Debugging ZOO Services

Several methods can be used in order to debug ZOO-Services. The most common solutions are web or command line.


Any problem can be checked in the Apache server log file when using http WPS requests.

On Unix, the log files is usually located in /var/log/apache2 and the relevant one is named error_log. A simple way to read this file is to use the tail command, as it allows to see the file updates for each request

tail -f /var/log/apache2/error_log

If the log is not clear enough, you still have the possibility to add more debug information to your source code, writing to standard errors.


Using Python, you can for example do this:

import sys

#add this line when you want see an own message
sys.stderr.write("My message")


Using JavaScript, you can use alert to print a string to standard error, for example:

// add this line when you want to see own message
alert('My message')
// you can debug value of inputs, outputs or conf


If you try to pass an object it will only return [object Object]

Command line

ZOO-Kernel (zoo_loader.cgi) can also be used from command line. This is really useful for debugging services in a deeper way, for example:.

# in order to use it you have to copy and HelloPy.zcfg from
# the example services
./zoo_loader.cgi "service=wps&version=1.0.0&request=execute&identifier=HelloPy&datainputs=a=your name&responsedocument=Result"

Working this way you can use the standard debug system of the actual programming language used to develop your service.

In case you should simulate POST requests, you can use the following command to tell the ZOO-Kernel to use the file /tmp/req.xml as the input XML request:

# Define required environment settings
export CONTENT_TYPE=text/xml
# Run the request stored in a file
./zoo_loader.cgi < /tmp/req.xml


From command line you can use also the command line tool GDB to debug zoo_loader.cgi, you have to run:

# launch zoo_loader.cgi from gdb
gdb zoo_loader.cgi
# now run your request
run "service=wps&version=1.0.0&request=execute&identifier=HelloPy&datainputs=a=your name&responsedocument=Result"


You can use the same parameter used before to simulate POST requests when running from gdb.

If nothing helped, you can ask help at the ZOO mailing list copying the result of the command.


For Python, you can use pdb, more info at

import pdb

# add this line when you want investigate your code in more detail


You can use alert also to print in the console, more info in the Javascript web section