I am working on a web app that opens binary files and allows them to be edited.
This process is basically ondrop -> dataTransfer.files[0] -> FileReader -> Uint8Array
Essentially, I want to be able to save the modified file back as a binary file. Ideally as a file download with a specified file name.
There doesn't seem to be any standard method of doing this, and that sucks, because everything up to that point is well supported.
I am currently converting the array to a string using String.fromCharCode(), base64 encoding that, and using a data uri in a hyperlink like data:application/octet-stream;base64,.., along with the download attribute to specify filename.
It seems to work, but it's quite hacky and I think converting the raw bytes to a string might introduce encoding issues depending on the byte values. I don't want the data to become corrupt or break the string.
Barring that, is there a better/proper method for getting an array of bytes as a binary file to the user?
These are utilities that I use to download files cross-browser. The nifty thing about this is that you can actually set the download property of a link to the name you want your filename to be.
FYI the mimeType for binary is application/octet-stream
var downloadBlob, downloadURL;
downloadBlob = function(data, fileName, mimeType) {
var blob, url;
blob = new Blob([data], {
type: mimeType
});
url = window.URL.createObjectURL(blob);
downloadURL(url, fileName);
setTimeout(function() {
return window.URL.revokeObjectURL(url);
}, 1000);
};
downloadURL = function(data, fileName) {
var a;
a = document.createElement('a');
a.href = data;
a.download = fileName;
document.body.appendChild(a);
a.style = 'display: none';
a.click();
a.remove();
};
Usage:
downloadBlob(myBinaryBlob, 'some-file.bin', 'application/octet-stream');
(shorter) ES6 version of the top answer:
const downloadURL = (data, fileName) => {
const a = document.createElement('a')
a.href = data
a.download = fileName
document.body.appendChild(a)
a.style.display = 'none'
a.click()
a.remove()
}
const downloadBlob = (data, fileName, mimeType) => {
const blob = new Blob([data], {
type: mimeType
})
const url = window.URL.createObjectURL(blob)
downloadURL(url, fileName)
setTimeout(() => window.URL.revokeObjectURL(url), 1000)
}
Related
In React, I uploaded a file using:
let reader = new FileReader();
reader.readAsDataURL(file);
reader.onloadend = function() {
let base64data = reader.result;
uploadFile(base64data);
return;
}
This gives me a Base64 encoded text data:application/octet-stream;base64,JVBERi0xLj...
This is fine as when I decode 'JVBERi0xLj...' I get the correct text in case of a text file.
When a download request is made to the server I get the same data back but I'm having a difficulty downloading the file. I receive the same base64 encoded string in the response from the server but unable to open the downloaded file.
I have done the following:
const blob = new Blob([fetchData], { type: 'application/pdf' })
let url = window.URL.createObjectURL(blob);
let a = document.createElement('a');
a.href = blob;
a.download = 'doc.pdf';
a.click();
Any ideas?
Note: The upload file is converted to base64 to avoid any http communication issues.
Solution following your suggestions:
let fetchDataModified = `data:application/pdf;base64,${fetchData }`;
let a = document.createElement("a");
a.href = fetchData;
a.download = 'doc.pdf';
a.click();
When converting to Base64 during upload the data type was set to 'application/octet-stream'. However, when downloading I changed that to 'application/pdf' following Vaibhav's suggestion and used createElement instead of createObjectURL and it worked. Thank you
“data:application/pdf” + the base64 string that you saved into our database
I am trying to make a JavaScript/HTML local webpage that just gets opened from my local computer's files. I would like to make it save data in JSON form. But I've been having trouble finding out how to make a local JavaScript program read and write to a file in its same directory.
You can not write files to the local machine if you're using Javascript in the browser.
But you can download the JSON file to your local machine using Blob
You can use this code:
const data = {
key: "value"
};
const fileName = "data.json";
const saveFile = (() => {
const a = document.createElement("a");
document.body.appenChild(a);
return (data, filename) => {
const json = JSON.stringify(a);
const blob = new Blob([json], { type: "application/json" });
const url = window.URK.createObjectURL(blob);
a.href = url;
a.download = filename;
a.click();
window.URL.revokeObjectURL(url);
}
})
saveData(data, fileName);
I'm making an ajax POST call to my server, generating an ugly remote download URL, passing that to nginx with proxy_pass and then serving the file to the client. See here for process. The image seems to make it to the client, I just can't get it to download.
