Python BaseHTTPServer，如何捕获/捕获“损坏的管道”错误？

Question

我用 Python 构建了一个短 url 翻译引擎，我看到了大量“断管”错误，我很好奇如何在使用 BaseHTTPServer 类时最好地捕获它。这不是完整的代码，但让您了解我到目前为止正在做的事情：

    from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
    import memcache

    class clientThread(BaseHTTPRequestHandler):

            def do_GET(self):
                    content = None
                    http_code,response_txt,long_url = \
                            self.ag_trans_url(self.path,content,'GET')
                    self.http_output( http_code, response_txt, long_url )
                    return

            def http_output(self,http_code,response_txt,long_url):
                    self.send_response(http_code)
                    self.send_header('Content-type','text/plain')
                    if long_url:
                            self.send_header('Location', long_url)
                    self.end_headers()
                    if response_txt:
                            self.wfile.write(response_txt)
                    return

        def ag_trans_url(self, orig_short_url, post_action, getpost):
                short_url = 'http://foo.co' + orig_short_url

                # fetch it from memcache
                long_url = mc.get(short_url)

                # other magic happens to look it up from db if there was nothing
                # in memcache, etc
                return (302, None, log_url)

def populate_memcache()
        # connect to db, do lots of mc.set() calls

def main():
        populate_memcache()
        try:
                port = 8001
                if len(sys.argv) > 1:
                        port = int(sys.argv[1])
                server = HTTPServer(('',port), clientThread)
                #server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                print '[',str(datetime.datetime.now()),'] short url processing has begun'

                server.serve_forever()
        except KeyboardInterrupt,SystemExit:
                print '^C received, shutting down server'
                server.socket.close()

代码本身运行良好，但在生产时几乎立即开始抛出错误：

Traceback (most recent call last):
  File "/usr/lib/python2.5/SocketServer.py", line 222, in handle_request
    self.process_request(request, client_address)
  File "/usr/lib/python2.5/SocketServer.py", line 241, in process_request
    self.finish_request(request, client_address)
  File "/usr/lib/python2.5/SocketServer.py", line 254, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.5/SocketServer.py", line 522, in __init__
    self.handle()
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 316, in handle
    self.handle_one_request()
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 310, in handle_one_request
    method()
  File "/opt/short_url_redirector/shorturl.py", line 38, in do_GET
    self.http_output( http_code, response_txt, long_url )
  File "/opt/short_url_redirector/shorturl.py", line 52, in http_output
    self.send_response(http_code)
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 370, in send_response
    self.send_header('Server', self.version_string())
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 376, in send_header
    self.wfile.write("%s: %s\r\n" % (keyword, value))
  File "/usr/lib/python2.5/socket.py", line 274, in write
    self.flush()
  File "/usr/lib/python2.5/socket.py", line 261, in flush
    self._sock.sendall(buffer)
error: (32, 'Broken pipe')

这些错误的大部分似乎源于出现问题调用 send_header() 方法，其中我所写的内容如下：

self.send_header('Location', long_url)

所以我很好奇在我的代码中的何处尝试捕获此 IO 异常...我是否在每个self.send_header/self.end_headers/self.wfile.write 调用？我不时看到的另一个错误是这个，但不确定要观察哪个异常才能捕获这个错误：

Traceback (most recent call last):
  File "/usr/lib/python2.5/SocketServer.py", line 222, in handle_request
    self.process_request(request, client_address)
  File "/usr/lib/python2.5/SocketServer.py", line 241, in process_request
    self.finish_request(request, client_address)
  File "/usr/lib/python2.5/SocketServer.py", line 254, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.5/SocketServer.py", line 522, in __init__
    self.handle()
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 316, in handle
    self.handle_one_request()
  File "/usr/lib/python2.5/BaseHTTPServer.py", line 299, in handle_one_request
    self.raw_requestline = self.rfile.readline()
  File "/usr/lib/python2.5/socket.py", line 381, in readline
    data = self._sock.recv(self._rbufsize)
error: (104, 'Connection reset by peer')

Answer 1

这似乎是 SocketServer 中的一个错误，请参阅此链接 Python Bug: 14574

修复（适用于我） Python 2.7）是重写 SocketServer.StreamRequestHandler finish() 方法，如下所示：

...
def finish(self,*args,**kw):
  try:
    if not self.wfile.closed:
      self.wfile.flush()
      self.wfile.close()
  except socket.error:
    pass
  self.rfile.close()

  #Don't call the base class finish() method as it does the above
  #return SocketServer.StreamRequestHandler.finish(self)

Answer 2

“损坏的管道”异常意味着您的代码尝试写入另一端已关闭的套接字/管道。如果另一端是网络浏览器，则用户可能已停止请求。您可以忽略回溯；这并不表明存在严重问题。如果您想抑制该消息，可以在 http_output 函数中的所有代码周围放置一个 try ... except 块，并根据需要记录异常。

此外，如果您希望 HTTP 服务器一次处理多个请求，则需要您的服务器类使用 SocketServer.ForkingMixIn 和 SocketServer.ThreadingMixIn 类之一。有关详细信息，请查看 SocketServer 模块的文档。

添加：“连接由对等方重置”异常意味着您的代码尝试从死套接字读取。如果要抑制回溯，则需要扩展 BaseHTTPServer 类并重写 handle_one_request 方法以添加 try ... except 块。无论如何，您将需要一个新的服务器类，以实现先前关于一次处理多个请求的建议。

Answer 3

在我的应用程序中，错误没有发生在 finish() 中，而是发生在 handle() 中。此修复捕获了损坏的管道错误：

class MyHTTPRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):

    ...

    def handle(self):
        try:
            BaseHTTPServer.BaseHTTPRequestHandler.handle(self)
        except socket.error:
            pass