socketserver.py

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    - get_request() -> request, client_address
    - verify_request(request, client_address)
    - process_request(request, client_address)
    - close_request(request)
    - handle_error()

    Methods for derived classes:

    - finish_request(request, client_address)

    Class variables that may be overridden by derived classes or
    instances:

    - address_family
    - socket_type
    - request_queue_size (only for stream sockets)
    - reuse_address

    Instance variables:

    - server_address
    - RequestHandlerClass
    - socket

    """

    address_family = socket.AF_INET

    socket_type = socket.SOCK_STREAM

    request_queue_size = 5

    allow_reuse_address = 0

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor.  May be extended, do not override."""
        BaseServer.__init__(self, server_address, RequestHandlerClass)
        self.socket = socket.socket(self.address_family,
                                    self.socket_type)
        self.server_bind()
        self.server_activate()

    def server_bind(self):
        """Called by constructor to bind the socket.

        May be overridden.

        """
        if self.allow_reuse_address:
            self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.socket.bind(self.server_address)

    def server_activate(self):
        """Called by constructor to activate the server.

        May be overridden.

        """
        self.socket.listen(self.request_queue_size)

    def server_close(self):
        """Called to clean-up the server.

        May be overridden.

        """
        self.socket.close()

    def fileno(self):
        """Return socket file number.

        Interface required by select().

        """
        return self.socket.fileno()

    def get_request(self):
        """Get the request and client address from the socket.

        May be overridden.

        """
        return self.socket.accept()

    def close_request(self, request):
        """Called to clean up an individual request."""
        request.close()


class UDPServer(TCPServer):

    """UDP server class."""

    allow_reuse_address = 0

    socket_type = socket.SOCK_DGRAM

    max_packet_size = 8192

    def get_request(self):
        data, client_addr = self.socket.recvfrom(self.max_packet_size)
        return (data, self.socket), client_addr

    def server_activate(self):
        # No need to call listen() for UDP.
        pass

    def close_request(self, request):
        # No need to close anything.
        pass

class ForkingMixIn:

    """Mix-in class to handle each request in a new process."""

    active_children = None
    max_children = 40

    def collect_children(self):
        """Internal routine to wait for died children."""
        while self.active_children:
            if len(self.active_children) < self.max_children:
                options = os.WNOHANG
            else:
                # If the maximum number of children are already
                # running, block while waiting for a child to exit
                options = 0
            try:
                pid, status = os.waitpid(0, options)
            except os.error:
                pid = None
            if not pid: break
            self.active_children.remove(pid)

    def process_request(self, request, client_address):
        """Fork a new subprocess to process the request."""
        self.collect_children()
        pid = os.fork()
        if pid:
            # Parent process
            if self.active_children is None:
                self.active_children = []
            self.active_children.append(pid)
            self.close_request(request)
            return
        else:
            # Child process.
            # This must never return, hence os._exit()!
            try:
                self.finish_request(request, client_address)
                os._exit(0)
            except:
                try:
                    self.handle_error(request, client_address)
                finally:
                    os._exit(1)


class ThreadingMixIn:
    """Mix-in class to handle each request in a new thread."""

    def process_request_thread(self, request, client_address):
        """Same as in BaseServer but as a thread.

        In addition, exception handling is done here.

        """
        try:
            self.finish_request(request, client_address)
            self.close_request(request)
        except:
            self.handle_error(request, client_address)
            self.close_request(request)

    def process_request(self, request, client_address):
        """Start a new thread to process the request."""
        import threading
        t = threading.Thread(target = self.process_request_thread,
                             args = (request, client_address))
        t.start()


class ForkingUDPServer(ForkingMixIn, UDPServer): pass
class ForkingTCPServer(ForkingMixIn, TCPServer): pass

class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass
class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass

if hasattr(socket, 'AF_UNIX'):

    class UnixStreamServer(TCPServer):
        address_family = socket.AF_UNIX

    class UnixDatagramServer(UDPServer):
        address_family = socket.AF_UNIX

    class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass

    class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): pass

class BaseRequestHandler:

    """Base class for request handler classes.

    This class is instantiated for each request to be handled.  The
    constructor sets the instance variables request, client_address
    and server, and then calls the handle() method.  To implement a
    specific service, all you need to do is to derive a class which
    defines a handle() method.

    The handle() method can find the request as self.request, the
    client address as self.client_address, and the server (in case it
    needs access to per-server information) as self.server.  Since a
    separate instance is created for each request, the handle() method
    can define arbitrary other instance variariables.

    """

    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        try:
            self.setup()
            self.handle()
            self.finish()
        finally:
            sys.exc_traceback = None    # Help garbage collection

    def setup(self):
        pass

    def handle(self):
        pass

    def finish(self):
        pass


# The following two classes make it possible to use the same service
# class for stream or datagram servers.
# Each class sets up these instance variables:
# - rfile: a file object from which receives the request is read
# - wfile: a file object to which the reply is written
# When the handle() method returns, wfile is flushed properly


class StreamRequestHandler(BaseRequestHandler):

    """Define self.rfile and self.wfile for stream sockets."""

    # Default buffer sizes for rfile, wfile.
    # We default rfile to buffered because otherwise it could be
    # really slow for large data (a getc() call per byte); we make
    # wfile unbuffered because (a) often after a write() we want to
    # read and we need to flush the line; (b) big writes to unbuffered
    # files are typically optimized by stdio even when big reads
    # aren't.
    rbufsize = -1
    wbufsize = 0

    def setup(self):
        self.connection = self.request
        self.rfile = self.connection.makefile('rb', self.rbufsize)
        self.wfile = self.connection.makefile('wb', self.wbufsize)

    def finish(self):
        self.wfile.flush()
        self.wfile.close()
        self.rfile.close()


class DatagramRequestHandler(BaseRequestHandler):

    # XXX Regrettably, I cannot get this working on Linux;
    # s.recvfrom() doesn't return a meaningful client address.

    """Define self.rfile and self.wfile for datagram sockets."""

    def setup(self):
        import StringIO
        self.packet, self.socket = self.request
        self.rfile = StringIO.StringIO(self.packet)
        self.wfile = StringIO.StringIO()

    def finish(self):
        self.socket.sendto(self.wfile.getvalue(), self.client_address)