SOAP

What is SOAP?

SOAP (Simple Object Access Protocol) is an XML-based messaging protocol for exchanging information among computers. It was the dominant standard for enterprise web services before REST took over.

SOAP is rigorous, standardized, and highly extensible. It relies heavily on XML schemas and formal contracts, making it popular in industries that require strict reliability and security, such as banking and telecommunications.

Core Concepts

WSDL (Web Services Description Language): An XML file that acts as the "manual" for the API. It defines exactly what endpoints exist, what parameters they accept, and what they return.

XML Envelope: Every SOAP message is wrapped in a specific XML structure.

ACID Compliance: SOAP is designed to support atomic transactions (all-or-nothing), essential for financial transfers.

Code Example: The Envelope

A SOAP message has a specific anatomy:

<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
  <!-- Optional Header for Auth / Metadata -->
  <soap:Header>
    <Authentication>
       <User>admin</User>
       <Token>12345</Token>
    </Authentication>
  </soap:Header>
  
  <!-- The Actual Payload -->
  <soap:Body>
    <m:GetAccountBalance xmlns:m="http://bank.org/accounts">
      <m:AccountNumber>987654321</m:AccountNumber>
    </m:GetAccountBalance>
  </soap:Body>
</soap:Envelope>

Comparisons: SOAP vs. REST

Feature	REST	SOAP
Format	JSON (usually), XML, Text	XML only
Philosophy	Resource-based (URI)	Action-based (Remote Procedure)
Contract	Loose (OpenAPI optional)	Strict (WSDL required)
Transport	HTTP/HTTPS	HTTP, SMTP, TCP, JMS
Errors	HTTP Status Codes (404, 500)	SOAP Faults (in XML body)

Debugging SOAP in Apidog

Although SOAP is legacy, Apidog fully supports it via its HTTP client.

1. Configure the Request

Since SOAP is just HTTP POST with XML:

Set Method to POST.

Set Header Content-Type to text/xml or application/soap+xml.

In Body, select XML.

2. Enter the Envelope

Paste your XML Envelope into the body editor. Apidog provides Syntax Highlighting and XML Formatting to help manage large XML structures.

<soap:Envelope ...>
   ...
</soap:Envelope>

3. Parse the WSDL (Optional)

While Apidog doesn't currently auto-generate collections from WSDL (like it does for OpenAPI), you can often find the endpoint URL inside the <soap:address> tag in the WSDL file.

See details SOAP/WebService

Key Takeaways

Enterprise Standard: SOAP is strictly standardized and reliable, widely used in banking and legacy enterprise systems.

XML-Based: It uses XML for message format and WSDL for service definition.

ACID Compliance: Designed for atomic transactions where partial failure is not an option.

Apidog Compatibility: While legacy, you can fully test SOAP services in Apidog using the standard HTTP Client with XML bodies.

Continue with → Chapter Summary

What is SOAP?#

Core Concepts#

Code Example: The Envelope#

Comparisons: SOAP vs. REST#

Debugging SOAP in Apidog#

1. Configure the Request#

2. Enter the Envelope#

3. Parse the WSDL (Optional)#

Key Takeaways#