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In this era of technology where functioning is so dynamic, application programming interfaces (APIs) serve as the backbone of modern software development, enabling different software systems to communicate with each other seamlessly. a concept that applies everywhere, from command-line tools to enterprise code, microservices, and cloud-native architectures. It is basically an interface that software developers use to programmatically interact with software components or resources outside of their own code.
APIs are made up of two related elements:
The software that wants to access the features and capabilities of the API is said to ”call” it, and the software that creates the API is said to ”publish” it.
A simple way to understand how APIs work is to look at a common example—third-party payment processing. When a user purchases a product on an e-commerce site, the site might prompt the user to “Pay with PayPal” or another type of third-party system. This function relies on APIs to make the connection.
While the data transfer differs depending on the web service used, the requests and responses all happen through an API. There is no visibility on the user interface, meaning APIs exchange data within the computer or application and appear to the user as a seamless connection.
APIs authorize and grant access to data that users and other applications request. Access is authenticated to a service or portion of functionality using predefined roles that govern who or what service can access specific actions and data. APIs also provide an audit trail that details who and what had system access and when it happened.
Applications that call APIs were traditionally written in specific programming languages. Web APIs can be called through any programming language, but webpages created in Hypertext Markup Language (HTML) or application generator tools can also access them.
The most common architectures for APIs are Representational State Transfer (REST) and Simple Object Access Protocol (SOAP), which define a standard communication protocol specification for a message exchange based on Extensible Markup Language, or XML. SOAP requires less low-level infrastructure-related code than REST. However, REST APIs are easier to scale and redeploy, and simpler to implement and integrate with websites and services. REST APIs are most often used today, particularly for web interactions.
There are four types of APIs: private, public, partner, and composite.
APIs are also classified as local, web, remote, and program.
1) Local APIs offer OS or middleware services to applications. Examples of local APIs include Microsoft’s.NET APIs, the telephony API for voice applications, and database access APIs. Web APIs are designed to represent resources such as HTML pages and are accessed using a simple hypertext transfer protocol, or HTTP. Any web URL activates a web API. Web APIs are often called RESTful APIs because the publisher of REST interfaces doesn’t save any data internally between requests. As such, requests from many users can be intermingled as they would be on the internet.
A REST resource is any information that can be named, such as a document, an image, or a service. Each resource is identified by a URL and can be manipulated using standard HTTP methods.
A RESTful web service is created for services reading, updating, and deleting resources using HTTP with conformance to REST principles. It is stateless and provides a uniform interface to interact with the resources.
2) Remote APIs interact through a communication network to manipulate resources outside of the computer making the request. This is a broader category that includes, but is not limited to, web APIs. Remote APIs do not need to be designed based on web standards, though many are. The Java Database Connectivity API and the Java Remote Method Invocation API are two examples of remote APIs.
3) Program APIs are based on remote procedure call (RPC) technology that makes a remote program component appear to be local to the rest of the software. Service-oriented architecture APIs, such as Microsoft’s WS-series of APIs, are program APIs.
A payload in the context of an API is the data carried by the request or response. It is the actual data sent or received.
API documentation is a manual that explains how to use an API. It typically includes information about the endpoints, request/response formats, parameters, authentication methods, and examples.
Traditionally, API referred to an interface connected to an application created with any of the low-level programming languages, such as JavaScript. However, modern APIs vary in their architectures and use of data formats. They are typically built for HTTP, resulting in developer-friendly interfaces that are easily accessible and widely understood by applications written in Java, Ruby, Python, and many other languages.
As the use of web APIs has increased, it has led to the development and use of certain protocols, styles, standards, and languages. These structures provide users with a set of defined rules, or API specifications, that create accepted data types, commands, and syntax. In effect, these API protocols facilitate standardized information exchange.
SOAP is a lightweight XML-based messaging protocol specification that enables endpoints to send and receive data through a range of communication protocols, including SMTP (simple mail transfer protocol) and HTTP (hypertext transfer protocol). SOAP is independent, which allows SOAP APIs to share information between apps or software components running in different environments or written in different languages.
A remote procedure call (RPC) is a protocol that provides the high-level communications paradigm used in the operating system. RPC presumes the existence of a low-level transport protocol, such as transmission control protocol/internet protocol (TCP/IP) or user datagram protocol (UDP), for carrying the message data between communicating programs
RPC implements a logical client-to-server communications system designed specifically for the support of network applications. The RPC protocol enables users to work with remote procedures as if the procedures were local.
The XML-RPC protocol relies on a specific XML format to transfer data. XML-RPC is older than SOAP but simpler and relatively lightweight in that it uses the minimum bandwidth.
Like XML-RPC, JSON-RPC is a remote procedure call that uses JSON (JavaScript Object Notation) instead of XML. JSON is a lightweight format for data exchange that is simple to parse and uses name-value pairs and ordered lists of values. Because JSON uses universal data structures, it can be used with any programming language.
gRPC is a high-performance, open-source RPC framework initially developed by Google. gRPC uses the network protocol HTTP/2 and Protocol Buffers data formats and is commonly used to connect services in a microservices architecture.
WebSocket APIs enable bidirectional communication between client and server. This type of API does not require a new connection to be established for each communication; once the connection is established, it allows for continuous exchange. This makes Web socket APIs ideal for real-time communication.
REST is a set of web API architecture principles. REST APIs—also known as RESTful APIs—are APIs that adhere to certain REST architectural constraints. REST APIs use HTTP requests such as GET, PUT, HEAD, and DELETE to interact with resources. REST makes data available as resources, with each resource represented by a unique URI. Clients request a resource by providing its URI.
