Excellent Export and the Chrome URL limit

One key difference between junior and senior developers is that when they encounter a bug, senior developers are much more likely to blame themselves before others, because experience moves you up the Dunning-Kruger curve.

I was given a bug report recently where Chrome was unable to download a particular spreadsheet, and IE didn’t work either. Other spreadsheets worked OK. It was fairly obvious that one feature of this spreadsheet was the likely candidate : it was by far the largest spreadsheet in the system.

I tried to recreate the bug, and I use Firefox, because I prefer the developer tools. And the spreadsheet download worked as expected. So it’s a difference between browsers. It might still be my fault, but it’s looking less likely.

The library we used for the export is a Javascript library called excellentexport, which converts an HTML table into an Excel-compatible spreadsheet. It uses the data: URI scheme to encode the spreadsheet directly into the page, so that the spreadsheet can be generated entirely server-side. Internet Explorer does not support data: so displays the link, but clicking on it has no effect. Chrome and Firefox both support it, but it turns out Chrome reduced the URI limit from (what I think is) 256Mb to 2Mb, and I wasn’t able to see why. This originally caused the tab to crash, and still can under the right conditions, but for URIs just bigger than 2Mb (in our case 3.5Mb), the click is processed, but the data URI is rendered empty, so a null file is downloaded.

This can be a tricky one to diagnose, hence this post. If you ever encounter this, the solution is to switch to CreateObjectUrl, which is supported in all recent browsers, including Edge, but not IE (but as it doesn’t support data: you’re not losing out there). I’ve submitted a Pull Request to excellentexport demonstrating the change required. Worth remembering if you ever need to create a download link client side.