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# read a stream from a fifo

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from twisted.internet import reactor, interfaces

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from twisted.python import log

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from zope.interface import implements

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import os, fcntl, errno

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class EOF (Exception) : pass

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BUF_SIZE = 2048

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class Fifo (object) :

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    implements(interfaces.IReadDescriptor)

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    def __init__ (self, path) :

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        self.path = path

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        self._open()

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    def _open (self) :

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        self.fd = os.open(self.path, os.O_RDONLY | os.O_NONBLOCK)

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        reactor.addReader(self)

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        log.msg("opened fifo %s as %d" % (self.path, self.fd))

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    def _close (self) :

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        if self.fd :

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            reactor.removeReader(self)

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            os.close(self.fd)

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            log.msg("closed fifo %d at %s" % (self.fd, self.path))

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            self.fd = None

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    close = _close

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    def reopen (self) :

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        """

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            Close and re-open the fifo. This is useful for handling EOF

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        """

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        self._close()

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        self._open()

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    def _read (self, length) :

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        log.msg("(read %d bytes from %d:%s)" % (length, self.fd, self.path))

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        try :

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            data = os.read(self.fd, length)

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        except OSError, e :

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            if e.errno == errno.EAGAIN :

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                log.msg("\tEAGAIN")

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                return None

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            else :

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                log.msg("\tERROR: %s" % e)

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                raise

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        if not data :

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            log.msg("\tEOF")

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            raise EOF()

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        log.msg("\tDATA: %d: %r" % (len(data), data))

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        return data

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    def fileno (self) :

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        return self.fd

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    def doRead (self) :

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        while True :

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            log.msg("fifo doRead loop")

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            try :

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                data = self._read(BUF_SIZE)

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            except EOF :

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                self.handleEOF()

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                return

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            if data :

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                self.dataReceived(data)

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            else :

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                break

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    def dataReceived (self, data) :

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        pass

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    def handleEOF (self) :

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        pass

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    def connectionLost (self, reason) :

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        self.close()

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    def logPrefix (self) :

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        return "FIFO:%d:%s" % (self.fd, self.path)

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    def __del__ (self) :

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        """

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            !!! this is important

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        """

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        self.close()

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