Fix native message examples with python3 (#157)

Provide a single .py that handles both Python 2.x and Python 3.x

* Fix python3

* Use one Python file to handle both Python 3.x and Python 2.x

* Actually add the new file this time

* Remove unnecessary parentheses

native-messaging/app/ping_pong.py

@@ -1,34 +1,62 @@
 #!/usr/bin/env python
+
+import sys
 import json
 import struct
-import sys
 
+try:
+    # Python 3.x version
+    # Read a message from stdin and decode it.
+    def getMessage():
+        rawLength = sys.stdin.buffer.read(4)
+        if len(rawLength) == 0:
+            sys.exit(0)
+        messageLength = struct.unpack('@I', rawLength)[0]
+        message = sys.stdin.buffer.read(messageLength).decode('utf-8')
+        return json.loads(message)
 
-# Read a message from stdin and decode it.
-def getMessage():
-    rawLength = sys.stdin.read(4)
-    if len(rawLength) == 0:
-        sys.exit(0)
-    messageLength = struct.unpack('@I', rawLength)[0]
-    message = sys.stdin.read(messageLength)
-    return json.loads(message)
+    # Encode a message for transmission,
+    # given its content.
+    def encodeMessage(messageContent):
+        encodedContent = json.dumps(messageContent).encode('utf-8')
+        encodedLength = struct.pack('@I', len(encodedContent))
+        return {'length': encodedLength, 'content': encodedContent}
 
+    # Send an encoded message to stdout
+    def sendMessage(encodedMessage):
+        sys.stdout.buffer.write(encodedMessage['length'])
+        sys.stdout.buffer.write(encodedMessage['content'])
+        sys.stdout.buffer.flush()
 
-# Encode a message for transmission,
-# given its content.
-def encodeMessage(messageContent):
-    encodedContent = json.dumps(messageContent)
-    encodedLength = struct.pack('@I', len(encodedContent))
-    return {'length': encodedLength, 'content': encodedContent}
+    while True:
+        receivedMessage = getMessage()
+        if receivedMessage == "ping":
+            sendMessage(encodeMessage("pong3"))
+except AttributeError:
+    # Python 2.x version (if sys.stdin.buffer is not defined)
+    # Read a message from stdin and decode it.
+    def getMessage():
+        rawLength = sys.stdin.read(4)
+        if len(rawLength) == 0:
+            sys.exit(0)
+        messageLength = struct.unpack('@I', rawLength)[0]
+        message = sys.stdin.read(messageLength)
+        return json.loads(message)
 
+    # Encode a message for transmission,
+    # given its content.
+    def encodeMessage(messageContent):
+        encodedContent = json.dumps(messageContent)
+        encodedLength = struct.pack('@I', len(encodedContent))
+        return {'length': encodedLength, 'content': encodedContent}
 
-# Send an encoded message to stdout
-def sendMessage(encodedMessage):
-    sys.stdout.write(encodedMessage['length'])
-    sys.stdout.write(encodedMessage['content'])
-    sys.stdout.flush()
+    # Send an encoded message to stdout
+    def sendMessage(encodedMessage):
+        sys.stdout.write(encodedMessage['length'])
+        sys.stdout.write(encodedMessage['content'])
+        sys.stdout.flush()
 
-while True:
-    receivedMessage = getMessage()
-    if receivedMessage == 'ping':
-        sendMessage(encodeMessage('pong'))
+    while True:
+        receivedMessage = getMessage()
+        if receivedMessage == "ping":
+            sendMessage(encodeMessage("pong2"))