tailfd

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

Example

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();

install

npm install tailfd

argument structure

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":undefined, //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! =)

events

• 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

events inherited from watchfd

• 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}

tailInfo properties

• 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

watch file and watch may behave differently on different systems here is the doc for it.

• 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