path: root/wsgitools/scgi/forkpool.py

"""
The L{forkpool.SCGIServer} adapts a wsgi application to a scgi service.

It works with multiple processes that are periodically cleaned up to prevent
memory leaks having an impact to the system.
"""

import socket
import os
import select
import sys
import errno
import signal

if sys.version_info[0] >= 3:
    def exc_info_for_raise(exc_info):
        return exc_info[0](exc_info[1]).with_traceback(exc_info[2])
else:
    def exc_info_for_raise(exc_info):
        return exc_info[0], exc_info[1], exc_info[2]

class SocketFileWrapper:
    """Wraps a socket to a wsgi-compliant file-like object."""
    def __init__(self, sock, toread):
        """@param sock: is a C{socket.socket()}"""
        self.sock = sock
        self.buff = ""
        self.toread = toread

    def _recv(self, size=4096):
        """
        internal method for receiving and counting incoming data
        @raise socket.error:
        """
        toread = min(size, self.toread)
        if not toread:
            return ""
        try:
            data = self.sock.recv(toread)
        except socket.error, why:
            if why[0] in (errno.ECONNRESET, errno.ENOTCONN, errno.ESHUTDOWN):
                data = ""
            else:
                raise
        self.toread -= len(data)
        return data

    def close(self):
        """Does not close the socket, because it might still be needed. It
        reads all data that should have been read as given by C{CONTENT_LENGTH}.
        """
        try:
            while self.toread > 0:
                if not self._recv(min(self.toread, 4096)):
                    return
        except socket.error:
            pass

    def read(self, size=None):
        """
        see pep333
        @raise socket.error:
        """
        if size is None:
            retl = []
            data = self.buff
            self.buff = ""
            while True:
                retl.append(data)
                try:
                    data = self._recv()
                except socket.error:
                    break
                if not data:
                    break
            return "".join(retl)
        datalist = [self.buff]
        datalen = len(self.buff)
        while datalen < size:
            try:
                data = self._recv(min(4096, size - datalen))
            except socket.error:
                break
            if not data:
                break
            datalist.append(data)
            datalen += len(data)
        self.buff = "".join(datalist)

        if size <= len(self.buff):
            ret, self.buff = self.buff[:size], self.buff[size:]
            return ret
        ret, self.buff = self.buff, ""
        return ret

    def readline(self, size=None):
        """
        see pep333
        @raise socket.error:
        """
        while True:
            try:
                split = self.buff.index('\n') + 1
                if size is not None and split > size:
                    split = size
                ret, self.buff = self.buff[:split], self.buff[split:]
                return ret
            except ValueError:
                if size is not None:
                    if len(self.buff) < size:
                        data = self._recv(size - len(self.buff))
                    else:
                        ret, self.buff = self.buff[:size], self.buff[size:]
                        return ret
                else:
                    data = self._recv(4096)
                if not data:
                    ret, self.buff = self.buff, ""
                    return ret
                self.buff += data

    def readlines(self):
        """
        see pep333
        @raise socket.error:
        """
        data = self.readline()
        while data:
            yield data
            data = self.readline()
    def __iter__(self):
        """see pep333"""
        return self
    def next(self):
        """
        see pep333
        @raise socket.error:
        """
        data = self.read(4096)
        if not data:
            raise StopIteration
        return data
    def flush(self):
        """see pep333"""
        pass
    def write(self, data):
        """see pep333"""
        assert isinstance(data, str)
        try:
            self.sock.sendall(data)
        except socket.error:
            # ignore all socket errors: there is no way to report
            return
    def writelines(self, lines):
        """see pep333"""
        for line in lines:
            self.write(line)

class SCGIServer:
    """Usage: create an L{SCGIServer} object and invoke the run method which
    will then turn this process into an scgi server."""
    class WorkerState:
        """state: 0 means idle and 1 means working.
        These values are also sent as strings '0' and '1' over the socket."""
        def __init__(self, pid, sock, state):
            self.pid = pid
            self.sock = sock
            self.state = state

