Let’s understand what an API is

Let’s understand what an API is

The basic principles for building REST APIs are based on knowing mostly HTTP, something that is not optional for a web developer.

What is REST?

REST, REpresentational State Transfer, is a type of web development architecture that is fully supported by the HTTP standard.

REST allows us to create services and applications that can be used by any device or client that understands HTTP, so it is incredibly simpler and more conventional than other alternatives that have been used in the last ten years as SOAP and XML-RPC.

REST was defined in 2000 by Roy Fielding, co-author also of the HTTP specification. We could consider REST as a framework to build web applications respecting HTTP.

Therefore REST is the most natural and standard type of architecture to create APIs for Internet-oriented services.
There are three levels of quality when REST is applied in the development of a web application and, more specifically, an API that is collected in a model called Richardson’s Maturity Model in honor of the type that established it, Leonard Richardson, father of architecture oriented to resources.

These levels are:

  1. Correct use of URIs.
  2. The correct use of HTTP.
  3. Implement Hypermedia.

In addition to these three rules, you should never save state on the server, all the information that is required to show the information that is requested must be in the query by the client.

By not saving state, REST gives us a lot of play, since we can scale better without having to worry about issues such as storage of session variables and even, we can play with different technologies to serve certain parts or resources of the same API.

Level 1: Correct use of URIs

When we develop a web or a web application, the URLs allow us to access each of the pages, sections or documents of the website.

Each page, information in a section, file, when we talk about REST, we name them as resources.

The resource is, therefore, the information that we want to access, modify or eliminate, regardless of its format.

The URL, Uniform Resource Locator, is a type of URI, Uniform Resource Identifier, which, in addition to allowing to identify the resource in a unique way, allows us to locate it to access or share its location.

A URL is structured as follows:

{protocol}://{domain or hostname}[:port (optional)]/{resource route}?{filtering query}

There are several basic rules to name the URI of a resource:

  • URI names should not imply an action, therefore, you should avoid using verbs in them.
  • They must be unique, we must not have more than one URI to identify the same resource.
  • They must be independent of format.
  • They must maintain a logical hierarchy.
  • Filtering the information of a resource is not done in the URI.

URIs should not involve actions and should be unique.

For example, the URI /invoices/234/edit would be incorrect since we have the verb edit in it.

For the invoice resource with the identifier 234, the following URI would be the correct one, regardless of whether we are going to edit it, delete it, consult it or read only one of its concepts: /invoices/234.

URIs must be independent of format

For example, the URI /invoices/234.pdf would not be a correct URI, since we are indicating the pdf extension in it.

For the invoice resource with the identifier 234, the following URI would be the correct one, regardless of whether we are going to consult it in pdf format, epub, txt, xml or json: /invoices/234.

URIs must maintain a logical hierarchy

For example, the URI /invoices/234/client/007 would not be a correct URI, since it does not follow a logical hierarchy.

For the invoice resource with the identifier 234 of the client 007, the following URI would be the correct one: /clients/007/invoices/234.

Filtering and other operations

To filter, sort, search or search information in a resource, we must make a query about the URI, using HTTP parameters instead of including them in it.

For example, the URI /invoices/order/desc/date-from/2007/page/2 would be incorrect, since the invoice listing resource would be the same, but we would use a different URI to filter, classify or locate it.

The correct URI in this case would be:

/invoices?date-from=2007&order=DESC&page=2

Level 2: HTTP

Knowing well HTTP is not optional for a web developer who cares about their work. Although the RFC is easy to read, if you are interested in learning the basics of this protocol well, the orientation of O’Reilly is strongly recommended.

To develop the REST APIs, the key aspects that must be mastered and clarified are:

  • HTTP methods.
  • Status codes.
  • Acceptance of content types.

Methods

As we have seen in the previous level, when creating URI we should not put verbs that imply action, even if we want to manipulate the resource.

To manipulate resources, HTTP gives us the following methods with which we must operate:

  • GET: To consult and read resources.
  • POST: To create resources.
  • PUT: To edit resources.
  • DELETE: To eliminate resources.
  • PATCH: To edit specific parts of a resource.

For example, for an invoice resource:

  • GET /invoices → Allows us to access the list of invoices.
  • POST /invoices → Allows us to create a new invoice.
  • GET /invoice/123 → Allows us to access the detail of an invoice.
  • *PUT /invoices/123 *→ Allows us to edit the invoice, replacing the entire previous information with the new one.
  • DELETE /invoices/123 → Allows us to delete the invoice.
  • PATCH /invoices/123 → It allows us to modify certain information of the invoice, such as the number or date of the invoice.