As seen in screenshots, the chrome response preview shows the jpeg, the headers look good (content-disposition attachment).
How can I turn this response into a downloadable file for the user?
I've tried https://stackoverflow.com/a/23797348/5697126, however, the file that gets downloaded is corrupted and 150% size of the real image. Here's my attempt, it does download a file, but the file is corrupted with the message - Error interpreting JPEG image file (Not a JPEG file: starts with 0xef 0xbf)
const filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
const matches = filenameRegex.exec(_responseHeaders['content-disposition']);
let fileName = '';
if (matches != null && matches[1])
{
fileName = matches[1].replace(/['"]/g, '');
}
let fileType = _responseHeaders['content-type'];
let blob = new Blob([_response], {type: fileType});
let URL = window.URL || window.webkitURL;
let downloadUrl = URL.createObjectURL(blob);
if (fileName)
{
// use HTML5 a[download] attribute to specify filename
let a = document.createElement('a');
// safari doesn't support this yet
if (typeof a.download === 'undefined')
{
window.location = downloadUrl;
}
else
{
a.href = downloadUrl;
a.download = fileName;
document.body.appendChild(a);
a.click();
}
}
else
{
window.location = downloadUrl;
}
setTimeout(function ()
{
URL.revokeObjectURL(downloadUrl);
}, 100); // cleanup
Solved!
I had to set the ajax (axios) response type to 'blob' as the default is json. See - https://github.com/axios/axios/issues/448
Once the response was blob, I just piped the _response to URL.createObjectURL and then rest of the code I posted worked like a charm
I have a web service that returns PDF file content in its response. I want to download this as a pdf file when user clicks the link. The javascript code that I have written in UI is as follows:
$http.get('http://MyPdfFileAPIstreamURl').then(function(response){
var blob=new File([response],'myBill.pdf',{type: "text/pdf"});
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="myBill.pdf";
link.click();
});
'response' contains the PDF byte array from servlet outputstream of 'MyPdfFileAPIstreamURl'. And also the stream is not encrypted.
So when I click the link, a PDF file gets downloaded successfully of size around 200KB. But when I open this file, it opens up with blank pages. The starting content of the downloaded pdf file is in the image.
I can't understand what is wrong here. Help !
This is the downloaded pdf file starting contents:
solved it via XMLHttpRequest and xhr.responseType = 'arraybuffer';
code:
var xhr = new XMLHttpRequest();
xhr.open('GET', './api/exportdoc/report_'+id, true);
xhr.responseType = 'arraybuffer';
xhr.onload = function(e) {
if (this.status == 200) {
var blob=new Blob([this.response], {type:"application/pdf"});
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="Report_"+new Date()+".pdf";
link.click();
}
};
xhr.send();
i fetched the data from server as string(which is base64 encoded to string) and then on client side i decoded it to base64 and then to array buffer.
Sample code
function solution1(base64Data) {
var arrBuffer = base64ToArrayBuffer(base64Data);
// It is necessary to create a new blob object with mime-type explicitly set
// otherwise only Chrome works like it should
var newBlob = new Blob([arrBuffer], { type: "application/pdf" });
// IE doesn't allow using a blob object directly as link href
// instead it is necessary to use msSaveOrOpenBlob
if (window.navigator && window.navigator.msSaveOrOpenBlob) {
window.navigator.msSaveOrOpenBlob(newBlob);
return;
}
// For other browsers:
// Create a link pointing to the ObjectURL containing the blob.
var data = window.URL.createObjectURL(newBlob);
var link = document.createElement('a');
document.body.appendChild(link); //required in FF, optional for Chrome
link.href = data;
link.download = "file.pdf";
link.click();
window.URL.revokeObjectURL(data);
link.remove();
}
function base64ToArrayBuffer(data) {
var binaryString = window.atob(data);
var binaryLen = binaryString.length;
var bytes = new Uint8Array(binaryLen);
for (var i = 0; i < binaryLen; i++) {
var ascii = binaryString.charCodeAt(i);
bytes[i] = ascii;
}
return bytes;
};
I was facing the same problem in my React project.
