terom@31: """
terom@49:     Iterate over input lines in files. 
terom@49:     
terom@49:     Can be read up to eof, on blocking inputs, or polled with a timeout (see: pvl.syslog.syslog.SyslogSource)
terom@31: """
terom@31: 
terom@31: import os
terom@31: 
terom@49: import logging; log = logging.getLogger('pvl.syslog.tail')
terom@31: 
terom@49: class Tail (object) :
terom@31:     """
terom@49:         Follow a file-like object, reading lines until EOF.
terom@49: 
terom@49:         Works with python file objects that buffer readlines() when using e.g. `tail -f ... | python -u ...`.
terom@31:     """
terom@31: 
terom@49:     def __init__ (self, file) :
terom@49:         self.file = file
terom@46: 
terom@49:     def readline (self) :
terom@31:         """
terom@49:             Reads a line from the file, without trailing \n
terom@49: 
terom@49:             Raises EOF on end-of-file.
terom@31:         """
terom@31: 
terom@49:         line = self.file.readline()
terom@31: 
terom@49:         if not line :
terom@49:             raise EOFError()
terom@49:         else :
terom@49:             return line.rstrip('\n')
terom@31: 
terom@49:     def readlines (self) :
terom@31:         """
terom@49:             Reads any available lines from the file.
terom@31:         """
terom@31: 
terom@49:         while True :
terom@49:             try :
terom@49:                 line = self.readline()
terom@31: 
terom@49:             except EOFError :
terom@49:                 log.debug("EOF")
terom@49:                 break
terom@49: 
terom@49:             else :
terom@49:                 yield line
terom@49: 
terom@49:     def skip (self) :
terom@49:         """
terom@49:             Skip any available lines.
terom@49:         """
terom@49: 
terom@49:         for line in self.readlines() :
terom@49:             pass
terom@49: 
terom@49:     __iter__ = readlines
terom@49: 
terom@49: class TailFile (Tail) :
terom@49:     """
terom@49:         Follow a file on the filesystem, reading lines until EOF, and re-opening if replaced.
terom@49:     """
terom@49: 
terom@49:     def __init__ (self, path) :
terom@49:         self.path = path
terom@49:         self.reopen()
terom@49:     
terom@49:     def stat (cls) :
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@49:     
terom@49:     def open (cls) :
terom@49:         return open(self.path, 'r')
terom@31: 
terom@49:     def reopen (cls) :
terom@49:         self.file = self.open()
terom@49:         self._stat = self.stat()
terom@31: 
terom@49:     def changed (self) :
terom@31:         """
terom@31:             Has the underlying file changed?
terom@31:         """
terom@31: 
terom@49:         return self.stat() != self._stat
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@49:                 if self.changed() :
terom@49:                     log.debug("EOF: reopen")
terom@49:                     self.reopen()
terom@31:                     
terom@31:                     if eof_mark :
terom@49:                         yield None # special token
terom@49:                     
terom@49:                     # keep going
terom@49:                     continue
terom@31: 
terom@31:                 else :
terom@49:                     log.debug("EOF")
terom@49:                     break # wait
terom@31: 
terom@31:             else :
terom@49:                 yield line
terom@31: 
terom@31:     __iter__ = readlines
terom@31: