Run on Python2 and 3; add debugging to file; fix double-json decoding issue

Author: DB

README.md

@@ -183,10 +183,12 @@ The important parts are the **`name`**, which uniquely identifies the NM host, t
 
 This NM manifest has to be copied or symlinked [to the correct location for your operating system](https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_manifests), under Linux a suitable location is `~/.mozilla/native-messaging-hosts/<name>.json`, in our case thus `~/.mozilla/native-messaging-hosts/runwith.json`.
 
-A Python NM program that works the way the addon expects (**`runwith.py`**) [is included in the repo](https://github.com/waldner/Firefox-RunWith/blob/master/runwith.py), so you should copy it somewhere and update its path in the NM manifest.
+A Python NM program that works the way the addon expects (**`runwith.py`**) [is included in the repo](https://github.com/waldner/Firefox-RunWith/blob/master/runwith.py), so you should copy it somewhere and update its path in the NM manifest. It should work with Python 2 and Python 3.
 
 **`runwith.py`** speaks the NM protocol, it expects to receive on stdin a JSON array with the command to run and its arguments, runs the command according to the user's shell/wait preferences, then writes back (to the extension) a brief summary of the execution (in case you're interested, it can be seen in the browser console, which can be opened with CTRL+SHIFT+J, along with other debugging messages output by the [**`background.js`**](https://github.com/waldner/Firefox-RunWith/blob/master/addon/background.js) script).
 
+Inside `runwith.py`, you can set the **`enable_debug`** variable to `True` to dump the various incoming and outgoing messages it processes to a file (by default, `/tmp/runwith_debug.log`, see the `debug_file` variable).
+
 #### What do "`shell`" and "`wait`" do exactly?
 
 Let's assume you have a command like the following for an action in your configuration:

runwith.py

@@ -1,40 +1,70 @@
-#!/usr/bin/python2
+#!/usr/bin/python
+
 # Note that running python with the `-u` flag is required on Windows,
 # in order to ensure that stdin and stdout are opened in binary, rather
 # than text, mode.
 
 import sys, json, struct, os
 import subprocess
 
+def debug(msg):
+  if enable_debug:
+    with open(debug_file, 'a') as outfile:
+      outfile.write(msg)
+      outfile.write("\n")
+
 # Read a message from stdin and decode it.
 def getMessage():
-  rawLength = sys.stdin.read(4)
+  rawLength = our_stdin.read(4)
   if len(rawLength) == 0:
       sys.exit(0)
   messageLength = struct.unpack('@I', rawLength)[0]
-  message = sys.stdin.read(messageLength)
+  debug("getMessage: messageLength is %s" % messageLength)
+  message = our_stdin.read(messageLength).decode()
+  debug("getMessage: message is %s" % message)
   return json.loads(message)
 
 # Encode a message for transmission, given its content.
 def encodeMessage(messageContent):
+  debug("encodeMessage: messageContent is %s" % messageContent)
   encodedContent = json.dumps(messageContent)
+  debug("encodeMessage: encodedContent is %s\n" % encodedContent)
   encodedLength = struct.pack('@I', len(encodedContent))
-  return {'length': encodedLength, 'content': encodedContent}
+  debug("encodeMessage: encodedLength is %s" % encodedLength)
+  return {'length': encodedLength, 'content': encodedContent.encode()}
 
 # Send an encoded message to stdout.
 def sendMessage(encodedMessage):
-  sys.stdout.write(encodedMessage['length'])
-  sys.stdout.write(encodedMessage['content'])
-  sys.stdout.flush()
 
+  debug("sendMessage: encodedMessage is %s" % encodedMessage)
+  debug("sendMessage: encodedMessage['length'] is %s" % encodedMessage['length'])
+  debug("sendMessage: encodedMessage['content'] is %s" % encodedMessage['content'])
+
+  our_stdout.write(encodedMessage['length'])
+  our_stdout.write(encodedMessage['content'])
+  our_stdout.flush()
+
+# determine Python version
+python_version = sys.version_info[0]   # should be 2 or 3
+
+if python_version == 2:
+  our_stdin = sys.stdin
+  our_stdout = sys.stdout
+else:
+  our_stdin = sys.stdin.buffer
+  our_stdout = sys.stdout.buffer
 
-receivedMessage = getMessage()
 
-msg = json.loads(receivedMessage)
+# set this to true to dump things to the debug_file
+enable_debug = False
+debug_file = "/tmp/runwith_debug.log"
 
-cmd = msg['cmd']
-shell = msg['shell']
-wait = msg['wait']
+receivedMessage = getMessage()
+debug("main: receivedMessage is %s" % receivedMessage)
+
+cmd = receivedMessage['cmd']
+shell = receivedMessage['shell']
+wait = receivedMessage['wait']
 
 use_shell = False
 command = cmd
@@ -43,21 +73,25 @@ def sendMessage(encodedMessage):
   command = ' '.join(cmd)
 
 devnull = open(os.devnull, 'w')
-stdout = devnull
-stderr = devnull
+child_stdout = devnull
+child_stderr = devnull
 close_fds = True
 if wait:
-  stdout = subprocess.PIPE
-  stderr = subprocess.PIPE
+  child_stdout = subprocess.PIPE
+  child_stderr = subprocess.PIPE
   close_fds = False
 
-proc = subprocess.Popen(command, stdout = stdout, stderr = stderr, shell = use_shell, close_fds = close_fds)
+proc = subprocess.Popen(command, stdout = child_stdout, stderr = child_stderr, shell = use_shell, close_fds = close_fds)
+
+msg = { 'pid': proc.pid, 'shell': use_shell, 'wait': wait }
 
 if wait:
   stdout, stderr = proc.communicate()
   exit_code = proc.returncode
-  msg = "command ran, exit status: %s, stderr: %s" % (exit_code, stderr)
+  msg['exit-status'] = exit_code
+  msg['stderr'] = stderr.decode()
 else:
-  msg = "async process launched, PID: %s" % proc.pid
+  msg['exit-status'] = 'N/A'
+  msg['stderr'] = 'N/A'
 
 sendMessage(encodeMessage(msg))