pEpJSONServerAdapter/README.md

# p≡p JSON Server Adapter

## Introduction

The p≡p JSON Server Adapter provides a REST-like jQuery-compatible API to
connect with the p≡p engine.  It is language-independent and can be used by
any client.

## Getting started - build and run

In order to use the p≡p JSON Server Adapter, you need to build and run it.
Currently, Linux and OSX/macOS are supported, Windows is about to follow.

### Building on Linux

The p≡p JSON Server Adapter can be build on Debian and Ubuntu.  Other
distributions should work, but are not yet officially supported.

#### System requirements

Debian 9 or Ubuntu 16.04. Newer versions should also work (file a bug report
if not) but are not in our main focus, yet.

#### Dependencies
* C++ compiler: tested with g++ 4.8 and 4.9, and clang++ 2.8. Newer versions should work, too.
* GNU make
* libboost-thread-dev (tested with 1.58)
* libboost-program-options-dev  (tested with 1.58)
* libboost-filesystem-dev (tested with 1.58)
* libevent-dev 2.0.21 or 2.0.22 (or build from source, see below)
* [p≡p Engine](https://letsencrypt.pep.foundation/trac/wiki/Basic%20Concepts%20of%20p%E2%89%A1p%20engine) (which needs gpgme-thread,
  a patched libetpan, libboost-system-dev)

#### Build steps

1. Build [p≡p Engine](https://letsencrypt.pep.foundation/trac/wiki/Basic%20Concepts%20of%20p%E2%89%A1p%20engine)
2. Build [libevent](http://libevent.org/)
   * tested with version 2.0.21 and 2.0.22, newer versions should work, too. 2.1.x is not yet tested.
   * Can be configured without dependency to OpenSSL, because the JSON Server Adapter does not use SSL/TLS.
   * A user-install in $HOME/local/ is fine. 
3. Edit the library and include paths server/Makefile so p≡p & libevent will be found
4. Run "make" in the server/ path

```
cd server
make
```

### Building on macOS

The p≡p JSON Server Adapter can be built on OS X or macOS with MacPorts.

#### System requirements

* OS X or macOS

#### Preconditions

For compiling the p≡p JSON Server Adapter and its dependencies, make sure
you have the LANG variable set.

```
export LANG=en_US.UTF-8
```

#### Dependencies

The following dependencies need to be installed in order to be able to build
the p≡p JSON Server Adapter.

##### MacPorts
[Install MacPorts](https://www.macports.org/install.php) for your version of OS X/macOS.

If MacPorts is already installed on your machine, but was installed by a
different user, make sure your `PATH` variable is set as follows in
`~/.profile`:

```
export PATH="/opt/local/bin:/opt/local/sbin:$PATH"
```

Install dependencies packaged with MacPorts as follows.

```
sudo port install openssl boost ossp-uuid
```

##### libevent

Install [libevent](http://libevent.org/).

```
cd libevent-2.0.22-stable
export LDFLAGS=-L/opt/local
export CFLAGS=-I/opt/local/include

./configure --prefix "$HOME"

make
make install
```

#### Build steps

1. Install dependencies
2. Run "make" in the server/ path

```
cd server
make
```

### Running the pEp JSON Adapter

1. Run ./pep-json-server.  This creates a file that is readable only by the
   current user (/tmp/pEp-json-token-${USER}) and contains the address and
   port the JSON adapter is listening on, normally 127.0.0.1:4223 and a
   "security-token" that must be given in each function call to authenticate
   you as the valid user.

   ```
   ./pep-json-server
   ```

2. Visit that address (normally http://127.0.0.1:4223/) in your
   JavaScript-enabled web browser to see the test JavaScript client.
3. Call any function ("version()" or "get_gpg_path()" should work just
   fine) with the correct security token.

## Using the p≡p JSON Adapter

In the following section, you'll find background information on how to use
the adapter and its functions.

