Are REST APIs and HTTP APIs the same thing?
Summary
Nowadays, many people seem to interchangeably use the words REST APIs and HTTP APIs. However, they are two different things. Through this post, I will introduce their differences. Before doing that, I will first explain REST and HTTP.
REST
Representational State Transfer or REST is not a standard or a specification.1 It is an architectural style or โconceptโ2for distributed hypermedia systems. It sets a series of constraints about how Server and Client should interact.
Resources and Representations
The core concept of RESTful systems involves resources. A resource is something that is uniquely identifiable in a system. It can be a web page, a video stream, or an image. It can even be an abstract concept like list of users in a database. Unique identification is the key constraint of REST resources.
Resources may be available in multiple representations or formats, such as JSON and XML. You are using a โrepresentationโ of a resource to transfer resource state on the server into application state on the client. For example, in a client-server model, client requests an information of a user in JSON format.
Uniform Interface
RESTful systems require clients to access all resources using the same set of standard operations.
Stateless
All operations in a RESTful system should be stateless. Server should not store any state. Every request to the server should include all required data for the server to fulfill the request. This stateless feature gives visibility, reliability, and scalability to systems.
RESTful API
REST stands for REpresentational State Transfer.
When a RESTful API is called, the server transfers to the client a representation of the requested resourceโs state.3
For example, when an application calls some REST API to fetch a user(resource) named โchoi,โ the API will return the state of the user choi. This state may include full name, telephone number, and number of friends.
The representation of the state can be in various formats, such as JSON, XML, and HTML. Furthermore, any transfer protocol, not just HTTP, can be used in RESTful APIs.
HTTP
The HyperText Transfer Protocol or HTTP is a communication protocol with a given mechanism for server-client data transfer. It is a standard with well-defined constraints.
HTTP shows many features of a RESTful system and it is not a coincidence because HTTP 1.1 protocol was designed to follow the principles and constraints of REST. HTTP is commonly used in REST API, and this is why the confusion between HTTP API and REST API began.
URLs and Media types
Resources are addressable using unique URLs, and clients can choose different representations for resources. Different representations are handled by headers and media types in HTTP.
HTTP Methods
HTTP follows the principles of REST by providing the same set of methods for every resource. The common HTTP methods are POST, GET, PUT, and DELETE. They are part of HTTP RFC.
HTTP is Not Always RESTful
Modern web servers use cookies and sessions to store state. These cookies and session data are also used to represent the state on the server, which is not stateless.
Using URLs can violate the uniform interface. For example,
https://www.choi.com/api/v1/users?id=1&action=run
The above URL is using the predefined HTTP method GET, but is using the query parameter action=run that is not available to all resources in the system.
REST APIs and HTTP APIs
As mentioned above, REST is an architectural style, while HTTP is a protocol. REST is not necessarily tied to HTTP2. This architectural style may use HTTP, FTP, or other communication protocols (HTTP is widely used, though).
A RESTful API is an API that adheres to all the REST constraints. A HTTP API, on the other hand, is any API that uses HTTP as their transfer protocol.4
Many developers often call HTTP APIs as โREST APIs,โ but not all of the claimed APIs are truly RESTful.5
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