Understanding Rest Client for Visual Studio Code

Hypertext Transfer Protocol

The web servers and the browsers communicate with each other using the Hypertext Transfer Protocol (HTTP). Making HTTP a protocol which allows the fetching of resources (like HTML documents).

HTTP follows a classic client-server model, with a client opening a connection to make a request, then waiting until it receives a response. HTTP is a stateless protocol, meaning that the server does not keep any data (state) between requests.

When you are developing web applications, understanding and being able to test the behaviour of HTTP requests is a task you cannot overlook.

The API Developement Hill and the Underdog

There are many tools out there for API development. Among them, Postman is perhaps the most popular and well-known. However, if you use Visual Studio Code, you should definitely try REST Client instead of Postman. REST Client allows you to send HTTP requests and view their responses in Visual Studio Code directly.

Once the plugin is installed (so go ahead and install it clicking here if you haven't already), using it can be very simple and efficient for testing HTTP requests. For the purposes of this exercise we will be using {JSON} Placeholder a popular free fake API for testing and prototyping.

REST Client

Create in your root directory a new app.rest file where we will define a simple HTTP request:

//Send Request
GET https://jsonplaceholder.typicode.com/posts

Once you prepared a request, by clicking the Send Request link above the request (which will appear if the file's language mode is HTTP), the REST Client will execute the HTTP request and the response from the server will open in the editor.

You can get granular if you check Rest Client's docs. In the spirit of keeping things simple, we will explore some tips around the minimum HTTP requests necessary to create a Create, read, update and delete (CRUD) application:

GET requests a representation of the specified resource. This request should only retrieve data.

POST used to submit an entity to the specified resource.

PUT replaces all current representation of the target resource with the request payload.

DELETE deletes the specified resource.

So to make your life easier, here are the things I'd recommend you try using REST Client for the development of your next application:

GET Multiple Query Parameters / Create Multiple Requests

Even though you are able to write query string in the same request line. When you have multiple query parameters in a single request, writing all of them in the same line is difficult to read and modify.

Luckily, REST Client allows you to spread query parameters into multiple lines (one line, one query parameters), parsing the lines in immediately after the request line which starts with ? and &, like:

//Traditional way
GET https://jsonplaceholder.typicode.com/posts?userId=1&id=2

###

//REST Client's way
GET https://jsonplaceholder.typicode.com/posts
    ?userId=1
    &id=2

Not to overlook! Using three or more consecutive # as a delimiter, allows REST Client to recognize multiple requests for in a single file.

POST PUT & DELETE Request Headers

POST https://jsonplaceholder.typicode.com/posts
content-type: application/json

{
    "title": "Ditching Postman for REST Client",
    "body": "My 44 year old wife rates this idea very nice :)",
    "userId": 777
}

GET POST PUT & DELETE Using Variables

REST Client supports file variables defined by the user to use througout the .rest file. The definition syntax must be set as @variableName = variableValue which occupies a complete line. Keep in mind a variable MUST NOT contain any spaces. As for the variable value, it can contain any characters or whitespaces (leading and trailing whitespaces will be trimmed).

File variables can be defined in a separate request block only filled with variable definitions, as well as define request variables before any request url, which needs an extra blank line between variable definitions and request url (I'd recommend the former more than the latter).

Here an easy example of setting up a variable for the baseUrl used on a DELETE HTTP request:

@baseUrl = https://jsonplaceholder.typicode.com

###

DELETE {{baseUrl}}/posts/50

Also, why not, let's use some variables to also set a defined userId for a PUT HTTP request and correct my non-existing wife's age:

@baseUrl = https://jsonplaceholder.typicode.com
@userId = 777

###

PUT {{baseUrl}}/posts/100
content-type: application/json

{
    "title": "Ditching Postman for REST Client",
    "body": "My 24 year old wife rates this idea very nice :)",
    "userId": {{userId}}
}

Great thing is that, no matter where you defined your file variables, they can be referenced in any HTTP request. They also neatly display a reference count to let you know how many times the variable been used in the file.

Why am I choosing REST Client

It's always good to have options. However, the main selling point for me was that REST Client does have the upper hand over Postman given that requests are handily available at the root directory of your projects and can be distributed to everyone in the development team. This makes it easy to test your HTTP requests and ensure that your application development is progressively being made the right way. So give it a try, below you will find a link to a Github repository with all of the example requests listed above. Download/Pull the repository, install REST Client and test it out.

Thank you for reading and happy REST-ing!

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