### Session handling

When using the p≡p engine, a session is needed to which any adapter can
connect. The p≡p JSON Server Adapter automatically creates one session per
HTTP client connection (and also closes that session automatically when the
client connections is closed). Therefore, the client does not need to take
care of the session management. However, the client has to set up a [HTTP
persistent
connection](https://en.wikipedia.org/wiki/HTTP_persistent_connection).

### API Principles

All C data types are mapped the same way, so some day the JSON wrapper can
be generated from the p≡p Engine header files (or the JSON wrapper and the
p≡p engine header are both generated from a common interface description
file).

| C type | JSON mapping |
|--|--|
| `bool` | JSON boolean |
| `int` | JSON decimal number |
| `size_t` | JSON decimal number |
| `char*` (representing a UTF-8-encoded NULL-terminated string | JSON string |
| `char*` (representing a binary string | base64-encoded JSON string |
| `enum` | either JSON decimal number or JSON object containing one decimal number as member |
| `struct` | JSON object |
| linked lists (e.g. `bloblist_t`, `stringlist_t`, `identity_list` etc.) | JSON array of their member data type (without the `next` pointer) |

The parameter type PEP_SESSION is handled automatically by the JSON Server
Adapter and the PEP_SESSION parameter is omitted from the JSON API.

#### enum types

Enum types are represented as JSON objects with one member, whose name is
derived from the enum type name, holding the numeric value of the enum.

Some enum types are still represented directly as JSON decimal number. It
shall be changed in a future version of the JSON Adapter.

#### String types

The JSON Server Adapter does automatic memory management for string
parameters. The current p≡p Engine's API distinguish between `const char*`
parameters and `char*` parameters.  `const char*` normally means: the
"ownership" of the string remains at the caller, so the JSON Adapter frees
the string automatically after the call.  `char*` normally means: the
"ownership" of the string goes to the Engine, so the JSON Adapter does _not_
free string.

If there are functions that have a different semantics the behavior of the
JSON wrapper has to be changed.

#### Parameter (value) restrictions

Some API functions have restrictions on their parameter values.  The JSON
Adapter does not know these restrictions (because it does not know the
semantics of the wrapped functions at all).  So it is the client's
responsibility to fulfill these parameter restrictions!  Especially when
there are restrictions that are checked with assert() within the p≡p Engine,
it is impossible for the JSON Adapter to catch failed assertions - the
Engine and the Adapter process will be terminated immediatetely when the
Engine is compiled in debug mode (= with enabled assert() checking).

Currently there are no range checks for numerical parameter types (e.g. a
JSON decimal number can hold a bigger value than the `int` parameter type of
a certain C function).

### API Reference

An complete overview with all functions that are callable from the client
can be found in the [API Reference](pEp JSON Server Adapter/API Reference).

Most of the callable functions are functions from the C API of the p≡p
Engine.  They are described in detail, incl.  pre- and post-conditions in
the appropriate C header files of the Engine.


## Extending / customizing

If you want to extend or customize the p≡p JSON Adapter, there are several
rules and definitions to take into account.

### Definitions

* The `FunctionMap function` in `json-adapter.cc` defines which functions
  are callable via the JSON-RPC interface.  The existing entries show the
  syntax of that map.

* For each type there must exist specializations of the template classes
  "In" (for input parameters) and "Out" (for output parameters).
  The linker will tell you, which specializations are needed.

* The specializations for "generic types" are in `function_map.cc`.

* The specializations for "p≡p-specific types" are in `pep-types.cc`.


## TODOs

The following issues are planned but not yet implemented.

* Windows build:
    * implement get_token_filename() for MS Windows (security-token.cc line 43)
    * do the Windows-specific stuff to build the software on Windows

* Add unit tests

* Fix the bugs that are found by the Unit tests, if any.

* Generate all the tedious boiler plate code
    * the content of pep-types.cc
    * perhaps the FunctionMap 'function' in mt-server.cc
    * perhaps the JavaScript side of the HTML test page to ensure to be
      consistent with the server side in pep-types.cc

* Adapt the "p≡p Transport API", when it is final. (either manually or by
  code generator, if ready)