MIDAS Web Services Implementation Guide

MIDAS Web Services Implementation Guide

This document describes the implementation of Web Services within the MIDAS infrastructure using the TclHttpd package. Client access is possible using either a Web Browser and Html + Javascript or an application using packages based on the SOAP protocol. An simple example of a service which returns the current time is used and the necessary files required to implement this service are explained.

This document complements the document Implementation of XML/SOAP client and server facilities within MIDAS which contains additional code examples.

Also see the document Installation of the MIDAS Web Services applications which contains information for downloading and installating the software.

The SOAP service name is TimeServer and the HTML resource name is TimeService
Note that since TclHttpd provides both of these features the names MUST be different.

In the examples replace [TimeServerHost] with the name of your server system.
Also replace [MIDASBASE] with the base of your software installation (default is /MIDAS)

Client

SOAP
The WSDL file for the Time Service is [MIDASBASE]/TclHttpd/Html/MIDASWebServices/TimeServer.wsdl.
This can be used with a package such as gSOAP to produce a client-end access library.
Within the MIDAS environment source the file [MIDASBASE]/SOAP/tcl/TimeClient.tcl which defines the procedure TimeClient__GetTime. Calls on the procedure TimeClient__GetTime will use the SOAP mechanism to call the procedure GetTime in the target namespace urn:TimeServer within the TclHttpd server at [TimeServerHost].

Httpd
Use a web browser to access the URL http://[TimeServerHost]:8015/TimeService

Server
The file [MIDASBASE]/TclHttpd/Linux/TclHttpd-server is a shell script which starts tclsh with the script [MIDASBASE]/TclHttpd/bin/httpd-Server.tcl. During startup the file [MIDASBASE]/config/TclHttpd/[SystemName]/startup.tcl is searched for where [SystemName] can be the result of the command uname -n; localhost or omitted. This startup script loads the system specific services required. The following would load the implementation of the TimeServer.
```
global env 
source [file join $env(MIDASBASE) TclHttpd tcl TimeServer.tcl
```

SOAP
The file [MIDASBASE]/TclHttpd/tcl/TimeServer.tcl contains the server implementation of the TimeServer. The SOAP client procedure TimeClient__GetTime calls the procedure GetTime within the TimeServer namespace which is provided in this example file. This simply calls the procedure do_GetTime which returns the current date and time as a string. GetTime then returns a structure which builds the required SOAP/XML response to the client.

Httpd
The file [MIDASBASE]/TclHttpd/Html/index.tml is used to build the response to a request to the URL http://[TimeServerHost]:8015. This dynamically builds a page containing a menu of the Web Services available. See a screen dump of a basic menu offering just the Time Service.
The file [MIDASBASE]/TclHttpd/Html/TimeService/index.tml is the implementation of the Time Service and is used to build the response to a request to the URL http://[TimeServerHost]:8015/TimeService which is also the result of following the hyperlink on the menu page. See a screen dump of the Time Service.
Note that the implementation calls the procedure do_GetTime within the namespace TimeServer which was seen in the SOAP implementation above thus pulling together the two access methods.

V Pucknell; STFC; Daresbury Lab 17 Feb 2009