haskell-webservice

This project contains a web service written in Haskell using Happstack and SQLite. The web service provides an interface to (fictitious, randomly generated) weather readings taken at the North Pole during 2017. It has one endpoint, weather/date/,
the response to which will depend on the request type.

If the webservice is running on localhost on port 8000 and receives a GET or POST request to http://localhost:8000/weather/date/YYYY-mm-dd then it will return a JSON object with the data for that date. If weather data is held for that date, the response code will be 200 and the body will consist of JSON something like this:

[{"date":"2017-01-01","temperature":-23.164497}]

If no data exists for the date in question, the response code will be 404 and the body will consist of an empty JSON object.

We can also make PUT requests to insert or update a date/temperature pair in the database. In this case the URL needs to include the temperature, e.g.

http://localhost:8000/date/1970-01-01/0

If the date already exists, the temperature is updated. If not, a new record is added to the database. This call will return 200 and an empty JSON object if everything went OK.

Installation

If you are using Windows, you should install CygWin and use the CygWin terminal instead of the Windows command prompt, as several of the packages you need require a bash-like environment.

If you are working on this code in the labs, do not install it on a Windows drive (e.g. ~/W_DRIVE or ~/M_DRIVE), as cabal is known to have problems with Windows network shares.

To set the project up you need to start by making sure that you have the latest version of cabal-install on this machine:

$ cabal update
$ cabal install cabal-install

Now you can grab the code and start building it:

$ git clone https://github.com/jimburton/haskell-webservice
$ cd haskell-webservice
$ cabal sandbox init
$ cabal configure

This last step may report that several libraries are missing. For example:

$ cabal configure
Resolving dependencies...
Configuring haskell-webservice-0.1.0.0...
cabal: At least the following dependencies are missing:
aeson -any,
happstack-server -any,
hslogger -any,
sqlite-simple -any

If so, install them now:

$ cabal install aeson happstack-server hslogger sqlite-simple

Now you should be able to continue building the application:

$ cabal configure
$ cabal build
$ cabal install
$ cabal run DB-setup

The step to build the database only needs to be done once but you can run it any time you want to restore the database to its original state. Now you can start the webservice:

$ cabal run webservice 
Listening for http:// on port 8000

Once the service is running you can interact with it in the browser or using something like curl:

$ curl http://localhost:8000/weather/date/2017-01-01
[{"date":"2017-01-01","temperature":-23.164497}]

While the service is running open a new terminal and run the tests with cabal test. Read the log, which will be in a file called something like dist/test/haskell-webservice-0.1.0.0-test-webservice.log.

Assignment

Your assignment is to extend the webservice in various ways. Before doing so you should read the first two chapters of the HappStack Book. You may also need to check the docs for HappStack and sqlite-simple, the library we are using to interact with the database. As you work on the methods, keep running the tests and calling the webservice with curl or a browser to see what comes back.

1. Add a new endpoint to the webservice, weather/range/d1/d2, where d1 and d2 are dates in the format YYYY-mm-dd. When this endpoint receives a GET request it should return all records in the database that fall between d1 and d2 (i.e. greater than or equal to d1 and less than or equal to d2) as an array of JSON objects.

2. Add a new endpoint to the webservice, weather/max/d1/d2, where d1 and d2 are dates in the format YYYY-mm-dd. When this endpoint receives a GET request it should return the details of the day with the maximum temperature between d1 and d2 (i.e. greater than or equal to d1 and less than or equal to d2) as an array containing a single JSON object.

3. Add a new endpoint to the webservice, weather/above/t, where t is a signed floating point number. When this endpoint receives a GET request it should return all records in the database where the temperature is greater than or equal to t as an array of JSON objects. Other request methods should result in a 405 response code ("Method not allowed") and an empty JSON object.

4. Extension Convert the web service to use the web-routes library as described in chapter 7 of the HappStack Book.

Submission instructions

Make a github account if you don't have one already. Clone this repository and save your work there. To submit your work, submit the address of your repository on studentcentral. No other form of submission is accepted.

Marking criteria

20 marks are available for each of the four criteria, with 20 marks available for the elegance, efficiency and readability of the code. Read one of the Haskell style guides linked to from studentcentral and use the hlint tool to improve your mark in this criterion. These marking criteria are indicative, meaning that I may award extra marks for work that uses an interesting approach and shows independent learning.