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docs: Add browser example for ReadableStreams
feat: Allows for byte offsets when using ipfs.files.cat and friends to request slices of files
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‎examples/README.md‎

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@@ -21,6 +21,7 @@ Let us know if you find any issue or if you want to contribute and add a new tut
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- [js-ipfs in the browser with a `<script>` tag](./browser-script-tag)
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- [js-ipfs in electron](./run-in-electron)
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- [Using streams to add a directory of files to ipfs](./browser-add-readable-stream)
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- [Streaming video from ipfs to the browser using `ReadableStream`s](./browser-readablestream)
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## Understanding the IPFS Stack
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‎examples/browser-readablestream/README.md‎

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# Streaming video from IPFS using ReadableStreams
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We can use the execllent [`videostream`](https://www.npmjs.com/package/videostream) to stream video from IPFS to the browser. All we need to do is return a [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream)-like object that contains the requested byte ranges.
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Take a look at [`index.js`](./index.js) to see a working example.
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## Running the demo
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In this directory:
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```
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$ npm install
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$ npm start
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```
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Then open [http://localhost:8888](http://localhost:8888) in your browser.

‎examples/browser-readablestream/index.html‎

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<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="Content-type" content="text/html; charset=utf-8"/>
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<title><%= htmlWebpackPlugin.options.title %></title>
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<style type="text/css">
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body {
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margin: 0;
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padding: 0;
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}
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#container {
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display: flex;
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height: 100vh;
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}
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pre {
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flex-grow: 2;
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padding: 10px;
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height: calc(100vh - 45px);
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overflow: auto;
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}
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#form-wrapper {
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padding: 20px;
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}
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form {
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padding-bottom: 10px;
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display: flex;
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}
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#hash {
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display: inline-block;
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margin: 0 10px 10px 0;
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font-size: 16px;
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flex-grow: 2;
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padding: 5px;
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}
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button {
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display: inline-block;
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font-size: 16px;
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height: 32px;
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}
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video {
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max-width: 50vw;
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}
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</style>
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</head>
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<body>
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<div id="container" ondrop="dropHandler(event)" ondragover="dragOverHandler(event)">
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<div id="form-wrapper">
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<form>
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<input type="text" id="hash" placeholder="Hash" disabled />
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<button id="gobutton" disabled>Go!</button>
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</form>
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<video id="video" controls></video>
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</div>
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<pre id="output" style="display: inline-block"></pre>
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</div>
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</body>
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</html>

‎examples/browser-readablestream/index.js‎

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'use strict'
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/* eslint-env browser */
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const Ipfs = require('../../')
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const videoStream = require('videostream')
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const ipfs = new Ipfs({ repo: 'ipfs-' + Math.random() })
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const {
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dragDrop,
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statusMessages,
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createVideoElement,
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log
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} = require('./utils')
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log('IPFS: Initialising')
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const timeouts = []
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ipfs.on('ready', () => {
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// Set up event listeners on the <video> element from index.html
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const videoElement = createVideoElement()
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const hashInput = document.getElementById('hash')
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const goButton = document.getElementById('gobutton')
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let stream
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goButton.onclick = function (event) {
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event.preventDefault()
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log(`IPFS: Playing ${hashInput.value.trim()}`)
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// Set up the video stream an attach it to our <video> element
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videoStream({
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createReadStream: function createReadStream (opts) {
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const start = opts.start
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// The videostream library does not always pass an end byte but when
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// it does, it wants bytes between start & end inclusive.
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// catReadableStream returns the bytes exclusive so increment the end
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// byte if it's been requested
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const end = opts.end ? start + opts.end + 1 : undefined
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log(`Stream: Asked for data starting at byte ${start} and ending at byte ${end}`)
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// If we've streamed before, clean up the existing stream
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if (stream && stream.destroy) {
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stream.destroy()
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}
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// This stream will contain the requested bytes
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stream = ipfs.files.catReadableStream(hashInput.value.trim(), {
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offset: start,
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length: end && end - start
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})
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// Log error messages
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stream.on('error', (error) => log(error))
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if (start === 0) {
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// Show the user some messages while we wait for the data stream to start
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statusMessages(stream, log)
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}
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return stream
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}
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}, videoElement)
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}
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// Allow adding files to IPFS via drag and drop
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dragDrop(ipfs, log)
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log('IPFS: Ready')
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log('IPFS: Drop an .mp4 file into this window to add a file')
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log('IPFS: Then press the "Go!" button to start playing a video')
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hashInput.disabled = false
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goButton.disabled = false
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})

‎examples/browser-readablestream/package.json‎

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{
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"name": "browser-videostream",
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"version": "1.0.0",
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"description": "",
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"main": "index.js",
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"scripts": {
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"test": "echo \"Error: no test specified\" && exit 1",
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"build": "webpack",
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"start": "npm run build && http-server dist -a 127.0.0.1 -p 8888"
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},
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"author": "",
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"license": "ISC",
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"devDependencies": {
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"html-webpack-plugin": "^2.30.1",
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"http-server": "^0.11.1",
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"uglifyjs-webpack-plugin": "^1.2.0",
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"webpack": "^3.11.0"
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},
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"dependencies": {
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"videostream": "^2.4.2"
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}
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}

