REST vs SOAP API: Differences Between Web Services

 The Key differences are:

• SOAP stands for Simple Object Access Protocol whereas REST stands for Representational State Transfer.
• SOAP is a protocol whereas REST is an architectural pattern.
• SOAP uses service interfaces to expose its functionality to client applications while REST uses Uniform Service locators to access to the components on the hardware device.
• SOAP needs more bandwidth for its usage whereas REST doesn’t need much bandwidth.
• Comparing SOAP vs REST API, SOAP only works with XML formats whereas REST work with plain text, XML, HTML and JSON.
• SOAP cannot make use of REST whereas REST can make use of SOAP.

What is SOAP?

SOAP is a protocol which was designed before REST and came into the picture. The main idea behind designing SOAP was to ensure that programs built on different platforms and programming languages could exchange data in an easy manner. 

What is REST?

REST was designed specifically for working with components such as media components, files, or even objects on a particular hardware device. Any web service that is defined on the principles of REST can be called a RestFul web service. A Restful service would use the normal HTTP verbs of GET, POST, PUT and DELETE for working with the required components. 

When to use REST?

One of the most highly debatable topics is when REST should be used or when to use SOAP while designing web services. Below are some of the key factors that determine when REST and SOAP API technology should be used for web services REST services should be used in the following instances

• Limited resources and bandwidth – Since SOAP messages are heavier in content and consume a far greater bandwidth, REST should be used in instances where network bandwidth is a constraint.
• Statelessness – If there is no need to maintain a state of information from one request to another then REST should be used. If you need a proper information flow wherein some information from one request needs to flow into another then SOAP is more suited for that purpose. We can take the example of any online purchasing site. These sites normally need the user first to add items which need to be purchased to a cart. All of the cart items are then transferred to the payment page in order to complete the purchase. This is an example of an application which needs the state feature. The state of the cart items needs to be transferred to the payment page for further processing.
• Caching – If there is a need to cache a lot of requests then REST is the perfect solution. At times, clients could request for the same resource multiple times. This can increase the number of requests which are sent to the server. By implementing a cache, the most frequent queries results can be stored in an intermediate location. So whenever the client requests for a resource, it will first check the cache. If the resources exist then, it will not proceed to the server. So caching can help in minimizing the amount of trips which are made to the web server.
• Ease of coding – Coding REST Services and subsequent implementation is far easier than SOAP. So if a quick win solution is required for web services, then REST is the way to go.

When to use SOAP?

SOAP should be used in the following instances

1. Asynchronous processing and subsequent invocation – if there is a requirement that the client needs a guaranteed level of reliability and security then the new SOAP standard of SOAP 1.2 provides a lot of additional features, especially when it comes to security.
2. A Formal means of communication – if both the client and server have an agreement on the exchange format then SOAP 1.2 gives the rigid specifications for this type of interaction. An example is an online purchasing site in which users add items to a cart before the payment is made. Let’s assume we have a web service that does the final payment. There can be a firm agreement that the web service will only accept the cart item name, unit price, and quantity. If such a scenario exists then, it’s always better to use the SOAP protocol.
3. Stateful operations – if the application has a requirement that state needs to be maintained from one request to another, then the SOAP 1.2 standard provides the WS* structure to support such requirements.

Challenges in REST API

1. Lack of Security – REST does not impose any sort of security like SOAP. This is why REST is very appropriate for public available URL’s, but when it comes down to confidential data being passed between the client and the server, REST is the worst mechanism to be used for web services.
2. Lack of state – Most web applications require a stateful mechanism. For example, if you had a purchasing site which had the mechanism of having a shopping cart, it is required to know the number of items in the shopping cart before the actual purchase is made. Unfortunately, the burden of maintaining this state lies with the client, which just makes the client application heavier and difficult to maintain.

Challenges in SOAP API

API is known as the Application Programming Interface and is offered by both the client and the server. In the client world, this is offered by the browser whereas in the server world it’s what is provided by the web service which can either be SOAP or REST.

Challenges with the SOAP API

1. WSDL file – One of the key challenges of the SOAP API is the WSDL document itself. The WSDL document is what tells the client of all the operations that can be performed by the web service. The WSDL document will contain all information such as the data types being used in the SOAP messages and what all operations are available via the web service. The below code snippet is just part of a sample WSDL file.

 <?xml version="1.0"?>
<definitions name="Tutorial"             
	targetNamespace=http://demo.guru99.com/Tutorial.wsdl             
	xmlns:tns=http://demo.guru99.com/Tutorial.wsdl             
	xmlns:xsd1=http://demo.guru99.com/Tutorial.xsd            
	xmlns:soap=http://schemas.xmlsoap.org/wsdl/soap/
	xmlns="http://schemas.xmlsoap.org/wsdl/"> 

	<types>  
		<schema targetNamespace=http://Demo.guru99.com/Tutorial.xsd
		xmlns="http://www.w3.org/2000/10/XMLSchema">

      	<element name="TutorialNameRequest">    
			<complexType>          
				<all>           
					<element name="TutorialName" type="string"/>         
				</all>       
			</complexType>    
		</element>     
	<element name="TutorialIDRequest">        
		<complexType>          
			<all>           
				<element name="TutorialID" type="number"/>         
			</all>       
		</complexType>      
	</element>   
	</schema>  
</types>	

As per the above WSDL file, we have an element called “TutorialName”  which is of the type
String which is part of the element 
TutorialNameRequest.

Now, suppose if the WSDL file were to change as per the business requirements and the 
TutorialName has to become TutorialDescription. 

This would mean that all the clients who are currently connecting to  this web service 
would then need to make this corresponding change in their code to accommodate the 
change in the WSDL file. 

This shows the biggest challenge of the WSDL file which is the tight contract between the
client and the server and that one change could cause a large impact, on the whole, 
client applications.

2. Document size – The other key challenge is the size of the SOAP messages which get 
transferred from the client to the server.  Because of the large messages, using SOAP 
in places where bandwidth is a constraint can be a big issue.
Sources: Google, guru99.com