Added AFB Helper Guide in Developer Guides

Revised and added AFB Helper Guide as a part of Developer Guides.

Bug-AGL: [SPEC-3633]

Signed-off-by: Shankho Boron Ghosh <shankhoghosh123@gmail.com>
Change-Id: I3df9265ae0570e987d80bc4bd2d3d14e7743b26a
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/25665
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>

8 files changed, 1643 insertions, 0 deletions

diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/1_Usage.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/1_Usage.md
new file mode 100644
index 0000000..80c2c08
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/1_Usage.md
@@ -0,0 +1,83 @@
+---
+title: Usage
+---
+
+## Installation
+
+The afb-helpers library is integrated by default in the AGL SDK since the Guppy
+version (>=7) and is also available as a package for the AGL supported linux
+distributions.
+
+You could find the SDK build from Yocto which embed the afb-helpers library
+here:
+
+- **x86** : [qemux86-64](https://download.automotivelinux.org/AGL/snapshots/master/latest/qemux86-64/deploy/sdk/poky-agl-glibc-x86_64-agl-demo-platform-crosssdk-corei7-64-qemux86-64-toolchain-10.90.0+snapshot.sh)
+
+- **ARM 32 bit** : [qemuarm](https://download.automotivelinux.org/AGL/snapshots/master/latest/qemuarm/deploy/sdk/poky-agl-glibc-x86_64-agl-demo-platform-crosssdk-armv7vet2hf-neon-vfpv4-qemuarm-toolchain-10.90.0+snapshot.sh)
+
+- **AARCH64 - ARM 64bit** : [qemuarm64](https://download.automotivelinux.org/AGL/snapshots/master/latest/qemuarm64/deploy/sdk/poky-agl-glibc-x86_64-agl-demo-platform-crosssdk-aarch64-qemuarm64-toolchain-10.90.0+snapshot.sh)
+
+Then use your package manager to install the library.
+
+### OpenSuse
+
+```bash
+sudo zypper ref
+sudo zypper install agl-libafb-helpers-devel
+```
+
+### Fedora
+
+```bash
+sudo dnf ref
+sudo dnf install agl-libafb-helpers-devel
+```
+
+### Ubuntu/Debian
+
+```bash
+sudo apt-get update
+sudo apt-get install agl-libafb-helpers-dev
+```
+
+## (Optional) Remove the git submodule version
+
+If you already use the afb-helpers component but using the submodule version
+then you have to get rid of it to be sure to link and use the library version.
+To do so, you have to do the following:
+
+* Deinitialize the submodule using `git`
+
+```bash
+# This example assumes that the git submodule is named app-afb-helpers-submodule
+# and is located at your root project repository.
+git submodule deinit app-afb-helpers-submodule
+```
+
+* Remove the submodule relatives lines from the `.gitmodules` file
+
+```bash
+vim .gitmodules
+```
+
+* Remove the `afb-helpers` target link from any CMake target you specified.
+ Those lines look like:
+
+```bash
+TARGET_LINK_LIBRARIES(${TARGET_NAME}
+    afb-helpers # REMOVE THIS LINE
+    ${link_libraries}
+    )
+```
+
+## Add the libafb-helpers as a static library to your binding
+
+In your `config.cmake` file, add a dependency to the controller library, i.e:
+
+```cmake
+set(PKG_REQUIRED_LIST
+	json-c
+	afb-daemon
+	afb-helpers --> this is the afb-helpers library dependency name.
+)
+```
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/2_AFB_Timer.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/2_AFB_Timer.md
new file mode 100644
index 0000000..3af5385
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/2_AFB_Timer.md
@@ -0,0 +1,50 @@
+---
+title: AFB Timer functions
+---
+
+## TimerHandleT
+
+Members are:
+
+* `count`: integer representing the number of times the timers should run.
+* `delay`: millisecond integer representing the delay to wait before and between
+ the callback run.
+* `uid`: a string identifying the timer.
+* `context`: an opaq pointer that could be used in the callback function.
+* `evtSource`: a systemd event source struct. Should be NULL.
+* `api`: the AFB api pointer.
+* `callback`: a function pointer for the callback to call at timer expiration
+* `freeCB`: a function pointer called after expiration of the timer. Mainly meant
+ to release the context pointer by example.
+
+## void TimerEvtStart(afb_api_t api, TimerHandleT *timerHandle, timerCallbackT callback, void *context)
+
+Start a timer which invokes the callback when the delay expires for `count`
+times.
+
+* `api`: AFB api pointer.
+* `timerHandle`: pointer to struct representing a timer.
+* `callback`: a function pointer for the callback to call at timer expiration
+* `context`: an opaq pointer that could be used in the callback function.
+
+## void TimerEvtStop(TimerHandleT *timerHandle)
+
+Manually stop the timer's run. If the `count` isn't finished then it will end
+the timer and no other runs will occur.
+
+* `timerHandle`: pointer to struct representing a timer.
+
+## uint64_t LockWait(afb_api_t api, uint64_t utimeout)
+
+It is function acting like a non-blocking sleep for an API. It lets the main API
+event loop runs while you are waiting and will unlock at the first received
+event and returns the remaining time to wait if an event occurs or 0 if no events
+occured and timeout hits. Then you have to manually ensure that once an event
+has been received that it was the one you are waiting for and if not launch again
+the wait with the remaining time returned.
+
+* `api`: AFB api pointer.
+* `timeout`: timeout in microsecond.
+
+Returns the remaining time in microsecond to wait if an event occurs or 0 if no
+events occured and timeout hits.
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/3_CURL_wrapper.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/3_CURL_wrapper.md
new file mode 100644
index 0000000..c0361fe
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/3_CURL_wrapper.md
@@ -0,0 +1,113 @@
+---
+title: CURL wrapping functions
+---
+
+## int curl_wrap_perform (CURL * curl, char **result, size_t * size)
+
+Perform the CURL operation for 'curl' and put the result in memory. If 'result'
+isn't NULL it receives the returned content that then must be freed. If 'size'
+isn't NULL, it receives the size of the returned content. Note that if not NULL,
+the real content is one byte greater than the read size and the last byte
+zero. This facility allows to handle the returned content as a null terminated
+C-string.
+
+## void curl_wrap_do(CURL *curl, void (*callback)(void *closure, int status, CURL *curl, const char *result, size_t size), void *closure)
+
+Will perform the CURL operation and on success invokes the callback with the
+result and size of the operation or error on a failure.
+
+## int curl_wrap_content_type_is (CURL * curl, const char *value)
+
+Request `Content-Type` information from the curl session with this function
+
+Returns non-zero value if the CURL content type match the `value` and 0 otherwize
+
+## long curl_wrap_response_code_get(CURL *curl)
+
+Request the response code to a CURL operation.
+
+Returns the response code received on success or 0 on failure.
+
+## CURL *curl_wrap_prepare_get_url(const char *url)
+
+Prepare a GET CURL operation on the url given as parameter and Returns the CURL
+pointer.
+
+## CURL *curl_wrap_prepare_get(const char *base, const char *path, const char * const *args)
+
+Prepare a GET CURL operation on the decomposed url and escape it. The `url` has been
+decomposed in 3 parts:
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `args`: optionnal array of arguments provided for the GET request.
+
+Returns the prepared CURL request.
+
+## int curl_wrap_add_header(CURL *curl, const char *header)
+
+Add a header to a CURL operation.
+
+Returns the prepared CURL request.
+
+## int curl_wrap_add_header_value(CURL *curl, const char *name, const char *value)
+
+Add a tuple `name`, `value` to the header of a CURL operation.
+
+Returns the prepared CURL request.
+
+## CURL *curl_wrap_prepare_post_url_data(const char *url, const char *datatype, const char *data, size_t szdata)
+
+Prepare a POST CURL operation on the provided `url`.
+
+* `url`: a HTTP url.
+* `datatype`: HTTP `Content-Type` to use for the operation.
+* `data`: data to send.
+* `szdata`: size of the data to send.
+
+Returns the prepared CURL request.
+
+## CURL *curl_wrap_prepare_post_simple_unescaped(const char *base, const char *path, const char *args)
+
+Prepare a POST CURL operation on an unescaped `url` with arguments provided as
+a simple string.
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `args`: optionnals argument for the POST http request.
+
+Returns the prepared CURL request.
+
+## CURL *curl_wrap_prepare_post_simple_escaped(const char *base, const char *path, char *args)
+
+Prepare a POST CURL operation on an escaped `url` with arguments provided as
+a simple string.
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `args`: optionnals argument for the POST http request.
+
+Returns the prepared CURL request.
