Electron - How to save base64 dataUrl to file - javascript

I'm working with an existing Electron project (convert web app to desktop app), which has a task that is to export content on screen to pdf/png/jpg.
Here is the situation:
The desktop app is purely client-side code, it doesn't connect to any API or server (just in case you suggest a solution using Nodejs server-side code)
I got the dataUrl from canvas object already (it's a base64 string of the file)
How can I save that dataUrl into a file (pdf/png/jpg)?
Here are some ways that I tried:
The good old window.location = dataUrl (nothing happens)
Create a form inside the div, action = dataUrl, then submit the form
Both ways are not working!
Thank you very much

For the download to occur the MIME type of the data URI needs to be changed to "application/octet-stream"
var dataURL = "data:text/plain,123";
var form = document.createElement("form");
form.action = dataURL.replace(/:[\w-/]+(?=,)/, ":application/octet-stream");
form.method = "GET";
document.body.appendChild(form);
form.submit();
Using <a> element with download attribute
var dataURL = "data:text/plain,123";
var a = document.createElement("a");
a.download = "file";
a.href = dataURL;
document.body.appendChild(a);
a.click();
See also How to download a file without using <a> element with download attribute or a server??

Related

Download PDF from url react

I have a publicly accessible url to a PDF in Google Cloud Storage. I want to be able to create a button/link in react which allows users to download this PDF to their own computer. I'm wondering what is the best approach to do this and which libraries would be of help? Is there any documentation on this? Thanks
In order to force download a file, you have a number of options. First, the easiest is using the download attribute of an anchor tag:
PDF
However, this is not supported on IE and a number of other browsers in their earlier versions. But the maximum impact of this is it will open in a new tab which in my opinion is graceful degradation. See the full list of supported versions.
If this is not enough, you have to make some changes server-side. You can configure a server in many ways, but as an example, a .htaccess file can have the following:
<Files *.pdf>
Header set Content-Disposition attachment
</Files>
You can dynamically generate a link or button. Snippet bellow:
var sampleBytes = new Int8Array(4096); // In your case it should be your file
var saveByteArray = (function () {
var a = document.createElement("a");
document.body.appendChild(a);
a.style = "display: none";
return function (data, name) {
var blob = new Blob(data, {type: "octet/stream"}), // or application/pdf
url = window.URL.createObjectURL(blob);
a.href = url;
a.download = name;
a.click();
window.URL.revokeObjectURL(url);
};
}());
saveByteArray([sampleBytes], 'example.txt'); // You can define the filename

How download base64 data as image?

I use vue-signature Library and I Don't know how to download base64 data generated as image,
Here is Link of library : https://www.npmjs.com/package/vue-signature
I've already read the documentation and see That "Save()" Methods Save image as PNG/JPG… but it give me base64 data,
thank you for your collaboration, I use vue js
This is not the most optimized solution, But it works.
var a = document.createElement("a"); //Create <a>
a.href = "data:image/png;base64," + ImageBase64; //Image Base64 Goes here
a.download = "Image.png"; //File name Here
a.click(); //Downloaded file
In your case you can try this
var canvas = document.querySelector("canvas");
var signaturePad = new SignaturePad(canvas);
// Returns signature image as data URL (see https://mdn.io/todataurl for the list of possible parameters)
signaturePad.toDataURL("image/jpeg"); // save image as JPEG
source : https://vuejsexamples.com/vue-signature-pad-component/

Polymer Iron Ajax PDF Response - Prevent Chrome Pop-up blocked

I'm using Polymer Iron Ajax to get a PDF document from the server. However, when forcing a download on the client, Chrome (Version 65.0.3325.181) shows the message "Pop-up blocked" - which is not acceptable from a usability point of view. Any ideas how to get around this so the download is not blocked? I've simplified the code below as the PDF is dynamically generated using Puppeteer from data contained in the ajax request.
Server code using Express.js:
response.type('application/pdf');
response.attachment('resume.pdf');
response.send(mypdf);
app.listen(8080)
Polymer App code:
<iron-ajax id="myironajax" method="GET" handle-as="blob" on-response="handlePdfResponse" url="http://localhost:8080/pdf"></iron-ajax>
handlePdfResponse(e) {
var file = new Blob([e.detail.response], { type: 'application/pdf' });
var fileURL = URL.createObjectURL(file);
var a = document.createElement('a');
a.href = fileURL;
a.target = '_blank';
a.download = 'myfile.pdf';
document.body.appendChild(a);
a.click();
}
Any help greatly appreciated. Thanks.

