tailfd

Tail a file. This will continue to work even if a file is unlinked rotated or truncated. It is also ok if the path doesnt exist before watching it

Tails a file. it should work great. it will continue to work even if a file is unlinked rotated or truncated. It is also ok if the path doesnt exist before watching it

 
var tail = require('tailfd').tail,
watcher = tail('/some.log',function(line,tailInfo){
  //default line listener. optional. 
  console.log('line of data> ',line);
});
 

when you are done

watcher.close();
 
npm install tailfd

tailfd.tail(filename, [options], listener)

  • filename

    • this should be a regular file or non existent. the behavior is undefined in the case of a directory.
  • options. supported custom options are

    {
     
    "start":, //defaults to the first reported stat.size 
    //optional. a hard start position in the file for tail to start emitting data events. 
     
    "offset":0,
    //optional.  offset is negtively applied to the start position 
     
    "delimiter":"\n",
    //optional. defaults to newline but can be anything 
     
    "maxBytesPerRead":10240,
    // optional. this is how much data will be read off of a file descriptor in one call to fs.read. defaults to 10k. 
    // the maximum data buffer size for each tail is  
    //  maxBufferPerRead + the last incomplete line from the previous read.length 
     
    "readAttempts":3,
    //optional. if fs.read cannot read the offset from a file it will try attempts times before is gives up with a range-unreadable event 
    // defaults to 3 attempts 
     
    "maxLineLength":102400
    // optional. defaults to 1 mb 
    //  if the line excedes this length it's data will be emitted as a line-part event 
        //  this is a failsafe so that a single line cant eat all of the memory. 
    //  all gathered line-parts are complete with the value of the next line event for that file descriptor. 
     
    }
     
    // the options object is passed to watchfd as well. With watchfd you may configure 
     
    {
     
    "timeout": 60*60*1000, //defaults to one hour 
    //how long an inactive file descriptor can remain inactive before being cleared 
     
    "timeoutInterval":60*5*1000 //every five minutes 
    // how often to check for inactive file descriptors 
     
    }
     
    //the options object is also passed directly to fs.watch and fs.watchFile so you may configure 
     
    {
    "persistent":true, //defaults to true 
    //persistent indicates whether the process should continue to run as long as files are being watched 
     
    "interval":0, //defaults 0 
    //interval indicates how often the target should be polled, in milliseconds. (On Linux systems with inotify, interval is ignored.)  
    }
     
  • callback

    • this is bound to the line event of the watcher. its optional.

      callback(line,tailInfo)
       

    cur and prev are instances of fs.Stats

  • @returns TailFD Watcher

Watcher.pause

  • pause data and line events on all underlying descriptors

Watcher.resume

  • get it goin again! =)
  • line
    • String line, Object tailInfo
  • data
    • Buffer buffer, Object tailInfo
  • line-part
    • String linePart, Object tailInfo
      • if line length excedes the options.maxLineLength the linePart is emitted. This is to prevent cases where unexpected values in logs can eat all of the memory.
  • range-unreadable
    • Array errors, Number fromPos,Number toPos,Object tailInfo
      • After configured readAttempts the offset could still not be read. This range will be skipped
  • change
    • fs.Stats cur, fs.Stats prev
  • open
    • fs.Stats cur,{fd:file descriptor,stat:fs.Stats cur}
  • unlink
    • fs.Stats cur,{fd:file descriptor,stat:fs.Stats cur}
  • timeout
    • fs.Stats cur,{fd:file descriptor,stat:fs.Stats cur}
  • stat
    • instanceof fs.Stats
  • pos
    • current seek position in the file
  • fd
    • file descriptor being tailed
  • buf
    • string containing the last data fragment from delimiter parsing
  • http://nodejs.org/api/fs.html#fs_fs_writefile_filename_data_encoding_callback
  • http://nodejs.org/api/fs.html#fs_fs_watch_filename_options_listener