+
+## CURL *curl_wrap_prepare_post_unescaped(const char *base, const char *path, const char *separator, const char * const *args)
+
+Prepare a POST CURL operation on an unescaped `url` with arguments provided as
+an array of string concatened with a provided separator string.
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `separator`: string used as a separator when concatening the arguments.
+* `args`: optionnal array of arguments for the POST http request.
+
+Returns the prepared CURL request.
+
+## CURL *curl_wrap_prepare_post_escaped(const char *base, const char *path, const char * const *args)
+
+Prepare a POST CURL operation on an unescaped `url` with arguments provided as
+an array of string concatened without any separator.
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `args`: optionnal array of arguments for the POST http request.
+
+Returns the prepared CURL request.
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/4_URL_Escaping.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/4_URL_Escaping.md
new file mode 100644
index 0000000..4070acb
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/4_URL_Escaping.md
@@ -0,0 +1,39 @@
+---
+title: Escaping helpers functions
+---
+
+## char *escape_url(const char *base, const char *path, const char * const *args, size_t *length)
+
+Escape an `url` and `arguments` and returned it as a string.
+
+* `base`: representing the FQDN of the url.
+* `path`: the path to the requested page.
+* `args`: optionnal array of arguments provided for the GET request.
+* `length`: length of the returned `url`.
+
+Returns the escaped `url`.
+
+## const char *escape_args(const char * const *args, size_t *length)
+
+Escape an array of arguments and returned the lenght of the escaped arguments
+string.
+
+* `args`: array of arguments provided for the GET request.
+* `length`: length of the returned `arguments`.
+
+Returns the escaped `arguments`.
+
+## const char *escape_str(const char *str, size_t *length)
+
+Escape a string and returns it.
+
+* `str`: the string to escape.
+* `length`: length of the returned string.
+
+Returns the escaped string.
+
+## const char **unescape_args(const char *args)
+
+Unescape an argument and returns it.
+
+* `args`: the argument to unescape.
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/5_Filescan_Utils.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/5_Filescan_Utils.md
new file mode 100644
index 0000000..5b220e1
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/5_Filescan_Utils.md
@@ -0,0 +1,82 @@
+---
+title: Filescan Utils functions
+---
+
+## const char *GetMiddleName(const char *name)
+
+Get rid of the binder name prefix 'afbd-'
+
+* name will be typically the full binder name
+
+Returns the process middle name of the running binder.
+
+## const char *GetBinderName()
+
+Get the Binder Name without the prefix set by the AGL appfw 'afbd-'
+
+Returns the Binder name without the prefix.
+
+## json_object* ScanForConfig (const char* searchPath, CtlScanDirModeT mode, const char *prefix, const char *extension)
+
+Scan a directory searching all files matching pattern: 'prefix*extention'.
+
+* `searchPath`: directory where to begin the searching.
+* `mode`: either or not the search will be recursive.
+* `prefix`: file prefix that will be looking for.
+* `extention`: file extention that will be looking for.
+
+Returns a json_object array of object with 2 parts a 'fullpath' describing the
+fullpath to reach the file and 'filename' containing the matched files.
+
+## char *GetAFBRootDirPathUsingFd(int fd)
+
+Get the binder root directory path (the path specified with '--rootdir' option
+at binder launch, if the option is not used, the path from where the binder
+is launched) using binder root directory file descriptor.
+
+* `fd` : Binder root directory file descriptor.
+
+Returns a string representing the path to binder root directory.
+
+## char *GetAFBRootDirPath(afb_api_t apiHandle)
+
+For binding with a version >= 3, same as 'GetAFBRootDirPathUsingFd' function,
+but use pointer to the AFB API as parameter instead of
+binder root directory file descriptor.
+
+* `apiHandle` : pointer to the AFB API.
+
+Returns a string representing the path to binder root directory.
+
+## char* GetBindingDirPath()
+
+For binding with a version <= 2, same as 'GetAFBRootDirPath' function,
+but the pointer to the AFB API is not needed.
+Kept for compatibility issues.
+
+## char* GetBindingDirPath(afb_api_t api)
+
+For binding with a version >= 3, same as 'GetAFBRootDirPath' function.
+Deprecated, please use 'GetAFBRootDirPath' function.
+Kept for compatibility issues.
+
+## char *GetRunningBindingDirPath(afb_api_t api)
+
+For binding with a version >= 3, get the binding directory path
+(the path to the directory that contains the binding).
+
+* `api` : pointer to the AFB API.
+
+Returns a string representing the path to the binding directory.
+
+## const char *getEnvDirList(const char *prefix, const char *suffix)
+
+Get the environment directory colon separated path list. This take the prefix
+add the binder's name then the suffix as environment variable name and also
+search for another variable without the binder's name (so only prefix+suffix).
+
+* `prefix`: Environment variable prefix
+* `suffix`: Environment variable suffix
+
+Returns a string representing a colon separated path list or NULL is case of
+error or none environment variables found.
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/6_Qt_AFB_Websocket_client.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/6_Qt_AFB_Websocket_client.md
new file mode 100644
index 0000000..5572548
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/6_Qt_AFB_Websocket_client.md
@@ -0,0 +1,41 @@
+---
+title: Qt AFB Websocket client
+---
+
+## QAfbWebsocketClient(QObject* parent = nullptr)
+
+Default constructor.
+
+* `parent`: Parent object.
+
+## QAbstractSocket::SocketError error()
+
+Get and return the last error code.
+
+## QString errorString()
+
+Get and return the last error as a string.
+
+## bool isValid()
+
+Check if connection is ready or not.
+
+Returns `true` if the connected is ready to read and write, `false` otherwise.
+
+## void call(const QString& api, const QString& verb, const QJsonValue& arg = QJsonValue(), closure_t closure = nullptr)
+
+Call an api's verb with an argument.
+
+* `api`: Api to call.
+* `verb`: Verb to call.
+* `arg`: Argument to pass.
+* `closure`: callback function to call at the verb reply
+
+## void QAfbWebsocketClient::sendTextMessage(QString msg)
+
+Send a text message over the websocket.
+
+This is use for test only, you should not use this method because it sent text
+**as-is**, so you have to follow the binder's protocol by your self.
+
+* `msg`: Message to send.
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/7_JSON_library_for_modern_C++.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/7_JSON_library_for_modern_C++.md
new file mode 100644
index 0000000..e807476
--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/7_JSON_library_for_modern_C++.md
@@ -0,0 +1,894 @@
+---
+title: JSON library for modern C++
+---
+
+## Design goals
+
+There are myriads of [JSON](http://json.org) libraries out there, and each may even have its reason to exist. Our class had these design goals:
+
+- **Intuitive syntax**. In languages such as Python, JSON feels like a first class data type. We used all the operator magic of modern C++ to achieve the same feeling in your code. Check out the [examples below](#examples) and you'll know what I mean.
+
+- **Trivial integration**. Our whole code consists of a single header file [`json.hpp`](https://github.com/nlohmann/json/blob/develop/src/json.hpp). That's it. No library, no subproject, no dependencies, no complex build system. The class is written in vanilla C++11. All in all, everything should require no adjustment of your compiler flags or project settings.
+
+- **Serious testing**. Our class is heavily [unit-tested](https://github.com/nlohmann/json/blob/master/test/src/unit.cpp) and covers [100%](https://coveralls.io/r/nlohmann/json) of the code, including all exceptional behavior. Furthermore, we checked with [Valgrind](http://valgrind.org) that there are no memory leaks. To maintain high quality, the project is following the [Core Infrastructure Initiative (CII) best practices](https://bestpractices.coreinfrastructure.org/projects/289).
+
+Other aspects were not so important to us:
+
+- **Memory efficiency**. Each JSON object has an overhead of one pointer (the maximal size of a union) and one enumeration element (1 byte). The default generalization uses the following C++ data types: `std::string` for strings, `int64_t`, `uint64_t` or `double` for numbers, `std::map` for objects, `std::vector` for arrays, and `bool` for Booleans. However, you can template the generalized class `basic_json` to your needs.
+
+- **Speed**. There are certainly [faster JSON libraries](https://github.com/miloyip/nativejson-benchmark#parsing-time) out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a `std::vector` or `std::map`, you are already set.
+
+See the [contribution guidelines](https://github.com/nlohmann/json/blob/master/.github/CONTRIBUTING.md#please-dont) for more information.
+
+## Integration
+
+The single required source, file `json.hpp` is in the `src` directory or [released here](https://github.com/nlohmann/json/releases). All you need to do is add
+
+```cpp
+#include "json.hpp"
+
+// for convenience
+using json = nlohmann::json;
+```
+
+to the files you want to use JSON objects. That's it. Do not forget to set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and Clang).
