Application programming interface (API) allows different software applications to communicate with one another to share data. It acts as an abstraction layer to help developers integrate different software components and leverage existing services without understanding the implementation details. APIs use different protocols to transfer data. In this Answer, we will explore different API protocols.
There are multiple API protocols, and the choice depends on the application's requirements and use cases. Below we can see some common API protocols.
SOAP (Simple Object Access Protocol)
REST (representational state transfer)
RPC (remote procedure call)
SOAP is a protocol that uses XML format to exchange data between client and server applications. They contain an envelope tag that encapsulates the message and its related information. The related information includes the headers and the message body. It is flexible as it isn't tied to any specific programming language. Rather, it allows software applications written in different programming languages to communicate by adhering to the SOAP protocol rules.
Let's see what a SOAP request and response look like. Both the response and request can be sent through an HTTP request.
A SOAP request is in XML format. The SOAP request XML format is shown below:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:example="http://www.example.com/"><soapenv:Header/><soapenv:Body><example:MyRequest><example:Parameter1>Value1</example:Parameter1><example:Parameter2>Value2</example:Parameter2></example:MyRequest></soapenv:Body></soapenv:Envelope>
Line 1: The <soapenv:Envelope>
is the root element that encapsulates the entire SOAP message. xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
specifies that any elements in the SOAP message with the soapenv
prefix belong to the SOAP envelope namespace.
Line 2: The <soapenv:Header>
element is optional and can contain headers for additional information.
Line 3: The <soapenv:Body>
element encapsulates the actual request body.
Line 4: The <example:MyRequest>
element represents the specific request operation that we invoke.
Lines 5–6: <example:Parameter1>
and <example:Parameter2>
are parameters with specific values that the server will need.
The server sends the SOAP response once the operations on the request are completed. Below we can see the XML format for the SOAP response:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:example="http://www.example.com/"><soapenv:Header/><soapenv:Body><example:MyResponse><example:Result>Success</example:Result></example:MyResponse></soapenv:Body></soapenv:Envelope>
Line 4: The <example:MyResponse>
element represents the response for the specific request operation.
Line 5: <example:Result>
represents the result of the operation, in this case, Success
.
REST is the most popular architectural approach to building APIs. It utilizes the standard HTTP methods and resource-based URLs to perform operations. REST APIs are stateless, which means that they do not store any client-related information. The client sends a request and transfers a resource's state representation to the server. It is usually transferred in one of the formats; JSON, XML, or plain text.
Below we can see an example of a REST API request in Javascript.
const apiUrl = 'https://api.example.com/users';// Define the request parametersconst requestOptions = {method: 'GET', // HTTP method (e.g., GET, POST, PUT, DELETE)headers: {'Content-Type': 'application/json' // Set the content type of the request},};// Make the API requestfetch(apiUrl, requestOptions).then(response => response.json()).then(data => {// Process the response dataconsole.log(data);}).catch(error => {// Handle any errors that occurred during the requestconsole.error('Error:', error);});
Line 1: The apiUrl
variable is set to the REST API endpoint URL.
Lines 4–9: The requestOptions
object is created to define the request parameters, including the HTTP method (GET
) and the headers with the content type set to application/json
.
Line 12: The fetch()
function is called with the apiUrl
and requestOptions
as arguments to initiate the API request.
Line 13: The .then()
method is used to handle the promise returned by fetch()
. It takes a callback function that receives the response and calls response.json()
to parse the response data as JSON.
A remote procedure call (RPC) invokes functions or procedures on a remote system. It follows a client-server model where the client initiates a call, and the server executes the procedure requested. The client invokes the remote procedure call using a normal function syntax abstracting the complexities of network communication. It helps distributed systems to collaborate by invoking procedures as if they were a local call. The popular frameworks of remote procedure calls (RPC) are gRPC, Apache Thrift, XML RPC, JSON RPC, etc. An illustration of a remote procedure call is shown below:
API protocols are vital in facilitating communication and interoperability between clients and servers, enabling the development of robust and scalable web services. Choosing the right protocol based on project requirements ensures standardized and efficient data exchange in modern web development.