REST APIs are stateless—they do not save client data between requests. It’s possible to build RESTful APIs with SOAP protocols, but practitioners usually view the two standards as competing specifications.
GraphQL is an open-source query language and server-side runtime that specifies how clients should interact with APIs. GraphQL allows users to make API requests with just a few lines, rather than having to access complex endpoints with many parameters. This capability can make it easier to generate and respond to API queries, particularly more complex or specific requests that target multiple resources.
API design: Easy-to-use, reliable, and scalable APIs are characteristics of good API design. It generally includes endpoint definitions, methods, request formats, response formats, and security of the API.
Caching best practices for APIs include:
API testing is testing APIs to check whether they meet conditions of desired expectation to work correctly in areas of functionality, reliability, performance, and security.
API performance testing is doing tests for API speed, responsiveness, and stability under specific workloads. It ensures the API works well under the various conditions.
There are a number of API testing tools in the market. Some popular tools are:
The latency is the time that elapses between the moment a request forms from the client and the response processed by the server. In API testing, it reflects the point in time at which an API started processing a request.
Unit testing of a web API involves testing individual endpoints to ensure they function correctly. Tools like NUnit, JUnit, or pytest can be used along with mocking frameworks to isolate and test components.
Basic HTTP authentication is an authentication scheme which is quite simple. Indeed, it is even built in within the HTTP protocol. It basically consists of sending a base64-encoded string with the username and password in the Authorization header.
The ubiquity of the internet, the expanded use of cloud computing, and a shift from monolithic applications to microservices have all contributed to increased API use. Trends around APIs include the following:
Web API calls can come from any programming language, but webpages created in HTML or application generator tools can also make them. The increased role of the internet and the cloud in daily life and business activities has expanded the use of APIs and simple programming tools, or even no programming at all, for API access.
Both REST and SOAP can invoke, connect to, manage, and interact with cloud services. REST is increasingly preferred for web APIs because it uses less bandwidth and offers more options for programming languages, such as JavaScript and Python. Large websites, such as Amazon, Google, LinkedIn, and Twitter, use RESTful APIs.
Cloud computing introduces new capabilities to divide software into reusable components, connect components to requests, and scale the number of copies of software as demand changes.
These cloud capabilities have shifted the focus of APIs from simple RPC-based programmer-centric models to RESTful web-centric models and even to what is called functional programming or lambda models of services that can be instantly scaled as needed in the cloud.
The trend to think of APIs as representing general resources has changed. Many applications and users do make use of APIs as a general tool, but they are also considered services and will normally require more controlled development and deployment.
SOAs and microservices are examples of service APIs. Services are the hottest trend in APIs, to the point where it’s possible that all APIs in the future will be seen as representing services.
AI and machine learning are increasingly being used to automatically generate documentation and monitor API usage trends.
APIs simplify the design and development of new applications and services and the integration and management of existing ones. They also offer significant benefits to developers and organizations at large.
The average enterprise uses almost 1200 cloud applications (links reside outside ibm.com), many of which are disconnected. APIs enable integration so that these platforms and apps can seamlessly communicate with one another. Through this integration, companies can automate workflows and improve workplace collaboration. Without APIs, many enterprises would lack connectivity, causing information silos that compromise productivity and performance.
APIs offer flexibility, allowing companies to make connections with new business partners and offer new services to their existing market. This flexibility also enables companies to access new markets that can boost returns and drive digital transformation.
For example, Stripe began as an API with just seven lines of code. The company has since worked with many of the biggest enterprises in the world. Stripe has diversified to offer loans and corporate cards and received a recent valuation of USD 65 billion (link resides outside ibm.com).
Many companies choose to offer APIs for free, at least initially, so that they can build an audience of developers around their brand and forge relationships with potential partners. If the API grants access to valuable digital assets, a business monetizes it by selling access. This practice is referred to as the API economy.
When AccuWeather started its self-service developer portal to sell a wide range of API packages, it took just 10 months to attract 24,000 developers, selling 11,000 API keys. This move helped to build a thriving community in the process.
APIs separate the requesting application from the infrastructure of the responding service and offer layers of security between the two as they communicate. For example, API calls typically require authentication credentials. HTTP headers, cookies, or query strings can provide additional security during data exchange. An API gateway can control access to further minimize security threats.
APIs provide added protection within a network. They can also provide another layer of protection for personal users. When a website requests a user’s location (a location API provides this information), the user can decide whether to allow or deny this request.
Many web browsers and desktop and mobile operating systems have built-in permission structures. When an app must access files through an API, operating systems such as iOS, macOS, Windows, and Linux use permissions for that access.
API endpoints are the final touchpoints in the API communication system. These include server URLs, services, and other specific digital locations from which information is sent and received between systems. API endpoints are critical to enterprises for two main reasons:
API endpoints make the system vulnerable to attack. API monitoring is crucial for preventing misuse.
API endpoints, especially high-traffic ones, can cause bottlenecks and affect system performance.
Error handling in Web API involves returning appropriate HTTP status codes and messages to the client in case of an error. This would need to be supported by error messages, logging, and exception handling mechanisms that handle errors gracefully.
HTTP status codes are basically standard responses that a web server returns after completing the request made by an end client. It normally consists of these statuses:
Web APIs can be consumed by various clients, including web browsers, mobile applications, desktop applications, and other servers.
Application Programming Interfaces (APIs) are essential building blocks of modern software development. They enable communication between different systems, facilitate data exchange, and support integration with third-party services. As technology continues to evolve, APIs will play an increasingly important role in shaping the future of software development.
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