+
+:beer: If you are using OS X and [Homebrew](http://brew.sh), just type `brew tap nlohmann/json` and `brew install nlohmann_json` and you're set. If you want the bleeding edge rather than the latest release, use `brew install nlohmann_json --HEAD`.
+
+If you are using the [Meson Build System](http://mesonbuild.com), then you can wrap this repo as a subproject.
+
+If you are using [Conan](https://www.conan.io/) to manage your dependencies, merely add `jsonformoderncpp/x.y.z@vthiery/stable` to your `conanfile.py`'s requires, where `x.y.z` is the release version you want to use. Please file issues [here](https://github.com/vthiery/conan-jsonformoderncpp/issues) if you experience problems with the packages.
+
+If you are using [hunter](https://github.com/ruslo/hunter/) on your project for external dependencies, then you can use the [nlohman_json package](https://github.com/ruslo/hunter/wiki/pkg.nlohmann_json). Please see the hunter project for any issues regarding the packaging.
+
+:warning: [Version 3.0.0](https://github.com/nlohmann/json/wiki/Road-toward-3.0.0) is currently under development. Branch `develop` is used for the ongoing work and is probably **unstable**. Please use the `master` branch for the last stable version 2.1.1.
+
+## Examples
+
+Beside the examples below, you may want to check the [documentation](https://nlohmann.github.io/json/) where each function contains a separate code example (e.g., check out [`emplace()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a602f275f0359ab181221384989810604.html#a602f275f0359ab181221384989810604)). All [example files](https://github.com/nlohmann/json/tree/develop/doc/examples) can be compiled and executed on their own (e.g., file [emplace.cpp](https://github.com/nlohmann/json/blob/develop/doc/examples/emplace.cpp)).
+
+### JSON as first-class data type
+
+Here are some examples to give you an idea how to use the class.
+
+Assume you want to create the JSON object
+
+```json
+{
+  "pi": 3.141,
+  "happy": true,
+  "name": "Niels",
+  "nothing": null,
+  "answer": {
+    "everything": 42
+  },
+  "list": [1, 0, 2],
+  "object": {
+    "currency": "USD",
+    "value": 42.99
+  }
+}
+```
+
+With the JSON class, you could write:
+
+```cpp
+// create an empty structure (null)
+json j;
+
+// add a number that is stored as double (note the implicit conversion of j to an object)
+j["pi"] = 3.141;
+
+// add a Boolean that is stored as bool
+j["happy"] = true;
+
+// add a string that is stored as std::string
+j["name"] = "Niels";
+
+// add another null object by passing nullptr
+j["nothing"] = nullptr;
+
+// add an object inside the object
+j["answer"]["everything"] = 42;
+
+// add an array that is stored as std::vector (using an initializer list)
+j["list"] = { 1, 0, 2 };
+
+// add another object (using an initializer list of pairs)
+j["object"] = { {"currency", "USD"}, {"value", 42.99} };
+
+// instead, you could also write (which looks very similar to the JSON above)
+json j2 = {
+  {"pi", 3.141},
+  {"happy", true},
+  {"name", "Niels"},
+  {"nothing", nullptr},
+  {"answer", {
+    {"everything", 42}
+  }},
+  {"list", {1, 0, 2}},
+  {"object", {
+    {"currency", "USD"},
+    {"value", 42.99}
+  }}
+};
+```
+
+Note that in all these cases, you never need to "tell" the compiler which JSON value you want to use. If you want to be explicit or express some edge cases, the functions `json::array` and `json::object` will help:
+
+```cpp
+// a way to express the empty array []
+json empty_array_explicit = json::array();
+
+// ways to express the empty object {}
+json empty_object_implicit = json({});
+json empty_object_explicit = json::object();
+
+// a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]]
+json array_not_object = { json::array({"currency", "USD"}), json::array({"value", 42.99}) };
+```
+
+### Serialization / Deserialization
+
+#### To/from strings
+
+You can create an object (deserialization) by appending `_json` to a string literal:
+
+```cpp
+// create object from string literal
+json j = "{ \"happy\": true, \"pi\": 3.141 }"_json;
+
+// or even nicer with a raw string literal
+auto j2 = R"(
+  {
+    "happy": true,
+    "pi": 3.141
+  }
+)"_json;
+```
+
+Note that without appending the `_json` suffix, the passed string literal is not parsed, but just used as JSON string value. That is, `json j = "{ \"happy\": true, \"pi\": 3.141 }"` would just store the string `"{ "happy": true, "pi": 3.141 }"` rather than parsing the actual object.
+
+The above example can also be expressed explicitly using `json::parse()`:
+
+```cpp
+// parse explicitly
+auto j3 = json::parse("{ \"happy\": true, \"pi\": 3.141 }");
+```
+
+You can also get a string representation (serialize):
+
+```cpp
+// explicit conversion to string
+std::string s = j.dump();    // {\"happy\":true,\"pi\":3.141}
+
+// serialization with pretty printing
+// pass in the amount of spaces to indent
+std::cout << j.dump(4) << std::endl;
+// {
+//     "happy": true,
+//     "pi": 3.141
+// }
+```
+
+#### To/from streams (e.g. files, string streams)
+
+You can also use streams to serialize and deserialize:
+
+```cpp
+// deserialize from standard input
+json j;
+std::cin >> j;
+
+// serialize to standard output
+std::cout << j;
+
+// the setw manipulator was overloaded to set the indentation for pretty printing
+std::cout << std::setw(4) << j << std::endl;
+```
+
+These operators work for any subclasses of `std::istream` or `std::ostream`. Here is the same example with files:
+
+```cpp
+// read a JSON file
+std::ifstream i("file.json");
+json j;
+i >> j;
+
+// write prettified JSON to another file
+std::ofstream o("pretty.json");
+o << std::setw(4) << j << std::endl;
+```
+
+Please note that setting the exception bit for `failbit` is inappropriate for this use case. It will result in program termination due to the `noexcept` specifier in use.
+
+#### Read from iterator range
+
+You can also read JSON from an iterator range; that is, from any container accessible by iterators whose content is stored as contiguous byte sequence, for instance a `std::vector<std::uint8_t>`:
+
+```cpp
+std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
+json j = json::parse(v.begin(), v.end());
+```
+
+You may leave the iterators for the range [begin, end):
+
+```cpp
+std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
+json j = json::parse(v);
+```
+
+### STL-like access
+
+We designed the JSON class to behave just like an STL container. In fact, it satisfies the [**ReversibleContainer**](http://en.cppreference.com/w/cpp/concept/ReversibleContainer) requirement.
+
+```cpp
+// create an array using push_back
+json j;
+j.push_back("foo");
+j.push_back(1);
+j.push_back(true);
+
+// also use emplace_back
+j.emplace_back(1.78);
+
+// iterate the array
+for (json::iterator it = j.begin(); it != j.end(); ++it) {
+  std::cout << *it << '\n';
+}
+
+// range-based for
+for (auto& element : j) {
+  std::cout << element << '\n';
+}
+
+// getter/setter
+const std::string tmp = j[0];
+j[1] = 42;
+bool foo = j.at(2);
+
+// comparison
+j == "[\"foo\", 1, true]"_json;  // true
+
+// other stuff
+j.size();     // 3 entries
+j.empty();    // false
+j.type();     // json::value_t::array
+j.clear();    // the array is empty again
+
+// convenience type checkers
+j.is_null();
+j.is_boolean();
+j.is_number();
+j.is_object();
+j.is_array();
+j.is_string();
+
+// create an object
+json o;
+o["foo"] = 23;
+o["bar"] = false;
+o["baz"] = 3.141;
+
+// also use emplace
+o.emplace("weather", "sunny");
+
+// special iterator member functions for objects
+for (json::iterator it = o.begin(); it != o.end(); ++it) {
+  std::cout << it.key() << " : " << it.value() << "\n";
+}
+
+// find an entry
+if (o.find("foo") != o.end()) {
+  // there is an entry with key "foo"
+}
+
+// or simpler using count()
+int foo_present = o.count("foo"); // 1
+int fob_present = o.count("fob"); // 0
+
+// delete an entry
+o.erase("foo");
+```
+
+### Conversion from STL containers
+
+Any sequence container (`std::array`, `std::vector`, `std::deque`, `std::forward_list`, `std::list`) whose values can be used to construct JSON types (e.g., integers, floating point numbers, Booleans, string types, or again STL containers described in this section) can be used to create a JSON array. The same holds for similar associative containers (`std::set`, `std::multiset`, `std::unordered_set`, `std::unordered_multiset`), but in these cases the order of the elements of the array depends how the elements are ordered in the respective STL container.