‎examples/browser-readablestream/utils.js‎

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const log = (line) => {
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const output = document.getElementById('output')
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let message
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if (line.message) {
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message = `Error: ${line.message.toString()}`
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} else {
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message = line
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}
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if (message) {
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const node = document.createTextNode(`${message}\r\n`)
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output.appendChild(node)
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output.scrollTop = output.offsetHeight
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return node
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}
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}
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const dragDrop = (ipfs) => {
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const container = document.querySelector('#container')
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container.ondragover = (event) => {
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event.preventDefault()
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}
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container.ondrop = (event) => {
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event.preventDefault()
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for (let i = 0; i < event.dataTransfer.items.length; i++) {
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const item = event.dataTransfer.items[i]
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if (item.kind !== 'file') {
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continue
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}
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const file = item.getAsFile()
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const progress = log(`IPFS: Adding ${file.name} 0%`)
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const reader = new window.FileReader()
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reader.onload = (event) => {
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ipfs.files.add({
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path: file.name,
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content: ipfs.types.Buffer.from(event.target.result)
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}, {
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progress: (addedBytes) => {
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progress.textContent = `IPFS: Adding ${file.name} ${parseInt((addedBytes / file.size) * 100)}%\r\n`
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}
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}, (error, added) => {
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if (error) {
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return log(error)
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}
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const hash = added[0].hash
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log(`IPFS: Added ${hash}`)
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document.querySelector('#hash').value = hash
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})
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}
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reader.readAsArrayBuffer(file)
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}
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if (event.dataTransfer.items && event.dataTransfer.items.clear) {
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event.dataTransfer.items.clear();
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}
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if (event.dataTransfer.clearData) {
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event.dataTransfer.clearData();
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}
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}
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}
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module.exports.statusMessages = (stream) => {
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let time = 0
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const timeouts = [
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'Stream: Still loading data from IPFS...',
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'Stream: This can take a while depending on content availability',
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'Stream: Hopefully not long now',
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'Stream: *Whistles absentmindedly*',
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'Stream: *Taps foot*',
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'Stream: *Looks at watch*',
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'Stream: *Stares at floor*',
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'Stream: *Checks phone*',
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'Stream: *Stares at ceiling*',
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'Stream: Got anything nice planned for the weekend?'
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].map(message => setTimeout(() => log(message), time += 5000))
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stream.once('data', () => {
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log('Stream: Started receiving data')
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timeouts.forEach(clearTimeout)
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})
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stream.once('error', () => {
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timeouts.forEach(clearTimeout)
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})
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}
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const createVideoElement = () => {
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const videoElement = document.getElementById('video')
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videoElement.addEventListener('loadedmetadata', () => {
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videoElement.play()
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.catch(log)
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})
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const events = [
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'playing',
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'waiting',
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'seeking',
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'seeked',
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'ended',
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'loadedmetadata',
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'loadeddata',
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'canplay',
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'canplaythrough',
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'durationchange',
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'play',
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'pause',
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'suspend',
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'emptied',
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'stalled',
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'error',
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'abort'
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]
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events.forEach(event => {
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videoElement.addEventListener(event, () => {
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log(`Video: ${event}`)
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})
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})
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videoElement.addEventListener('error', () => {
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log(videoElement.error)
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})
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return videoElement
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}
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module.exports.log = log
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module.exports.dragDrop = dragDrop
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module.exports.createVideoElement = createVideoElement

‎examples/browser-readablestream/webpack.config.js‎

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'use strict'
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const path = require('path')
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const UglifyJsPlugin = require('uglifyjs-webpack-plugin')
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const HtmlWebpackPlugin = require('html-webpack-plugin')
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module.exports = {
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devtool: 'source-map',
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entry: [
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'./index.js'
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],
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plugins: [
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new UglifyJsPlugin({
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sourceMap: true,
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uglifyOptions: {
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mangle: false,
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compress: false
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}
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}),
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new HtmlWebpackPlugin({
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title: 'IPFS Videostream example',
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template: 'index.html'
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})
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],
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output: {
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path: path.join(__dirname, 'dist'),
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filename: 'bundle.js'
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}
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}

‎package.json‎

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"hapi-set-header": "^1.0.2",
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"hoek": "^5.0.3",
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"human-to-milliseconds": "^1.0.0",
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"ipfs-api": "^19.0.0",
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"ipfs-api": "^20.0.0",
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"ipfs-bitswap": "~0.19.0",
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"ipfs-block": "~0.6.1",
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"ipfs-block-service": "~0.13.0",
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"ipfs-unixfs": "~0.1.14",
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"ipfs-unixfs-engine": "~0.27.0",
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"ipld": "^0.15.0",
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"ipld-dag-pb": "^0.13.1",
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"is-ipfs": "^0.3.2",
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"is-stream": "^1.1.0",
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"joi": "^13.1.2",
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"libp2p-websockets": "~0.10.5",
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"lodash.flatmap": "^4.5.0",
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"lodash.get": "^4.4.2",
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"lodash.set": "^4.3.2",
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"lodash.sortby": "^4.7.0",
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"lodash.values": "^4.3.0",
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"mafmt": "^4.0.0",

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