merge #674 - Support munin's cgi dynazoom

CHANGELOG.md

 CHANGELOG
 =========
 
+In Development
+--------------
+
+Control panel:
+
+* Munin system monitoring graphs are now zoomable.
+
 v0.17b (March 1, 2016)
 ----------------------
 

management/daemon.py

 #!/usr/bin/python3
 
 import os, os.path, re, json
-
+import subprocess
 from functools import wraps
 
-from flask import Flask, request, render_template, abort, Response, send_from_directory
+from flask import Flask, request, render_template, abort, Response, send_from_directory, make_response
 
 import auth, utils, multiprocessing.pool
 from mailconfig import get_mail_users, get_mail_users_ex, get_admins, add_mail_user, set_mail_password, remove_mail_user
@@ -504,6 +504,64 @@ def munin(filename=""):
 	if filename == "": filename = "index.html"
 	return send_from_directory("/var/cache/munin/www", filename)
 
+@app.route('/munin/cgi-graph/<path:filename>')
+@authorized_personnel_only
+def munin_cgi(filename):
+	""" Relay munin cgi dynazoom requests
+	/usr/lib/munin/cgi/munin-cgi-graph is a perl cgi script in the munin package
+	that is responsible for generating binary png images _and_ associated HTTP
+	headers based on parameters in the requesting URL. All output is written
+	to stdout which munin_cgi splits into response headers and binary response
+	data.
+	munin-cgi-graph reads environment variables as well as passed input to determine
+	what it should do. It expects a path to be in the env-var PATH_INFO, and a
+	querystring to be in the env-var QUERY_STRING as well as passed as input to the
+	command.
+	munin-cgi-graph has several failure modes. Some write HTTP Status headers and
+	others return nonzero exit codes.
+	Situating munin_cgi between the user-agent and munin-cgi-graph enables keeping
+	the cgi script behind mailinabox's auth mechanisms and avoids additional
+	support infrastructure like spawn-fcgi.
+	"""
+
+	COMMAND = 'su - munin --preserve-environment --shell=/bin/bash -c /usr/lib/munin/cgi/munin-cgi-graph "%s"'
+	# su changes user, we use the munin user here
+	# --preserve-environment retains the environment, which is where Popen's `env` data is
+	# --shell=/bin/bash ensures the shell used is bash
+	# -c "/usr/lib/munin/cgi/munin-cgi-graph" passes the command to run as munin
+	# "%s" is a placeholder for where the request's querystring will be added
+
+	if filename == "":
+		return ("a path must be specified", 404)
+
+	query_str = request.query_string.decode("utf-8", 'ignore')
+
+	env = {'PATH_INFO': '/%s/' % filename, 'QUERY_STRING': query_str}
+	cmd = COMMAND % query_str
+	code, binout = utils.shell('check_output',
+							   cmd.split(' ', 5),
+							   # Using a maxsplit of 5 keeps the last 2 arguments together
+							   input=query_str.encode('UTF-8'),
+							   env=env,
+							   return_bytes=True,
+							   trap=True)
+
+	if code != 0:
+		# nonzero returncode indicates error
+		app.logger.error("munin_cgi: munin-cgi-graph returned nonzero exit code, %s", process.returncode)
+		return ("error processing graph image", 500)
+
+	# /usr/lib/munin/cgi/munin-cgi-graph returns both headers and binary png when successful.
+	# A double-Windows-style-newline always indicates the end of HTTP headers.
+	headers, image_bytes = binout.split(b'\r\n\r\n', 1)
+	response = make_response(image_bytes)
+	for line in headers.splitlines():
+		name, value = line.decode("utf8").split(':', 1)
+		response.headers[name] = value
+	if 'Status' in response.headers and '404' in response.headers['Status']:
+		app.logger.warning("munin_cgi: munin-cgi-graph returned 404 status code. PATH_INFO=%s", env['PATH_INFO'])
+	return response
+
 # APP
 
 if __name__ == '__main__':

setup/munin.sh

@@ -7,7 +7,8 @@ source /etc/mailinabox.conf # load global vars
 
 # install Munin
 echo "Installing Munin (system monitoring)..."
-apt_install munin munin-node
+apt_install munin munin-node libcgi-fast-perl
+# libcgi-fast-perl is needed by /usr/lib/munin/cgi/munin-cgi-graph
 
 # edit config
 cat > /etc/munin/munin.conf <<EOF;
@@ -19,6 +20,9 @@ tmpldir /etc/munin/templates
 
 includedir /etc/munin/munin-conf.d
 
+# path dynazoom uses for requests
+cgiurl_graph /admin/munin/cgi-graph
+
 # a simple host tree
 [$PRIMARY_HOSTNAME]
 address 127.0.0.1
@@ -29,6 +33,10 @@ contact.admin.command mail -s "Munin notification ${var:host}" administrator@$PR
 contact.admin.always_send warning critical
 EOF
 
+# The Debian installer touches these files and chowns them to www-data:adm for use with spawn-fcgi
+chown munin. /var/log/munin/munin-cgi-html.log
+chown munin. /var/log/munin/munin-cgi-graph.log
+
 # ensure munin-node knows the name of this machine
 tools/editconf.py /etc/munin/munin-node.conf -s \
 	host_name=$PRIMARY_HOSTNAME