I’m trying to generate a stream of JSON from an Ecto stream to be sent out via send_chunked/2 and chunk/2.
It appears that all the JSON libraries I can find are only for parsing.
With the exception of GitHub - TreyE/json_stream_encoder: Streaming encoder for JSON in elixir.
I got stuck trying to use this library since it’s built around IO.binwrite which needs an IO device; I’m more comfortable with streams at the moment.
The gist of what I need is IO’ish device or a Stream of strings, but gives me the opportunity to format things as I go.
Individual items in the response aren’t big on their own, but there could be thousands of them.
Is there any library or approach anyone can share?
Ecto streams are not arbitrary, but essentially chunks. You always get a fixed(max) number of full rows, never partial rows. So your stream could essentially be:
rows = Stream.map(ecto_stream, &Jason.encode!/1)
Stream.concat([["["], Stream.intersperse(rows, ","), ["]"]])
Or switch to ndjson and just join the rows with newlines.
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They might even query records as JSON, if the database supports it, and skip encoding in the application altogether.
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Thanks for this, I was going down this route but it felt clunky; but one thing that weirdly ironed out a lot was see that (from your example) that you can concat Streams with other enums. Which in hindsight feels obvious! 
Anyway, thanks!
Nice idea, I do that elsewhere in our app with LiveView, didn’t think of doing that with an HTTP api - I might just do that.
I think @LostKobrakai’s example applies equally to this as well, getting ecto to emit a stream of strings and wrapping them like that works just as well.
I’m understanding you correctly right?
Yeah. Stream vs Enum APIs is about the output, not the input. The inputs are usually similar / the same and accept any Enumerables.