On the API I was using res.download() of express to attach the PDF file in the response. By doing that, I was receiving a string based file. That was the real reason why the file was opening blank or corrupted.
In my case the solution was to force the responseType to 'blob'. Since I was making the request via axios, I just simply added this attr in the option object:
axios.get('your_api_url_here', { responseType: 'blob' })
After, to make the download happen, you can do something like this in your 'fetchFile' method:
const response = await youtServiceHere.fetchFile(id)
const pdfBlob = new Blob([response.data], { type: "application/pdf" })
const blobUrl = window.URL.createObjectURL(pdfBlob)
const link = document.createElement('a')
link.href = blobUrl
link.setAttribute('download', customNameIfYouWantHere)
link.click();
link.remove();
URL.revokeObjectURL(blobUrl);
solved it thanks to rom5jp but adding the sample code for golang and nextjs
in golang using with gingonic context
c.Header("Content-Description", "File-Transfer")
c.Header("Content-Transfer-Encoding", "binary")
c.Header("Content-Disposition","attachment; filename="+fileName)
c.Header("Content-Type", "application/pdf; charset=utf-8")
c.File(targetPath)
//c.FileAttachment(targetPath,fileName)
os.RemoveAll(targetPath)
in next js
const convertToPDF = (res) => {
const uuid = generateUUID();
var a = document.createElement('a');
var url = window.URL.createObjectURL(new Blob([res],{type: "application/pdf"}));
a.href = url;
a.download = 'report.pdf';
a.click();
window.URL.revokeObjectURL(url);
}
const convertFile = async() => {
axios.post('http://localhost:80/fileconverter/upload', {
"token_id" : cookies.access_token,
"request_type" : 1,
"url" : url
},{
responseType: 'blob'
}).then((res)=>{
convertToPDF(res.data)
}, (err) => {
console.log(err)
})
}
I was able to get this working with fetch using response.blob()
fetch(url)
.then((response) => response.blob())
.then((response) => {
const blob = new Blob([response], {type: 'application/pdf'});
const link = document.createElement('a');
link.download = 'some.pdf';
link.href = URL.createObjectURL(blob);
link.click();
});
Changing the request from POST to GET fixed it for me
In my Ext Js solution I am calling a service which is returning this JSON format
{"success":true,"filename":"spreadsheet.xlsx","file":[80,75,3,4,20,0,...(many more)]}
How can I make a file download dialog with the filename and the content of the byte array (file) ?
UPDATE
So I found this bit to start the downlaod
var a = window.document.createElement('a');
a.href = window.URL.createObjectURL(new Blob(data.file, { type: 'application/octet-stream' }));
a.download = data.filename;
// Append anchor to body.
document.body.appendChild(a)
a.click();
// Remove anchor from body
document.body.removeChild(a)
So far good
But the file I get is corrupted so I suspect I need to Encode/Decode the file variable?
I had to convert the file into a Uint8Array before passing it to the Blob
var arr = data.file;
var byteArray = new Uint8Array(arr);
var a = window.document.createElement('a');
a.href = window.URL.createObjectURL(new Blob([byteArray], { type: 'application/octet-stream' }));
a.download = data.filename;
// Append anchor to body.
document.body.appendChild(a)
a.click();
// Remove anchor from body
document.body.removeChild(a)
Reading this answer helped a lot https://stackoverflow.com/a/16245768/1016439
Building on Jepzen's response, I was able to use this technique to download a document from AWS S3 from within the browser. +1 Jepzen
s3.getObject(params, function(err, data) {
if (err === null) {
var arr = data.Body;
var byteArray = new Uint8Array(arr);
var a = window.document.createElement('a');
a.href = window.URL.createObjectURL(new Blob([byteArray], { type: 'application/octet-stream' }));
a.download = fName; //fName was the file name portion of the key what was passed in as part of the key value within params.
// Append anchor to body.
document.body.appendChild(a)
a.click();
// Remove anchor from body
document.body.removeChild(a)
} else {
result = 'failure'
console.log("Failed to retrieve an object: " + err);
}
});