python/qmp: add parse_address classmethod

This takes the place of qmp-shell's __get_address function. It also
allows other utilities to share the same parser and syntax for
specifying QMP locations.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210603003719.1321369-4-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/qmp/__init__.py

@@ -92,6 +92,12 @@ def __init__(self, reply: QMPMessage):
         self.reply = reply
 
 
+class QMPBadPortError(QMPError):
+    """
+    Unable to parse socket address: Port was non-numerical.
+    """
+
+
 class QEMUMonitorProtocol:
     """
     Provide an API to connect to QEMU via QEMU Monitor Protocol (QMP) and then
@@ -219,6 +225,26 @@ def __exit__(self,
         # Implement context manager exit function.
         self.close()
 
+    @classmethod
+    def parse_address(cls, address: str) -> SocketAddrT:
+        """
+        Parse a string into a QMP address.
+
+        Figure out if the argument is in the port:host form.
+        If it's not, it's probably a file path.
+        """
+        components = address.split(':')
+        if len(components) == 2:
+            try:
+                port = int(components[1])
+            except ValueError:
+                msg = f"Bad port: '{components[1]}' in '{address}'."
+                raise QMPBadPortError(msg) from None
+            return (components[0], port)
+
+        # Treat as filepath.
+        return address
+
     def connect(self, negotiate: bool = True) -> Optional[QMPMessage]:
         """
         Connect to the QMP Monitor and perform capabilities negotiation.

scripts/qmp/qmp-shell

@@ -89,8 +89,6 @@ class QMPCompleter(list):
 class QMPShellError(Exception):
     pass
 
-class QMPShellBadPort(QMPShellError):
-    pass
 
 class FuzzyJSON(ast.NodeTransformer):
     '''This extension of ast.NodeTransformer filters literal "true/false/null"
@@ -109,7 +107,7 @@ class FuzzyJSON(ast.NodeTransformer):
 #       _execute_cmd()). Let's design a better one.
 class QMPShell(qmp.QEMUMonitorProtocol):
     def __init__(self, address, pretty=False):
-        super(QMPShell, self).__init__(self.__get_address(address))
+        super(QMPShell, self).__init__(self.parse_address(address))
         self._greeting = None
         self._completer = None
         self._pretty = pretty
@@ -118,21 +116,6 @@ class QMPShell(qmp.QEMUMonitorProtocol):
         self._histfile = os.path.join(os.path.expanduser('~'),
                                       '.qmp-shell_history')
 
-    def __get_address(self, arg):
-        """
-        Figure out if the argument is in the port:host form, if it's not it's
-        probably a file path.
-        """
-        addr = arg.split(':')
-        if len(addr) == 2:
-            try:
-                port = int(addr[1])
-            except ValueError:
-                raise QMPShellBadPort
-            return ( addr[0], port )
-        # socket path
-        return arg
-
     def _fill_completion(self):
         cmds = self.cmd('query-commands')
         if 'error' in cmds:
@@ -437,7 +420,7 @@ def main():
 
         if qemu is None:
             fail_cmdline()
-    except QMPShellBadPort:
+    except qmp.QMPBadPortError:
         die('bad port number in command-line')
 
     try: