REST (Representational State Transfer) and SOAP (Simple Object Access Protocol)

REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) are both approaches for building web services, but they differ significantly in their design principles and usage. REST is an architectural style that emphasizes flexibility and efficiency, often using JSON for data exchange, while SOAP is a protocol with strict rules and primarily uses XML for messaging.
Here are other similarities between SOAP and REST:

• They both describe rules and standards on how applications make, process, and respond to data requests from other applications
• They both use HTTP, the standardized internet protocol, to exchange information
• They both support SSL/TLS for secure, encrypted communication

SOAP relies on XML in three ways Envelope - that defines what is in the message and how to process it.
A set of encoding rules for data types, and finally the layout of the procedure calls and responses gathered.
This envelope is sent via a transport (HTTP/HTTPS), and an RPC (Remote Procedure Call) is executed, and the envelope is returned with information in an XML formatted document.
The important point is that one of the advantages of SOAP is the use of the “generic” transport but REST uses HTTP/HTTPS. SOAP can use almost any transport to send the request but REST cannot. So here we got an advantage of using SOAP.
When we are talking about REST over HTTP, all security measures applied HTTP are inherited, and this is known as transport level security and it secures messages only while it is inside the wire but once you delivered it on the other side you don’t know how many stages it will have to go through before reaching the real point where the data will be processed. And of course, all those stages could use something different than HTTP. So REST is not safer completely.
But SOAP supports SSL just like REST additionally it also supports WS-Security which adds some enterprise security features. WS-Security offers protection from the creation of the message to it’s consumption. So, for transport level security whatever loophole we found that can be prevented using WS-Security.
Apart from that, as REST is limited by its HTTP protocol so its transaction support is neither ACID compliant nor can provide two-phase commit across distributed transactional resources.
But SOAP has comprehensive support for both ACID based transaction management for short-lived transactions and compensation-based transaction management for long-running transactions. It also supports two-phase commit across distributed resources.

Key Differences:

• Protocol vs. Architectural Style: SOAP is a protocol with defined standards, while REST is an architectural style with guiding principles.
• Messaging Format: SOAP primarily uses XML for message formatting, while REST is more flexible and can use XML, JSON, or plain text.
• Flexibility: REST is generally considered more flexible due to its less rigid structure and ability to use different data formats, while SOAP has stricter rules and a more rigid structure.
• Performance: REST is often favored for its lightweight nature and faster performance, especially for mobile applications and scenarios where bandwidth is a concern, while SOAP can be more heavyweight due to its XML structure.
• Security: While both can be secured, SOAP has built-in security features like WS-Security, whereas REST relies on standard HTTP security mechanisms.
• Complexity: REST is generally considered simpler to implement and understand than SOAP, making it easier to adopt for many developers.

Reasons for using REST

• REST uses standard HTTP it is much simpler in just about every way.
• REST is easier to implement, requires less bandwidth and resources.
• REST permits many different data formats whereas SOAP only permits XML. REST allows better support for browser clients due to its support for JSON.
• REST has better performance and scalability. REST reads can be cached, SOAP based reads cannot be cached.
• If security is not a major concern and we have limited resources. Or we want to create an API that will be easily used by other developers publicly then we should go with REST.
• If we need Stateless CRUD operations then go with REST.
• REST is commonly used in social media, web chat, mobile services and Public APIs like Google Maps.
• RESTful service returns various Media Types for the same resource, depending on the request header parameter "Accept" as application/xml or application/Json for POST and /user/1234.json or GET /user/1234.xml for GET.
• REST services are meant to be called by the client-side application and not the end user directly.
• ST in REST comes from State Transfer. You transfer the state around instead of having the server store it, this makes REST services scalable.

Reasons for using SOAP

• SOAP is not very easy to implement and requires more bandwidth and resources.
• SOAP message request is processed slower as compared to REST and it does not use web caching mechanism.
• WS-Security: While SOAP supports SSL (just like REST) it also supports WS-Security which adds some enterprise security features.
• WS-AtomicTransaction: Need ACID Transactions over a service, you’re going to need SOAP.
• WS-ReliableMessaging: If your application needs Asynchronous processing and a guaranteed level of reliability and security. Rest doesn’t have a standard messaging system and expects clients to deal with communication failures by retrying.
• If the security is a major concern and the resources are not limited then we should use SOAP web services. Like if we are creating a web service for payment gateways, financial and telecommunication related work then we should go with SOAP as here high security is needed.

When to Choose Which:

REST: Ideal for public APIs, mobile applications, and scenarios where flexibility, performance, and ease of development are crucial.
SOAP: Preferred for enterprise-level applications, complex business logic, and situations where strict security and transaction management are required.

In summary, REST is a more modern, flexible, and efficient approach, while SOAP offers a more robust and standardized solution, particularly in enterprise environments.