    def __init__(self, wsgiapp, port, interface="localhost", error=sys.stderr,
                 minworkers=2, maxworkers=32, maxrequests=1000, config={}):
        """
        @param wsgiapp: is the WSGI application to be run.
        @type port: int
        @param port: is the tcp port to listen on
        @type interface: str
        @param interface: is the interface to bind to (default: C{"localhost"})
        @param error: is a file-like object beeing passed as C{wsgi.error} in
                environ
        @type minworkers: int
        @param minworkers: is the number of worker processes to spawn
        @type maxworkers: int
        @param maxworkers: is the maximum number of workers that can be spawned
                on demand
        @type maxrequests: int
        @param maxrequests: is the number of requests a worker processes before
                dying
        @type config: {}
        @param config: the environ dictionary is updated using these values for
                each request.
        """
        assert hasattr(error, "write")
        self.wsgiapp = wsgiapp
        self.port = port
        self.interface = interface
        self.minworkers = minworkers
        self.maxworkers = maxworkers
        self.maxrequests = maxrequests
        self.config = config
        self.error = error
        self.server = None # becomes a socket
        # maps filedescriptors to WorkerStates
        self.workers = {}
        self.running = False
        self.ischild = False

    def enable_sighandler(self, sig=signal.SIGTERM):
        """
        Changes the signal handler for the given signal to terminate the run()
        loop.
        @param sig: is the signal to handle
        @returns: self
        """
        signal.signal(sig, self.shutdownhandler)
        return self

    def run(self):
        """
        Serve the wsgi application.
        """
        self.server = socket.socket()
        self.server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.server.bind((self.interface, self.port))
        self.server.listen(5)
        self.running = True
        while self.running:
            while (len(self.workers) < self.minworkers or # less than min
                    (len(self.workers) < self.maxworkers and # less than max
                        not len([w for w in # no inactive
                                 self.workers.values() if w.state == 0]))):
                self.spawnworker()
            try:
                rs, _, _ = select.select(self.workers.keys(), [], [])
            except select.error, e:
                if e[0] != errno.EINTR:
                    raise
                rs = []
            for s in rs:
                try:
                    data = self.workers[s].sock.recv(1)
                except socket.error:
                    # we cannot handle errors here, so drop the connection.
                    data = ''
                if data == '':
                    self.workers[s].sock.close()
                    del self.workers[s]
                elif data in ('0', '1'):
                    self.workers[s].state = int(data)
                else:
                    raise RuntimeError("unexpected data from worker")
            try:
                pid = 1
                while pid > 0:
                    pid, _ = os.waitpid(0, os.WNOHANG)
            except OSError:
                pass
        self.server.close()
        self.server = None
        self.killworkers()

    def killworkers(self, sig=signal.SIGTERM):
        """
        Kills all worker children.
        @param sig: is the signal used to kill the children
        """
        while self.workers:
            _, state = self.workers.popitem()
            state.sock.close()
            os.kill(state.pid, sig)
            # TODO: handle working children with a timeout

    def shutdownhandler(self, sig=None, stackframe=None):
        """
        Signal handler function for stopping the run() loop. It works by
        setting a variable that run() evaluates in each loop. As a signal
        interrupts accept the loop is terminated, the accepting socket is
        closed and the workers are killed.
        @param sig: ignored for usage with signal.signal
        @param stackframe: ignored for usage with signal.signal
        """
        if self.ischild:
            sys.exit()
        else:
            self.running = False

    def spawnworker(self):
        """
        internal! spawns a single worker
        """
        srvsock, worksock = socket.socketpair()

        pid = os.fork()
        if pid == 0:
            self.ischild = True
            # close unneeded sockets
            srvsock.close()
            for worker in self.workers.values():
                worker.sock.close()
            del self.workers

            try:
                self.work(worksock)
            except socket.error:
                pass

            sys.exit()
        elif pid > 0:
            # close unneeded sockets
            worksock.close()

