Base64 decoder for async streams?

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My use case is:

I'm using tokio. I'm receiving Base64-encoded bytes via an async stream. I want to decode the bytes on the fly, and send the decoded bytes to their destination (a tokio::fs::File).

The decoder in the base64 crate supports Read inputs, but not AsyncRead. I couldn't find any crates that do support AsyncRead.

I think I can work around this by using spawn_blocking():

  1. Send the base64-encoded bytes to a tokio channel
  2. Use spawn_blocking() to run a synchronous task that decodes them, and sends the decoded bytes to a second tokio channel.
  3. Have another tokio task that receives the decode bytes and sends them to their final destination.

This is my fallback, but it's a bit clunky, to say the least.

Really what I need is a "stateful" base64 decoder, one to which I can submit the next batch of input bytes, and get back the next batch of decoded bytes (if any). I looked at the crates base64, base64ct, and base64-stream, but none of them provide a stateful decoder (base64ct supports "incremental decoding", but you still have to supply all the encoded data up front).

Does anyone know of a stateful Base64 decoder, or a way of decoding an async stream on the fly?

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Hmm, it suddenly occurs to me that any Base64 decoder is "stateful", if you divide the input into chunks of multiples of 4 bytes first. Maybe that's the way...

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Yes this worked nicely :slight_smile:

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