Web Services for C and C++ Applications

By Darren Barefoot

These days, it seems like every programming language is getting a Web service
implementation. The languages C and C++ are no exception. Robert van
Engelen, an assistant professor in the Computer Science department at
Florida State University, has developed gSOAP, an open
source set of Web service-enabling tools for C and C++ applications.

Professor van Engelen began the project three years ago while working on
high-performance systems. "I was looking to integrate several systems running
programs written in different languages. Since C, C++, and Fortran are most
often used in high-performance computing, I decided to focus on Java, C, and C++
and use a C-to-Fortran bridge when necessary. Not with SOAP, but our own XML
serialization format. I adopted SOAP shortly after SOAP 1.1 was published and
became interesting." Frustrated by current solutions, van Engelen notes that "I
was also displeased with simple (class) library-based APIs. Writing wrapper code
is the last thing users want to work on."

One important aspect of gSOAP, and Web services in general, is their impact
on grid computing efforts. The concept of computational resource sharing is at
the center of the Web services paradigm. Professor van Engelen believes grid
computing will benefit from Web services where the parties involved have
radically different configurations. "The impact in distributed computing between
disparate parties will be significant. However, some P2P applications such as
SETI@Home won't change either as the single program approach to P2P (single peer
ported to different platforms) doesn't require SOAP for interoperability."

The C programming language has been around for about 30 years now, so it's
only logical that a Web services implementation would emerge. There is a
tremendous amount of intellectual capital invested in C and C++. Much of this,
sooner or later, will be exposed as Web services. In terms of building on that
capital, van Engelen cites two important factors: ease-of-use and performance.
"Toolkits must be easy to use and offer more than a simple API. That was one of
the main reasons for building gSOAP. The other reason was performance. I don't
believe Java SOAP implementations will ever reach the speed of C/C++
applications because of Java's fundamental design choices. They might be easier
to program though!"

In terms of performance, independent testing proves that while gSOAP may be
slower than some specialized SOAP implementations, it leaves other open source
products like Apache Axis in the dust. Unlike these specialized SOAP stacks,
gSOAP is a complete SOAP implementation and therefore takes longer to fully
process a SOAP message at runtime.

The gSOAP team have completed several rounds of interoperability
testing on more than 30 SOAP-based products, including Cape Clear's
CapeConnect. "The interoperability tests with CapeConnect fared very well,"
according to van Engelen. "Nice work. Even SOAP 1.1 partial arrays are supported
and can be exchanged, unlike in many other toolkits."

For organizations like Adobe Systems and
IBM alphaWorks, gSOAP has proven an
excellent strategy for developing Web services based on C and C++ applications.
In IBM's case, they've used gSOAP as part of their Web Services Tool Kit for Mobile
Devices. The following are a few highlights from the gSOAP feature list. For
the complete list, go to http://www.cs.fsu.edu/~engelen/soapfeatures.html.

• A unique SOAP-to-C/C++ binding enables gSOAP to provide an automated mapping
  of native C/C++ and user-definedapplication data types to SOAP data types
  through the use of compiler technology.
• gSOAP includes a true RPC compiler for SOAP that supports
  application-specific data types, enabling legacy application integration.
• Small memory footprint means that Web services and client executables can be
  as small as 90 KB on Linux with a 150 KB total memory footprint.
• Multi-threaded stand-alone SOAP servers: automatic C and/or C++ source code
  generation for efficient SOAP Web services (gSOAP 2.0 and higher).
• Operating systems supported include Windows, UNIX, Linux, Pocket PC, Mac OS
  X, and so on.
• Integrated WSDL generator for convenient Web Service publishing.
• WSDL importer and proxy class generator for automated SOAP client
  application development.
• Supports HTTPS/SSL for robust security.
• Supports HTTP cookies and SOAP headers.
• SOAP in DIME attachments are fully automated.
• SOAP 1.1 (except SOAP root) and 1.2 compliant.