+
+```cpp
+std::vector<int> c_vector {1, 2, 3, 4};
+json j_vec(c_vector);
+// [1, 2, 3, 4]
+
+std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6};
+json j_deque(c_deque);
+// [1.2, 2.3, 3.4, 5.6]
+
+std::list<bool> c_list {true, true, false, true};
+json j_list(c_list);
+// [true, true, false, true]
+
+std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543};
+json j_flist(c_flist);
+// [12345678909876, 23456789098765, 34567890987654, 45678909876543]
+
+std::array<unsigned long, 4> c_array {{1, 2, 3, 4}};
+json j_array(c_array);
+// [1, 2, 3, 4]
+
+std::set<std::string> c_set {"one", "two", "three", "four", "one"};
+json j_set(c_set); // only one entry for "one" is used
+// ["four", "one", "three", "two"]
+
+std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"};
+json j_uset(c_uset); // only one entry for "one" is used
+// maybe ["two", "three", "four", "one"]
+
+std::multiset<std::string> c_mset {"one", "two", "one", "four"};
+json j_mset(c_mset); // both entries for "one" are used
+// maybe ["one", "two", "one", "four"]
+
+std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"};
+json j_umset(c_umset); // both entries for "one" are used
+// maybe ["one", "two", "one", "four"]
+```
+
+Likewise, any associative key-value containers (`std::map`, `std::multimap`, `std::unordered_map`, `std::unordered_multimap`) whose keys can construct an `std::string` and whose values can be used to construct JSON types (see examples above) can be used to create a JSON object. Note that in case of multimaps only one key is used in the JSON object and the value depends on the internal order of the STL container.
+
+```cpp
+std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} };
+json j_map(c_map);
+// {"one": 1, "three": 3, "two": 2 }
+
+std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} };
+json j_umap(c_umap);
+// {"one": 1.2, "two": 2.3, "three": 3.4}
+
+std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
+json j_mmap(c_mmap); // only one entry for key "three" is used
+// maybe {"one": true, "two": true, "three": true}
+
+std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
+json j_ummap(c_ummap); // only one entry for key "three" is used
+// maybe {"one": true, "two": true, "three": true}
+```
+
+### JSON Pointer and JSON Patch
+
+The library supports **JSON Pointer** ([RFC 6901](https://tools.ietf.org/html/rfc6901)) as alternative means to address structured values. On top of this, **JSON Patch** ([RFC 6902](https://tools.ietf.org/html/rfc6902)) allows to describe differences between two JSON values - effectively allowing patch and diff operations known from Unix.
+
+```cpp
+// a JSON value
+json j_original = R"({
+  "baz": ["one", "two", "three"],
+  "foo": "bar"
+})"_json;
+
+// access members with a JSON pointer (RFC 6901)
+j_original["/baz/1"_json_pointer];
+// "two"
+
+// a JSON patch (RFC 6902)
+json j_patch = R"([
+  { "op": "replace", "path": "/baz", "value": "boo" },
+  { "op": "add", "path": "/hello", "value": ["world"] },
+  { "op": "remove", "path": "/foo"}
+])"_json;
+
+// apply the patch
+json j_result = j_original.patch(j_patch);
+// {
+//    "baz": "boo",
+//    "hello": ["world"]
+// }
+
+// calculate a JSON patch from two JSON values
+json::diff(j_result, j_original);
+// [
+//   { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] },
+//   { "op": "remove","path": "/hello" },
+//   { "op": "add", "path": "/foo", "value": "bar" }
+// ]
+```
+
+### Implicit conversions
+
+The type of the JSON object is determined automatically by the expression to store. Likewise, the stored value is implicitly converted.
+
+```cpp
+// strings
+std::string s1 = "Hello, world!";
+json js = s1;
+std::string s2 = js;
+
+// Booleans
+bool b1 = true;
+json jb = b1;
+bool b2 = jb;
+
+// numbers
+int i = 42;
+json jn = i;
+double f = jn;
+
+// etc.
+```
+
+You can also explicitly ask for the value:
+
+```cpp
+std::string vs = js.get<std::string>();
+bool vb = jb.get<bool>();
+int vi = jn.get<int>();
+
+// etc.
+```
+
+### Arbitrary types conversions
+
+Every type can be serialized in JSON, not just STL-containers and scalar types. Usually, you would do something along those lines:
+
+```cpp
+namespace ns {
+    // a simple struct to model a person
+    struct person {
+        std::string name;
+        std::string address;
+        int age;
+    };
+}
+
+ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
+
+// convert to JSON: copy each value into the JSON object
+json j;
+j["name"] = p.name;
+j["address"] = p.address;
+j["age"] = p.age;
+
+// ...
+
+// convert from JSON: copy each value from the JSON object
+ns::person p {
+    j["name"].get<std::string>(),
+    j["address"].get<std::string>(),
+    j["age"].get<int>()
+};
+```
+
+It works, but that's quite a lot of boilerplate... Fortunately, there's a better way:
+
+```cpp
+// create a person
+ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60};
+
+// conversion: person -> json
+json j = p;
+
+std::cout << j << std::endl;
+// {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
+
+// conversion: json -> person
+ns::person p2 = j;
+
+// that's it
+assert(p == p2);
+```
+
+#### Basic usage
+
+To make this work with one of your types, you only need to provide two functions:
+
+```cpp
+using nlohmann::json;
+
+namespace ns {
+    void to_json(json& j, const person& p) {
+        j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
+    }
+
+    void from_json(const json& j, person& p) {
+        p.name = j.at("name").get<std::string>();
+        p.address = j.at("address").get<std::string>();
+        p.age = j.at("age").get<int>();
+    }
+} // namespace ns
+```
+
+That's all! When calling the `json` constructor with your type, your custom `to_json` method will be automatically called.
+Likewise, when calling `get<your_type>()`, the `from_json` method will be called.
+
+Some important things:
+
+- Those methods **MUST** be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace `ns`, where `person` is defined).
+- When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](http://en.cppreference.com/w/cpp/concept/DefaultConstructible). (There is a way to bypass this requirement described later.)
+- In function `from_json`, use function [`at()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a93403e803947b86f4da2d1fb3345cf2c.html#a93403e803947b86f4da2d1fb3345cf2c) to access the object values rather than `operator[]`. In case a key does not exists, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
+- In case your type contains several `operator=` definitions, code like `your_variable = your_json;` [may not compile](https://github.com/nlohmann/json/issues/667). You need to write `your_variable = your_json.get<decltype your_variable>();` instead.
+- You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
+
+#### How do I convert third-party types?
+
+This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:
+
+The library uses **JSON Serializers** to convert types to json.
+The default serializer for `nlohmann::json` is `nlohmann::adl_serializer` (ADL means [Argument-Dependent Lookup](http://en.cppreference.com/w/cpp/language/adl)).
+
+It is implemented like this (simplified):
+
+```cpp
+template <typename T>
+struct adl_serializer {
+    static void to_json(json& j, const T& value) {
+        // calls the "to_json" method in T's namespace
+    }
+
+    static void from_json(const json& j, T& value) {
+        // same thing, but with the "from_json" method
+    }
+};
+```
+
+This serializer works fine when you have control over the type's namespace. However, what about `boost::optional`, or `std::filesystem::path` (C++17)? Hijacking the `boost` namespace is pretty bad, and it's illegal to add something other than template specializations to `std`...
+
+To solve this, you need to add a specialization of `adl_serializer` to the `nlohmann` namespace, here's an example:
+
+```cpp
+// partial specialization (full specialization works too)
+namespace nlohmann {
+    template <typename T>
+    struct adl_serializer<boost::optional<T>> {
+        static void to_json(json& j, const boost::optional<T>& opt) {
+            if (opt == boost::none) {
+                j = nullptr;
+            } else {
+              j = *opt; // this will call adl_serializer<T>::to_json which will
+                        // find the free function to_json in T's namespace!
+            }
+        }
+
+        static void from_json(const json& j, boost::optional<T>& opt) {
+            if (j.is_null()) {
+                opt = boost::none;
+            } else {
+                opt = j.get<T>(); // same as above, but with
+                                  // adl_serializer<T>::from_json
+            }
+        }
+    };
+}
+```
+
+#### How can I use `get()` for non-default constructible/non-copyable types?
