SOAP vs REST

SOAP and REST are the two common API paradigms for interacting with web services. SOAP was initially developed by Microsoft and has been around for a long time. REST was created in response to the shortcomings of SOAP and tries to solve SOAP problems and provide an easier way to access web services.

What are the key differences between SOAP and REST?

  • SOAP is a communication protocol, whereas REST is just an architectural pattern
  • SOAP requires more bandwidth to use, whereas REST is more data-driven and requires less bandwidth
  • SOAP only works with XML, while REST can work with plain text, XML, HTML, and JSON
  • SOAP is better suited to integrate with enterprise-grade security tools
  • SOAP has built-in ACID compliance that protects database integrity, and REST is not ACID compliant
  • SOAP-based calls cannot be cached, and REST calls can be cached

What is API?

API stands for Application Programming Interface and is a way to interact with other software components programmatically. The API allows two applications to communicate with each other. For example, every time you send an instant message over the phone or check the weather in your browser, you are using the API. There are several models for developing APIs, but the two most common are SOAP and REST.

What is SOAP?

SOAP is a simple object access protocol developed by Microsoft to replace older technologies that do not work well on the Internet, such as the DCOM (Distributed Component Object Model) and the Shared CORBA (Object Request Broker Architecture). DCOM and CORBA fail because they rely on binary messages, while SOAP uses XML and works better over the Internet.

The main idea behind SOAP was that programs built on different platforms and programming languages ​​could easily exchange data. SOAP relies exclusively on XML and, together with schemas, defines a very strongly typed messaging structure. Each operation provided by a service is explicitly defined along with the request and response XML structure for that operation. In SOAP, each input parameter is similarly defined and bound to a type: for example, an integer, string, or other complex objects. All of this is encrypted in WSDL - web service descriptions (or definitions in later versions). WSDL is often referred to as the contract between the provider and the consumer of a service. From a programming perspective, WSDL can be thought of as a method signature for a web service.

An example of a SOAP message that contains a SOAP header and body blocks.

SOAP Envelope Example
<?xml version='1.0' Encoding='UTF-8' ?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> 
 <env:Header>
  <m:reservation xmlns:m="https://website.com/reservation" env:role="http://www.w3.org/2003/05/soap-envelope/role/next">
   <m:reference>uuid:11111-22222-333333-444444-555555</m:reference>
   <m:dateAndTime>2020-01-01</m:dateAndTime>
  </m:reservation>
  <n:passenger xmlns:n="https://website.com/employees" env:role="http://www.w3.org/2003/05/soap-envelope/role/next">
   <n:name>John Smith</n:name>
  </n:passenger>
 </env:Header>
 <env:Body>
  <p:itinerary xmlns:p="https://website.com/reservation/travel">
   <p:departure>
     <p:departing>New York</p:departing>
     <p:arriving>Los Angeles</p:arriving>
     <p:departureDate>2020-01-01</p:departureDate>
   </p:departure>
  </p:itinerary>
 </env:Body>
</env:Envelope>

Complete SOAP Request Example:

SOAP Request Example
POST /Reservation HTTP/1.1
Host: website.com
Content-Type: text/xml; charset = utf-8
Content-Length: 874

<?xml version='1.0' Encoding='UTF-8' ?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> 
 <env:Header>
  <m:reservation xmlns:m="https://website.com/reservation" env:role="http://www.w3.org/2003/05/soap-envelope/role/next">
   <m:reference>uuid:11111-22222-333333-444444-555555</m:reference>
   <m:dateAndTime>2020-01-01</m:dateAndTime>
  </m:reservation>
  <n:passenger xmlns:n="https://website.com/employees" env:role="http://www.w3.org/2003/05/soap-envelope/role/next">
   <n:name>John Smith</n:name>
  </n:passenger>
 </env:Header>
 <env:Body>
  <p:itinerary xmlns:p="https://website.com/reservation/travel">
   <p:departure>
     <p:departing>New York</p:departing>
     <p:arriving>Los Angeles</p:arriving>
     <p:departureDate>2020-01-01</p:departureDate>
   </p:departure>
  </p:itinerary>
 </env:Body>
</env:Envelope>

What is REST?

REST (Representative State Transfer) was developed in response to the complexity of SOAP to work with components such as media components, files, or even to interact with hardware devices. Any web service defined in terms of REST principles can be called a RestFul web service. REST is a software architecture style based on a stateless communication protocol and provides a lighter alternative to SOAP. Many developers found SOAP cumbersome and harder to use.

Instead of using XML to submit a request, REST (usually) relies on a target URL. Of course, you have to provide more information in some situations, but most web services using REST rely solely on using the URL approach. The Restful service uses the usual HTTP methods GET, POST, PUT, and DELETE to accomplish its tasks.

Unlike SOAP, REST does not enforce XML to respond. You can find REST-based web services that output CSV (Command Separated Values), JSON (JavaScript Object Notation), and RSS (Really Simple Syndication). However, the JSON format is the most widely used because it is lighter and can be used in browsers. REST is data-driven versus SOAP, which is function-driven.

