如何在Python中创建自定义xmlrpc故障错误

Question

在使用 xmlrpclib 这个库时，如果服务器端出现错误，客户端会收到一个 xmlrpclib.Fault 的错误信息。例如，如果服务器端的某个方法出现了 division by zero（也就是除以零的错误），通常会显示类似下面的内容：

xmlrpclib.Fault: <Fault 1: "<type 'exceptions.ZeroDivisionError'>:integer division or modulo by zero">

这个信息很有用，因为它指出了错误的类型，但并没有告诉我们错误发生的具体位置。那么，如何才能修改 xmlrpclib.Fault 这个方法（在 SimpleXMLRPCServer 中）呢？这样可以让它在报告错误时，像下面这样显示：

xmlrpclib.Fault: <Fault 1: "<type 'exceptions.ZeroDivisionError'>:integer division or modulo by zero MODULE: myMethod.py  LINE: 657">

也就是说，能够包含出错的模块名称和行号。这样做在服务器端是否可行，而不需要抛出自定义的异常？所有的错误都应该在客户端以相同的方式报告。

Answer 1

如果你使用 SimpleXMLRPCServer，你可以重写内部的 _marshaled_dispatch 方法，以便在生成的 Fault() 实例中添加一些信息：

这是原始的方法：

def _marshaled_dispatch(self, data, dispatch_method = None, path = None):
    try:
        params, method = xmlrpclib.loads(data)

        # generate response
        if dispatch_method is not None:
            response = dispatch_method(method, params)
        else:
            response = self._dispatch(method, params)
        # wrap response in a singleton tuple
        response = (response,)
        response = xmlrpclib.dumps(response, methodresponse=1,
                                   allow_none=self.allow_none, encoding=self.encoding)
    except:
        # report low level exception back to server
        # (each dispatcher should have handled their own
        # exceptions)
        exc_type, exc_value = sys.exc_info()[:2]
        response = xmlrpclib.dumps(
            xmlrpclib.Fault(1, "%s:%s" % (exc_type, exc_value)),
            encoding=self.encoding, allow_none=self.allow_none)
    return response

你可以创建一个新的类，继承 SimpleXMLRPCServer.SimpleXMLRPCServer，并重写这个方法：

import SimpleXMLRPCServer
import sys
import xmlrbclib

class VerboseFaultXMLRPCServer(SimpleXMLRPCServer.SimpleXMLRPCServer):
    def _marshaled_dispatch(self, data, dispatch_method = None, path = None):
        try:
            params, method = xmlrpclib.loads(data)

            # generate response
            if dispatch_method is not None:
                response = dispatch_method(method, params)
            else:
                response = self._dispatch(method, params)
            # wrap response in a singleton tuple
            response = (response,)
            response = xmlrpclib.dumps(response, methodresponse=1,
                                       allow_none=self.allow_none, encoding=self.encoding)
        except:
            # report low level exception back to server
            # (each dispatcher should have handled their own
            # exceptions)
            exc_type, exc_value, tb = sys.exc_info()
            while tb.tb_next is not None:
                tb = tb.tb_next  # find last frame of the traceback
            lineno = tb.tb_lineno
            code = tb.tb_frame.f_code
            filename = code.co_filename
            name = code.co_name
            response = xmlrpclib.dumps(
                xmlrpclib.Fault(1, "%s:%s FILENAME: %s LINE: %s NAME: %s" % (
                    exc_type, exc_value, filename, lineno, name)),
                encoding=self.encoding, allow_none=self.allow_none)
        return response

然后用 VerboseFaultXMLRPCServer 替代 SimpleXMLRPCServer.SimpleXMLRPCServer。