Ensure files are only downloaded once

[melton-jason]

Fixes #2638

The issue here is that for certain browsers the load event was being triggered twice where the iframe.contentWindow was not null

specify7/specifyweb/frontend/js_src/lib/components/Molecules/FilePicker.tsx

Lines 136 to 153 in 1e9be50

	iframe.addEventListener('load', () => {
	if (iframe.contentWindow === null) return;
	const element = iframe.contentWindow.document.createElement('a');
	element.setAttribute(
	'href',
	`data:text/plain;charset=utf-8,${encodeURIComponent(text)}`
	);
	element.setAttribute('download', fileName);
	element.style.display = 'none';
	iframe.contentWindow.document.body.append(element);
	element.click();
	globalThis.setTimeout(() => {
	iframe.remove();
	resolve();
	}, 100);
	});

The load event was being fired and caught both when the iframe was appended to the document and when the content within the iframe was being closed. In both cases the iframe.contentWindow was not null, so the initial return was never caught and the element.click() was called twice.

specify7/specifyweb/frontend/js_src/lib/components/Molecules/FilePicker.tsx

Lines 155 to 158 in 1e9be50

	document.body.append(iframe);
	iframe.contentWindow?.document.open();
	iframe.contentWindow?.document.write(html);
	iframe.contentWindow?.document.close();

Checklist

• Self-review the PR after opening it to make sure the changes look good
  and self-explanatory (or properly documented)
• Add automated tests
• Add relevant issue to release milestone

Testing instructions

In each of Google Chrome, Firefox, and Safari, try actions which would download a file directly, not using the Notification system.
(#2638 did not affect files downloaded from the notification system)

Here are a few places in Specify where this can be accomplished:
(This likely do not all need to be tested, as they all utilize the same downloadFile function for functionality)

• Exporting Query Results (when at least one result is selected)
• Downloading Statistics as TSV
• Downloading an AppResource
• Downloading a Viewset
• Downloading the content of the Crash Report Visualizer as HTML
  • Accessible by navigating to /specify/developer/crash-report-visualizer
• Downloading System/Specify information from the About Specify page
  • Accessible via User Tools
• Downloading the Specify datamodel/schema from the Database Schema page
  • Accessible via User Tools

If other browsers are tested, please mention them in your comment.

[grantfitzsimmons]

Google Chrome (Version 120.0.6099.216 (Official Build) (arm64))

• Exporting Query Results (when at least one result is selected)
• Downloading Statistics as TSV
• Downloading an AppResource
• Downloading a Viewset
• Downloading the content of the Crash Report Visualizer as HTML
• Accessible by navigating to /specify/developer/crash-report-visualizer
• Downloading System/Specify information from the About Specify page
• Downloading the Specify datamodel/schema from the Database Schema page

Firefox (Version 120.0.1 (64-bit))

• Exporting Query Results (when at least one result is selected)
• Downloading Statistics as TSV
• Downloading an AppResource
• Downloading a Viewset
• Downloading the content of the Crash Report Visualizer as HTML
• Accessible by navigating to /specify/developer/crash-report-visualizer
• Downloading System/Specify information from the About Specify page
• Downloading the Specify datamodel/schema from the Database Schema page

[maxpatiiuk]

ah, now that makes sense
another mystery solved - thanks!

[maxpatiiuk]

Also, see my ominous warning 😈:

specify7/specifyweb/frontend/js_src/lib/components/Molecules/FilePicker.tsx

Lines 119 to 120 in 1e9be50

	* A hacky way to download a file on the front-end
	* May stop working in the future

I just couldn't find any other way that didn't involve back-end, didn't force HTTPs, gave us control over the file name, didn't require third-party libraries, and worked accorss browsers (somewhat)

[grantfitzsimmons]

Which release will this be included with? @CarolineDenis @melton-jason

This seems like another PR that can be included in 7.9.3, though I don't want to be expand the scope if you feel it would be better to add in 7.9.4.

[specifysoftware]

This pull request has been mentioned on Specify Community Forum. There might be relevant details there:

https://discourse.specifysoftware.org/t/specify-7-9-3-release-announcement/1499/1