current != 0 && !variant.isEnclosed()) {
       // We don't detect trailing characters earlier, so we need to check now
@@ -44,7 +50,11 @@ class JsonDeserializer {
 
   char current() {
     if (!_loaded) {
+      ARDUINOJSON_ASSERT(!_ended);
       int c = _reader.read();
+#ifdef ARDUINOJSON_DEBUG
+      if (c <= 0) _ended = true;
+#endif
       _current = static_cast<char>(c > 0 ? c : 0);
       _loaded = true;
     }
@@ -61,27 +71,61 @@ class JsonDeserializer {
     return true;
   }
 
-  DeserializationError parseVariant(VariantData &variant) {
+  template <typename TFilter>
+  DeserializationError parseVariant(VariantData &variant, TFilter filter) {
     DeserializationError err = skipSpacesAndComments();
     if (err) return err;
 
     switch (current()) {
       case '[':
-        return parseArray(variant.toArray());
+        if (filter.allowArray())
+          return parseArray(variant.toArray(), filter);
+        else
+          return skipArray();
 
       case '{':
-        return parseObject(variant.toObject());
+        if (filter.allowObject())
+          return parseObject(variant.toObject(), filter);
+        else
+          return skipObject();
 
       case '\"':
       case '\'':
-        return parseStringValue(variant);
+        if (filter.allowValue())
+          return parseStringValue(variant);
+        else
+          return skipString();
 
       default:
-        return parseNumericValue(variant);
+        if (filter.allowValue())
+          return parseNumericValue(variant);
+        else
+          return skipNumericValue();
     }
   }
 
-  DeserializationError parseArray(CollectionData &array) {
+  DeserializationError skipVariant() {
+    DeserializationError err = skipSpacesAndComments();
+    if (err) return err;
+
+    switch (current()) {
+      case '[':
+        return skipArray();
+
+      case '{':
+        return skipObject();
+
+      case '\"':
+      case '\'':
+        return skipString();
+
+      default:
+        return skipNumericValue();
+    }
+  }
+
+  template <typename TFilter>
+  DeserializationError parseArray(CollectionData &array, TFilter filter) {
     if (_nestingLimit == 0) return DeserializationError::TooDeep;
 
     // Check opening braket
@@ -94,15 +138,48 @@ class JsonDeserializer {
     // Empty array?
     if (eat(']')) return DeserializationError::Ok;
 
+    TFilter memberFilter = filter[0UL];
+
     // Read each value
     for (;;) {
-      // Allocate slot in array
-      VariantData *value = array.add(_pool);
-      if (!value) return DeserializationError::NoMemory;
+      if (memberFilter.allow()) {
+        // Allocate slot in array
+        VariantData *value = array.add(_pool);
+        if (!value) return DeserializationError::NoMemory;
 
-      // 1 - Parse value
+        // 1 - Parse value
+        _nestingLimit--;
+        err = parseVariant(*value, memberFilter);
+        _nestingLimit++;
+        if (err) return err;
+      } else {
+        _nestingLimit--;
+        err = skipVariant();
+        _nestingLimit++;
+        if (err) return err;
+      }
+
+      // 2 - Skip spaces
+      err = skipSpacesAndComments();
+      if (err) return err;
+
+      // 3 - More values?
+      if (eat(']')) return DeserializationError::Ok;
+      if (!eat(',')) return DeserializationError::InvalidInput;
+    }
+  }
+
+  DeserializationError skipArray() {
+    if (_nestingLimit == 0) return DeserializationError::TooDeep;
+
+    // Check opening braket
+    if (!eat('[')) return DeserializationError::InvalidInput;
+
+    // Read each value
+    for (;;) {
+      // 1 - Skip value
       _nestingLimit--;
-      err = parseVariant(*value);
+      DeserializationError err = skipVariant();
       _nestingLimit++;
       if (err) return err;
 
@@ -116,7 +193,8 @@ class JsonDeserializer {
     }
   }
 
-  DeserializationError parseObject(CollectionData &object) {
+  template <typename TFilter>
+  DeserializationError parseObject(CollectionData &object, TFilter filter) {
     if (_nestingLimit == 0) return DeserializationError::TooDeep;
 
     // Check opening brace
@@ -136,27 +214,37 @@ class JsonDeserializer {
       err = parseKey(key);
       if (err) return err;
 
-      VariantData *variant = object.get(adaptString(key));
-      if (!variant) {
-        // Allocate slot in object
-        VariantSlot *slot = object.addSlot(_pool);
-        if (!slot) return DeserializationError::NoMemory;
-
-        slot->setOwnedKey(make_not_null(key));
-
-        variant = slot->data();
-      }
-
       // Skip spaces
       err = skipSpacesAndComments();
       if (err) return err;  // Colon
       if (!eat(':')) return DeserializationError::InvalidInput;
 
