libnss 0.5.0

Rust bindings for creating libnss modules
Documentation 
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# libnss-rs
Rust bindings for creating libnss modules.

Currently supports the following databases:
- passwd
- shadow
- group
- hosts

## Getting started
- Create a new library

```bash
cargo new nss_example --lib
```

- Change library type to ```cdylib``` in your ```Cargo.toml```

```yaml
[lib]
name = "nss_example"
crate-type = [ "cdylib" ]
```
*** NOTE *** The name of the crate itself is not important, however the library itself must follow the ```nss_xxx``` pattern.

- Add ```libnss``` to your ```Cargo.toml```

```yaml
[dependencies]
libc = "0.2.0"
lazy_static = "1.3.0"
paste = "0.1"
libnss = "0.1.0"
```

- Add the following to your ```src/main.rs```

```rust
extern crate libc;
#[macro_use]
extern crate lazy_static;
#[macro_use]
extern crate libnss;
```

- Implement a ```passwd``` database

```rust
use libnss::passwd::{PasswdHooks, Passwd};

struct ExamplePasswd;
libnss_passwd_hooks!(example, ExamplePasswd);
```
It is important that the first param of ```libnss_passwd_hooks``` is the name of your final library ```libnss_example.so.2```

````rust
impl PasswdHooks for HardcodedPasswd {
    fn get_all_entries() -> Vec<Passwd> {
        vec![
            Passwd {
                name: "test".to_string(),
                passwd: "x".to_string(),
                uid: 1005,
                gid: 1005,
                gecos: "Test Account".to_string(),
                dir: "/home/test".to_string(),
                shell: "/bin/bash".to_string(),
            }
        ]
    }

    fn get_entry_by_uid(uid: libc::uid_t) -> Option<Passwd> {
        if uid == 1005 {
            return Some(Passwd {
                name: "test".to_string(),
                passwd: "x".to_string(),
                uid: 1005,
                gid: 1005,
                gecos: "Test Account".to_string(),
                dir: "/home/test".to_string(),
                shell: "/bin/bash".to_string(),
            });
        }

        None
    }

    fn get_entry_by_name(name: String) -> Option<Passwd> {
        if name == "test" {
            return Some(Passwd {
                name: "test".to_string(),
                passwd: "x".to_string(),
                uid: 1005,
                gid: 1005,
                gecos: "Test Account".to_string(),
                dir: "/home/test".to_string(),
                shell: "/bin/bash".to_string(),
            });
        }

        None
    }
}
````

- Install the library

```bash
cd target/release
cp libnss_example.so libnss_example.so.2
sudo install -m 0644 libnss_example.so.2 /lib
sudo /sbin/ldconfig -n /lib /usr/lib
```

- Enable your nss module in ```/etc/nsswitch.conf```

eg:
```
passwd:         example files systemd
```

The name in here must follow the final library name ```libnss_example.so.2```

- Look at the examples for more information