XML-RPC (Extensible
Markup Language Remote Procedure Call) allows software
on different operating systems to make procedure calls over the
internet. XML-RPC uses HTTP for the transport and XML
for the encoding. It sends the procedure call to a remote server
through HTTP. The call is an XML document and it receives the
response as XML.
XML-RPC is a protocol for web services,
similar to SOAP but much simpler.
It is easy to use and fast. You can easily transmit and return
data structures. See http://www.xmlrpc.org.
The WinCC OA
CtrlXmlRpc is a CONTROL extension
including XML-RPC functions. Therefore, you have to load the CONTROL extension in your code or load
it in the config.level file (see
chapter To
load CONTROL library).
In order to run an XML-RPC server, you have to
start the HTTP server and install a handler. The default URL for
XML-RPC is "/RPC2". See chapters xmlrpcHandler()
and httpConnect().
Furthermore, you have to start the client and establish
a connection to the server (see the functions at the end of this
chapter). XML-RPC clients support authentication via Basic or
Negotiate, if required by the server. User name and Password for
"Basic" authentication are either given in the host
parameter (e.g. "root:@localhost" or "http://root:@localhost")
or are retrieved from the config file entries "userName"
and "password". You can also build a secure HTTPS connection
to the server. Under Windows
the OpenSSL installation is required for the HTTPS connection.
OpenSSL is an open source implementation of the SSL
and TLS protocols and implements
cryptographic functions. See http://www.openssl.org/source/.
The transfer can also be compressed by using the
WinCC OA gzip functions. To use the gzip
functions, you have to load the CtrlZlib. It is a shared library
with functions for data compression. It is based on libz (gzip,
gunzip).
Several standard XML-RPC methods are additionally
available in the xmlrpcHandlerCommon.ctl located in wincc_oa_path/scripts/libs.
Using these methods you can query data points etc. in the XML-RPC
handler (see the figures below).
Figure: XML-RPC overview
Figure: XML-RPC transfer (detailed)
For more information on the individual XML-RPC
functions, see the specific chapters:
xmlrpcHandler()
xmlrpcConnectToServer()
xmlrpcClient()
xmlrpcCall()
xmlrpcDecodeRequest()
xmlrpcEncodeResponse()
xmlrpcCloseServer()
xmlrpcEncodeValue()
xmlrpcDecodeValue()
xmlrpcSetGzipLimit()
For more information on the individual
zip functions for compression,
see the specific chapters:
gzip()
gunzip()
gzread()
gzwrite() |