-      // Parse value
-      _nestingLimit--;
-      err = parseVariant(*variant);
-      _nestingLimit++;
-      if (err) return err;
+      TFilter memberFilter = filter[key];
+
+      if (memberFilter.allow()) {
+        VariantData *variant = object.get(adaptString(key));
+        if (!variant) {
+          // Allocate slot in object
+          VariantSlot *slot = object.addSlot(_pool);
+          if (!slot) return DeserializationError::NoMemory;
+
+          slot->setOwnedKey(make_not_null(key));
+
+          variant = slot->data();
+        }
+
+        // Parse value
+        _nestingLimit--;
+        err = parseVariant(*variant, memberFilter);
+        _nestingLimit++;
+        if (err) return err;
+      } else {
+        _stringStorage.reclaim(key);
+        _nestingLimit--;
+        err = skipVariant();
+        _nestingLimit++;
+        if (err) return err;
+      }
 
       // Skip spaces
       err = skipSpacesAndComments();
@@ -172,6 +260,46 @@ class JsonDeserializer {
     }
   }
 
+  DeserializationError skipObject() {
+    if (_nestingLimit == 0) return DeserializationError::TooDeep;
+
+    // Check opening brace
+    if (!eat('{')) return DeserializationError::InvalidInput;
+
+    // Skip spaces
+    DeserializationError err = skipSpacesAndComments();
+    if (err) return err;
+
+    // Empty object?
+    if (eat('}')) return DeserializationError::Ok;
+
+    // Read each key value pair
+    for (;;) {
+      // Skip key
+      err = skipVariant();
+      if (err) return err;
+
+      // Skip spaces
+      err = skipSpacesAndComments();
+      if (err) return err;  // Colon
+      if (!eat(':')) return DeserializationError::InvalidInput;
+
+      // Skip value
+      _nestingLimit--;
+      err = skipVariant();
+      _nestingLimit++;
+      if (err) return err;
+
+      // Skip spaces
+      err = skipSpacesAndComments();
+      if (err) return err;
+
+      // More keys/values?
+      if (eat('}')) return DeserializationError::Ok;
+      if (!eat(',')) return DeserializationError::InvalidInput;
+    }
+  }
+
   DeserializationError parseKey(const char *&key) {
     if (isQuote(current())) {
       return parseQuotedString(key);
@@ -254,6 +382,21 @@ class JsonDeserializer {
     return DeserializationError::Ok;
   }
 
+  DeserializationError skipString() {
+    const char stopChar = current();
+
+    move();
+    for (;;) {
+      char c = current();
+      move();
+      if (c == stopChar) break;
+      if (c == '\0') return DeserializationError::IncompleteInput;
+      if (c == '\\') _reader.read();
+    }
+
+    return DeserializationError::Ok;
+  }
+
   DeserializationError parseNumericValue(VariantData &result) {
     char buffer[64];
     uint8_t n = 0;
@@ -302,6 +445,15 @@ class JsonDeserializer {
     return DeserializationError::InvalidInput;
   }
 
+  DeserializationError skipNumericValue() {
+    char c = current();
+    while (c && c != '}' && c != ',' && c != ']' && c != ':') {
+      move();
+      c = current();
+    }
+    return DeserializationError::Ok;
+  }
+
   DeserializationError parseHex4(uint16_t &result) {
     result = 0;
     for (uint8_t i = 0; i < 4; ++i) {
@@ -401,33 +553,92 @@ class JsonDeserializer {
   uint8_t _nestingLimit;
   char _current;
   bool _loaded;
+#ifdef ARDUINOJSON_DEBUG
+  bool _ended;
+#endif
 };
 
+// deserializeJson(JsonDocument&, const std::string&, ...)
 template <typename TInput>
 DeserializationError deserializeJson(
     JsonDocument &doc, const TInput &input,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<JsonDeserializer>(doc, input, nestingLimit);
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit,
+                                       AllowAllFilter());
 }
-
 template <typename TInput>
 DeserializationError deserializeJson(
-    JsonDocument &doc, TInput *input,
+    JsonDocument &doc, const TInput &input, Filter filter,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<JsonDeserializer>(doc, input, nestingLimit);
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
 }
-
 template <typename TInput>
-DeserializationError deserializeJson(
-    JsonDocument &doc, TInput *input, size_t inputSize,
-    NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<JsonDeserializer>(doc, input, inputSize, nestingLimit);
+DeserializationError deserializeJson(JsonDocument &doc, const TInput &input,
+                                     NestingLimit nestingLimit, Filter filter) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
 }
 
