I'm using expo to build a cross-platform application. In my app, I have a screen where user can select images or videos to upload.
When I use expo-image-picker to select image it gives me an object which its uri starts with file:/// and I can use this uri to display the image.
When I use expo-image-picker-multiple to select multiple images it gives me objects and the uri starts with asset-library:// and I can't use this uri to display the content of it nor send it to server.
How can I convert this asset-library:// to file://? What keyword should I use to get better results when doing google search on this problem or which tool should I use? I can't really find a proper solution to this one. This occurs on IOS devices.
Thanks!
[EDIT]
here is my code
var assetUri = 'asset-library://....'
var tempDir = `${FileSystem.cacheDirectory}${Math.random().toString(36).substring(7)}.jpg`
FileSystem.copyAsync({
from: assetUri,
to: tempDir
})
try {
var assetResult = await FileSystem.readAsStringAsync(tempDir, {
encoding: FileSystem.EncodingType.UTF8
})
console.log(assetResult)
}
catch(e) {
console.log(e)
}
File 'file:///var/mobile/Containers/Data/Application/0E-FC42-4630-B3C7-537D5EFB7D1F/Library/Caches/ExponentExperienceData/ichardexpohong/gwmke.jpg' could not be read.
I wanted only the filename so i used
let filename= result.assets[0].uri.split('/')[result.assets[0].uri.split('/').length-1]
so maybe if the path after both asset-library and file:// are the same you can use
take away the asset-library:// then replace it with file://
let uri='file://' + object.uri.split('asset-library://')[1]
hope it helps
Using Adobe PDF Embed API, you can register a callback:
this.adobeDCView = new window.AdobeDC.View(config);
this.adobeDCView.registerCallback(
window.AdobeDC.View.Enum.CallbackType.SAVE_API, (metaData, content, options) => {
})
Content is according to the docs here: https://www.adobe.io/apis/documentcloud/dcsdk/docs.html?view=view
content: The ArrayBuffer of file content
When I debug this content using chrome inspector, it shows me that content is a Int8Array.
Normally when we upload a pdf file, the user selects a file and we read as dataURI and get base64 and push that to AWS. So I need to convert this PDF's data (Int8Array) to Base64, so I can also push it to AWS.
Everything I have found online uses UInt8Array to base64, and I don't understand how to go from Int8Array to UInt8Array. I would think you can just add 128 to the signed int to get a ratio between 0-256, but this doesn't seem to work.
I have tried using this:
let decoder = new TextDecoder('utf8');
let b64 = btoa(decoder.decode(content));
console.log(b64);
But I get this error:
ERROR DOMException: Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.
Please help me figure out how to go from Int8Array to Base64.
I use the function in this answer.
For Embed API, use the "content" parameter from the save callback as the input to the function.
You can see a working example at this CodePen. The functional part is below.
adobeDCView.registerCallback(
AdobeDC.View.Enum.CallbackType.SAVE_API,
function (metaData, content, options) {
/* Add your custom save implementation here...and based on that resolve or reject response in given format */
var base64PDF = arrayBufferToBase64(content);
var fileURL = "data:application/pdf;base64," + base64PDF;
$("#submitButton").attr("href", fileURL);
/* End save code */
return new Promise((resolve, reject) => {
resolve({
code: AdobeDC.View.Enum.ApiResponseCode.SUCCESS,
data: {
/* Updated file metadata after successful save operation */
metaData: { fileName: urlToPDF.split("/").slice(-1)[0] }
}
});
});
},
saveOptions
);
In my project I am retrieving gallery's albums using react-native-photos-framework which giving me gallery's album. Then using those album object I am fetching images of that particular album, which returning assets array. Those assets contains uri which look like this :
"photos://C5E8291B-09C6-2231-856D-989D929392FA2/L0/001"
How I can get the base64 string of that image.
I tried to get using react-native-image-base64 and react-native-fs but none of working.
Here is a code in which I used react-native-image-base64 :
const base64 = await ImgToBase64.getBase64String("photos://C5E8291B-09C6-2231-856D-989D929392FA2/L0/001");
But, this giving me following error :
JSON value '' of type NSNull cannot be converted to NSString
Here is code using react-native-fs :
const base64 = await RNFS.readFile('photos://C5E8291B-09C6-2231-856D-989D929392FA2/L0/001','base64');
Above code giving me this error :
"ENOENT: no such file or directory, open 'photos://C5E8291B-09C6-2231-856D-989D929392FA2/L0/001'"
Please help me how to solve !!!
I have several html templates I require to "compile" and convert to base64 format. By compile I mean injecting JS and CSS inline, and then converting it to base64 format.
I tried gulp-base64 but that only works for images in CSS. Any ideas?
