Deno.Reader

Reads up to p.byteLength bytes into p. It resolves to the number of bytes read (0 < n <= p.byteLength) and rejects if any error encountered. Even if read() resolves to n < p.byteLength, it may use all of p as scratch space during the call. If some data is available but not p.byteLength bytes, read() conventionally resolves to what is available instead of waiting for more.

When read() encounters end-of-file condition, it resolves to EOF (null).

When read() encounters an error, it rejects with an error.

Callers should always process the n > 0 bytes returned before considering the EOF (null). Doing so correctly handles I/O errors that happen after reading some bytes and also both of the allowed EOF behaviors.

Implementations should not retain a reference to p.

Use itereateReader from from https://deno.land/std/streams/conversion.ts to turn a Reader into an AsyncIterator.