SocketServer.py 淺析

SocketServer.py

Creating network servers.

contents

• SocketServer.py
  • contents
  • file head
  • BaseServer
    • BaseServer.serve_forever
    • BaseServer.shutdown
    • BaseServer.handle_request
    • BaseServer._handle_request_noblock
    • BaseServer Overridden functions
  • TCPServer
  • UDPServer
  • ForkingMixIn
  • ThreadingMixIn
  • BaseRequestHandler
  • StreamRequestHandler
  • DatagramRequestHandler
  • 版權

file head

__version__ = "0.4"


import socket
import select
import sys
import os
import errno
try:
    import threading
except ImportError:
    import dummy_threading as threading

__all__ = ["TCPServer","UDPServer","ForkingUDPServer","ForkingTCPServer",
           "ThreadingUDPServer","ThreadingTCPServer","BaseRequestHandler",
           "StreamRequestHandler","DatagramRequestHandler",
           "ThreadingMixIn", "ForkingMixIn"]
if hasattr(socket, "AF_UNIX"):
    __all__.extend(["UnixStreamServer","UnixDatagramServer",
                    "ThreadingUnixStreamServer",
                    "ThreadingUnixDatagramServer"])

# 出現 EINTR 則從新調用
def _eintr_retry(func, *args):
    """restart a system call interrupted by EINTR"""
    while True:
        try:
            return func(*args)
        except (OSError, select.error) as e:
            if e.args[0] != errno.EINTR:
                raise
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BaseServer

RequestHandlerClass 註冊 handle 函數。
finish_request 中實例化，調用用戶定義的 handle 函數

class BaseServer:
    timeout = None

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor. May be extended, do not override."""
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def server_activate(self):
        """Called by constructor to activate the server. May be overridden. """
        pass
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BaseServer.serve_forever

服務循環

1. 監聽端口
2. 處理請求

def serve_forever(self, poll_interval=0.5):
        """Handle one request at a time until shutdown. Polls for shutdown every poll_interval seconds. Ignores self.timeout. If you need to do periodic tasks, do them in another thread. """
        self.__is_shut_down.clear()
        try:
            while not self.__shutdown_request:
                # 調用 select 監視請求，處理 EINTR 異常
                r, w, e = _eintr_retry(select.select, [self], [], [],
                                       poll_interval)
                # 有請求進來
                if self in r:
                    self._handle_request_noblock()
        finally:
            self.__shutdown_request = False
            self.__is_shut_down.set()
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BaseServer.shutdown

中止 serve_forever 循環.
__is_shut_down 通知外部，循環已經退出
注意 threading.Event() 的用法，只設置一次，避免使用 Event 進行頻繁的設置/清除。 須要在與 serve_forever 不一樣的線程中調用.
由於調用 shutdown 後須要 wait 信號量，程序會 block，block 後 serve_forever 沒法執行
serve_forever 收到請求後才能退出設置信號量

注意
self.__shutdown_request 的讀寫操做，屬於原子操做，在多線程中使用是安全的

def shutdown(self):
        """Stops the serve_forever loop. Blocks until the loop has finished. This must be called while serve_forever() is running in another thread, or it will deadlock. """
        self.__shutdown_request = True
        self.__is_shut_down.wait()
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BaseServer.handle_request

和 serve_forever 並列的函數 若是不調用 server_forever, 在外面循環調用 handle_request

# The distinction between handling, getting, processing and
    # finishing a request is fairly arbitrary. Remember:
    #
    # - handle_request() is the top-level call. It calls
    # select, get_request(), verify_request() and process_request()
    # - get_request() is different for stream or datagram sockets
    # - process_request() is the place that may fork a new process
    # or create a new thread to finish the request
    # - finish_request() instantiates the request handler class;
    # this constructor will handle the request all by itself

    def handle_request(self):
        """Handle one request, possibly blocking. Respects self.timeout. """
        # Support people who used socket.settimeout() to escape
        # handle_request before self.timeout was available.