Edit: I just got an idea that maybe I could use gulp-foreach to process each file individually and then use a Buffer to convert each file's content's to base64 format. I know I could do something like:
> console.log(new Buffer("Hello World").toString('base64'));
SGVsbG8gV29ybGQ=
> console.log(new Buffer("SGVsbG8gV29ybGQ=", 'base64').toString('ascii'))
Hello World
But I'm not really sure how to do it since I don't understand quite well how file streams (I think it's called vinyl) work yet in gulp. Any help would be greatly appreciated.
I found your question while looking for a solution to the same problem. Your suggestion to use gulp-foreach led me to a solution, although I didn't use that package:
// import the appropriate plugins
//
const each = require('gulp-each');
const htmlToJs = require('gulp-html-to-js');
// I'm compiling a couple of small PDF files
//
gulp.task('compile:pdf', () =>
gulp.src('./files/**/*.pdf')
// use gulp-each to iterate over the files & convert the
// files to a base64-encoded data URL
//
.pipe(each((content, file, callback) => {
const output = `data:application/pdf;base64,${new Buffer(content).toString('base64')}`;
// the first arg in this callback is the error; the second
// is the content to pass along via the stream
//
callback(null, output)
}))
// use gulp-html-to-js to convert the data URL to a JS module
// which can be imported
//
.pipe(htmlToJs())
// and set the destination...
//
.pipe(gulp.dest('./client/modules/helpers/files'))
);
The end result is a JS file with contents that look like this:
'use strict';
module.exports = 'data:application/pdf;base64,... base64 encoded string...';
I am having trouble with blob URLs.
I was searching for src of a video tag on YouTube and I found that the video src was like:
src="blob:https://video_url"
I opened the blob URL that was in src of the video, but it gave an error. I can't open the link, but it was working with the src tag. How is this possible?
I have a few questions:
What is a blob URL?
Why it is used?
Can I make my own blob URL on a server?
Any additional details about blob URLs would be helpful as well.
Blob URLs (ref W3C, official name) or Object-URLs (ref. MDN and method name) are used with a Blob or a File object.
src="blob:https://crap.crap" I opened the blob url that was in src of
video it gave a error and i can't open but was working with the src
tag how it is possible?
Blob URLs can only be generated internally by the browser. URL.createObjectURL() will create a special reference to the Blob or File object which later can be released using URL.revokeObjectURL(). These URLs can only be used locally in the single instance of the browser and in the same session (ie. the life of the page/document).
What is blob url?
Why it is used?
Blob URL/Object URL is a pseudo protocol to allow Blob and File objects to be used as URL source for things like images, download links for binary data and so forth.
For example, you can not hand an Image object raw byte-data as it would not know what to do with it. It requires for example images (which are binary data) to be loaded via URLs. This applies to anything that require an URL as source. Instead of uploading the binary data, then serve it back via an URL it is better to use an extra local step to be able to access the data directly without going via a server.
It is also a better alternative to Data-URI which are strings encoded as Base-64. The problem with Data-URI is that each char takes two bytes in JavaScript. On top of that a 33% is added due to the Base-64 encoding. Blobs are pure binary byte-arrays which does not have any significant overhead as Data-URI does, which makes them faster and smaller to handle.
Can i make my own blob url on a server?
No, Blob URLs/Object URLs can only be made internally in the browser. You can make Blobs and get File object via the File Reader API, although BLOB just means Binary Large OBject and is stored as byte-arrays. A client can request the data to be sent as either ArrayBuffer or as a Blob. The server should send the data as pure binary data. Databases often uses Blob to describe binary objects as well, and in essence we are talking basically about byte-arrays.
if you have then Additional detail
You need to encapsulate the binary data as a BLOB object, then use URL.createObjectURL() to generate a local URL for it:
var blob = new Blob([arrayBufferWithPNG], {type: "image/png"}),
url = URL.createObjectURL(blob),
img = new Image();
img.onload = function() {
URL.revokeObjectURL(this.src); // clean-up memory
document.body.appendChild(this); // add image to DOM
}
img.src = url; // can now "stream" the bytes
This Javascript function supports to show the difference between the Blob File API and the Data API to download a JSON file in the client browser:
/**
* Save a text as file using HTML <a> temporary element and Blob
* #author Loreto Parisi
*/
var saveAsFile = function(fileName, fileContents) {
if (typeof(Blob) != 'undefined') { // Alternative 1: using Blob
var textFileAsBlob = new Blob([fileContents], {type: 'text/plain'});
var downloadLink = document.createElement("a");
downloadLink.download = fileName;
if (window.webkitURL != null) {
downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob);
} else {
downloadLink.href = window.URL.createObjectURL(textFileAsBlob);
downloadLink.onclick = document.body.removeChild(event.target);
downloadLink.style.display = "none";
document.body.appendChild(downloadLink);
}
downloadLink.click();
} else { // Alternative 2: using Data
var pp = document.createElement('a');
pp.setAttribute('href', 'data:text/plain;charset=utf-8,' +
encodeURIComponent(fileContents));
pp.setAttribute('download', fileName);
pp.onclick = document.body.removeChild(event.target);
pp.click();
}
} // saveAsFile
/* Example */
var jsonObject = {"name": "John", "age": 30, "car": null};
saveAsFile('out.json', JSON.stringify(jsonObject, null, 2));
The function is called like saveAsFile('out.json', jsonString);. It will create a ByteStream immediately recognized by the browser that will download the generated file directly using the File API URL.createObjectURL.
