Simple Load Balancer

This Python 3 script makes use of the 'xmlQueueStatus.dyn' query in XML Access Option to identify that printer. If the script is executed with one argument for the job to be printed, it will send that job to the most available printer.

Here is the output of the script, and the full source code is below.

Python 3 Source Code

# Sample load balancer for one or more copies of Wasatch SoftRIP installed with
# 'identical' printers.  This is based on the Wasatch XML Access Option
# query: 'xmlQueueStatus.dyn'.   See that document to understand this script.
#
# This simple example finds the Print Unit with the least number of copies queued
# to be printed, based on inspection of 'copies' in both the RIP and Print Queuee.
# Many other definitions of 'most available print unit' are possible, but this
# is simple.
#
import urllib.request
import xml.etree.ElementTree as ET
import sys

ripsToScan = ['127.0.0.1:80' ]  # just localhost in this example - more can be added here
printUnitsPerRip = 4

#globals updated by this scan:
minCopies = 1000000  # just a really big number
unitWithLeastCopies = 0
ripWithLeastCopies = 'unknown'

def analyzeXML(x, wasatchSoftRIP, printUnit):
    xmlRoot = ET.fromstring(x) # parse the XML returned by Wasatch SoftRIP
    copyCount = 0
    for item in xmlRoot.iter('ITEM'):
        copyCount += int(item.attrib['copies'])
    global minCopies
    if copyCount <= minCopies:
        minCopies = copyCount
        global unitWithLeastCopies
        global ripWithLeastCopies
        unitWithLeastCopies = printUnit
        ripWithLeastCopies = wasatchSoftRIP
    print("Copies queued to be printed on Print Unit " + str(printUnit) + " = " + str(copyCount))

def scanPrintUnits(wasatchSoftRIP, maxPrintUnits):
    for printUnit in range(1, maxPrintUnits + 1):
        url = 'http://' + wasatchSoftRIP + '/xmlQueueStatus.dyn?PRINTUNIT=' + str(printUnit)
        try:
            p = urllib.request.urlopen(url)
            mybytes = p.read()  
            p.close()
            x = mybytes.decode("utf-8")
            if not 'Not configured' in x:
                analyzeXML(x, wasatchSoftRIP, printUnit)
        except:
            print("Could not open " + url)
            break

#
# the loop to scan the pool of RIP's follows
#
if len(sys.argv) < 2:
	print("DEMONSTRATION ONLY - This script is running with no file to print.")
    
for r in ripsToScan:
    scanPrintUnits(r, printUnitsPerRip)

print("Result!")
print("Print Unit with least copies queued to be printed is Unit: " + str(unitWithLeastCopies) + ", on " + ripWithLeastCopies)

#
# Code to actually submit a job, if one was on command line, follows
#
if len(sys.argv) > 1:  # this was run as a command line with an argument - something to submit
    copiesToPrint = 0
    
    url = 'http://' + ripWithLeastCopies + '/xmlSubmission.dyn?'
    data = '<WASATCH ACTION=JOB><PRINTUNIT>' + str(unitWithLeastCopies) + '</PRINTUNIT><PAGE>'
    data += '<FILENAME>' + sys.argv[1] + '</FILENAME>'
    data += '<Copies>' + str(copiesToPrint) + '</Copies>'
    data += '</PAGE></WASATCH>'
    url += urllib.parse.quote_plus(data)  # escape all special characters in data
    try:
        p = urllib.request.urlopen(url)
        mybytes = p.read()
        p.close()
        print("Submitted " + sys.argv[1])
    except:
        print("Failed to submit " + sys.argv[1])