Perhaps due to ignorance or the support of certain browsers, web developers have used, during the last few years, only the GET and POST methods to perform all these actions. If we work with REST, this would be a basic error and can give us problems even when it comes to assigning a name to our resources, which forces us to put verbs in the URLs.

Status codes

One of the most frequent errors when creating an API is to reinvent the wheel when creating our own tools instead of using those that have already been created, thought and tested. The most reinvented wheel in the development of the APIs are the error codes and the status codes.

When we perform an operation, it is vital to know if this operation has been carried out successfully or, in the opposite case, why it has failed.

A common mistake would be for example:

Request
=======
PUT /invoices/123

Response
========
Status Code 200
Content:
{
  success: false,
  code:    734,
  error:   "Insufficient data"
}

In this example, a status code of 200 is returned, which means that the request was successful, however, we are returning an error in the body of the response and not in the requested resource in the URL.

This is a common error that has several drawbacks:

  • It is not REST nor is it standard.
  • The client that accesses this API must know the special operation and how to deal with its errors, so it requires an important additional effort to work with us.
  • We have to worry about keeping our own codes or error messages, with all that implies.

HTTP has a very wide range that covers all the possible indications that we are going to have to add in our answers when the operations have gone well or badly. It is imperative to know them and know when to use them, regardless of what you develop following REST.

The previous example would be correct in the following way:

Request
=======
PUT /invoices/123

Response
========
Status Code 400
Content:
{
  message: "A customer id must be specified for the invoice"
}

Types and formats of content

When we talked about URL, we also saw that it was not correct to indicate the type of format of a resource that we want to access or manipulate.

HTTP allows us to specify in what format we want to receive the resource, being able to indicate several in order of preference, for this we use the Accept header.

Our API will return the resource in the first available format and, if the resource can not be displayed in any of the formats indicated by the client using the Accept header, it will return the HTTP status code 406.

In the answer, the Content-Type header will be returned, so that the client knows what format is returned, for example:

Request
=======
GET /invoices/123
Accept: application/epub+zip, application/pdf, application/json

Response
========
Status Code 200
Content-Type: application/pdf

In this case, the client requests the invoice in compressed epub with ZIP and if not, in pdf or json in order of preference. The server finally returns the invoice in pdf.

Level 3: Hypermedia

Despite what may lead us to think about the term retrofuturist hypermedia, the concept and purpose it tries to describe is quite simple: connect through the links of client applications with APIs, allowing these customers worry about knowing in advance how to access resources.

With Hypermedia we basically add extra information to the resource about its connection to other resources related to it.

Here an example:

<order>
  <id>666</id>
  <status>Processed</status>
  <links>
    <link rel="invoice">
        http://example.com/api/order/666/invoice
    </link>
  </links>
</order>

In this example we see how to indicate in an xml that represents an order, the link to the resource of the invoice related to it.

However, we need the client that accesses our API to understand that this information is not specific to the resource, but is added information that can be used to link the order with the invoice.

To do this, we must use the Accept and Content Type headers, so that both the client and the API know they are talking about hypermedia.

For example:

Request
=======
GET /order/666
Accept: application/our_api+xml, text/xml
Response
========
Status Code: 200
Content-Type: application/our_api+xml
Content:
<order>
  <id>666</id>
  <status>Processed</status>
  <links>
    <link rel="invoice">
         http://example.com/api/order/666/invoice
    </link>
  </links>
</order>

As we can see, the client requests the application/our_api+xml format preferably in text/xml format. In this way, it tells the web service, that it understands its hypermedia format and can take advantage of it.

The web service therefore, as it implements hypermedia, returns the resource information and hypermedia information that the client can use.

Hypermedia is useful for example so that the client does not have to know the URLs of the resources, avoiding having to do maintenance on each of them if in the future said URLs change (which should not happen). It is also useful for automating processes between APIs without human interaction.

Conclusion

As we have seen, the basic principles for building REST APIs are based on knowing mostly HTTP, something that is not optional for a web developer.

Thanks for reading ❤

If you liked this post, share it with all of your programming buddies!

What is REST API? | Restful Web Service

What is REST API? | Restful Web Service

In this post "Restful Web Service", you'll learn: What is Web services, what is API, What is REST API, How REST works and Implementation of REST API

What is REST API? | Restful Web Service

A REST API defines a set of functions to process requests and responses via HTTP protocol.

REST is used in mobile application as well as in web applications.


