From a73e7766952759e7eebb656e553008f07b16a209 Mon Sep 17 00:00:00 2001
From: Matthieu Coudron <mattator@gmail.com>
Date: Tue, 10 Jul 2018 17:47:49 +0900
Subject: [PATCH] fix "which" calls always returning true

The redirection of stderr towards stdout means calls to "which program"
always return something even when "program" is not installed.

This patch checks for the return value instead before returning the
value.

See #814.
---
 mininet/node.py | 10 +++++-----
 mininet/util.py |  5 +++++
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/mininet/node.py b/mininet/node.py
index 7429b0b..4423cce 100644
--- a/mininet/node.py
+++ b/mininet/node.py
@@ -63,7 +63,7 @@ from time import sleep
 from mininet.log import info, error, warn, debug
 from mininet.util import ( quietRun, errRun, errFail, moveIntf, isShellBuiltin,
                            numCores, retry, mountCgroups, BaseString, decode,
-                           encode, Python3 )
+                           encode, Python3, which )
 from mininet.moduledeps import moduleDeps, pathCheck, TUN
 from mininet.link import Link, Intf, TCIntf, OVSIntf
 from re import findall
@@ -1447,7 +1447,7 @@ class Controller( Node ):
     @classmethod
     def isAvailable( cls ):
         "Is controller available?"
-        return quietRun( 'which controller' )
+        return which( 'controller' )
 
 
 class OVSController( Controller ):
@@ -1459,9 +1459,9 @@ class OVSController( Controller ):
 
     @classmethod
     def isAvailable( cls ):
-        return ( quietRun( 'which ovs-controller' ) or
-                 quietRun( 'which test-controller' ) or
-                 quietRun( 'which ovs-testcontroller' ) ).strip()
+        return (which( 'ovs-controller' ) or
+                which( 'test-controller' ) or
+                which( 'ovs-testcontroller' ))
 
 class NOX( Controller ):
     "Controller to run a NOX application."
diff --git a/mininet/util.py b/mininet/util.py
index 1881318..9ce61db 100644
--- a/mininet/util.py
+++ b/mininet/util.py
@@ -171,6 +171,11 @@ def quietRun( cmd, **kwargs ):
     "Run a command and return merged stdout and stderr"
     return errRun( cmd, stderr=STDOUT, **kwargs )[ 0 ]
 
+def which(cmd, **kwargs ):
+    "Run a command and return merged stdout and stderr"
+    out, _, ret = errRun( ["which", cmd], stderr=STDOUT, **kwargs )
+    return out.rstrip() if ret == 0 else None
+
 # pylint: enable=maybe-no-member
 
 def isShellBuiltin( cmd ):