# Notes for ndn-tools developers

## Licensing Requirements

Contributions to ndn-tools must be licensed under the GPL v3 or a compatible license.
If you choose the GPL v3, please use the following license boilerplate in all `.hpp`
and `.cpp` files:

```cpp
/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) [Year(s)], [Copyright Holder(s)].
 *
 * This file is part of ndn-tools (Named Data Networking Essential Tools).
 * See AUTHORS.md for complete list of ndn-tools authors and contributors.
 *
 * ndn-tools is free software: you can redistribute it and/or modify it under the terms
 * of the GNU General Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 *
 * ndn-tools is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE.  See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * ndn-tools, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
 */
```

## Directory Structure and Build Script

All tools are placed in subdirectories of the [`tools`](tools) directory.

A tool can consist of one or more programs.
For instance, a pair of consumer and producer programs that are designed to work together
should be considered a single tool, not two separate tools.

Each tool must have a `wscript` build script in its subdirectory. This script will be
invoked automatically if the corresponding tool is selected for the build. It should
compile the source code and produce one or more binaries in the `build/bin` directory
(e.g., use `target='../../bin/foo'`).

### Shared Modules

Modules shared among multiple tools should be placed in the [`core`](core) directory.
They are available for use in all tools.

A header in `core/` can be included in a tool like `#include "core/foo.hpp"`.

The `wscript` of a tool can link a program with modules in `core/` with `use='core-objects'`.

### Documentation

A file named `README.md` in the subdirectory of each tool should provide a brief
description.

Manual pages for each program should be written in reStructuredText format
and placed in the [`manpages`](manpages) directory.

## Code Guidelines

C++ code should conform to the
[ndn-cxx code style](https://docs.named-data.net/ndn-cxx/current/code-style.html).

### Namespace

Types in each tool should be declared in a sub-namespace inside `namespace ndn`.
For example, a tool in `tools/foo` directory has namespace `ndn::foo`.
This allows the tool to reference ndn-cxx types with unqualified name lookup.
This also prevents name conflicts between ndn-cxx and tools.

Types in `core/` should be declared directly inside `namespace ndn`,
or in a sub-namespace if desired.

### main Function

The `main` function of a program should be declared as a static function in
the namespace of the corresponding tool. This allows referencing types in
ndn-cxx and the tool via unqualified name lookup.

Then, another (non-static) `main` function must be defined in the global
namespace, and from there call the `main` function in the tool namespace.

These two functions should appear in a file named `main.cpp` in the tool's
subdirectory.

Example:

```cpp
namespace ndn {
namespace foo {

class Bar
{
public:
  explicit
  Bar(Face& face);

  void
  run();
};

static int
main(int argc, char* argv[])
{
  Face face;
  Bar program(face);
  program.run();
  return 0;
}

} // namespace foo
} // namespace ndn

int
main(int argc, char* argv[])
{
  return ndn::foo::main(argc, argv);
}
```

### Command Line Arguments

[Boost.Program\_options](https://www.boost.org/doc/libs/1_71_0/doc/html/program_options.html)
is strongly preferred over `getopt(3)` for parsing command line arguments.