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SOAP Tutorial: What Is SOAP Basics

SOAP (Simple Object Access Protocol) is an XML-based protocol used for message exchange over the web. This guide is suitable for beginners.

In today's world of web services and APIs, SOAP and REST are two common terms. SOAP, which stands for Simple Object Access Protocol, has been around since the late 1990s and relies on XML for messaging. In this guide, we'll cover the basics of SOAP and walk you through a sample SOAP request and response to illustrate how it works.

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For SOAP requests in Apidog, manually set the Header's Content-Type and Body format to XML, then click Send to invoke the API and receive XML-formatted responses. Apidog simplifies SOAP API workflows through its comprehensive documentation, mocking, and automated testing capabilities.

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What is SOAP (Simple Object Access Protocol)?

SOAP (Simple Object Access Protocol) is an XML-based protocol used for message exchange over the web. It enables applications to interact in a distributed environment and supports communication between different operating systems and programming languages.

What are the Basics of SOAP?

A SOAP request consists of an XML-formatted SOAP envelope sent to a web service. The service parses the request, processes it, and returns a SOAP response. SOAP messages have a specific structure with elements like envelopes, headers, bodies, and faults. Clients and servers communicate using this protocol.

SOAP Building Blocks

SOAP is a messaging protocol used for web communication. It consists of several building blocks that define the structure of SOAP messages.

The SOAP Envelope is the root element of a SOAP message and encapsulates the entire message. It provides the framework for organizing the different parts of the message.

The SOAP Header is an optional element that carries additional information about the SOAP message. It can contain details such as authentication credentials or routing information.

The SOAP Body carries the actual content of the SOAP message. It holds the request or response data that needs to be exchanged between the sender and receiver.

The SOAP Fault is used to represent error conditions during message processing. It provides standardized error reporting, including fault codes, fault strings, and optional fault details.

These building blocks, including the SOAP Envelope, SOAP Header, SOAP Body, and SOAP Fault, work together to define the structure and error-handling capabilities of SOAP messages. They enable interoperability and standardization in web communication.

SOAP Envelope Element

The SOAP envelope element is a crucial part of the SOAP message structure. It serves as the container for the SOAP message, encapsulating the header and body elements. The envelope element is defined within the SOAP namespace and ensures proper identification and interpretation of the XML elements.

It can specify the role and encoding style of the SOAP message. The mustUnderstand attribute indicates whether the SOAP header entries are critical for processing. The envelope element enables reliable and standardized data exchange, promoting interoperability across platforms and languages.

How Does SOAP API Work?

Let's illustrate how SOAP works with a simple example of a weather service using SOAP to request weather information. If you also want to know the guide on how to making the SOAP request in Postman, read this post:

Scenario: Imagine a client application that wants to retrieve weather data from a remote server using SOAP.

SOAP Request from Client:

The client creates a SOAP request message in XML format and sends it to the server's SOAP endpoint. Here's an example of a SOAP request:

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:ws="http://example.com/weatherservice">
    <soap:Header>
        <!-- Optional authentication information can be included here -->
    </soap:Header>
    <soap:Body>
        <ws:GetWeather>
            <ws:City>New York</ws:City>
        </ws:GetWeather>
    </soap:Body>
</soap:Envelope>

SOAP Server Processing:

The server receives the SOAP request, parses the XML, and extracts the necessary information from the <soap:Body> element. It then processes the request, fetching weather data for New York.

SOAP Response from Server:

After processing, the server constructs a SOAP response message and sends it back to the client. Here's an example of a SOAP response:

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:ws="http://example.com/weatherservice">
    <soap:Header>
        <!-- Optional response headers can be included here -->
    </soap:Header>
    <soap:Body>
        <ws:GetWeatherResponse>
            <ws:City>New York</ws:City>
            <ws:Temperature>72°F</ws:Temperature>
            <ws:Condition>Sunny</ws:Condition>
        </ws:GetWeatherResponse>
    </soap:Body>
</soap:Envelope>

<soap:Envelope> is again the root element for the SOAP envelope.
<soap:Header> can include optional response headers.
<soap:Body> contains the response data, which includes the weather information for New York.

Client Processing:

The client receives the SOAP response, parses it, and extracts the weather data from the <soap:Body>. In this case, it retrieves the temperature (72°F) and weather condition (Sunny) for New York.

SOAP Protocol Advantages and Disadvantages

Simple Object Access Protocol is still widely used, especially in large enterprises while it has some drawbacks, go on and have a look.

Advantages of the SOAP Protocol:

The main advantages of the SOAP protocol are its platform and language independence.

Since SOAP uses XML format to define message structure, it can communicate between different operating systems and programming languages.
The SOAP protocol supports various security mechanisms, such as digital signatures and encryption, to ensure message transmission security.

Disadvantages of the SOAP Protocol:

However, the SOAP protocol also has some disadvantages.

The message format of SOAP can be verbose, which may result in inefficient transmission.
The SOAP protocol requires the use of additional protocol layers, such as HTTP or SMTP, to transmit messages, which can add complexity to the system.

API Tool for Making SOAP Requests: Apidog

In conclusion, we have introduced the SOAP protocol. Now, is there a handy tool that allows us to easily and efficiently invoke SOAP API? The answer is yes, and that tool is Apidog.

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Apidog is an integrated API collaboration platform that provides comprehensive API documentation, debugging, mocking, and automated testing capabilities. It is an advanced tool for API design, development, and testing. Apidog offers a unified solution for API management, allowing you to design, debug, test, and collaborate on your APIs within a single platform.

It eliminates the need for switching between different tools and ensures data consistency. Apidog simplifies your API workflow and enables efficient collaboration among front-end, back-end, and testing teams.

For SOAP API, you only need to manually set the Content-Type value of the Header to text/xml; charset=utf-8 or application/soap+xml according to the actual request, and then set the Body format to xml. Click "Send," and you will receive the XML-formatted data returned by the SOAP request.

SOAP vs REST: The Difference between SOAP and REST API

SOAP and REST are two different architectural styles for designing web services APIs. SOAP stands for Simple Object Access Protocol and relies on XML for message formatting and WSDL for request definition. SOAP APIs tend to be more rigid and structured. REST stands for Representational State Transfer and utilizes HTTP methods to implement CRUD operations. REST APIs follow a resource-oriented approach and are generally more lightweight and flexible.

The main differences are that SOAP is protocol-based while REST is an architectural style, SOAP uses XML for messaging while REST uses plain HTTP, SOAP APIs are tightly coupled while REST APIs are loosely coupled, and SOAP defines standards while REST does not enforce strict standards. Overall, REST APIs have become more popular in recent years due to their simplicity and scalability.

Conclusion

The SOAP protocol is an XML-based protocol used for message exchange over the web. It offers advantages such as platform and language independence, as well as support for various security mechanisms. However, SOAP messages can be verbose, leading to inefficient transmission, and the protocol requires additional layers for message delivery, adding complexity to the system.