        # 若是用戶使用 socket.settimeout() 設置了超時時間，則選取一個小的
        timeout = self.socket.gettimeout()
        if timeout is None:
            timeout = self.timeout
        elif self.timeout is not None:
            timeout = min(timeout, self.timeout)
        # select,監聽鏈接，會阻塞直到超時
        fd_sets = _eintr_retry(select.select, [self], [], [], timeout)
        if not fd_sets[0]:
            self.handle_timeout()
            return
        # 處理請求
        self._handle_request_noblock()
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BaseServer._handle_request_noblock

真正的請求處理函數

1. get_request: 接收請求 accept
2. verify_request: 驗證，作一些驗證工做，好比 ip 過濾
3. process_request: 處理請求，子類重寫該方法後，須要 調用 SocketServer.BaseServer.process_request,
4. BaseServer.process_request 中有 BaseRequestHandler 的回調動做,實例化用戶定義的 handler, __init__ 中完成對 handle() 的調用
5. shutdown_reques: 關閉鏈接

def _handle_request_noblock(self):
        """Handle one request, without blocking. I assume that select.select has returned that the socket is readable before this function was called, so there should be no risk of blocking in get_request(). """
        try:
            # 接收請求
            # get_request 由子類實現，通常爲接收請求，返回 socket
            request, client_address = self.get_request()
        except socket.error:
            return
        if self.verify_request(request, client_address):
            try:
                self.process_request(request, client_address)
            except:
                self.handle_error(request, client_address)
                self.shutdown_request(request)
        else:
            self.shutdown_request(request)
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BaseServer Overridden functions

def handle_timeout(self):
        """Called if no new request arrives within self.timeout. Overridden by ForkingMixIn. """
        pass

    def verify_request(self, request, client_address):
        """Verify the request. May be overridden. Return True if we should proceed with this request. """
        return True

    def process_request(self, request, client_address):
        """Call finish_request. Overridden by ForkingMixIn and ThreadingMixIn. """
        self.finish_request(request, client_address)
        self.shutdown_request(request)

    def server_close(self):
        """Called to clean-up the server. May be overridden. """
        pass

    def finish_request(self, request, client_address):
        """Finish one request by instantiating RequestHandlerClass."""
        self.RequestHandlerClass(request, client_address, self)

    def shutdown_request(self, request):
        """Called to shutdown and close an individual request."""
        self.close_request(request)

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

    def handle_error(self, request, client_address):
        """Handle an error gracefully. May be overridden. The default is to print a traceback and continue. """
        print '-'*40
        print 'Exception happened during processing of request from',
        print client_address
        import traceback
        traceback.print_exc() # XXX But this goes to stderr!
        print '-'*40
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TCPServer

shutdown_request 先調用 socket.shutdown 後調用 socket.close

• close()releases the resource associated with a connection but does not necessarily close the connection immediately. If you want to close the connection in a timely fashion, callshutdown() beforeclose().
• Shut down one or both halves of the connection. If how is SHUT_RD, further receives are disallowed. If how is SHUT_WR, further sends are disallowed. Ifhow is SHUT_RDWR, further sends and receives are disallowed. Depending on the platform, shutting down one half of the connection can also close the opposite half (e.g. on Mac OS X, shutdown(SHUT_WR) does not allow further reads on the other end of the connection).

class TCPServer(BaseServer):

    address_family = socket.AF_INET

    socket_type = socket.SOCK_STREAM

    request_queue_size = 5

    allow_reuse_address = False

    def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
        """Constructor. May be extended, do not override."""
        BaseServer.__init__(self, server_address, RequestHandlerClass)
        self.socket = socket.socket(self.address_family,
                                    self.socket_type)
        if bind_and_activate:
            try:
                self.server_bind()
                self.server_activate()
            except:
                self.server_close()
                raise

    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)
        self.server_address = self.socket.getsockname()

    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()

    # 調用 shutdown 後調用 close，當即關閉並釋放資源
    def shutdown_request(self, request):
        """Called to shutdown and close an individual request."""
        try:
            #explicitly shutdown. socket.close() merely releases
            #the socket and waits for GC to perform the actual close.
            request.shutdown(socket.SHUT_WR)
        except socket.error:
            pass #some platforms may raise ENOTCONN here
        self.close_request(request)

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

UDPServer get_request 返回的是一個 (data, socket) 的 tuple，而 TCPServer 返回的是 socket
handle 中要區分處理 msg, sock = self.request
msg 已經獲取，無需額外 recv

對於數據的傳送， 你應該使用 socket 的 sendto() 和 recvfrom() 方法。 儘管傳統的 send() 和 recv() 也能夠達到一樣的效果， 可是前面的兩個方法對於 UDP 鏈接而言更廣泛。
from python3-cookbook

from SocketServer import BaseRequestHandler, UDPServer
import time

class TimeHandler(BaseRequestHandler):
    def handle(self):
        print('Got connection from', self.client_address)
        # Get message and client socket
        msg, sock = self.request
        resp = time.ctime()
        sock.sendto(resp.encode('ascii'), self.client_address)

if __name__ == '__main__':
    serv = UDPServer(('', 20000), TimeHandler)
    serv.serve_forever()

