What is SOAP and how does it differ from REST?

SOAP (Simple Object Access Protocol) is a protocol for exchanging structured messages in distributed computing, based on XML. It defines a strict set of rules for message formatting, uses security and transaction standards, and typically operates over HTTP, SMTP, or other protocols.

REST (Representational State Transfer) is an architectural style for interacting with web services, based on using standard HTTP methods (GET, POST, PUT, DELETE) and URIs to access resources. REST does not require a strictly defined message format, often using JSON.

Main differences:

• Message format: SOAP uses XML, REST more often uses JSON, but can also use XML.
• Strictness: SOAP is a protocol with strict standards, REST is an architectural style with more flexibility.
• Complexity: SOAP is more complex to implement and requires more resources.
• Transaction and security support: SOAP has built-in standards like WS-Security, REST usually relies on HTTPS and external mechanisms.
• Caching: REST supports caching via HTTP, SOAP does not.

Example REST request to get a user:

GET /users/123 HTTP/1.1
Host: example.com
Accept: application/json

Example SOAP message (fragment):

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ex="http://example.com/">
   <soapenv:Header/>
   <soapenv:Body>
      <ex:GetUser>
         <ex:UserId>123</ex:UserId>
      </ex:GetUser>
   </soapenv:Body>
</soapenv:Envelope>