From 1e53abeb9ed447d99df3d93f116d00572bb0f9f3 Mon Sep 17 00:00:00 2001
From: David Lamparter <equinox@diac24.net>
Date: Sun, 15 Feb 2015 15:34:14 +0000
Subject: envmon: make error handling less fnord-y

---
 envmon/onewire-sysfs.py    | 43 +++++++++++++++++++++++++++++++------------
 envmon/onewire2graphite.py |  2 ++
 2 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/envmon/onewire-sysfs.py b/envmon/onewire-sysfs.py
index 5623483..c10e83f 100644
--- a/envmon/onewire-sysfs.py
+++ b/envmon/onewire-sysfs.py
@@ -3,12 +3,19 @@ Onewire interface using w1 sysfs
 """
 
 import os
+import errno
 import re
 import sys
 import time
 
 class OnewireException(Exception):
 	pass
+class SensorNotPresent(OnewireException):
+	pass
+class ReadFailed(OnewireException):
+	pass
+class OutOfRange(OnewireException):
+	pass
 
 _sensors = {}
 with open(os.path.join(os.path.realpath(os.path.dirname(__file__)), 'onewire-sensors.txt'), 'r') as sensors_file:
@@ -25,33 +32,45 @@ class SensorFacade(object):
 		self._addr = addr
 		self._name = name
 
-	def get_temperature(self):
+	def _path(self):
 		addr = self._addr.replace('.', '-').lower()
-		path = '/sys/devices/w1_bus_master1/{0}/w1_slave'.format(addr)
+		return '/sys/devices/w1_bus_master1/{0}/w1_slave'.format(addr)
+
+	def get_temperature(self):
+		path = self._path()
+
+		try:	os.stat(path)
+		except OSError, ose:
+			if ose.errno == errno.ENOENT:
+				raise SensorNotPresent, path
+			else:
+				raise
 
 		with open(path, 'r') as w1_file:
 			w1_data = w1_file.read()
 
+		if w1_data.strip() == '':
+			raise ReadFailed, path
+
 		match = re.search(r'\st=(\d+)', w1_data)
 		temp = float(match.group(1)) / 1000
 		return temp
 
 	@property
 	def temperature(self):
-		for i in range(1,3):
+		for i in range(2, 0,-1):
 			try:
 				rv = self.get_temperature()
-			except Exception:
+				if rv > 65 or rv < -25:
+					raise OutOfRange, (self._path(), rv)
+				return rv
+			except SensorNotPresent:
+				raise
+			except Exception, e:
+				if i == 1:
+					raise
 				sys.excepthook(*sys.exc_info())
 				time.sleep(0.5)
-				continue
-
-			if rv > 65:
-				continue
-			if rv < -25:
-				continue
-			return rv
-		raise OnewireException("Bus error for %s" % self._name)
 
 def sensor(name):
 	if name not in _sensors:
diff --git a/envmon/onewire2graphite.py b/envmon/onewire2graphite.py
index 73e6b8d..46bc94e 100755
--- a/envmon/onewire2graphite.py
+++ b/envmon/onewire2graphite.py
@@ -19,6 +19,8 @@ while True:
     for sensor in onewire.sensors():
         try:
             message += "%s %f %d\n" % (prefix + sensor, onewire.sensor(sensor).temperature, time.time())
+        except onewire.SensorNotPresent, e:
+            print >>sys.stderr, 'SensorNotPresent:', str(e)
         except Exception:
             print >>sys.stderr, "On %s: Could not retrieve temperature for '%s':" % (
                 time.strftime('%a, %d %b %Y %T %z'), sensor)
-- 
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