+
+There is a way, if your type is [MoveConstructible](http://en.cppreference.com/w/cpp/concept/MoveConstructible). You will need to specialize the `adl_serializer` as well, but with a special `from_json` overload:
+
+```cpp
+struct move_only_type {
+    move_only_type() = delete;
+    move_only_type(int ii): i(ii) {}
+    move_only_type(const move_only_type&) = delete;
+    move_only_type(move_only_type&&) = default;
+
+    int i;
+};
+
+namespace nlohmann {
+    template <>
+    struct adl_serializer<move_only_type> {
+        // note: the return type is no longer 'void', and the method only takes
+        // one argument
+        static move_only_type from_json(const json& j) {
+            return {j.get<int>()};
+        }
+
+        // Here's the catch! You must provide a to_json method! Otherwise you
+        // will not be able to convert move_only_type to json, since you fully
+        // specialized adl_serializer on that type
+        static void to_json(json& j, move_only_type t) {
+            j = t.i;
+        }
+    };
+}
+```
+
+#### Can I write my own serializer? (Advanced use)
+
+Yes. You might want to take a look at [`unit-udt.cpp`](https://github.com/nlohmann/json/blob/develop/test/src/unit-udt.cpp) in the test suite, to see a few examples.
+
+If you write your own serializer, you'll need to do a few things:
+
+- use a different `basic_json` alias than `nlohmann::json` (the last template parameter of `basic_json` is the `JSONSerializer`)
+- use your `basic_json` alias (or a template parameter) in all your `to_json`/`from_json` methods
+- use `nlohmann::to_json` and `nlohmann::from_json` when you need ADL
+
+Here is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL.
+
+```cpp
+// You should use void as a second template argument
+// if you don't need compile-time checks on T
+template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type>
+struct less_than_32_serializer {
+    template <typename BasicJsonType>
+    static void to_json(BasicJsonType& j, T value) {
+        // we want to use ADL, and call the correct to_json overload
+        using nlohmann::to_json; // this method is called by adl_serializer,
+                                 // this is where the magic happens
+        to_json(j, value);
+    }
+
+    template <typename BasicJsonType>
+    static void from_json(const BasicJsonType& j, T& value) {
+        // same thing here
+        using nlohmann::from_json;
+        from_json(j, value);
+    }
+};
+```
+
+Be **very** careful when reimplementing your serializer, you can stack overflow if you don't pay attention:
+
+```cpp
+template <typename T, void>
+struct bad_serializer
+{
+    template <typename BasicJsonType>
+    static void to_json(BasicJsonType& j, const T& value) {
+      // this calls BasicJsonType::json_serializer<T>::to_json(j, value);
+      // if BasicJsonType::json_serializer == bad_serializer ... oops!
+      j = value;
+    }
+
+    template <typename BasicJsonType>
+    static void to_json(const BasicJsonType& j, T& value) {
+      // this calls BasicJsonType::json_serializer<T>::from_json(j, value);
+      // if BasicJsonType::json_serializer == bad_serializer ... oops!
+      value = j.template get<T>(); // oops!
+    }
+};
+```
+
+### Binary formats (CBOR and MessagePack)
+
+Though JSON is a ubiquitous data format, it is not a very compact format suitable for data exchange, for instance over a network. Hence, the library supports [CBOR](http://cbor.io) (Concise Binary Object Representation) and [MessagePack](http://msgpack.org) to efficiently encode JSON values to byte vectors and to decode such vectors.
+
+```cpp
+// create a JSON value
+json j = R"({"compact": true, "schema": 0})"_json;
+
+// serialize to CBOR
+std::vector<std::uint8_t> v_cbor = json::to_cbor(j);
+
+// 0xa2, 0x67, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63, 0x74, 0xf5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6d, 0x61, 0x00
+
+// roundtrip
+json j_from_cbor = json::from_cbor(v_cbor);
+
+// serialize to MessagePack
+std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j);
+
+// 0x82, 0xa7, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63, 0x74, 0xc3, 0xa6, 0x73, 0x63, 0x68, 0x65, 0x6d, 0x61, 0x00
+
+// roundtrip
+json j_from_msgpack = json::from_msgpack(v_msgpack);
+```
+
+## Supported compilers
+
+Though it's 2016 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
+
+- GCC 4.9 - 7.1 (and possibly later)
+- Clang 3.4 - 5.0 (and possibly later)
+- Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
+- Microsoft Visual C++ 2017 / Build Tools 15.1.548.43366 (and possibly later)
+
+I would be happy to learn about other compilers/versions.
+
+Please note:
+
+- GCC 4.8 does not work because of two bugs ([55817](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55817) and [57824](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57824)) in the C++11 support. Note there is a [pull request](https://github.com/nlohmann/json/pull/212) to fix some of the issues.
+- Android defaults to using very old compilers and C++ libraries. To fix this, add the following to your `Application.mk`. This will switch to the LLVM C++ library, the Clang compiler, and enable C++11 and other features disabled by default.
+
+```bb
+    APP_STL := c++_shared
+    NDK_TOOLCHAIN_VERSION := clang3.6
+    APP_CPPFLAGS += -frtti -fexceptions
+```
+
+The code compiles successfully with [Android NDK](https://developer.android.com/ndk/index.html?hl=ml), Revision 9 - 11 (and possibly later) and [CrystaX's Android NDK](https://www.crystax.net/en/android/ndk) version 10.
+
+- For GCC running on MinGW or Android SDK, the error `'to_string' is not a member of 'std'` (or similarly, for `strtod`) may occur. Note this is not an issue with the code,  but rather with the compiler itself. On Android, see above to build with a newer environment.  For MinGW, please refer to [this site](http://tehsausage.com/mingw-to-string) and [this discussion](https://github.com/nlohmann/json/issues/136) for information on how to fix this bug. For Android NDK using `APP_STL := gnustl_static`, please refer to [this discussion](https://github.com/nlohmann/json/issues/219).
+
+The following compilers are currently used in continuous integration at [Travis](https://travis-ci.org/nlohmann/json) and [AppVeyor](https://ci.appveyor.com/project/nlohmann/json):
+
+| Compiler        | Operating System             | Version String |
+|-----------------|------------------------------|----------------|
+| GCC 4.9.4       | Ubuntu 14.04.5 LTS           | g++-4.9 (Ubuntu 4.9.4-2ubuntu1~14.04.1) 4.9.4 |
+| GCC 5.4.1       | Ubuntu 14.04.5 LTS           | g++-5 (Ubuntu 5.4.1-2ubuntu1~14.04) 5.4.1 20160904 |
+| GCC 6.3.0       | Ubuntu 14.04.5 LTS           | g++-6 (Ubuntu/Linaro 6.3.0-18ubuntu2~14.04) 6.3.0 20170519 |
+| GCC 7.1.0       | Ubuntu 14.04.5 LTS           | g++-7 (Ubuntu 7.1.0-5ubuntu2~14.04) 7.1.0
+| Clang 3.5.0     | Ubuntu 14.04.5 LTS           | clang version 3.5.0-4ubuntu2~trusty2 (tags/RELEASE_350/final) |
+| Clang 3.6.2     | Ubuntu 14.04.5 LTS           | clang version 3.6.2-svn240577-1~exp1 (branches/release_36) |
+| Clang 3.7.1     | Ubuntu 14.04.5 LTS           | clang version 3.7.1-svn253571-1~exp1 (branches/release_37) |
+| Clang 3.8.0     | Ubuntu 14.04.5 LTS           | clang version 3.8.0-2ubuntu3~trusty5 (tags/RELEASE_380/final) |
+| Clang 3.9.1     | Ubuntu 14.04.5 LTS           | clang version 3.9.1-4ubuntu3~14.04.2 (tags/RELEASE_391/rc2) |
+| Clang 4.0.1     | Ubuntu 14.04.5 LTS           | clang version 4.0.1-svn305264-1~exp1 (branches/release_40) |
+| Clang 5.0.0     | Ubuntu 14.04.5 LTS           | clang version 5.0.0-svn310902-1~exp1 (branches/release_50) |
+| Clang Xcode 6.4 | Darwin Kernel Version 14.3.0 (OSX 10.10.3) | Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn) |
+| Clang Xcode 7.3 | Darwin Kernel Version 15.0.0 (OSX 10.10.5) | Apple LLVM version 7.3.0 (clang-703.0.29) |
+| Clang Xcode 8.0 | Darwin Kernel Version 15.6.0 | Apple LLVM version 8.0.0 (clang-800.0.38) |
+| Clang Xcode 8.1 | Darwin Kernel Version 16.1.0 (macOS 10.12.1) | Apple LLVM version 8.0.0 (clang-800.0.42.1) |
+| Clang Xcode 8.2 | Darwin Kernel Version 16.1.0 (macOS 10.12.1) | Apple LLVM version 8.0.0 (clang-800.0.42.1) |
+| Clang Xcode 8.3 | Darwin Kernel Version 16.5.0 (macOS 10.12.4) | Apple LLVM version 8.1.0 (clang-802.0.38) |
+| Clang Xcode 9 beta | Darwin Kernel Version 16.6.0 (macOS 10.12.5) | Apple LLVM version 9.0.0 (clang-900.0.26) |
+| Visual Studio 14 2015 | Windows Server 2012 R2 (x64) | Microsoft (R) Build Engine version 14.0.25420.1 |
+| Visual Studio 2017 | Windows Server 2016 | Microsoft (R) Build Engine version 15.1.1012.6693 |
+
+## License
+
+The class is licensed under the [MIT License](http://opensource.org/licenses/MIT):
+
+Copyright &copy; 2013-2017 [Niels Lohmann](http://nlohmann.me)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+## Thanks
+
+I deeply appreciate the help of the following people.
