async filesystem access

[senekor]

context

The webserver framework we are using is asynchronous. That means request handlers may be stopped and have to wait while other handlers continue their work. This leads to better performance, because while one handler is waiting for some IO operation like networking or access to the filesystem, another handler may do useful work in the meantime.

You may have noticed the keywords asnyc and await in the code base. An asnyc function can be stopped and wait for some other thing, while other tasks make progress. The await keyword is used to await the completion of such a task, like networking or filesystem access.

what to do

Even though we're technically using async, our filesystem access is using the blocking¹ functions from std. Our async runtime tokio has its own functions for accessing the filesystem in an asynchronous manner. Unlike the blocking operations from std, the return values of such asynchronous filesystem operations need to be awaited with .await. See the documentation of tokio for examples.

Replace the use of std::fs with tokio::fs.

Footnotes

1. "blocking" is the opposite of "async". When a blocking operation is waiting for something, like the filesystem, other tasks are blocked from making progress. We don't want that! ↩