QMP: Revamp the Python class example

This commit simplifies and fixes a number of problems in the Python
QEMUMonitorProtocol example class.

It's almost a rewrite and it DOES BREAK the qmp-shell script (which
is going to be fixed in the next commit).

However, I'm not going to split this in different commits because it
could get up to 10 commits, it's really not worth it for a simple
demo class.

Highlights:

 o TCP sockets support
 o QMP events support
 o Add documentation
 o Fix a number of unhandled errors
 o Simplify methods that send commands to the Monitor

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

QMP/qmp.py

@@ -1,6 +1,6 @@
 # QEMU Monitor Protocol Python class
 # 
-# Copyright (C) 2009 Red Hat Inc.
+# Copyright (C) 2009, 2010 Red Hat Inc.
 #
 # Authors:
 #  Luiz Capitulino <lcapitulino@redhat.com>
@@ -8,7 +8,9 @@
 # This work is licensed under the terms of the GNU GPL, version 2.  See
 # the COPYING file in the top-level directory.
 
-import socket, json
+import json
+import errno
+import socket
 
 class QMPError(Exception):
     pass
@@ -16,61 +18,114 @@ class QMPError(Exception):
 class QMPConnectError(QMPError):
     pass
 
+class QMPCapabilitiesError(QMPError):
+    pass
+
 class QEMUMonitorProtocol:
+    def __init__(self, address):
+        """
+        Create a QEMUMonitorProtocol class.
+
+        @param address: QEMU address, can be either a unix socket path (string)
+                        or a tuple in the form ( address, port ) for a TCP
+                        connection
+        @note No connection is established, this is done by the connect() method
+        """
+        self.__events = []
+        self.__address = address
+        self.__sock = self.__get_sock()
+        self.__sockfile = self.__sock.makefile()
+
+    def __get_sock(self):
+        if isinstance(self.__address, tuple):
+            family = socket.AF_INET
+        else:
+            family = socket.AF_UNIX
+        return socket.socket(family, socket.SOCK_STREAM)
+
+    def __json_read(self):
+        while True:
+            data = self.__sockfile.readline()
+            if not data:
+                return
+            resp = json.loads(data)
+            if 'event' in resp:
+                self.__events.append(resp)
+                continue
+            return resp
+
+    error = socket.error
+
     def connect(self):
-        self.sock.connect(self.filename)
-        data = self.__json_read()
-        if data == None:
-            raise QMPConnectError
-        if not data.has_key('QMP'):
+        """
+        Connect to the QMP Monitor and perform capabilities negotiation.
+
+        @return QMP greeting dict
+        @raise socket.error on socket connection errors
+        @raise QMPConnectError if the greeting is not received
+        @raise QMPCapabilitiesError if fails to negotiate capabilities
+        """
+        self.__sock.connect(self.__address)
+        greeting = self.__json_read()
+        if greeting is None or not greeting.has_key('QMP'):
             raise QMPConnectError
-        return data['QMP']['capabilities']
+        # Greeting seems ok, negotiate capabilities
+        resp = self.cmd('qmp_capabilities')
+        if "return" in resp:
+            return greeting
+        raise QMPCapabilitiesError
 
-    def close(self):
-        self.sock.close()
+    def cmd_obj(self, qmp_cmd):
+        """
+        Send a QMP command to the QMP Monitor.
 
-    def send_raw(self, line):
-        self.sock.send(str(line))
+        @param qmp_cmd: QMP command to be sent as a Python dict
+        @return QMP response as a Python dict or None if the connection has
+                been closed
+        """
+        try:
+            self.__sock.sendall(json.dumps(qmp_cmd))
+        except socket.error, err:
+            if err[0] == errno.EPIPE:
+                return
+            raise socket.error(err)
         return self.__json_read()
 
-    def send(self, cmdline):
-        cmd = self.__build_cmd(cmdline)
-        self.__json_send(cmd)
-        resp = self.__json_read()
-        if resp == None:
-            return
-        elif resp.has_key('error'):
-            return resp['error']
-        else:
-            return resp['return']
-
-    def __build_cmd(self, cmdline):
-        cmdargs = cmdline.split()
-        qmpcmd = { 'execute': cmdargs[0], 'arguments': {} }
-        for arg in cmdargs[1:]:
-            opt = arg.split('=')
-            try:
-                value = int(opt[1])
-            except ValueError:
-                value = opt[1]
-            qmpcmd['arguments'][opt[0]] = value
-        return qmpcmd
-
-    def __json_send(self, cmd):
-        # XXX: We have to send any additional char, otherwise
-        # the Server won't read our input
-        self.sock.send(json.dumps(cmd) + ' ')
+    def cmd(self, name, args=None, id=None):
+        """
+        Build a QMP command and send it to the QMP Monitor.
 
-    def __json_read(self):
+        @param name: command name (string)
+        @param args: command arguments (dict)
+        @param id: command id (dict, list, string or int)
+        """
+        qmp_cmd = { 'execute': name }
+        if args:
+            qmp_cmd['arguments'] = args
+        if id:
+            qmp_cmd['id'] = id
+        return self.cmd_obj(qmp_cmd)
+
+    def get_events(self):
+        """
+        Get a list of available QMP events.
+        """
+        self.__sock.setblocking(0)
         try:
-            while True:
-                line = json.loads(self.sockfile.readline())
-                if not 'event' in line:
-                    return line
-        except ValueError:
-            return
-
-    def __init__(self, filename):
-        self.filename = filename
-        self.sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
-        self.sockfile = self.sock.makefile()
+            self.__json_read()
+        except socket.error, err:
+            if err[0] == errno.EAGAIN:
+                # No data available
+                pass
+        self.__sock.setblocking(1)
+        return self.__events
+
+    def clear_events(self):
+        """
+        Clear current list of pending events.
+        """
+        self.__events = []
+
+    def close(self):
+        self.__sock.close()
+        self.__sockfile.close()