A brief overview of APIs

APIs, or application programming interfaces, facilitate communication between two software services through a series of requests and responses. For instance, when we receive a notification about a token’s price drop in our telephone app, it means that our app is communicating with a price provider such as CoinMarketCap via an API. To structure a request for the desired response, we must always refer to the relevant API documentation.

For a more comprehensive understanding of APIs, we can find additional information in the book Python API Development Fundamentals by Packt Publishing . Since we will frequently interact with APIs to extract information, it’s beneficial to review the primary characteristics of different APIs. This will greatly assist us when we aim to programmatically access information.

For this purpose, we will focus on the following:

• Remote Procedure Call (RPC) APIs: In RPC APIs, the client initiates a function on the server, and the server sends back the output. In practice, we include the method (endpoints) of the function in the URL and the arguments in the query string. In this case, the client needs to possess all the information about the endpoints, and sometimes it involves constructing a workflow with information queried from other URLs. An example of an RPC API encoded in JSON format is the Infura suite, which we have utilized in previous sections.
• Representational State Transfer (REST) API: This API is stateless, meaning that it does not save the client’s data between requests. This is one of the most popular methods on the market because it is lightweight and easy to maintain and scale.

  The client sends requests to the server in the form of a web URL, including methods such as GET, POST, PUT, or DELETE, and the server responds, typically in JSON format. A REST request typically comprises the HTTP method, endpoint, headers, and body. The endpoint identifies the resource online, headers provide server information, such as authentication, and the body contains the information the sender wishes to transmit to the server as a request.

An alternative approach was developed by Facebook as an open source query language named GraphQL. The key difference from the aforementioned APIs is that GraphQL is a query language, whereas REST is an architectural concept for software. GraphQL is a syntax for data retrieval that empowers the client to specify the required information, unlike the REST infrastructure, where queries return fixed datasets for each endpoint (sometimes including more information than necessary).

A noteworthy feature of GraphQL is its ability to construct requests that fetch data from multiple resources using a single API call. The Graph is an indexer and query protocol for the Ethereum network that is queried using GraphQL; we will delve into it further in Chapter 2.