kapow/spec/README.md

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

Tools with a rigid matching can't evade impedance mismatch. 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
    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
    Header: Content-Type: application/json
    Content:

  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body",
    "index": 0
  }
  

• Error Response

  • Code: 400 Bad Request
    Header: Content-Type: application/json
    Content: { "error": "Malformed JSON." }

  • Code: 400 Bad Request
    Header: Content-Type: application/json
    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
    Header: Content-Type: application/json
    Content:

  {
    "method": "GET",
    "url_pattern": "/hello",
    "entrypoint": null,
    "command": "echo Hello World | response /body",
    "index": 0
  }
  

• Error Response

  • Code: 400 Bad Request
    Header: Content-Type: application/json
    Content: { "error": "Malformed JSON." }

  • Code: 400 Bad Request
    Header: Content-Type: application/json
    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

• URL

  /routes/:id

• Method

  DELETE

• Success Response

  • Code: 200 OK
    Content: TODO

• Error Response

  • Code: 404 Not Found
    Header: Content-Type: application/json
    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