REST Request Example
POST /echo/post/json HTTP/1.1
Host: reqbin.com
Accept: application/json
Content-Type: application/json
Content-Length: 81

{
  "Id": 78912,
  "Customer": "Jason Sweet",
  "Quantity": 1,
  "Price": 18.00
}

What are the advantages of SOAP?

SOAP provides the following advantages over REST:
  • SOAP is language, platform, and transport agnostic (REST requires HTTP)
  • SOAP works well in distributed enterprise environments (REST assumes direct point-to-point communication)
  • SOAP is strictly standardized
  • SOAP provides significant pre-build extensibility in the form of the WS* standards
  • SOAP has built-in error handling

What are the advantages of REST?

REST provides the following advantages over SOAP:
  • REST requires less learning curve
  • REST is data-driven and efficient
  • REST is fast (no extensive processing required)
  • REST is closer to other web technologies in design philosophy
  • REST is easy to read by humans and computers

What is the difference between SOAP and REST APIs?

SOAP REST
SOAP is a communication protocol that has its own specification and includes a WSDL file that contains the necessary information about what a web service does, in addition to its location. REST is an architectural pattern. A web service can only be considered RESTful if it meets the following requirements:
  1. Client/server architecture
  2. Stateless
  3. Cacheable
SOAP cannot use REST because SOAP is a protocol and REST is an architectural pattern. REST can use SOAP because it is just an architectural pattern and can use any protocol, including SOAP.
SOAP exposes its functionality to client applications through service interfaces. The WSDL file provides the client with all the information about what services the web service offers. REST relies on Uniform Service locators to access components. The REST service does not provide any information about what services the web service offers. To do this, you must use the REST API documentation.
SOAP requires more bandwidth to use it. SOAP messages contain much ancillary information, the amount of data transfer using SOAP is usually significant. REST does not require much bandwidth when sending requests to the server since REST messages are mostly JSON messages and do not contain unnecessary information.
SOAP can only work with XML format, and all data is sent and received only in XML format. REST clients and servers mostly use JSON, but REST supports many other formats, including plain text, HTML, XML, and CSV.
SOAP has built-in success/retry error handling logic and provides end-to-end reliability even through SOAP intermediaries. REST has no built-in error handling and can only resolve communication failures by retrying.
SOAP-based calls cannot be cached. REST-based calls can be cached.
SOAP supports SSL and WS-Security and is better suited for integration with enterprise-grade security tools. REST supports SSL for end-to-end security.

What are the similarities between SOAP and REST?

Both SOAP and REST rely on well-defined rules that everyone has agreed to abide by in the interest of sharing information. And despite the global differences, they also have some similarities:

  • Both SOAP and REST provide communication between two applications through data that can be read by both humans and computers.
  • Both usually use HTTP protocol and methods (like GET, POST, DELETE), but can also use other network protocols.
  • Both can use XML format in requests and responses.

When to use SOAP?

SOAP should be used in the following situations:

  1. High reliability and security - if the client requires a guaranteed level of reliability and security in asynchronous data processing. SOAP has many useful features built in, especially when it comes to security.
  2. Strictly formalized interaction interface - if both the client and the server agree on an exchange format, then SOAP provides rigid specifications to support that format.
  3. Stateful Operations - if an application requires that this state be maintained from one request to the next, then the SOAP standard provides a WS* framework to support those requirements.

When to use REST?

REST services should be used in the following situations:

  1. Limited resources and bandwidth - Because REST requests are lighter and consume less bandwidth, REST should be used in situations where network bandwidth is a constraint (such as mobile applications).
  2. Stateless - unless you need to maintain state of information from one request to the next, you should use REST.
  3. Caching - if you can cache API requests, REST is the best solution. Caching can help minimize server hits and improve server performance.
  4. Reduced development time - developing REST services is much easier than SOAP.

SOAP vs REST comparison table

SOAP REST
Design A standardized protocol with predefined rules. An architectural style with clear guidelines and guidelines.
Approach Function-driven (data is available as a service, for example: "getPrice") Data-driven (data is available as resources, eg "/get/price").
Statefulness Stateless by default, but can make it stateful. Stateless (no server-side sessions).
Caching SOAP calls cannot be cached. REST calls can be cached.
Security Supports SSL and WS-Security. Built-in ACID compliance. Supports HTTPS and SSL.
Performance Requires more bandwidth and computing power. Requires less bandwidth and less computing power.
Message format Only XML. TXT, XML, JSON, CSV, and others.
Transfer protocols HTTP, Web Sockets, and others. Only HTTP
Recommended for Enterprise grade apps, financial and payment services. Public APIs for web and mobile services.
Advantages High security, reliability, standardized. Easy, better performance, flexibility.
Disadvantages Poorer performance, more complexity. Less security.

Conclusion

Both REST and SOAP have distinct advantages and disadvantages. The choice to use SOAP or REST depends on the project requirements, the qualifications of your development team, the programming language you are using, and the cost of ownership requirements. Both approaches have their advantages and disadvantages. While REST is the most popular and you can reduce development time with REST, SOAP is better suited when you need increased reliability and security. Developers tend to choose REST when there is no need for higher reliability and security, and there are no other additional requirements that make SOAP a better choice, for example, for enterprise applications.

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