tailing-stream

tailing-stream is a Node.js module that provides a Stream that can read continuously from a file that's being actively written to. This is in contrast to the standard fs.createReadStream. method, which returns a ReadableStream that stops reading once it gets to the last byte that existed at the time the stream was originally opened. It supports exactly the same interface as a Node ReadableStream, and its createReadStream method functions the same as fs.createReadStream.

Interface

A TailingReadableStream supports all the same methods and configuration options as a normal ReadableStream, so I suggest you read the node documentation if you're looking for a detailed description. The only difference is that a TailingReadableStream doesn't recognize the end option, since it wouldn't make much sense to create one if you planned to stop reading at a predetermined point!

TailingReadableStream Constructor

It takes two unique configuration options, timeout and pause.

timeout

• A Number that specifies the amount of time in milliseconds that should elapse before a file is considered to have 'finished' tailing. If omitted, it defaults to 5000ms. If set to a falsy value, the timeout is disabled and the stream will wait indefinitely for new content to arrive. Beware: if the timeout is set too low (say, to 1ms), the stream could very well close files that are still being written to if 'data' events don't come in quickly enough.

• If a timeout occurs, an end event is sent to replicate the file closing.

startPaused

• A Boolean that when set to true will prevent the underlying stream from immediately instantiating in addition to preventing fs.watch from emitting data events. Defaults to false.

• NOTE: If this option is set to true you must call resume() on your stream object in order to lazily instantiate the underlying stream and begin watching it for changes.

Implementation

Internally, TailingReadableStream uses the fs.watch method to watch for file changes, and creates ReadableStreams to read the changed contents. If fs.watch performs peculiarly on your platform of choice, its foibles will be replicated in TailingReadableStream.

License

tailing-stream is MIT licensed, so throw caution to the wind and have at it!