Web Development with Rust - 03/x: Create a REST API

Web Development with Rust - 03/x: Create a REST API

Since Rust is a static typed language with a strong compiler you won't face many of the common pitfalls about running a web service in production. Although there are still run time errors which you have to cover.

Content
  1. HTTP Requests
  2. POST/PUT/PATCH/DELETE are special
  3. The Job of a Framework
  4. Creating an API spec
  5. Crafting the API
  6. Input Validation
  7. Summary

APIs are the bread and butter of how a modern and fast-paced web environment. Frontend application, other web services and IoT devices need to be able to talk to your service. API endpoints are like doors to which you decide what comes in and in which format.

Since Rust is a static typed language with a strong compiler you won't face many of the common pitfalls about running a web service in production. Although there are still run time errors which you have to cover.

HTTP Requests

When we talk about creating an API we basically mean a web application which listens on certain paths and responds accordingly. But first things first. For two devices to be able to communicate with each other there has to be an established TCP connection.

TCP is a protocol which the two parties can use to establish a connection. After establishing this connection, you can receive and send messages to the other party. HTTP is another protocol, which is built on top of TCP, and it's defining the contents of the requests and responses.

So on the Rust side of things, TCP is implemented in the Rust core library, HTTP is not. Whatever framework you chose in the previous article they all implement HTTP and therefore are able to receive and send HTTP formatted messages.

An example GET requests for example looks like this:

GET / HTTP/1.1
Host: api.awesomerustwebapp.com
Accept-Language: en

It includes:

  • GET: the HTTP method
  • /: The path
  • HTTP/1.1: The version of the HTTP protocol
  • HOST: The host/domain of the server we want to request data from
  • Accept-Language: Which language we prefer and understand

The most common used HTTP methods are:

  • GET
  • POST
  • PUT
  • PATCH
  • DELETE
POST/PUT/PATCH/DELETE are special

We are using GET every time we browse the web. If we want to alter data however (like using POST to send data over to another server), we need to be more cautions and precise.

First, not everyone is allowed to just send a bunch of data to another server. Our API can for example say: "I just accept data from the server with the host name allowed.awesomerustapp.com.

Therefore, when you send a POST to another server, what actually happens is the CORS workflow:

We first ask the server what is allowed, where do you accept requests from and what are your accepted headers. If we fulfill all of these requirements, then we can send a POST.

Disclaimer: Not all frameworks (like rocket and tide) are implementing CORS in their core. However, in a professional environment, you handle CORS on the DevOps side of things and put it for example in your NGINX config.
The Job of a Framework

We use the hard work of other people to create web applications. Everything has to be implemented at some point, just not from you for most of the time. A framework covers the following concerns:

  • Start a web server and open a PORT
  • Listen to requests on this PORT
  • If a request comes in, look at the Path in the HTTP header
  • Route the request to the handler according to the Path
  • Help you extract the information out of the request
  • Pack the generated data and HTTP StatusCode (created from you) and form a response
  • Send the response back to the sender

The Rust web framework tide includes http-service, which provides the basic abstractions you need when working with HTTP calls. The crate http-service is built on top of hyper, which transforms TCP-Streams to valid HTTP requests and responses.

Your job is to create routes like /users/:id and add a route_handler which is a function to handle the requests on this particular path. The framework makes sure that it directs the incoming HTTP requests to this particular handler.

Creating an API spec

You have to define your resources first to get an idea what your application needs to handle and uncover relationships between them. So if you want to build a idea-up-voting site, you would have:

  • Users
  • Ideas
  • Votes

A simple spec for this scenario would look like this:

  • Users
  • POST /users
  • GET /users
  • PUT /users/:user_id
  • PATCH /users/:user_id
  • DELETE /users/:user_id
  • GET /users/:user_id

Ideas and Votes behave accordingly. A spec is helpful for two reasons:

  • It gives you guidelines not to forget a path
  • It helps to communicate to your API users what to expect

You can tools like swagger to write a full spec which also describes the structure of the data and the messages/responses for each path and route.

A more professional spec would include the return values for each route and the request and response bodies. However, the spec can be finalized once you know how your API should look like and behave. To get started, a simple list is enough.

Crafting the API

Depending on the framework you are using, your implementation will look different. You have to have the following features on your radar to look out for:

  • Creating routes for each method (like app.at("/users").post(post_users_handler))
  • Extracting information from the request (like headers, uri-params and JSON from the request body)
  • Creating responses with proper HTTP codes (200201400404 etc.)