In the else, it is possible to see the same result obtained via the href element plus the Data API, but this has several limitations that the Blob API has not.
I have modified working solution to handle both the case.. when video is uploaded and when image is uploaded .. hope it will help some.
HTML
<input type="file" id="fileInput">
<div> duration: <span id='sp'></span><div>
Javascript
var fileEl = document.querySelector("input");
fileEl.onchange = function(e) {
var file = e.target.files[0]; // selected file
if (!file) {
console.log("nothing here");
return;
}
console.log(file);
console.log('file.size-' + file.size);
console.log('file.type-' + file.type);
console.log('file.acutalName-' + file.name);
let start = performance.now();
var mime = file.type, // store mime for later
rd = new FileReader(); // create a FileReader
if (/video/.test(mime)) {
rd.onload = function(e) { // when file has read:
var blob = new Blob([e.target.result], {
type: mime
}), // create a blob of buffer
url = (URL || webkitURL).createObjectURL(blob), // create o-URL of blob
video = document.createElement("video"); // create video element
//console.log(blob);
video.preload = "metadata"; // preload setting
video.addEventListener("loadedmetadata", function() { // when enough data loads
console.log('video.duration-' + video.duration);
console.log('video.videoHeight-' + video.videoHeight);
console.log('video.videoWidth-' + video.videoWidth);
//document.querySelector("div")
// .innerHTML = "Duration: " + video.duration + "s" + " <br>Height: " + video.videoHeight; // show duration
(URL || webkitURL).revokeObjectURL(url); // clean up
console.log(start - performance.now());
// ... continue from here ...
});
video.src = url; // start video load
};
} else if (/image/.test(mime)) {
rd.onload = function(e) {
var blob = new Blob([e.target.result], {
type: mime
}),
url = URL.createObjectURL(blob),
img = new Image();
img.onload = function() {
console.log('iamge');
console.dir('this.height-' + this.height);
console.dir('this.width-' + this.width);
URL.revokeObjectURL(this.src); // clean-up memory
console.log(start - performance.now()); // add image to DOM
}
img.src = url;
};
}
var chunk = file.slice(0, 1024 * 1024 * 10); // .5MB
rd.readAsArrayBuffer(chunk); // read file object
};
jsFiddle Url
https://jsfiddle.net/PratapDessai/0sp3b159/
The OP asks:
What is blob URL? Why is it used?
Blob is just byte sequence. Browsers recognize Blobs as byte streams. It is used to get byte stream from source.
According to Mozilla's documentation
A Blob object represents a file-like object of immutable, raw data. Blobs represent data that isn't necessarily in a JavaScript-native format. The File interface is based on Blob, inheriting blob functionality and expanding it to support files on the user's system.
The OP asks:
Can i make my own blob url on a server?
Yes you can there are several ways to do so for example try http://php.net/manual/en/function.ibase-blob-echo.php
Read more here:
https://developer.mozilla.org/en-US/docs/Web/API/Blob
http://www.w3.org/TR/FileAPI/#dfn-Blob
https://url.spec.whatwg.org/#urls
blob urls are used for showing files that the user uploaded, but they are many other purposes, like that it could be used for secure file showing, like how it is a little difficult to get a YouTube video as a video file without downloading an extension. But, they are probably more answers. My research is mostly just me using Inspect to try to get a YouTube video and an online article.
Another use case of blob urls is to load resources from the server, apply hacks and then tell the browser to interpret them.
One such example would be to load template files or even scss files.
Here is the scss example:
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/sass.js/0.11.1/sass.sync.min.js"></script>
function loadCSS(text) {
const head = document.getElementsByTagName('head')[0]
const style = document.createElement('link')
const css = new Blob([text], {type: 'text/css'})
style.href = window.URL.createObjectURL(css)
style.type = 'text/css'
style.rel = 'stylesheet'
head.append(style)
}
fetch('/style.scss').then(res => res.text()).then(sass => {
Sass.compile(sass, ({text}) => loadCSS(text))
})
Now you could swap out Sass.compile for any kind of transformation function you like.
Blob urls keeps your DOM structure clean this way.
I'm sure by now you have your answers, so this is just one more thing you can do with it.