Newline-delimited JSON (NDJSON) encoding helper.

The JSON sibling of roadrunner_sse. item/1 frames one value as a compact JSON document followed by a single \\n delimiter and returns iodata, so it drops into every response shape unchanged. Set the response content-type to content_type/0 (application/x-ndjson).

A bounded result set as a buffered body — roadrunner_resp:ndjson/2 frames the whole list and sets the headers (it calls item/1 per row):

handle(Req) ->
    Rows = my_db:recent_orders(),
    {roadrunner_resp:ndjson(200, Rows), Req}.

A large or lazy result set, streamed one line per chunk without buffering the whole body (the {stream, ...} shape):

handle(Req) ->
    Fun = fun(Send) ->
        my_db:fold_orders(fun(Row, _Acc) ->
            Send(roadrunner_ndjson:item(Row), nofin)
        end, ok),
        Send(~"", fin)
    end,
    {{stream, 200, [{~"content-type", roadrunner_ndjson:content_type()}], Fun}, Req}.

A message-driven feed (token-by-token output, pub/sub): use the {loop, ...} shape and push each item from handle_info/3, exactly as the roadrunner_sse example does, with item/1 in place of roadrunner_sse:event/1.

json:encode/1 emits compact, single-line JSON (control characters in strings are escaped), so an item never carries a raw newline that would break the framing.