terom@31: """
terom@31:     `tail -f` style continuous file reads.
terom@31: 
terom@31:     Checks if the file was renamed on EOF, and reopens if so.
terom@31: """
terom@31: 
terom@31: import os
terom@31: 
terom@31: import logging; log = logging.getLogger('pvl.collectd.tail')
terom@31: 
terom@31: class TailFile (object) :
terom@31:     """
terom@31:         A file on the filesystem, that is appended to.
terom@31:     """
terom@31: 
terom@31:     def __init__ (self, path) :
terom@31:         self.path = path
terom@31:         self._file = None
terom@31:         self._id = None
terom@31: 
terom@31:         self._open()
terom@31:     
terom@31:     @property
terom@31:     def file (self) :
terom@31:         """
terom@31:             The underlying file objct, if opened.
terom@31:         """
terom@31: 
terom@31:         if self._file is None :
terom@31:             raise ValueError("I/O operation on closed file: {0}".format(self.path))
terom@31: 
terom@31:         return self._file
terom@31: 
terom@31:     @property
terom@31:     def fd (self) :
terom@31:         return self.file.fileno()
terom@31: 
terom@31:     def fileno (self) :
terom@31:         """
terom@31:             The underlying OS fd.
terom@31:         """
terom@31: 
terom@31:         return self.fd
terom@31: 
terom@31:     def _stat (self) :
terom@31:         """
terom@31:             Return a key identifying the file at our path.
terom@31:         """
terom@31: 
terom@31:         st = os.stat(self.path)
terom@31: 
terom@31:         return st.st_dev, st.st_ino
terom@31: 
terom@31:     def _open (self) :
terom@31:         assert self._file is None
terom@31: 
terom@31:         self._file = open(self.path, 'r')
terom@31:         self._id = self._stat()
terom@31: 
terom@31:     def _close (self) :
terom@31:         assert self._file is not None
terom@31: 
terom@31:         self._file.close()
terom@31:         self._file = None
terom@31: 
terom@31:     def _reopen (self) :
terom@31:         """
terom@31:             Re-open, in case the file changed..
terom@31:         """
terom@31: 
terom@31:         self._close()
terom@31:         self._open()
terom@31: 
terom@31:     def _changed (self) :
terom@31:         """
terom@31:             Has the underlying file changed?
terom@31:         """
terom@31: 
terom@31:         return self._stat() != self._id
terom@31: 
terom@31:     def poll (self, timeout) :
terom@31:         """
terom@31:             XXX: not really implemented...
terom@31:         """
terom@31: 
terom@31:         import time
terom@31: 
terom@31:         time.sleep(timeout)
terom@31:     
terom@31:     def readline (self) :
terom@31:         """
terom@31:             Reads a line from the file.
terom@31: 
terom@31:             Raises EOF on end-of-file.
terom@31:         """
terom@31: 
terom@31:         line = self.file.readline()
terom@31: 
terom@31:         # eof?
terom@31:         if not line :
terom@31:             raise EOFError()
terom@31:         
terom@31:         return line
terom@31: 
terom@31:     def readlines (self, eof_mark=False) :
terom@31:         """
terom@31:             Reads any available lines from the file.
terom@31: 
terom@31:             Reopens the file on EOF if the underlying file changed.
terom@31: 
terom@31:                 eof_mark:   yields a special None line when this happens.
terom@31:         """
terom@31: 
terom@31:         while True :
terom@31:             try :
terom@31:                 line = self.readline()
terom@31: 
terom@31:             except EOFError :
terom@31:                 if self._changed() :
terom@31:                     log.debug("EOF: file changed: reopen")
terom@31:                     self._reopen()
terom@31:                     
terom@31:                     if eof_mark :
terom@31:                         # special token
terom@31:                         yield None
terom@31: 
terom@31:                 else :
terom@31:                     log.debug("EOF: wait")
terom@31:                     # done reading
terom@31:                     return
terom@31: 
terom@31:             else :
terom@31:                 yield line.strip()
terom@31: 
terom@31:     __iter__ = readlines
terom@31: 
terom@31:     def close (self) :
terom@31:         """
terom@31:             Close the fifo.
terom@31:         """
terom@31: 
terom@31:         if self._file is None :
terom@31:             raise ValueError("File already closed: {0}".format(self.path))
terom@31: 
terom@31:         self._close()
terom@31: 
terom@31:     def __del__ (self) :
terom@31:         """
terom@31:             Cleanup
terom@31:         """
terom@31: 
terom@31:         if self._file is not None :
terom@31:             self._close()
terom@31: