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SOAP vs HTTP: Key Differences Explained

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This article compares SOAP and HTTP protocols, outlining the fundamental differences between them. Let’s delve into the basics of each.

SOAP Protocol

SOAP stands for Simple Object Access Protocol.

  • It utilizes XML messaging to facilitate information exchange between computers across the internet.
  • SOAP can leverage HTTP for XML messaging, acting as a data transport mechanism for web services. It’s capable of exchanging entire documents or invoking remote procedures.
  • It can be used to broadcast messages.
  • SOAP is platform and language-agnostic.
  • SOAP isn’t tied to any specific transport protocol. It can transmit messages via SMTP, HTTP, FTP, MQSeries, or MSMQ. HTTP remains the most common transport protocol for SOAP.

SOAP Protocol

Figure 1: SOAP Protocol Messages

As depicted in Figure 1, a SOAP message comprises the following elements:

  • Envelope: Defines the start and end of the message. This is a mandatory element.
  • Header: Contains optional attributes used for processing the message, either at intermediate points or the final destination. It’s optional.
  • Body: Contains the XML data comprising the message being transmitted. This is mandatory.
  • Fault: An optional element providing information about errors encountered during message processing.

SOAP Encoding

SOAP includes built-in rules for encoding data types. These data types are categorized into two broad types: scalar and compound. Scalar types hold a single value (e.g., last name, price), while compound types contain multiple values (e.g., PO, stock quote list). Compound types are further divided into arrays and structs. Scalar types include strings, floats, doubles, integers, date, time, boolean, decimal, binary, long, short, byte, etc.

HTTP Protocol

HTTP connection

Figure 2: HTTP Connection

Figure 2 illustrates an HTTP connection between a client (web user) and a web server. It uses a standard IP header for packet routing, and data is not encrypted before transmission by default.

HTTP consists of two main elements: the HTTP header and the HTTP body. When the HTTP body contains only a pure XML document, it’s referred to as plain HTTP. HTTP stands for Hypertext Transfer Protocol. It’s an application protocol used for distributed, collaborative, and hypermedia information systems, and it forms the foundation of the World Wide Web (WWW).

HTTP facilitates the exchange and transfer of hypertext between nodes. HTTPS is the secured version of HTTP.

Difference between SOAP and HTTP

The following table highlights the key differences between SOAP and HTTP protocols:

FeatureSOAPHTTP
Full FormSimple Object Access ProtocolHypertext Transfer Protocol
FeaturesSupports web sockets or WS-addressing, WS-security, and SOAP headers.HTTP message flows generally do not use web sockets or WS-addressing, WS-security, SWA, or MTOM.
FormatCommon SOAP messages have a logical tree format, independent of the bitstream format.HTTP utilizes different standards, such as REST or XML-RPC.
ValidationRuntime checking against WSDL is supported.Runtime checking against WSDL is not available.
AttachmentsAutomatic processing of SOAP with attachments (SwA) is possible, as is automatic processing of message transmission optimization mechanism (MTOM).HTTP nodes can process SwA messages, but require the use of the MIME message domain and custom flow design to explicitly handle the attachments. Custom logic to extract and parse the SOAP is needed.
FunctionA protocol for exchanging XML-based messages, often using HTTP for transport.A communication protocol for transporting messages over a network.
SecuritySupports WS-security and SSL.Not inherently secured; HTTPS is used for secure communication.

Conclusion

From the comparison of SOAP vs HTTP, we can conclude that:

  • HTTP sits on top of TCP/IP, while SOAP sits on top of HTTP.
  • HTTP contents include HTML, images, video, sound, etc. SOAP uses XML-style encoding for messages sent over HTTP/FTP/SMTP.