+
+- [Teemperor](https://github.com/Teemperor) implemented CMake support and lcov integration, realized escape and Unicode handling in the string parser, and fixed the JSON serialization.
+- [elliotgoodrich](https://github.com/elliotgoodrich) fixed an issue with double deletion in the iterator classes.
+- [kirkshoop](https://github.com/kirkshoop) made the iterators of the class composable to other libraries.
+- [wancw](https://github.com/wanwc) fixed a bug that hindered the class to compile with Clang.
+- Tomas Åblad found a bug in the iterator implementation.
+- [Joshua C. Randall](https://github.com/jrandall) fixed a bug in the floating-point serialization.
+- [Aaron Burghardt](https://github.com/aburgh) implemented code to parse streams incrementally. Furthermore, he greatly improved the parser class by allowing the definition of a filter function to discard undesired elements while parsing.
+- [Daniel Kopeček](https://github.com/dkopecek) fixed a bug in the compilation with GCC 5.0.
+- [Florian Weber](https://github.com/Florianjw) fixed a bug in and improved the performance of the comparison operators.
+- [Eric Cornelius](https://github.com/EricMCornelius) pointed out a bug in the handling with NaN and infinity values. He also improved the performance of the string escaping.
+- [易思龙](https://github.com/likebeta) implemented a conversion from anonymous enums.
+- [kepkin](https://github.com/kepkin) patiently pushed forward the support for Microsoft Visual studio.
+- [gregmarr](https://github.com/gregmarr) simplified the implementation of reverse iterators and helped with numerous hints and improvements. In particular, he pushed forward the implementation of user-defined types.
+- [Caio Luppi](https://github.com/caiovlp) fixed a bug in the Unicode handling.
+- [dariomt](https://github.com/dariomt) fixed some typos in the examples.
+- [Daniel Frey](https://github.com/d-frey) cleaned up some pointers and implemented exception-safe memory allocation.
+- [Colin Hirsch](https://github.com/ColinH) took care of a small namespace issue.
+- [Huu Nguyen](https://github.com/whoshuu) correct a variable name in the documentation.
+- [Silverweed](https://github.com/silverweed) overloaded `parse()` to accept an rvalue reference.
+- [dariomt](https://github.com/dariomt) fixed a subtlety in MSVC type support and implemented the `get_ref()` function to get a reference to stored values.
+- [ZahlGraf](https://github.com/ZahlGraf) added a workaround that allows compilation using Android NDK.
+- [whackashoe](https://github.com/whackashoe) replaced a function that was marked as unsafe by Visual Studio.
+- [406345](https://github.com/406345) fixed two small warnings.
+- [Glen Fernandes](https://github.com/glenfe) noted a potential portability problem in the `has_mapped_type` function.
+- [Corbin Hughes](https://github.com/nibroc) fixed some typos in the contribution guidelines.
+- [twelsby](https://github.com/twelsby) fixed the array subscript operator, an issue that failed the MSVC build, and floating-point parsing/dumping. He further added support for unsigned integer numbers and implemented better roundtrip support for parsed numbers.
+- [Volker Diels-Grabsch](https://github.com/vog) fixed a link in the README file.
+- [msm-](https://github.com/msm-) added support for american fuzzy lop.
+- [Annihil](https://github.com/Annihil) fixed an example in the README file.
+- [Themercee](https://github.com/Themercee) noted a wrong URL in the README file.
+- [Lv Zheng](https://github.com/lv-zheng) fixed a namespace issue with `int64_t` and `uint64_t`.
+- [abc100m](https://github.com/abc100m) analyzed the issues with GCC 4.8 and proposed a [partial solution](https://github.com/nlohmann/json/pull/212).
+- [zewt](https://github.com/zewt) added useful notes to the README file about Android.
+- [Róbert Márki](https://github.com/robertmrk) added a fix to use move iterators and improved the integration via CMake.
+- [Chris Kitching](https://github.com/ChrisKitching) cleaned up the CMake files.
+- [Tom Needham](https://github.com/06needhamt) fixed a subtle bug with MSVC 2015 which was also proposed by [Michael K.](https://github.com/Epidal).
+- [Mário Feroldi](https://github.com/thelostt) fixed a small typo.
+- [duncanwerner](https://github.com/duncanwerner) found a really embarrassing performance regression in the 2.0.0 release.
+- [Damien](https://github.com/dtoma) fixed one of the last conversion warnings.
+- [Thomas Braun](https://github.com/t-b) fixed a warning in a test case.
+- [Théo DELRIEU](https://github.com/theodelrieu) patiently and constructively oversaw the long way toward [iterator-range parsing](https://github.com/nlohmann/json/issues/290). He also implemented the magic behind the serialization/deserialization of user-defined types.
+- [Stefan](https://github.com/5tefan) fixed a minor issue in the documentation.
+- [Vasil Dimov](https://github.com/vasild) fixed the documentation regarding conversions from `std::multiset`.
+- [ChristophJud](https://github.com/ChristophJud) overworked the CMake files to ease project inclusion.
+- [Vladimir Petrigo](https://github.com/vpetrigo) made a SFINAE hack more readable and added Visual Studio 17 to the build matrix.
+- [Denis Andrejew](https://github.com/seeekr) fixed a grammar issue in the README file.
+- [Pierre-Antoine Lacaze](https://github.com/palacaze) found a subtle bug in the `dump()` function.
+- [TurpentineDistillery](https://github.com/TurpentineDistillery) pointed to [`std::locale::classic()`](http://en.cppreference.com/w/cpp/locale/locale/classic) to avoid too much locale joggling, found some nice performance improvements in the parser, improved the benchmarking code, and realized locale-independent number parsing and printing.
+- [cgzones](https://github.com/cgzones) had an idea how to fix the Coverity scan.
+- [Jared Grubb](https://github.com/jaredgrubb) silenced a nasty documentation warning.
+- [Yixin Zhang](https://github.com/qwename) fixed an integer overflow check.
+- [Bosswestfalen](https://github.com/Bosswestfalen) merged two iterator classes into a smaller one.
+- [Daniel599](https://github.com/Daniel599) helped to get Travis execute the tests with Clang's sanitizers.
+- [Jonathan Lee](https://github.com/vjon) fixed an example in the README file.
+- [gnzlbg](https://github.com/gnzlbg) supported the implementation of user-defined types.
+- [Alexej Harm](https://github.com/qis) helped to get the user-defined types working with Visual Studio.
+- [Jared Grubb](https://github.com/jaredgrubb) supported the implementation of user-defined types.
+- [EnricoBilla](https://github.com/EnricoBilla) noted a typo in an example.
+- [Martin Hořeňovský](https://github.com/horenmar) found a way for a 2x speedup for the compilation time of the test suite.
+- [ukhegg](https://github.com/ukhegg) found proposed an improvement for the examples section.
+- [rswanson-ihi](https://github.com/rswanson-ihi) noted a typo in the README.
+- [Mihai Stan](https://github.com/stanmihai4) fixed a bug in the comparison with `nullptr`s.
+- [Tushar Maheshwari](https://github.com/tusharpm) added [cotire](https://github.com/sakra/cotire) support to speed up the compilation.
+- [TedLyngmo](https://github.com/TedLyngmo) noted a typo in the README, removed unnecessary bit arithmetic, and fixed some `-Weffc++` warnings.
+- [Krzysztof Woś](https://github.com/krzysztofwos) made exceptions more visible.
+- [ftillier](https://github.com/ftillier) fixed a compiler warning.
+- [tinloaf](https://github.com/tinloaf) made sure all pushed warnings are properly popped.
+- [Fytch](https://github.com/Fytch) found a bug in the documentation.
+- [Jay Sistar](https://github.com/Type1J) implemented a Meson build description.
+- [Henry Lee](https://github.com/HenryRLee) fixed a warning in ICC and improved the iterator implementation.
+- [Vincent Thiery](https://github.com/vthiery) maintains a package for the Conan package manager.
+- [Steffen](https://github.com/koemeet) fixed a potential issue with MSVC and `std::min`.
+- [Mike Tzou](https://github.com/Chocobo1) fixed some typos.
