# Kapow!

## Why?

Because we think that:

- UNIX is great and we love it
- The UNIX shell is great
- HTTP interfaces are convenient and everywhere
- CGI is not a good way to mix them


## How?

So, how we can mix the **web** and the **shell**? Let's see...

The **web** and the **shell** are two different beasts, both packed with
history.

There are some concepts in HTTP and the shell that **resemble each other**.

```
                 +------------------------+-------------------------+
                 | HTTP                   | SHELL                   |
  +--------------+------------------------+-------------------------+
  | Input        | POST form-encoding     | Command line parameters |
  | Parameters   | GET parameters         | Environment variables   |
  |              | Headers                |                         |
  |              | Serialized body (JSON) |                         |
  +--------------+------------------------+-------------------------+
  | Data Streams | Response/Request Body  | Stdin/Stdout/Stderr     |
  |              | Websocket              | Input/Output files      |
  |              | Uploaded files         |                         |
  +--------------+------------------------+-------------------------+
  | Control      | Status codes           | Signals                 |
  |              | HTTP Methods           | Exit Codes              |
  +--------------+------------------------+-------------------------+
```

Any tool designed to give an HTTP interface to an existing shell command
**must map concepts of boths**. For example:

- "GET parameters" to "Command line parameters"
- "Headers" to "Environment variables"
- "Stdout" to "Response body"

Kapow! is not opinionated about the different ways you can map both worlds.
Instead it provides a concise set of tools used to express the mapping and a
set of common defaults.


### Why not tool "X"?

All the alternatives we found are **rigid** about how they match between HTTP
and shell concepts.

* [shell2http](https://github.com/msoap/shell2http): HTTP-server to execute
  shell commands. Designed for development, prototyping or remote control.
Settings through two command line arguments, path and shell command.
* [websocketd](https://github.com/joewalnes/websocketd): Turn any program that
  uses STDIN/STDOUT into a WebSocket server. Like inetd, but for WebSockets.
* [webhook](https://github.com/adnanh/webhook): webhook is a lightweight
  incoming webhook server to run shell commands.
* [gotty](https://github.com/yudai/gotty): GoTTY is a simple command line tool
  that turns your CLI tools into web applications. (For interactive commands
only)
* [shell-microservice-exposer](https://github.com/jaimevalero/shell-microservice-exposer):
  Expose your own scripts as a cool microservice API dockerizing it.

Tools with a rigid matching **can't evade** *[impedance
mismatch](https://haacked.com/archive/2004/06/15/impedance-mismatch.aspx/)*.
Resulting in an easy-to-use software, convenient in some scenarios but
incapable in others.


### Why not my good-old programming language "X"?

* Boilerplate
* Custom code = More bugs
* Security issues (Command injection, etc)
* Dependency on developers
* **"A programming language is low level when its programs require attention to
  the irrelevant"** *Alan Perlis*
* **There is more Unix-nature in one line of shell script than there is in ten
  thousand lines of C** *Master Foo*


### Why not CGI?

TODO: Small explanation and example.


## What?

We named it Kapow!. It is pronounceable, short and meaningless... like every
good UNIX command ;-)

TODO: Definition
TODO: Intro to Architecture


# HTTP API

Kapow! server interacts with the outside world only through its HTTP API. Any
program making the correct HTTP request to a Kapow! server, can change its
behavior.

## Design Principles

* All requests and responses will leverage JSON as the data encoding method.

* The API calls responses will have two distinct parts:
  * The HTTP status code (e.g., 400, Bad Request).  The target audience of this
    information is the client code. The client can thus use this information to
    control the program flow.
  * The JSON-encoded message. The target audience in this case is the human
    operating the client. The human can use this information to make a decision
    on how to proceed.

Let's illustrate these ideas with an example: TODO

  * All successful API calls will return a representation the *final* state
    attained by the objects which have been addressed (requested, set or
    deleted).

