Indy's Weblog
2015 Dec 26

Twitter Local

Check out the local buzz

Most things that happen in the world gets broadcasted on Twitter. Usually you follow people to receive their tweets. There’s also a public twitter feed that any registered client can listen to. This feed can be filtered by location. So in this post I’m going to present an F# script that shows tweets from this feed.

The code is fairly easy to understand if you're familiar with C#. I wrote this some time ago while I was learning F#. And I hope some one begining in F# would find the code useful.

If you are interested in learning more about how F# can be used, check out the F# Advent Calendar for a wide variety of posts this festive time.

Before going any further let me show you what the results look like:

First thing to do is to register a twitter app so that I can consume the API. is the place to register an app. This is very quick and easy process and I can immediately use the API. Registration gives me a few key pieces of information that I require for the rest of the code.

  • Consumer Key (API Key)
  • Consumer Secret (API Secret)
  • Access Token
  • Access Token Secret

In order to access the twitter API, I need to authenticate with Twitter, using OAuth. This is a convoluted process that is tedious and error prone, but once you painstakingly figure this out, the rest is easy.

The following code shows how to create a streaming web resource. The OAuth is tied to the endpoint URL that would be used, so in order for it to be reusable I pass in the endpoint and the associated parameters, in the GetStreamingWebResource(...) function.

Once the web resource is aquired, I can start listening to the tweets using ReadStreamingResponse(...) function. This is nothing more than looping around , reading in the size of the response, allocating necessary buffers and reading the payload. When I have the text payload, it has to be HTML decoded and then parsed into a JSON object. For JSON object parsing, I use FSharp.Data lib which contains necessary JSON type provider.

Most of the tweets these days contain a link to an image. On a webpage these are automatically downloaded and shown, but no such luck in the console. I check if a tweet contains a URL and if there's an image, then download it.

So I have an image but if I would be so brave, I could convert the image to grayscale, and map the intensities to a character set which roughly represents those intensities. And characters I could handle! oh the glory days of tty.

Image2Ascii(...) takes in an image and does a resize so that I can deal with the text mapping. Here I take into account that text on the terminal is not square. So with some fudging about, I can make a picture look proportional.

For grayscale conversion we use a formula from trusty Wikipedia and the charset for mapping intensities was shamelessly pinched from here

When all this is put together, lo and behold I get a fancy and frenzy Twitter feed reader like this…

tty ascii art

This is what tweeters in Tokyo are talking about.

All the code is on github as an F# script with JSON fragments.