I am using the latest version of tide for this web series. You can add it in your Cargo.toml file and use it for your web app:

[dependencies]
tide = "0.1.0"

Our first User implementation will look like this:

async fn handle_get_users(cx: Context<Database>) -> EndpointResult {
    Ok(response::json(cx.app_data().get_all()))
}

async fn handle_get_user(cx: Context<Database>) -> EndpointResult {
let id = cx.param("id").client_err()?;
if let Some(user) = cx.app_data().get(id) {
Ok(response::json(user))
} else {
Err(StatusCode::NOT_FOUND)?
}
}

async fn handle_update_user(mut cx: Context<Database>) -> EndpointResult<()> {
let user = await!(cx.body_json()).client_err()?;
let id = cx.param("id").client_err()?;

if cx.app_data().set(id, user) {
    Ok(())
} else {
    Err(StatusCode::NOT_FOUND)?
}

}

async fn handle_create_user(mut cx: Context<Database>) -> EndpointResult<String> {
let user = await!(cx.body_json()).client_err()?;
Ok(cx.app_data().insert(user).to_string())
}

async fn handle_delete_user(cx: Context<Database>) -> EndpointResult<String> {
let id = cx.param("id").client_err()?;
Ok(cx.app_data().delete(id).to_string())
}

fn main() {
// We create a new application with a basic, local database
// You can use your own implementation, or none: App::new(())
let mut app = App::new(Database::default());
app.at("/users")
.post(handle_create_user)
.get(handle_get_users);
app.at("/users/:id")
.get(handle_get_user)
.patch(handle_update_user)
.delete(handle_delete_user);

app.serve("127.0.0.1:8000").unwrap();

}

You can find the full implementation of the code in the GitHub repository to this series.

We see that we first have to create a new App

let mut app = App::new(())

add routes

app.at("/users")

and for each route add the HTTP requests we want to handle

app.at("/users").get(handle_get_users)

Each framework has a different method of extracting parameters and JSON bodies. Actix is using Extractors, rocket is using Query Guards.

With tide, you can access request parameters and bodies and database connections through Context. So when we want to update a User with a specific id, we send a PATCH to /users/:id. From there, we call the handle_update_user method.

Inside this method, we can access the id from the URI like this:

let id = cx.param("id").client_err()?;

Each framework is also handling its own way of sending responses back to the sender. Tide is using EndpointResult, rocket is using Response and actix HttpResponse.

Everything else is completely up to you. The framework might help you with session management and authentication, but you can also implement this yourself.

My suggestion is: Build the first skeleton of your app with the framework of your choice, figure out how to extract information out of requests and how to form responses. Once this is working, you can use your Rust skills to build small or big applications as you wish.

Input Validation

Your best friend in the Rust world will be serde. It will help you parse JSON and other formats, but will also allow you to serialize your data.

When we talk about input validation, we want to make sure the data we are getting has the right format. Lets say we are extracting the JSON body out of a request:

let user: User = serde_json::from_str(&request_body);

We are using serde_json here to transform a JSON-String into a Struct of our choice. So if we created this struct:

struct User {
name: String,
height: u32,
}

we want to make sure the sender is including name and height. If we just do serde_json::from_str, and the sender forgot to pass on the height, the app will panic and shut down, since we expect the response to be a user: let user: User.

We can improve the error handling like this:

let user: User = match serde_json::from_str(&request_body) {
Ok(user) => user,
Err(error) => handle_error_case(error),
};

We catch the error and call our handle_error_case method to handle it gracefully.

Summary
  1. Pick a framework of your choice
  2. rocket is nightly
  3. actix is stable
  4. tide is fostered close to the Rust Core and also works on Rust nightly
  5. Know that there is no common CORS handling (yet). Recommendation is to handle this on the DevOps side (NGINX for example)
  6. After picking a framework, spec out your resources (/users: GET, POST etc.)
  7. Figure out how the framework of your choice is handling extracting parameters and JSON from the request and how to form a response
  8. Validate your input via match and serde_json

Thanks For Visiting, Keep Visiting. If you liked this post, share it with all of your programming buddies!

Why you should learn the Rust programming language

☞ The Rust Programming Language

☞ Rust Vs. Haskell: Which Language is Best for API Design?

☞ An introduction to Web Development with Rust for Node.js Developers

☞ 7 reasons why you should learn Rust programming language in 2019

Why you should move from Node.js to Rust in 2019

☞ Rust: Building Reusable Code with Rust from Scratch

☞  Programming in Rust: the good, the bad, the ugly.

☞  An introduction to Web Development with Rust for Node.js Developers

☞ Intro to Web Development with Rust for NodeJS Developers

☞ Introducing the Rust Crash Course

3 Frameworks for Building APIs Using Rust


This post was originally published here

What is REST? What are RESTful Web Services?

