In this lab we will be using REST over HTTPS to send data to our cloud server.

In REST we use the appropriate HTTP method to transfer state from and to the server.

The most important methods are:

• GET to get ressources from the server.
• DELETE to delete a ressource on the server.
• POST to create a new ressource on the server.
• PUT to replace a ressource with a new one.

We will now manually use some of these methods to exchange information with the cloud server.

But first we will find the name of your device as we will use it to identify us later on. Execute the command below and remember its output, it will be something like nota-1 or nota-2.

[user@computer ~]$ uname -n
nota-x

Now open the cloud application in a new tab, when you successfully send data later on you should see it appear there (although you may have to refresh the page).

First we will send a new ressource to the server using the POST method.

Replace the nota-x part in the URL below by the name of your device, as found out before.

[user@computer ~]$ http -v POST https://nota-cloud/api/log/nota-x value:=1

Task: Execute the command multiple times with different values and observe the cloud application.

Next we want to get back the information sent to the server using the GET method.

First we request a list of device names that sent data to the server:

[user@computer ~]$  http -v GET https://nota-cloud/api/log
GET /api/log HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Connection: keep-alive
Host: nota-cloud
User-Agent: HTTPie/0.9.8



HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Connection: keep-alive
Content-Length: 40
Content-Type: application/json
Date: Mon, 01 Jan 2018 00:00:00 GMT
Server: nginx/1.10.3
Strict-Transport-Security: max-age=15768000

{
    "keys": [
        "nota-1",
        "nota-2",
        "nota-3"
    ]
}

We can see that the nota-1, nota-2 and nota-3 ressources exist on the server.

Next we can request one of these ressources from the server:

[user@computer ~]$ http -v GET https://nota-cloud/api/log/nota-1
GET /api/log/nota-1 HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Connection: keep-alive
Host: nota-cloud
User-Agent: HTTPie/0.9.8



HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Connection: keep-alive
Content-Length: 5343
Content-Type: application/json
Date: Mon, 1 Jan 2018 00:00:00 GMT
Server: nginx/1.10.3
Strict-Transport-Security: max-age=15768000

{
    "values": [
        {
            "timestamp": 1500000000.000000,
            "value": 1.0
        },
        {
            "timestamp": 1500000001.000000,
            "value": 2.0
        },
        …
    ]
}

Note: we did not perform any authentication of the user, for example using an username and password, so anyone can POST and GET data to and from the server. This was done as a simplificiation in the lab and is obviously bad practice.

Do not run unauthenticated services over the public internet!

In the response header we can see a Content-Type: application/json line that specifies the file type of the response body to be JSON.

JSON is a common internet data format based on the way JavaScript represents data objects.

In the response above we see the main JSON components.

• Collections of name/value pairs: {"name_1": "value_1", "name_2: "value_2"}
• Numbered collections: ["value_1", "value_2", "value_3"]
• Strings: "text"
• Numbers: 1.0

Names in collections are always strings, values can be any other type, even other collections allowing for nested structures.

How entries in a JSON file are represented and accessed depends on the programming language and library used but the following pseudo-code interaction should give you an intuition:

> var json_file = {
>    "values": [
>        { "timestamp": 1500000000.000000, "value": 1.0 },
>        { "timestamp": 1500000001.000000, "value": 2.0 }
>    ]
> };

> json_file["values"]
[
   { "timestamp": 1500000000.000000, "value": 1.0 },
   { "timestamp": 1500000001.000000, "value": 2.0 }
]

> json_file["values"][0]
{ "timestamp": 1500000000.000000, "value": 1.0 }

> json_file["values"][0]["timestamp"]
1500000000.000000