REST (Representational State Transfer) is an architectural style for building APIs that rely on HTTP requests to access and use data. A REST client is software that enables developers to access and interact with REST APIs. The client sends requests to REST endpoints (URLs) and receives responses, usually in JSON or XML format. In this article, we will dive into what exactly REST clients are, why they are useful, their capabilities, and provide examples of popular REST API clients.
What are REST Clients?
REST clients provide a simplified way for developers to interact with REST APIs. They handle all the HTTP requests and responses in the background, abstracting away the lower-level details. Developers can focus on working with the API using the client library’s interface.
Some key capabilities and benefits of REST clients include:
- Sending various HTTP requests like GET, POST, PUT, DELETE to access and manipulate data exposed by an API.
- Handling authorization including OAuth, API keys, and other mechanisms.
- Supporting different data formats like JSON, XML, YAML, etc.
- Providing an easy-to-use interface for working with resources & endpoints.
- Automatically encoding/decoding data in requests and responses.
- Handling retries, connection issues, and other network errors.
- Streamlining authentication & session management.
- Including developer-friendly features like code generators, built-in docs, etc.
By handling these complexities, REST clients make it much simpler for developers to get up and running with an API. The client abstracts away the underlying implementation and transport details.
Why Use a REST Client?
There are several key reasons why developers use dedicated REST clients instead of manually working with HTTP requests:
- Productivity – Handling HTTP, JSON, authentication, retries, etc takes significant development effort. REST clients encapsulate this functionality so developers can focus on using the API.
- Abstraction – Clients provide an abstract interface to the API that’s easy to understand and use. Developers don’t have to worry about underlying HTTP transport mechanics.
- Consistency – Centralizing the client code promotes consistency across applications using that API. It also facilitates moving between different languages.
- Stability – Client libraries stabilize API usage across versions. Updating the centralized client absorbs many API changes.
- Portability – Standardized clients allow easily switching between languages. The client handles translating API interactions into specific language environments.
- Developer Experience – Clients improve the experience working with APIs through great docs, code generation, testing support, etc.
In summary, using a purpose-built REST client optimizes the developer experience and reduces complexity when working with web APIs.
Core Capabilities
While REST clients’ specific features vary, they generally provide a common core set of capabilities:
HTTP Request Methods
REST clients can send various HTTP requests like GET, POST, PUT, PATCH, DELETE. This allows accessing resources from the API and manipulating them to perform CRUD (create, read, update, delete) operations.
Request & Response Serialization
The client automatically handles serializing request payloads (e.g. JSON) and deserializing response bodies into language-specific data structures like native dicts, objects, arrays, etc.
Authentication
Clients support different authentication mechanisms like API keys, OAuth 2.0, basic auth, etc. This relieves the developer from implementing auth manually.
Error Handling
Robust clients provide error handling capabilities like surfacing 4xx & 5xx status codes as exceptions in the target language.
Configurability
Developers can configure the client for different environments (prod, dev, test), retry policies, timeouts, etc.
Code Generation
Many clients support generating code stubs, docs, and models from the API description (OpenAPI, etc) to accelerate development.
Popular REST Clients
There are many excellent open source REST clients for various languages and frameworks. Here are some popular options:
Postman
Postman is one of the most widely used interactive REST clients. It offers an intuitive GUI for sending API requests and inspecting responses. Postman also provides collaboration features like shared workspaces.
Insomnia
Similar to Postman, Insomnia is a user-friendly REST client with a graphical interface. It competes closely with Postman and includes options like cookie management.
cURL
cURL is a venerable command-line HTTP client used widely in scripts and terminals for testing APIs. cURL allows sending most types of API requests and inspecting reponses.
requests
In Python, the requests library is the de facto standard for working with REST APIs. Its simple and elegant interface has made it hugely popular.
Axios
For JavaScript environments, Axios is a widely used promise-based client. It supports async/await, auto JSON serialization, and request cancellation.
Retrofit
Retrofit is a robust Type-Safe REST client for Android & Java. It uses OkHttp under the hood and provides an annotated interface to manage requests and responses.
HTTParty
HTTParty is a pragmatic Ruby gem for interacting with REST services. It provides a simple DSL for HTTP with JSON support.
There are many other excellent clients like RestSharp (C#/.NET), Feign (Java), etc. Most languages and frameworks have well-supported HTTP clients optimized for REST APIs.
Building Custom REST Clients
While third-party clients can handle most use cases, sometimes developers may want to build their own custom REST client. Reasons include:
- Tighter integration into app architecture
- Additional capabilities like caching, logging, metrics
- Better performance for high-traffic APIs
- Greater control over HTTP client implementations
- Customizing for specific team/organization needs
If building a custom client, key design decisions include:
- Transport Client – Which underlying HTTP library to use like requests, Axios, OkHttp, etc.
- Interface – How the client will be invoked in code – optionally leveraging annotations.
- Serialization – Support for JSON and other content types.
- Error Handling – How HTTP errors surface to the caller.
- Retries – Automatically retry failed requests with backoff.
- Caching – Optional local caching layer to avoid network roundtrips.
- Metrics & Logging – Instrumentation to track usage and debug issues.
There are also tools that can generate starter client code from an API definition like OpenAPI – for example OpenAPI Generator.
REST Client Best Practices
When working with REST clients, there are some best practices that help build robust applications:
- Leverage client libraries instead of hand-coding HTTP requests
- Use async/await instead of synchronous calls to avoid blocking
- Implement exponential backoff with retries for resilience
- Configure reasonable timeouts on requests
- Provide clean abstractions over clients in app code
- Add instrumentation/metrics for monitoring
- Support multiple environments like dev, test, staging
- Validate request parameters/payloads on the client side
- Handle and surface errors appropriately in the app
Adopting these patterns makes applications more reliable, performant and easy to manage when built on REST APIs.
Conclusion
REST clients provide a convenient way for developers to interact with RESTful APIs. They eliminate huge amounts of complex code to handle HTTP, serialization, authentication, and other responsibilities that would otherwise have to be implemented manually.
There are excellent open source REST clients available for most languages and platforms. REST clients encapsulate best practices and enable developers to focus on their application logic instead of API plumbing.
By leveraging a well-written REST client, developers can build applications faster while maximizing robustness, performance, and maintainability.