#-----------------------------
>>> from socket import socket, AF_INET, SOCK_DGRAM
>>> s = socket(AF_INET, SOCK_DGRAM)
>>> s.sendto(b'', ('localhost', 20000))
0
>>> s.recvfrom(8192)
('Thu Dec 20 10:01:01 2018', ('127.0.0.1', 20000))
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class UDPServer(TCPServer):

    """UDP server class."""

    allow_reuse_address = False

    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 shutdown_request(self, request):
        # No need to shutdown anything.
        self.close_request(request)

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

典型的 fork 使用，這裏咱們能看到 fork 多進程的典型使用

• 限定最大進程數，保證系統資源不至於耗盡
• 父進程 wait defunct 進程
• fork 後父進程返回
• 子進程處理請求後 _exit()

class ForkingMixIn:

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

    timeout = 300
    active_children = None
    max_children = 40

    def collect_children(self):
        """Internal routine to wait for children that have exited."""
        if self.active_children is None:
            return

        while len(self.active_children) >= self.max_children:
            try:
                pid, _ = os.waitpid(-1, 0)
                self.active_children.discard(pid)
            except OSError as e:
                if e.errno == errno.ECHILD:
                    # we don't have any children, we're done
                    self.active_children.clear()
                elif e.errno != errno.EINTR:
                    break

        # Now reap all defunct children.
        for pid in self.active_children.copy():
            try:
                pid, _ = os.waitpid(pid, os.WNOHANG)
                # if the child hasn't exited yet, pid will be 0 and ignored by
                # discard() below
                self.active_children.discard(pid)
            except OSError as e:
                if e.errno == errno.ECHILD:
                    # someone else reaped it
                    self.active_children.discard(pid)

    def handle_timeout(self):
        """Wait for zombies after self.timeout seconds of inactivity. May be extended, do not override. """
        self.collect_children()

    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 = set()
            self.active_children.add(pid)
            self.close_request(request) #close handle in parent process
            return
        else:
            # Child process.
            # This must never return, hence os._exit()!
            try:
                self.finish_request(request, client_address)
                self.shutdown_request(request)
                os._exit(0)
            except:
                try:
                    self.handle_error(request, client_address)
                    self.shutdown_request(request)
                finally:
                    os._exit(1)
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ThreadingMixIn

ThreadingMixIn 重載了 process_request 函數

1. 建立一個線程
2. 在線程中處理請求
3. 啓動線程

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

    # Decides how threads will act upon termination of the
    # main process
    daemon_threads = False

    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.shutdown_request(request)
        except:
            self.handle_error(request, client_address)
            self.shutdown_request(request)

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

基礎請求類，對外提供三個接口

1. setup()
2. handle()
3. finish()

使用時繼承該類，經過 BaseServer 註冊
BaseServer.finish_request 中實例化 BaseRequestHandler 類，在 __init__函數調用中完成繼承類重載的 handle() 接口的調用

class BaseRequestHandler:

    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        self.setup()
        try:
            self.handle()
        finally:
            self.finish()

    def setup(self):
        pass

    def handle(self):
        pass

    def finish(self):
        pass
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StreamRequestHandler

提供文件操做接口

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

    # A timeout to apply to the request socket, if not None.
    timeout = None

    # Disable nagle algorithm for this socket, if True.
    # Use only when wbufsize != 0, to avoid small packets.
    disable_nagle_algorithm = False

    def setup(self):
        self.connection = self.request
        if self.timeout is not None:
            self.connection.settimeout(self.timeout)
        if self.disable_nagle_algorithm:
            self.connection.setsockopt(socket.IPPROTO_TCP,
                                       socket.TCP_NODELAY, True)
        self.rfile = self.connection.makefile('rb', self.rbufsize)
        self.wfile = self.connection.makefile('wb', self.wbufsize)

    def finish(self):
        if not self.wfile.closed:
            try:
                self.wfile.flush()
            except socket.error:
                # A final socket error may have occurred here, such as
                # the local error ECONNABORTED.
                pass
        self.wfile.close()
        self.rfile.close()

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DatagramRequestHandler

class DatagramRequestHandler(BaseRequestHandler):

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

    def setup(self):
        try:
            from cStringIO import StringIO
        except ImportError:
            from StringIO import StringIO
        self.packet, self.socket = self.request
        self.rfile = StringIO(self.packet)
        self.wfile = StringIO()

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

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版權

做者：bigfish
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