send file from server to client on bokeh

I have made a user interface to fetch data from a MySQL table and visualize it. It is running on a bokeh server. My users connect remotely to the server using their browser (firefox). This works perfectly fine: I simply import the table into a pandas dataframe.
My users also need to download the table as excel. This means I cannot use the export_csv example which is pure javascript.
I have no experience with JavaScript. All I want is to transfer a file from the directory where my main.py is to the client side.
The technique I have tried so far is to join a normal on_click callback to a button, export the information I need to 'output.xls', then change a parameter from a dummy glyph which in turn runs a Javascript code. I got the idea from Bokeh widgets call CustomJS and Python callback for single event? . Note I haven't set the alpha to 0, so that I can see if the circle is really growing upon clicking the download button.
At the bottom of my message you can find my code. You can see I have tried with both XMLHttpRequest and with Fetch directly. In the former case, nothing happens. In the latter case I obtain a file named "mydata.xlsx" as expected, however it contains only this raw text: <html><title>404: Not Found</title><body>404: Not Found</body></html>.
Code:
p = figure(title='mydata')
#download button
download_b = Button(label="Download", button_type="success")
download_b.on_click(download)
#dummy idea from https://stackoverflow.com/questions/44212250/bokeh-widgets-call-customjs-and-python-callback-for-single-event
dummy = p.circle([1], [1],name='dummy')
JScode_xhr = """
var filename = p.title.text;
filename = filename.concat('.xlsx');
alert(filename);
var xhr = new XMLHttpRequest();
xhr.open('GET', '/output.xlsx', true);
xhr.responseType = 'blob';
xhr.onload = function(e) {
if (this.status == 200) {
var blob = this.response;
alert('seems to work...');
if (navigator.msSaveBlob) {
navigator.msSaveBlob(blob, filename);
}
else {
var link = document.createElement("a");
link = document.createElement('a');
link.href = URL.createObjectURL(blob);
window.open(link.href, '_blank');
link.download = filename;
link.target = "_blank";
link.style.visibility = 'hidden';
link.dispatchEvent(new MouseEvent('click'));
URL.revokeObjectURL(url);
}
}
else {
alert('Ain't working!');
}
};
"""
JScode_fetch = """
var filename = p.title.text;
filename = filename.concat('.xlsx');
alert(filename);
fetch('/output.xlsx').then(response => response.blob())
.then(blob => {
alert(filename);
//addresses IE
if (navigator.msSaveBlob) {
navigator.msSaveBlob(blob, filename);
}
else {
var link = document.createElement("a");
link = document.createElement('a')
link.href = URL.createObjectURL(blob);
window.open(link.href, '_blank');
link.download = filename
link.target = "_blank";
link.style.visibility = 'hidden';
link.dispatchEvent(new MouseEvent('click'))
URL.revokeObjectURL(url);
}
return response.text();
});
"""
dummy.glyph.js_on_change('size', CustomJS(args=dict(p=p),
code=JScode_fetch))
plot_tab = Panel(child=row(download_b,p),
title="Plot",
closable=True,
name=str(self.test))
def download():
writer = pd.ExcelWriter('output.xlsx')
data.to_excel(writer,'data')
infos.to_excel(writer,'info')
dummy = p.select(name='dummy')[0]
dummy.glyph.size = dummy.glyph.size +1
Trying out Eugene Pakhomov's answer, I found what was the issue.
The javascript code I named JScode_fetch is almost correct, however I get a 404 because it is not pointing correctly to the right path.
I made my application in the directory format: I changed my .py file to main.py, placed it into a folder called app, and changed this one line of code in JScode_fetch:
fetch('/app/static/output.xlsx', {cache: "no-store"}).then(response => response.blob())
[...]
You can see the problem was that it was trying to access localhost:5006/output.xlsx, instead of localhost:5006/app/output.xlsx. As it is in directory format, the right link is now localhost:5006/app/static/output.xlsx to count for the static directory.
I also changed a few lines in the download function:
def download():
dirpath = os.path.join(os.path.dirname(__file__),'static')
writer = pd.ExcelWriter(os.path.join(dirpath,'output.xlsx'))
writer = pd.ExcelWriter('output.xlsx')
data.to_excel(writer,'data')
infos.to_excel(writer,'info')
dummy = p.select(name='dummy')[0]
dummy.glyph.size = dummy.glyph.size +1
Now it is working flawlessly!
edit: I have added , {cache: "no-store"} within the fetch() function. Otherwise the browser thinks the file is the same if you have to download a different dataframe excel while using the same output.xlsx filename. More info here.
bokeh serve creates just a few predefined handlers to serve some static files and a WebSocket connection - by default, it doesn't have anything to serve files from the root of the project.
Instead of using the one-file format, you can try using the directory format, save your files to static directory and download them from /static/.
One downside of this approach is that you still have to write that convoluted code to just make your backend create the file before a user downloads it.
The best solution would be to go one step further and embed Bokeh Server as a library into your main application. Since you don't have any non-Bokeh code, the simplest way would be to go with Tornado (an example).
bokeh.server.server.Server accepts extra_patterns argument - you can add a handler there to dynamically create Excel files and serve them from, say, /data/. After all that, the only thing that you need in your front-end is a single link to the Excel file.

JavaScript: save base64 string as file

I have a base64 string, file type. File type can be image, text or even pdf. I need to show download link and when user clicks it should start downloading as expected file.
Concisely, server sends me file as base64 string, and I need to save it as file on browser. How can I save base64 string as file on browser? It would be best if solution works on IE9 also.
You can use download.js.
download(base64String, filename, mimeType)
Adapted from https://gist.github.com/RichardBray/23decdec877c0e54e6ac2bfa4b0c512f to work on Firefox.
function downloadBase64File(contentBase64, fileName) {
const linkSource = `data:application/pdf;base64,${contentBase64}`;
const downloadLink = document.createElement('a');
document.body.appendChild(downloadLink);
downloadLink.href = linkSource;
downloadLink.target = '_self';
downloadLink.download = fileName;
downloadLink.click();
}
You can do this from js to download pdf.
Use:
document.location = 'data:application/pdf;base64,' + base64String
You get the effect you desire (web page showing a link, and when user clicks, the save as dialog pops up) when the appropriate response headers are present when the browser requests the resource:
Content-Disposition: attachment; filename="yourfilename.extension"
If you're getting the file from the server as a base64 string embedded in your html, perhaps you can skip the embedding and simply embed a direct link to the file on your server, having the server serve it up to the user.
Related SO on Content-Disposition

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