What is REST? What are RESTful Web Services?

This tutorial provides an introduction to RESTful web services and goes over what REST is as well as HTTP.

REST stands for REpresentational State Transfer. It is a popular architectural approach to create your API's in today's world.

You Will Learn
  • What is REST?
  • What are the fundamentals of REST APIs?
  • How do you make use of HTTP when building REST API?
  • What is a Resource?
  • How do you identify REST API Resources?
  • What are some of the best practices in designing REST API?
What Is REST?

The acronym REST stands for REpresentational State Transfer. It was term originally coined by Roy Fielding, who was also the inventor of the HTTP protocol. The striking feature of REST services is that they want to make the best use of HTTP. Let's now have a quick overview of HTTP.

A Relook at HTTP

Let's open up the browser and visit a web page first:

And then click on one of the result pages:

Next, we can click on the link on the page we end up in:

And land upon another page:

This is how we typically browse the web.

When we browse the internet, there are a lot of things that happen behind the scenes. The following is a simplified view of what happens between the browser, and the servers running on the visited websites:

The HTTP Protocol

When you enter a URL such as https://www.google.com in the browser, a request is sent to the server on the website identified by the URL. That server then responds with a response. The important thing is the formats of these requests and responses. These formats are defined by a protocol called HTTPHyper Text Transfer Protocol.

When you type in a URL at the browser, it sends out a GET request to the identified server. The server then replies with an HTTP response that contains data in HTMLHyper Text Markup Language. The browser then takes this HTML and displays it on your screen.

Let's say you are filling in a form present on a web page with a list of details. In such a scenario when you click the Submit button, an HTTP POST request gets sent out to the server.

HTTP and RESTful Web Services

HTTP provides the base layer for building web services. Therefore, it is important to understand HTTP. Here are a few key abstractions.

Resource

A resource is a key abstraction that HTTP centers round. A resource is anything you want to expose to the outside world through your application. For instance, if we write a todo management application, instances of resources are:

  • A specific user
  • A specific todo
  • A list of todos

Resource URIs

When you develop RESTful services, you need to focus your thinking on the resources in the application. The way we identify a resource to expose, is to assign a URIUniform Resource Identifier — to it. For example:

  • The URI for the user Ranga is /user/ranga
  • The URI for all the todos belonging to Ranga is /user/Ranga/todos
  • The URI for the first todo that Ranga has is /user/Ranga/todos/1

Resource Representation

REST does not worry about how you represent your resource. It could be XML, HTML, JSON, or something entirely different! The only important thing is you clearly define your resource and perform whatever actions that are supported on it by making use of features already provided by HTTP. Examples are:

  • Create a user: POST /users
  • Delete a user: DELETE /users/1
  • Get all users: GET /users
  • Get a single user: GET /users/1
REST and Resources

A significant point to note is that with REST, you need to think about your application in terms of resources:

  • Identify what resources you want to expose to the outside world
  • Make use of the verbs already specified by HTTP to perform operations on these resources

Here is how a REST service is generally implemented:

  • Data Exchange Format: No restriction is imposed over here. JSON is a highly popular format, although other such as XML can be used as well
  • Transport: Always HTTP. REST is completely built on top of HTTP.
  • Service Definition: There is no standard to specify this, and REST is flexible. This could be a drawback in some scenarios, as it might be necessary for the consuming application to understand the request and response formats. There are widely used ones however, such as WADL (Web Application Definition Language) and Swagger.

REST focuses on resources and how effectively you perform operations on them using HTTP.

The Components of HTTP

HTTP defines the following for a request:

For the response, HTTP defines the:

HTTP Request Methods

The method used in a HTTP request indicates what action you want to perform with that request. Important examples are:

  • GET: Retrieve details of a resource
  • POST : Create a new resource
  • PUT: Update an existing resource
  • DELETE: Delete a resource

HTTP Response Status Code

A status code is always present in a HTTP response. Common examples are:

  • 200: Success
  • 404: Page not found
Summary

In this article, we had a high-level look at REST. We stressed the fact that HTTP is the building block of REST services. HTTP is a protocol that is used to define the structure of browser requests and responses. We saw that HTTP deals mainly with resources that are exposed on web servers. Resources are identified using URIs, and operations on these resources are performed using verbs defined by HTTP.

Finally, we looked at how REST services make the best use of features offered by HTTP to expose resources to the outside world. REST does not put any restrictions on the resource representation formats or on the service definition.