Using HTTP APIs For IOT -Beginners Guide

Many of the APIs today are Web API’s designed to access web services like Facebook ,Twitter etc. Because of their widespread use most IOT services (AZURE,AWS,Bluemix)  also support http based APIs.

To understand and use an http API you will need a reasonable understanding of the following:



HTTP API Basics

When using http based APIs the GET request is generally used for reading information and the POST request is used for writing information.

So if we take a switch as an example we would normally read the switch state using a GET request and set the state using a POST request.

However depending on the API design we can also set the switch state using a GET request and url parameters.

Below is a screen shot taken from the mystrom web page showing the use of the GET request to set the switch state using url parameters.

mystrom-api-get

IOT API Test Site and API

To learn to use IOT http APIs we also need a suitable simple IOT API to test against, and unfortunately there currently don’t appear to be any available on line.

Therefore I’ve created a basic API using node-red which is available as a flow.

If there is enough interest I will also make it available online.

Before we proceed I just would like to show you a typical IOT API provided by Amazon as an example:

amazon-api

You can see straight away that it using security certificates which makes it very difficult to use for simple demonstrations and learning.

Testing Tools

To use and test IOT applications that use http based APIs you will require suitable testing tools.

Because http based APIs are common on the web these tools are well developed, and you can even use a web browser for simple GET requests.

For all other requests (POST,PUT,DELETE etc ) you need a tool that lets you make these request types, and also gives you the ability to  change http request headers.

The ones you might want to consider are:

In this tutorial I will be using the advanced rest client and curl.

Introducing Our Home Made API

Our API will be used for controlling three simulated IOT devices.

  • A switch
  • A light Bulb
  • A temperature and humidity sensor.

The Switch

It is possible to change the state of the switch using the GET request or POST request.

The partial url for the switch is myapi/switch1

The complete url is

http://localhost:1880/myapi/switch1

however the complete url will depend on your installation.

Note: You need port 1880 as we are using node-red.

To view the state of the switch use the get request to the url.

To change the state of the switch use:

myapi/switch1?state=off or myapi/switch1?state=on

The following table shows the API commands supported for the switch:

Action Request Type url parameters Request Data
Get switch status GET myapi/switch1 None None
Set switch state on GET myapi/switch1 state=on None
Set switch state off GET myapi/switch1 state=off None
Set switch timer on GET myapi/switch1 timer =on None
Set switch timer off GET myapi/switch1 timer =off None
Set switch state on POST myapi/switch1 None “{“state”:”on”}”
Set switch state off POST myapi/switch1 None “{“state”:”off”}”
Set switch timer on POST myapi/switch1 None “{“timer”:”on”}”
Set switch timer off POST myapi/switch1 None “{“timer”:”off”}”

Note: Currently error and sanity checking is limited on the API.

For the bulb the url is:

myapi/bulb1

and you can set the state to off and also the colour values to 000000-FFFFFF

Examples:

http://myapi/bulb1?state=on
http://myapi/bulb1?colour=ff00ff

api-bulb
Command Table

Action Request Type url parameters Request Data
Get bulb status GET myapi/bulb1 None None
Set bulb state on GET myapi/bulb1 state=on None
Set bulb state off GET myapi/bulb1 state=off None
Set bulb colour GET myapi/bulb1 colour =xxxxxx None
Set bulb state on POST myapi/bulb1 None “{“state”:”on”}”
Set bulb state off POST myapi/bulb1 None “{“state”:”off”}”
Set bulb colour POST myapi/bulb1 None “{“colour”:x\”xxxxx\”}”

The temperature sensor is mainly read, but you can turn it on and off using both post and get requests.

Example usage:

http://localhost:1880/myapi/sensor1

api-temp-sensor

Using the POST Request

You will need a suitable tool as discussed above. I will demonstrate using the Advanced Rest client on Google chrome.

The first thing is to select the method (POST) and then enter the url.

Then set the header to JSON, other headers can be left as default.

api-arc-headers

Now click on the body and enter the JSON command as shown below:

api-post-arc-json

Once done click send and you should see the response:

api-arc-response

Using Curl

Curl is a command line tool and is often the tool used to demo APIs. The command is:

curl -X POST "content-type:application/JSON" "http://localhost:1880/myapi/switch1" -d '{\"state\":\"ON\"}'

The result is shown below:

api-post-curl

Note: not sure of the error but the command works

Resources

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