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libxget-js

Non-interractive, chunk-based, web content retriever

NPM Version NPM Downloads

NPM

Installing

Via NPM:

npm install libxget

This installs a CLI binary accessible with the xget command.

# Check if the xget command has been installed and accessible on your path
$ xget -V
v0.5.1

Usage

CLI

The xget command, utilizes the library to retrieve web content by its chunks according to specification

# Normal
xget https://google.com/doodle.png

# Write to output file
xget https://google.com/doodle.png image.png

# Piping output
xget https://myserver.io/runtime.log --no-bar | less

# Stream response in real time (e.g Watching the movie)
xget https://service.com/movie.mp4 | vlc -

Use --help to see full usage documentation.

Programmatically

// Node CommonJS
const xget = require('libxget');
// Or ES6 Modules
import xget from 'libxget';
// Or Typescript
import * as xget from 'libxget';

Examples

xget(
  'https://github.com/microsoft/TypeScript/archive/master.zip',
  {chunks: 10, retries: 10}
).pipe(fs.createWriteStream('master.zip'));

Get the master branch of the Typescript repository. With 10 simultaneous downloads. Retrying each one to a max of 10.

API

xget(url[, options])

XGETOptions extends RequestOpts: Object

  • chunks: <number> Number of chunked-simultaneous downloads. Default: 5
  • retries: <number> Number of retries for each chunk. Default: 5
  • timeout: <number> Network response timeout (ms). Default: 20000
  • start: <number> Position to start feeding the stream from. Default: 0
  • size: <number> Number of bytes to stream off the response.
  • hash: <string> Hash algorithm to use to create a crypto.Hash instance computing the stream hash.
  • use: <object> Key-value pairs of middlewares with which to pipe the response object through. keys are strings, values are Transformer generating functions (Alternatively, use the xget.use() method).
  • with: <object> Key-value pairs of middlewares with which to pipe the dataslice object through. keys are strings, values are functions whose return values are accessible within the store. (Alternatively, use the xget.with() method).

xget.store: Map

A map whose keys and values are tags and return types of content processed within the withStack of the xget object.

xget(URL)
  .with('variable', () => 5)
  .once('set', store => {
    /*
      `store` is a map whose key and values directly match tags and return types within
       > a with call or the with object in the xget options
    */
    console.log(store.get('variable')) // 5
  })
  .pipe(FILE);

xget.ended: Boolean

A readonly property that tells whether or not the xget instance has ended.

xget.loaded: Boolean

A readonly property that tells whether or not the xget instance has been loaded.

xget.bytesRead: Number

A readonly property that tells how many bytes has been processed by the underlying streams.

Class: XGETStream extends stream.Readable

The core multi-chunk request instance.

new xget.XGETStream(url[, options])

Event: 'end'

The 'end' event is emitted after the data from the URL has been fully flushed.

Event: 'set'

The 'set' event is emitted after all the middlewares defined in the with option of the XGETOptions or with the xget.with() method.

This event is fired after the 'loaded' event.

Event: 'error'

The 'error' event is emitted once a chunk has met it's maximum number of retries. At which point, it would abruptly destroy other chunk connections.

Event: 'retry'

  • retrySlice:
    • index: <number> The index count of the chunk.
    • retryCount: <number> The number of retry iterations so far.
    • maxRetries: <number> The maximum number of retries possible.
    • bytesRead: <number> The number of bytes previously read (if any).
    • totalBytes: <number> The total number of bytes that are to be read by the stream.
    • lastErr: <Error> The error emitted by the previous stream.
    • store: <xget.store> The shared internal data store.

The 'retry' event is emitted by every chunk once it has been re-initialized underneath. Based on the spec of the xresilient module, chunks are reinitialized once an error event is met.

Event: 'loaded'

  • loadData: <LoadData> The pre-computed config for the loaded data slice.

This is emitted immediately the head data is gotten, preprocessed, parsed and used to tailor the configuration for the chunk setup.

This loadData contains information like the actual size of the remote file and whether or not the server supports multiple connections, chunking, file resumption, etc.

This event is fired prior to the 'set' event.

xget.getHash([encoding])

  • encoding: <string> The character encoding to use. Default: 'hex'
  • Returns: <Buffer> | <string>

Calculates the digest of all data that has been processed by the library and its middleware transformers. This, creates a deep copy of the internal state of the current crypto.Hash object of which it calculates the digest.

This ensures you can get a hash of an instancce of the data even while still streaming from the URL response.

xget.getHashAlgorithm()

Returns the hash algorithm if any is in use.

xget.use(tag, handler)

Add a named handler to the use middleware stack whose return value would be used to transform the response stream in a series of pipes.

The handler method is called after the stream is requested from and we start pumping the underlying request instances for a data response stream.

The core expects the handler to return a stream.Duplex instance. (A readable, writable stream) to transform or passthrough the raw data streams along the way.

// Example, compressing the response content in real time
xget(URL)
  .use('compressor', () => zlib.createGzip())
  .pipe(createWriteStreamSomehow())

xget.with(tag, handler)

Add a named handler to the with middleware stack whose return value would be stored within the store after execution.

xget(URL)
  .with('bar', ({size}) => progressBar(size)) // Create a finite-sized progress bar
  .use('bar', (_, store) => store.get('bar').genStream()) // Create a stream handling object that updates the progressbar from the number of bytes flowing through itself
  .once('set', store => store.get('bar').print('Downloading...'))
  .pipe(createWriteStreamSomehow());

LoadData: Object

  • url: <string> The URL specified.
  • size: <number> Finite number returned if server responds appropriately, else Infinity.
  • start: <number> Sticks to specification if server allows chunking via content-ranges else, resets to 0.
  • chunkable: <number> Whether or not the URL feed can be chunked, supporting simultaneous connections.
  • chunkStack: <ChunkLoadInstance[]> The chunkstack array.

ChunkLoadInstance: Object

  • min: <number> The minimum extent for the chunk segment range.
  • max: <number> The maximum extent for the chunk segment range.
  • size: <number> The total size of the chunk segment.
  • stream: <ResilientStream> A resilient stream that wraps around a request instance.

WithMiddlewareFn: Function

This handler is called immediately after metadata from URL is loaded that describes the response. That is, pre-streaming data from the HEAD like size (content-length), content-type, filename (content-disposition), whether or not it's chunkable (accept-ranges) and a couple of other criterias.

This information is passed into a handler whose return value is filed within the store referenced by the tag.

UseMiddlewareFn: Function

ClI Info

  • To avoid the terminal being cluttered while using pipes, direct other chained binaries' stdout and stderr to /dev/null
# Watching from a stream, hiding vlc's log information
xget https://myserver.com/movie.mp4 | vlc - > /dev/null 2>&1

Development

Building

Feel free to clone, use in adherance to the license and perhaps send pull requests

git clone https://github.com/miraclx/libxget-js.git
cd libxget-js
npm install
# hack on code
npm run build

License

Apache 2.0 © Miraculous Owonubi (@miraclx) <omiraculous@gmail.com>