    FIXME: consider what to do when deleting objects. Isn't it too much to
    return the list of all deleted objects in such a request?

## API elements

### Servers

TODO: Define servers' API

### Routes

Routes are the mechanism that allows Kapow! to find the correct program to
respond to an external event (e.g. an incomming HTTP request).

#### List routes

Returns JSON data about the current routes.

* **URL**

  `/routes`

* **Method**

  `GET`

* **Success Response**

  * **Code**: `200 OK`<br />
    **Content**: TODO

* **Sample Call**

  TODO

* **Notes**

  Currently all routes are returned; in the future, a filter may be accepted.

#### Append route

  Accepts JSON data that defines a new route to be appended to the current routes.

* **URL**

  `/routes`

* **Method**

  `POST`

* **Header**: `Content-Type: application/json`

* **Data Params**

  * **Content**:
  ```
  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body"
  }
  ```

* **Success Response**

  * **Code**: `200 OK`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**:
  ```
  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body",
    "index": 0
  }
  ```

* **Error Response**

  * **Code**: `400 Bad Request`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**: `{ "error": "Malformed JSON." }`

  * **Code**: `400 Bad Request`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**: `{ "error": "Mandatory field(s) not provided." }`

* **Sample Call**
TODO

* **Notes**

  * A successful request will yield a response containing all the effective
    parameters that were applied.

#### Insert a route

  Accepts JSON data that defines a new route to be inserted at the specified
  index to the current routes.

* **URL**

  `/routes`

* **Method**

  `PUT`

* **Header**: `Content-Type: application/json`

* **Data Params**

  * **Content**:
  ```
  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body",
  }
  ```

* **Success Response**

  * **Code**: `200 OK`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**:
  ```
  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body",
    "index": 0
  }
  ```

* **Error Response**

  * **Code**: `400 Bad Request`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**: `{ "error": "Malformed JSON." }`

  * **Code**: `400 Bad Request`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**: `{ "error": "Mandatory field(s) not provided." }`

* **Sample Call**
TODO

* **Notes**

  * Route numbering starts at zero.
  * When `index` is not provided or is less than 0 the route will be inserted
    first, effectively making it index 0.
  * Conversely when `index` is greater than the number of entries on the route
    table it will be inserted last.
  * A successful request will yield a response containing all the effective
    parameters that were applied.

#### Delete a route

Removes the route identified by `:id`.

* **URL**

  `/routes/:id`

* **Method**

  `DELETE`

* **Success Response**

  * **Code**: `200 OK`<br />
    **Content**: TODO

* **Error Response**

  * **Code**: `404 Not Found`<br />
    **Header**: `Content-Type: application/json`<br />
    **Content**: `{ "error": "Unknown route", "route_id": "{{ :id }}" }`


* **Sample Call**
TODO

* **Notes**


### Handlers

#### Get the value for a handler key
* **URL**
* **Method**
* **URL Params**
* **Data Params**
* **Success Response**
* **Error Response**
* **Sample Call**
* **Notes**

#### Overwrite the value for a handler key
* **URL**
* **Method**
POST
* **URL Params**
* **Data Params**
* **Success Response**
* **Error Response**
* **Sample Call**
* **Notes**

#### Append to the value for a handler key
* **URL**
* **Method**
PUT
* **URL Params**
* **Data Params**
* **Success Response**
* **Error Response**
* **Sample Call**
* **Notes**

## Usage Example

## Test Suite Notes

The test suite is located on [blebleble] directory.
You can run it by ...


# Framework
## Commands
Any compliant implementation of Kapow! must provide these commands:

### `kapow`
This implements the server, yaddayadda

#### Example

### `kroute`
TODISCUSS: maybe consider using `kapow route` instead

#### Example

### `request`

#### Example

### `response`

#### Example

## Full-fledged example  (TODO: express it more simply)


## Test Suite Notes

# Server


## Test Suite Notes