# prx

An Erlang library for Unix process management and system programming
tasks.

prx provides:

* a safe, beam-friendly interface to system calls and other POSIX operations

* simple, reliable OS process management by mapping Erlang processes to
  a hierarchy of system processes

* an interface for privilege separation operations to restrict processes

* operations to isolate processes like containers and jails

## Build

```
$ rebar3 compile
```

## Quick Start

`prx` has two basic operations: fork and exec.

```
% Spawn a new system process
{ok, Task} = prx:fork(),

% And a child of the process
{ok, Child} = prx:fork(Task).
```

After fork()'ing, other calls can be made. For example:

```
UID = prx:getuid(Task),
PID = prx:getpid(Child).
```

Calling exec() causes the process I/O to be treated as streams of data:

```
ok = prx:execvp(Child, ["/bin/cat", "-n"]),
prx:stdin(Child, "test\n"),
receive
    {stdout,Child,Stdout} ->
        Stdout
end.
```

## Usage

* fork and exec /bin/cat

  ```
    {ok, Task} = prx:fork(),
    ok = prx:execvp(Task, ["/bin/cat", "-n"],
    prx:stdin(Task, "test\n"),
    receive {stdout, Task, _} = Out -> Out end.
  ```

* creating a pipeline of child processes

  prx processes can fork child prx processes:

```
beam
  |-erl_child_setup
  |   `-prx
  |       `-prx
```

After calling exec, the process tree looks like:

```
beam
  |-erl_child_setup
  |   `-prx
  |       `-cat
```

```
    {ok, Task} = prx:fork(),
    {ok, Child} = prx:fork(Task),
    OSPid = prx:getpid(Child),
    ok = prx:execvp(Child, ["/bin/cat", "-n"],
    prx:stdin(Child, "test\n"),
    receive {stdout, Child, _} = Out -> Out end.
```

* running `cat` within a containerized namespace

  ```
    application:set_env(prx, options, [{exec, "sudo -n"}]),
    {ok, Task} = prx:fork(),
    {ok, Child} = prx:clone(Task, [clone_newnet, clone_newpid, clone_newipc,
        clone_newuts, clone_newns]),
    OSPid = prx:getpid(Child),
    ok = prx:execvp(Child, ["/bin/cat", "-n"],
    prx:stdin(Child, "test\n"),
    receive {stdout, Child, _} = Out -> Out end.
  ```

## Documentation

https://hexdocs.pm/prx/

See also: [alcove](https://hexdocs.pm/alcove/)