+- [amrcode](https://github.com/amrcode) noted a missleading documentation about comparison of floats.
+- [Oleg Endo](https://github.com/olegendo) reduced the memory consumption by replacing `<iostream>` with `<iosfwd>`.
+- [dan-42](https://github.com/dan-42) cleaned up the CMake files to simplify including/reusing of the library.
+- [Nikita Ofitserov](https://github.com/himikof) allowed for moving values from initializer lists.
+- [Greg Hurrell](https://github.com/wincent) fixed a typo.
+- [Dmitry Kukovinets](https://github.com/DmitryKuk) fixed a typo.
+- [kbthomp1](https://github.com/kbthomp1) fixed an issue related to the Intel OSX compiler.
+- [Markus Werle](https://github.com/daixtrose) fixed a typo.
+- [WebProdPP](https://github.com/WebProdPP) fixed a subtle error in a precondition check.
+
+Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I forgot someone.
+
+## Used third-party tools
+
+The library itself contains of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!
+
+- [**American fuzzy lop**](http://lcamtuf.coredump.cx/afl/) for fuzz testing
+- [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows
+- [**Artistic Style**](http://astyle.sourceforge.net) for automatic source code identation
+- [**benchpress**](https://github.com/sbs-ableton/benchpress) to benchmark the code
+- [**Catch**](https://github.com/philsquared/Catch) for the unit tests
+- [**Clang**](http://clang.llvm.org) for compilation with code sanitizers
+- [**Cmake**](https://cmake.org) for build automation
+- [**Codacity**](https://www.codacy.com) for further [code analysis](https://www.codacy.com/app/nlohmann/json)
+- [**cotire**](https://github.com/sakra/cotire) to speed of compilation
+- [**Coveralls**](https://coveralls.io) to measure [code coverage](https://coveralls.io/github/nlohmann/json)
+- [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json)
+- [**cppcheck**](http://cppcheck.sourceforge.net) for static analysis
+- [**cxxopts**](https://github.com/jarro2783/cxxopts) to let benchpress parse command-line parameters
+- [**Doxygen**](http://www.stack.nl/~dimitri/doxygen/) to generate [documentation](https://nlohmann.github.io/json/)
+- [**git-update-ghpages**](https://github.com/rstacruz/git-update-ghpages) to upload the documentation to gh-pages
+- [**Github Changelog Generator**](https://github.com/skywinder/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md)
+- [**libFuzzer**](http://llvm.org/docs/LibFuzzer.html) to implement fuzz testing for OSS-Fuzz
+- [**OSS-Fuzz**](https://github.com/google/oss-fuzz) for continuous fuzz testing of the library
+- [**send_to_wandbox**](https://github.com/nlohmann/json/blob/develop/doc/scripts/send_to_wandbox.py) to send code examples to [Wandbox](http://melpon.org/wandbox)
+- [**Travis**](https://travis-ci.org) for [continuous integration](https://travis-ci.org/nlohmann/json) on Linux and macOS
+- [**Valgrind**](http://valgrind.org) to check for correct memory management
+- [**Wandbox**](http://melpon.org/wandbox) for [online examples](http://melpon.org/wandbox/permlink/4NEU6ZZMoM9lpIex)
+
+## Projects using JSON for Modern C++
+
+The library is currently used in Apple macOS Sierra and iOS 10. I am not sure what they are using the library for, but I am happy that it runs on so many devices.
+
+## Notes
+
+- The code contains numerous debug **assertions** which can be switched off by defining the preprocessor macro `NDEBUG`, see the [documentation of `assert`](http://en.cppreference.com/w/cpp/error/assert). In particular, note [`operator[]`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a2e26bd0b0168abb61f67ad5bcd5b9fa1.html#a2e26bd0b0168abb61f67ad5bcd5b9fa1) implements **unchecked access** for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an [assertion failure](https://github.com/nlohmann/json/issues/289) if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the [`at()` function](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a674de1ee73e6bf4843fc5dc1351fb726.html#a674de1ee73e6bf4843fc5dc1351fb726).
+- As the exact type of a number is not defined in the [JSON specification](http://rfc7159.net/rfc7159), this library tries to choose the best fitting C++ number type automatically. As a result, the type `double` may be used to store numbers which may yield [**floating-point exceptions**](https://github.com/nlohmann/json/issues/181) in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions.
+- The library supports **Unicode input** as follows:
+  - Only **UTF-8** encoded input is supported which is the default encoding for JSON according to [RFC 7159](http://rfc7159.net/rfc7159#rfc.section.8.1).
+  - Other encodings such as Latin-1, UTF-16, or UTF-32 are not supported and will yield parse errors.
+  - [Unicode noncharacters](http://www.unicode.org/faq/private_use.html#nonchar1) will not be replaced by the library.
+  - Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors.
+  - The strings stored in the library are UTF-8 encoded. When using the default string type (`std::string`), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.
+- The code can be compiled without C++ **runtime type identification** features; that is, you can use the `-fno-rtti` compiler flag.
+- **Exceptions** are used widely within the library. They can, however, be switched off with either using the compiler flag `-fno-exceptions` or by defining the symbol `JSON_NOEXCEPTION`. In this case, exceptions are replaced by an `abort()` call.
+- By default, the library does not preserve the **insertion order of object elements**. This is standards-compliant, as the [JSON standard](https://tools.ietf.org/html/rfc7159.html) defines objects as "an unordered collection of zero or more name/value pairs". If you do want to preserve the insertion order, you can specialize the object type with containers like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map).
+
+## Execute unit tests
+
+To compile and run the tests, you need to execute
+
+```sh
+$ make json_unit -Ctest
+$ ./test/json_unit "*"
+
+===============================================================================
+All tests passed (14504461 assertions in 48 test cases)
+```
+
+Alternatively, you can use [CMake](https://cmake.org) and run
+
+```sh
+mkdir build
+cd build
+cmake ..
+make
+ctest
+```
+
+For more information, have a look at the file [.travis.yml](https://github.com/nlohmann/json/blob/master/.travis.yml).
\ No newline at end of file
diff --git a/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md b/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md
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--- /dev/null
+++ b/docs/3_Developer_Guides/4_AFB_Helper_Guide/8_C_JSON_Wrapper.md
@@ -0,0 +1,341 @@
+---
+title: C JSON Wrapper
+---
+
+<!-- WARNING: This file is generated by fetch_docs.js using /home/boron/Documents/AGL/docs-webtemplate/site/_data/tocs/devguides/master/afb-helpers-function-references-afb-helpers-book.yml -->
+
+WRAP-JSON facility
+==================
+
+The facility wrap-json is based on the pack/unpack API on the
+library jansson. The two chapters below are copied from the
+documentation of jansson library copyrighted by Petri Lehtinen
+(see at end).
+
+Building Values
+---------------
+
+This section describes functions that help to create, or *pack*, complex
+JSON values, especially nested objects and arrays. Value building is
+based on a *format string* that is used to tell the functions about the
+expected arguments.
+
+For example, the format string `"i"` specifies a single integer value,
+while the format string `"[ssb]"` or the equivalent `"[s, s, b]"`
+specifies an array value with two strings and a boolean as its items:
+
+    /* Create the JSON integer 42 */
+    wrap_json_pack(&result, "i", 42);
+
+    /* Create the JSON array ["foo", "bar", true] */
+    wrap_json_pack(&result, "[ssb]", "foo", "bar", 1);
+
+Here's the full list of format specifiers. The type in parentheses
+denotes the resulting JSON type, and the type in brackets (if any)
+denotes the C type that is expected as the corresponding argument or
+arguments.
+
+- `s` (string) \[const char \*\]
+
+    Convert a null terminated UTF-8 string to a JSON string.
+
+- `s?` (string) \[const char \*\]
+
+    Like `s`, but if the argument is *NULL*, output a JSON null value.
+
+- `s*` (string) \[const char \*\]
+
+     Like `s`, but if the argument is *NULL*, do not output any value.
+    This format can only be used inside an object or an array. If used
+    inside an object, the corresponding key is additionally suppressed
+    when the value is omitted. See below for an example.
+
+- `s#` (string) \[const char \*, int\]
+
+    Convert a UTF-8 buffer of a given length to a JSON string.
+
+- `s%` (string) \[const char \*, size\_t\]
+
+     Like `s#` but the length argument is of type size\_t.
+
+- `+` \[const char \*\]
+
+     Like `s`, but concatenate to the previous string. Only valid after
+    `s`, `s#`, `+` or `+#`.
+
+- `+#` \[const char \*, int\]
+
+     Like `s#`, but concatenate to the previous string. Only valid after
+    `s`, `s#`, `+` or `+#`.
