Old Ya

RSSI	desc
-30 dBm	Maximum signal strength (NEAR)
-50 dBm	excellent signal strength
-60 dBm	reliable signal strength
-67 dBm	reliable signal strength
-70 dBm	Not a strong signal. Light browsing and email.
-80 dBm	Unreliable signal strength, will not suffice for most services. Connecting to the network.
-90 dBm	The chances of even connecting are very low at this level.

I have a REST API that expects url encoded request params as POST request body. So, API schema looks like

POST /login HTTP/1.1
Host: intro-api.com
Accept: */*
Content-Type: application/x-www-form-urlencoded
Content-Length: xxx

And, If you use curl request would look like,

curl -v --request POST -H "Content-Type: application/x-www-form-urlencoded" intro-api.com/login -d 'username=admin' -d 'password=admin'

Also, since content-type is urlencoded type, request params are in query string format. So -d "username=admin&password=admin" is valid as well.

Now,

I have a frontend(html/js) served by nodejs server which would have to validate user login by calling above REST api. This is what I'm talking in this article.

So, first of all I tried standard nodejs http library as a http client. But could not make it work for url encoded params. I was getting 408 error, which means it never sent the params?

function getUserSession(username, password) {

  const postData = qs.stringify({
    'username': username,
    'password': password
  });

  var options = {
    protocol: 'https:',
    host: 'intro.com',
    port: 443,
    path: '/login',
    method: 'POST',
    headers: {
      'Content-Type'  : 'application/x-www-form-urlencoded',
      'Content-Length': Buffer.byteLength(postData)
    }
  };

  https.request(options, function(resp){
    var response = '';
    resp.on('data', function(chunk){
      response += chunk;
      console.log(response)
    });
  }).on("error", function(e){
    console.log("Got error: " + e.message);
  });

}

So I ended up using request library. which needs to added to package.json (can also be done with npm install request, for more see official documentation).

Next, I will create auth.js with with a function that expects username and password and call the REST api, and respond the cookie value.

var request = require('request');

function getUserSessionId(username, password) {
  console.log("making login request")

  request.post({
    url: 'https://intro.com/login',
    form: {
      username: username,
      password: password
    }
  }).on("response", function(httpResponse) {
        var session = httpResponse.headers['set-cookie']
        console.log("session: " + session)
        return session
  });

}

var token = getUserSessionId('admin', 'admin')

Now, lets run it on terminal using node runtime (without having run it on http)

node auth.js

That is it to call "a REST api with url encoded params" using nodejs.

I am in love with fp these days. In my opinion the cool thing about fp is about being deterministic. Just like in mathematics where a function f(x) = x * x always returns a same output for a given input.

I have been in situtations where I had to debug in exising applications where reference is passed around all over the place and mutated in multiple places. It is very dificult to trace mutations. I'm still learning fp but this week decided to do some haskell as if I'm building a professional application so that I can also learn the tooling in haskell.

So, the first step is to install cabal package manager which is equivalent to sbt, gradle or maven in JVM world.

$ cabal --version
cabal-install version 2.0.0.0
compiled using version 2.0.0.2 of the Cabal library

With cabal installed in a machine next step is to create a create a haskell project with base structures which is what cabal init does.

mkdir infp
cd infp
cabal init

Otherwise there is always an option to create those file by yourself.

The structure of a project looks like

$ tree .
.
├── ChangeLog.md
├── LICENSE
├── Setup.hs
├── infp-world.cabal
└── src
    └── Main.hs

1 directory, 5 files

*.cabal equivalent to pom.xml of JVM world for dependency management and application artifact creation etc which will look like

name:                infp-world
version:             0.1.0.0
license:             BSD3
license-file:        LICENSE
author:              prayagupd
maintainer:          upd@upd.com
build-type:          Simple
extra-source-files:  ChangeLog.md
cabal-version:       >=1.10

executable infp-world
  main-is:             Main.hs
  hs-source-dirs:      src
  build-depends:       base >=4.10 && <4.11
  default-language:    Haskell98

build-depends section is where I have to add external dependencies which are available in http://hackage.haskell.org/packages/

For example if I need mongodb driver http://hackage.haskell.org/package/mongoDB could be the one which I would add as

build-depends:       base >=4.10 && <4.11,
                     mongodb == 2.4.0.0

For this application we simply want to print the system time so lets use the time package,

build-depends:       base >=4.10 && <4.11,
                     time == 1.9.2

Followed by cabal install to download the dependencies which will be installed to ~/.cabal/packages/ pretty much same as ~/.m2/repository in JVM world.

Now, now the next step is to add some functionality to get system time in main function.

To do that let's create following src/Main.hs. Note to edit the file, you can use vim or emacs with autocomplete (I use spacemacs - https://github.com/syl20bnr/spacemacs/tree/master/layers/%2Blang/haskell).

module Main where

import Data.Time
import Control.Applicative

main :: IO ()
main = do
  time <- getZonedTime
  putStrLn ("current time: " ++ show time)

lets build the project now which will create an executable in dist.

$ cabal build
Preprocessing executable 'infp-world' for infp-world-0.1.0.0..
Building executable 'infp-world' for infp-world-0.1.0.0..

It's good to see no compilation error, so it is good to run now with cabal run,

$ cabal run
Preprocessing executable 'infp-world' for infp-world-0.1.0.0..
Building executable 'infp-world' for infp-world-0.1.0.0..
Running infp-world...
current time: 2018-11-22 22:54:06.355117 PST

There we go, it prints current time: 2018-11-22 22:54:06.355117 PST which is the what we wanted.

So, there I end the hello world in haskell using cabal package manager. I am doing REST API on haskell as well so at some point plan to write a post on that.

Old Ya

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