Debugging PHP Web Services

One of the difficulties of doing distributed computing, is the difficulty of debugging when things are not going well. It is no exception for Web Services. Since messages are exchanged between services, clients, we have to have some mechanisms  to capture messages, view the soap messages exchanged, some known error messages etc.

Capturing Messages

One of the most well known technique in debugging web services calls is to  some tcp message capture tool to capture the messages exchanged. There are few such good tools for this task.

1. TCPMON tool from apache

             This is a very simple and easy to use tool which has very wide adoption and is quite popular among developers. You can download this tool from apache tcpmon site. 

2. SOAP UI

            This is another popular tool for debugging and developing SOAP based applications. This tool is able to generate request SOAP message for a given WSDL where you fill out the values and send a valid soap request and response. This is a very useful tool to get started with Web Services. You can download soap UI from soapui.org

3.   Ethereal

         This is another tool that is quite useful is capturing and analyzing messages. http://thud.ethereal.com/

Using debugging functions from framework

you can you framework provided functions for debugging. For example WSF/PHP provides two functions getLastRequest() and getLastResponse() on the WSClient class which returns the exchanged request and response messages. Also it provides functions to obtains the returned HTTP headers. Using these, you can also do some debugging.

Logging

Logging is another useful techniques to idenfity possible problems. You can look as the wsf_php_client.log and wsf_php_server.log files and get an idea of what went wrong. If you are not able to trace what's wrong using the logs , you can post your problem with the appropriate log messages to the forum  and get support.

Using Known Error Messages

Another useful technique is to go through the known set of error messages to locate what went wrong. In WSF/PHP, here are some of the error messages you can get.