+
+- `+%` (string) \[const char \*, size\_t\]
+
+     Like `+#` but the length argument is of type size\_t.
+
+- `y` (byte array) \[const uint8_t \*, size\_t\]
+
+     Convert the byte array whose length is given to
+    its base64url string representation.
+
+- `Y` (byte array) \[const uint8_t \*, size\_t\]
+
+     Like 'y' but output is base64.
+
+- `y?`, `Y?` (byte array or null) \[const uint8_t \*, size\_t\]
+
+     Like 'y' or 'Y' but allows to output a JSON null value
+    either when the buffer is *NULL* or when the size is *0*.
+
+- `y*`, `y*` (optional byte array) \[const uint8_t \*, size\_t\]
+
+     Like 'y' or 'Y' but do not put JSON value
+  either when the buffer is *NULL* or when the size is *0*.
+  This format can only be used inside an object or an array. If used
+  inside an object, the corresponding key is additionally suppressed
+  when the value is omitted. See below for an example.
+
+- `n` (null)
+
+     Output a JSON null value. No argument is consumed.
+
+- `b` (boolean) \[int\]
+
+     Convert a C int to JSON boolean value. Zero is converted to `false`
+    and non-zero to `true`.
+
+- `i` (integer) \[int\]
+
+     Convert a C int to JSON integer.
+
+- `I` (integer) \[json\_int\_t\]
+
+     Convert a C json\_int\_t to JSON integer.
+
+- `f` (real) \[double\]
+
+     Convert a C double to JSON real.
+
+- `o` (any value) \[json\_t \*\]
+
+     Output any given JSON value as-is. If the value is added to an array
+  or object, the reference to the value passed to `o` is stolen by the
+  container.
+
+- `O` (any value) \[json\_t \*\]
+
+     Like `o`, but the argument's reference count is incremented. This is
+  useful if you pack into an array or object and want to keep the
+  reference for the JSON value consumed by `O` to yourself.
+
+- `o?`, `O?` (any value) \[json\_t \*\]
+
+     Like `o` and `O`, respectively, but if the argument is *NULL*,
+  output a JSON null value.
+
+- `o*`, `O*` (any value) \[json\_t \*\]
+
+     Like `o` and `O`, respectively, but if the argument is *NULL*, do
+  not output any value. This format can only be used inside an object
+  or an array. If used inside an object, the corresponding key is
+  additionally suppressed. See below for an example.
+
+- `[fmt]` (array)
+
+     Build an array with contents from the inner format string. `fmt` may
+  contain objects and arrays, i.e. recursive value building is
+  supported.
+
+- `{fmt}` (object)
+
+     Build an object with contents from the inner format string `fmt`.
+  The first, third, etc. format specifier represent a key, and must be
+  a string (see `s`, `s#`, `+` and `+#` above), as object keys are
+  always strings. The second, fourth, etc. format specifier represent
+  a value. Any value may be an object or array, i.e. recursive value
+  building is supported.
+
+Whitespace, `:` and `,` are ignored.
+
+More examples:
+
+    /* Build an empty JSON object */
+    wrap_json_pack(&result, "{}");
+
+    /* Build the JSON object {"foo": 42, "bar": 7} */
+    wrap_json_pack(&result, "{sisi}", "foo", 42, "bar", 7);
+
+    /* Like above, ':', ',' and whitespace are ignored */
+    wrap_json_pack(&result, "{s:i, s:i}", "foo", 42, "bar", 7);
+
+    /* Build the JSON array [[1, 2], {"cool": true}] */
+    wrap_json_pack(&result, "[[i,i],{s:b}]", 1, 2, "cool", 1);
+
+    /* Build a string from a non-null terminated buffer */
+    char buffer[4] = {'t', 'e', 's', 't'};
+    wrap_json_pack(&result, "s#", buffer, 4);
+
+    /* Concatenate strings together to build the JSON string "foobarbaz" */
+    wrap_json_pack(&result, "s++", "foo", "bar", "baz");
+
+    /* Create an empty object or array when optional members are missing */
+    wrap_json_pack(&result, "{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL);
+    wrap_json_pack(&result, "[s*,o*,O*]", NULL, NULL, NULL);
+
+Parsing and Validating Values
+-----------------------------
+
+This section describes functions that help to validate complex values
+and extract, or *unpack*, data from them. Like building values
+&lt;apiref-pack&gt;, this is also based on format strings.
+
+While a JSON value is unpacked, the type specified in the format string
+is checked to match that of the JSON value. This is the validation part
+of the process. In addition to this, the unpacking functions can also
+check that all items of arrays and objects are unpacked. This check be
+enabled with the format specifier `!` or by using the flag
+`JSON_STRICT`. See below for details.
+
+Here's the full list of format specifiers. The type in parentheses
+denotes the JSON type, and the type in brackets (if any) denotes the C
+type whose address should be passed.
+
+- `s` (string) \[const char \*\]
+
+     Convert a JSON string to a pointer to a null terminated UTF-8
+  string. The resulting string is extracted by using
+  json\_string\_value() internally, so it exists as long as there are
+  still references to the corresponding JSON string.
+
+- `s%` (string) \[const char \*, size\_t \*\]
+
+     Convert a JSON string to a pointer to a null terminated UTF-8 string
+  and its length.
+
+- `y` (byte array) \[uint8_t \*\*, size\_t \*\]
+
+     Convert an input string base64url encoded to its
+  byte array representation. The result and its length
+  are stored. The returned buffer must be freed by the caller.
+
+- `Y` (byte array) \[uint8_t \*\*, size\_t \*\]
+
+     Like 'y' but input is base64.
+
+- `n` (null)
+
+     Expect a JSON null value. Nothing is extracted.
+
+- `b` (boolean) \[int\]
+
+     Convert a JSON boolean value to a C int, so that `true` is converted
+  to 1 and `false` to 0.
+
+- `i` (integer) \[int\]
+
+     Convert a JSON integer to C int.
+
+- `I` (integer) \[json\_int\_t\]
+
+     Convert a JSON integer to C json\_int\_t.
+
+- `f` (real) \[double\]
+
+     Convert a JSON real to C double.
+
+- `F` (integer or real) \[double\]
+
+     Convert a JSON number (integer or real) to C double.
+
+- `o` (any value) \[json\_t \*\]
+
+     Store a JSON value with no conversion to a json\_t pointer.
+
+- `O` (any value) \[json\_t \*\]
+
+     Like `O`, but the JSON value's reference count is incremented.
+
+- `[fmt]` (array)
+
+     Convert each item in the JSON array according to the inner format
+  string. `fmt` may contain objects and arrays, i.e. recursive value
+  extraction is supported.
+
+- `{fmt}` (object)
+
+     Convert each item in the JSON object according to the inner format
+  string `fmt`. The first, third, etc. format specifier represent a
+  key, and must be `s`. The corresponding argument to unpack functions
+  is read as the object key. The second fourth, etc. format specifier
+  represent a value and is written to the address given as the
+  corresponding argument. **Note** that every other argument is read
+  from and every other is written to.
+
+    `fmt` may contain objects and arrays as values, i.e. recursive value
+    extraction is supported.
+
+- `!`
+
+     This special format specifier is used to enable the check that all
+  object and array items are accessed, on a per-value basis. It must
+  appear inside an array or object as the last format specifier before
+  the closing bracket or brace.
+
+- `*`
+
+     This special format specifier is the opposite of `!`. This is the default.
+  It must appear inside an array or object as the last format specifier
+  before the closing bracket or brace.
+
+Whitespace, `:` and `,` are ignored.
+
+Examples:
+
+    /* root is the JSON integer 42 */
+    int myint;
+    wrap_json_unpack(root, "i", &myint);
+    assert(myint == 42);
+
+    /* root is the JSON object {"foo": "bar", "quux": true} */
+    const char *str;
+    int boolean;
+    wrap_json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
+    assert(strcmp(str, "bar") == 0 && boolean == 1);
+
+    /* root is the JSON array [[1, 2], {"baz": null} */
+    wrap_json_check(root, "[[i,i], {s:n}]", "baz");
+    /* returns 0 for validation success, nothing is extracted */
+
+    /* root is the JSON array [1, 2, 3, 4, 5] */
+    int myint1, myint2;
+    wrap_json_unpack(root, "[ii!]", &myint1, &myint2);
+    /* returns -1 for failed validation */
+
+    /* root is an empty JSON object */
+    int myint = 0, myint2 = 0, myint3 = 0;
+    wrap_json_unpack(root, "{s?i, s?[ii]}",
+                "foo", &myint1,
+                "bar", &myint2, &myint3);
+    /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
+
+Copyright
+---------
+
+Copyright (c) 2009-2016 Petri Lehtinen <petri@digip.org>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.