+// deserializeJson(JsonDocument&, const std::istream&, ...)
 template <typename TInput>
 DeserializationError deserializeJson(
     JsonDocument &doc, TInput &input,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<JsonDeserializer>(doc, input, nestingLimit);
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit,
+                                       AllowAllFilter());
 }
+template <typename TInput>
+DeserializationError deserializeJson(
+    JsonDocument &doc, TInput &input, Filter filter,
+    NestingLimit nestingLimit = NestingLimit()) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
+}
+template <typename TInput>
+DeserializationError deserializeJson(JsonDocument &doc, TInput &input,
+                                     NestingLimit nestingLimit, Filter filter) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
+}
+
+// deserializeJson(JsonDocument&, char*, ...)
+template <typename TChar>
+DeserializationError deserializeJson(
+    JsonDocument &doc, TChar *input,
+    NestingLimit nestingLimit = NestingLimit()) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit,
+                                       AllowAllFilter());
+}
+template <typename TChar>
+DeserializationError deserializeJson(
+    JsonDocument &doc, TChar *input, Filter filter,
+    NestingLimit nestingLimit = NestingLimit()) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
+}
+template <typename TChar>
+DeserializationError deserializeJson(JsonDocument &doc, TChar *input,
+                                     NestingLimit nestingLimit, Filter filter) {
+  return deserialize<JsonDeserializer>(doc, input, nestingLimit, filter);
+}
+
+// deserializeJson(JsonDocument&, char*, size_t, ...)
+template <typename TChar>
+DeserializationError deserializeJson(
+    JsonDocument &doc, TChar *input, size_t inputSize,
+    NestingLimit nestingLimit = NestingLimit()) {
+  return deserialize<JsonDeserializer>(doc, input, inputSize, nestingLimit,
+                                       AllowAllFilter());
+}
+template <typename TChar>
+DeserializationError deserializeJson(
+    JsonDocument &doc, TChar *input, size_t inputSize, Filter filter,
+    NestingLimit nestingLimit = NestingLimit()) {
+  return deserialize<JsonDeserializer>(doc, input, inputSize, nestingLimit,
+                                       filter);
+}
+template <typename TChar>
+DeserializationError deserializeJson(JsonDocument &doc, TChar *input,
+                                     size_t inputSize,
+                                     NestingLimit nestingLimit, Filter filter) {
+  return deserialize<JsonDeserializer>(doc, input, inputSize, nestingLimit,
+                                       filter);
+}
+
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -74,6 +74,10 @@ class MemoryPool {
     checkInvariants();
   }
 
+  void reclaimLastString(const char* s) {
+    _left = const_cast<char*>(s);
+  }
+
   void clear() {
     _left = _begin;
     _right = _end;

src/ArduinoJson/MsgPack/MsgPackDeserializer.hpp

@@ -26,7 +26,9 @@ class MsgPackDeserializer {
         _stringStorage(stringStorage),
         _nestingLimit(nestingLimit) {}
 
-  DeserializationError parse(VariantData &variant) {
+  // TODO: add support for filter
+  DeserializationError parse(VariantData &variant,
+                             AllowAllFilter = AllowAllFilter()) {
     uint8_t code;
     if (!readByte(code)) return DeserializationError::IncompleteInput;
 
@@ -317,27 +319,31 @@ template <typename TInput>
 DeserializationError deserializeMsgPack(
     JsonDocument &doc, const TInput &input,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit);
+  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit,
+                                          AllowAllFilter());
 }
 
 template <typename TInput>
 DeserializationError deserializeMsgPack(
     JsonDocument &doc, TInput *input,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit);
+  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit,
+                                          AllowAllFilter());
 }
 
 template <typename TInput>
 DeserializationError deserializeMsgPack(
     JsonDocument &doc, TInput *input, size_t inputSize,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<MsgPackDeserializer>(doc, input, inputSize, nestingLimit);
+  return deserialize<MsgPackDeserializer>(doc, input, inputSize, nestingLimit,
+                                          AllowAllFilter());
 }
 
 template <typename TInput>
 DeserializationError deserializeMsgPack(
     JsonDocument &doc, TInput &input,
     NestingLimit nestingLimit = NestingLimit()) {
-  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit);
+  return deserialize<MsgPackDeserializer>(doc, input, nestingLimit,
+                                          AllowAllFilter());
 }
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/StringStorage/StringCopier.hpp

@@ -19,6 +19,10 @@ class StringCopier {
     return StringBuilder(_pool);
   }
 
+  void reclaim(const char* s) {
+    _pool->reclaimLastString(s);
+  }
+
  private:
   MemoryPool* _pool;
 };

src/ArduinoJson/StringStorage/StringMover.hpp

@@ -34,6 +34,11 @@ class StringMover {
     return StringBuilder(&_ptr);
   }
 
+  // recover memory from last string
+  void reclaim(const char* str) {
+    _ptr = const_cast<char*>(str);
+  }
+
  private:
   char* _ptr;
 };

src/ArduinoJson/Variant/VariantData.hpp

@@ -181,7 +181,7 @@ class VariantData {
   }
 
   bool isEnclosed() const {
-    return isCollection() || isString();
+    return !isFloat();
   }
 
   void remove(size_t index) {