在客户端生成可下载的文件流

Question

I use GWT, but this is probably generally applicable to JavaScript.

I download a low single-digit number of megabytes of raw data from the server. I want to generate a downloadable CSV file from that raw data, but I want to do it on the client-side because the CSV will be huge compared to the raw data and transmitting all of that over the wire would be stupid.

Generating the entire file content at once and then prompting the user for a download seems to be possible, but concatenating hundrets of megabytes of strings into a URL would be stupid.

In any sane language I would read from the response stream into a buffer, process that buffer, generate a chunk of CSV text and write that to the file stream. Repeat until all of the raw data is processed.

Is something like this possible in JavaScript?
Does GWT have a predefined mechanism for this?

Ideally there should also be a way of showing progress.

Answer 1

You can use the browser's Fetch API.

When you call fetch it will return a Response object.

The Response.body getter returns a ReadableStream object which is the response stream you are wanting.

The browser API is accessible in GWT using the GWT elemental2 library.