SOAP vs REST: Key Differences and When to Use Each

REST APIs have been increasingly gaining traction when it comes to creating applications that are capable of communicating with web applications. They're an effective solution to help you build a connection between a client and a server.

When you're creating apps, there are several ways to make that connection, and two options people often discuss are SOAP and REST APIs. While SOAP APIs have been the standard for quite a while, many developers are now opting for the more straightforward REST APIs, which is why we're reviewing the critical differences between the two in this post and when to use each.

What Is SOAP?

The Simple Object Access Protocol (SOAP) is a communication protocol that allows two computers to exchange information over the internet.

SOAP is a standards-based web API that uses XML for its message format. Extensible Markup Language (XML) is one of the most popular languages used for data transfer, and the SOAP API uses it to exchange information between systems. The SOAP API also has a well-defined structure, which makes it easy to use with programming languages. However, the SOAP API can be slower and more complicated than the REST API.

SOAP messages are sent as XML documents. The XML document contains the SOAP envelope, which defines the start and end of the message, and the body, which has the message itself. The envelope also includes a header, which is optional, and a fault, which is also optional.

The header contains information about the message, such as who it's from and to whom it's addressed. The fault includes information on any errors that occurred while processing the message.

A SOAP server processes SOAP messages. The server reads the XML document and parses it to extract the envelope. It then processes the header and body according to the information in the envelope. If there are any errors, they're reported in the fault.

What Is REST?

REST stands for REpresentational State Transfer. It is a software architectural style for developing web services. REST services are typically built using the Web Services Description Language (WSDL). REST services often expose data from databases or other back-end systems. You may also use them to provide access to functionality such as creating or updating data.

REST is one of the most popular ways to build web services because it's simple to use and implement. It's also easy to scale, making it well suited for large-scale applications. The main idea behind REST is that, instead of using complex mechanisms like CORBA, RPC, or SOAP to connect between different systems, REST allows systems to communicate with each other by requesting resources that represent a specific state. For example, say a client requests a server to retrieve a resource representation. The server would then respond with the requested resource or an error message if it could not find the resource.

What Are the Differences Between the SOAP API and REST API?

There are several differences between SOAP and REST APIs. Let's understand a few of them.

First, developers typically use SOAP APIs for more complex applications requiring greater security and transaction management. REST APIs are more suited for simple CRUD-style applications.

Second, SOAP APIs are usually based on XML, while REST APIs can be based on either XML or JSON.

Third, SOAP APIs typically require a WSDL file for documentation, while REST APIs do not.

SOAP APIs are often more expensive to develop and maintain than REST APIs. They're more complex and require more overhead than REST APIs. REST APIs are more flexible and can be easily integrated with other systems.

Finally, a SOAP API is designed to take advantage of the existing infrastructure of the web. A REST API, on the other hand, works with web-based applications. Also, SOAP APIs are designed for interoperability, while REST APIs are designed for scalability.

Understanding the Difference With an Example

Let's look at an example to understand the difference between SOAP and REST. Imagine that you are a customer at some restaurant. The waiter takes your order and then goes to the kitchen to prepare your meal.

In the SOAP protocol, the waiter would be the client, and the kitchen would be the server. The waiter would send a message to the kitchen with your order. The kitchen would then prepare your meal and send a message back to the waiter with the finished product.

In the REST protocol, the customer (you) would be the client, and the restaurant would be the server. You would send a message to the restaurant with your order. The restaurant would then prepare your meal and send a message back to you with the finished product.

When to Use SOAP API and When to Use REST API

Developers can use both SOAP and REST APIs to access web services. However, there are some critical differences between using each. Let's discuss them in detail.

One is the nature of the data that you need to exchange. For instance, you may choose a REST API if your data is simple and you can easily represent it in a standard format such as JSON or XML. However, a SOAP API may be a better option if the data is complex or binary.

The second key factor is whether you need the full power of the SOAP protocol, which includes support for complex data structures, transactions, and security. A REST API may be a better choice if you don't need these features. A REST API is also generally simpler to use and easier to get started with.

Another consideration is the level of security required. SOAP APIs can take advantage of features such as WS-Security for added security, while REST APIs typically rely on HTTPS for security.

Finally, it's also worth considering the level of integration required. SOAP APIs are more tightly coupled and need more overhead to set up, while REST APIs are more loosely coupled and can be easier to integrate.

Also read: Need to decide what kind of testing is right for your project? Check out "Manual Testing vs. Automated Testing: Which to Use When."

Why Do Programmers Prefer REST API Over SOAP?

There are a few reasons why programmers might prefer a REST API over SOAP:

1. REST is generally much more straightforward to work with than SOAP. You can access a REST API using any standard HTTP client, meaning you don't need any special libraries or software.
2. A REST API usually returns data in a format more accessible for programmers to work with, such as JSON or XML. Also, a REST API is typically much faster than a SOAP API.
3. A REST API uses standard HTTP methods, which makes it easier to understand and use. SOAP uses complex XML, which can be challenging to parse and understand.

Conclusion

APIs are a powerful solution for building applications accessed over the internet and are flexible and scalable. SOAP and REST APIs are two different styles of cloud APIs, and each has its advantages.

While this post is not a comprehensive guide, we hope it gives you a better idea of when you should consider using SOAP and when REST is a better option. You can contact us anytime if you are interested in learning more about testing APIs.