            self.workers[srvsock.fileno()] = SCGIServer.\
                                             WorkerState(pid, srvsock, 0)
        else:
            raise RuntimeError("fork failed")

    def work(self, worksock):
        """
        internal! serves maxrequests times
        @raise socket.error:
        """
        for _ in range(self.maxrequests):
            (con, addr) = self.server.accept()
            # we cannot handle socket.errors here.
            worksock.sendall('1') # tell server we're working
            self.process(con)
            worksock.sendall('0') # tell server we've finished

    def process(self, con):
        """
        internal! processes a single request on the connection con.
        """
        # This is a little bit ugly:
        # The server has to send the length of the request followed by a colon.
        # We assume that 1. the colon is within the first seven bytes.
        # 2. the packet isn't fragmented.
        # Furthermore 1 implies that the request isn't longer than 999999 bytes.
        # This method however works. :-)
        try:
            data = con.recv(7)
        except socket.error:
            con.close()
            return
        if not ':' in data:
            con.close()
            return
        length, data = data.split(':', 1)
        if not length.isdigit(): # clear protocol violation
            con.close()
            return
        length = int(length)

        while len(data) != length + 1: # read one byte beyond
            try:
                t = con.recv(min(4096, length + 1 - len(data)))
            except socket.error:
                con.close()
                return
            if not t: # request too short
                con.close()
                return
            data += t

        # netstrings!
        data = data.split('\0')
        # the byte beyond has to be a ','.
        # and the number of netstrings excluding the final ',' has to be even
        if data.pop() != ',' or len(data) % 2 != 0:
            con.close()
            return

        environ = self.config.copy()
        while data:
            key = data.pop(0)
            value = data.pop(0)
            environ[key] = value

        # elements:
        # 0 -> None: no headers set
        # 0 -> False: set but unsent
        # 0 -> True: sent
        # 1 -> status string
        # 2 -> header list
        response_head = [None, None, None]

        def sendheaders():
            assert response_head[0] is not None # headers set
            if response_head[0] != True:
                response_head[0] = True
                try:
                    con.sendall('Status: %s\r\n%s\r\n\r\n' % (response_head[1],
                                    '\r\n'.join(map("%s: %s".__mod__,
                                                    response_head[2]))))
                except socket.error:
                    pass

        def dumbsend(data):
            sendheaders()
            try:
                con.sendall(data)
            except socket.error:
                pass

        def start_response(status, headers, exc_info=None):
            if exc_info and response_head[0]:
                try:
                    raise exc_info_for_raise(exc_info)
                finally:
                    exc_info = None
            assert not response_head[0] # unset or not sent
            response_head[0] = False # set but nothing sent
            response_head[1] = status
            response_head[2] = headers
            return dumbsend

        if not environ.get("CONTENT_LENGTH", "bad").isdigit():
            con.close()
            return

        sfw = SocketFileWrapper(con, int(environ["CONTENT_LENGTH"]))
        environ.update({
            "wsgi.version": (1, 0),
            "wsgi.input": sfw,
            "wsgi.errors": self.error,
            "wsgi.url_scheme": "http",
            "wsgi.multithread": False,
            "wsgi.multiprocess": True,
            "wsgi.run_once": False})
        if environ.get("HTTPS", "no").lower() in ('yes', 'y', '1'):
            environ["wsgi.url_scheme"] = "https"
        if "HTTP_CONTENT_TYPE" in environ:
            environ["CONTENT_TYPE"] = environ.pop("HTTP_CONTENT_TYPE")
        if "HTTP_CONTENT_LENGTH" in environ:
            del environ["HTTP_CONTENT_LENGTH"] # TODO: better way?

        result = self.wsgiapp(environ, start_response)
        assert hasattr(result, "__iter__")

        assert response_head[0] is not None
        result_iter = iter(result)
        for data in result_iter:
            assert isinstance(data, str)
            dumbsend(data)
        if response_head[0] != True:
            sendheaders()
        if hasattr(result, "close"):
            result.close()
        sfw.close()
        con.close()