Using dp_exchange_webull

EXPERIMENTAL. Not run in production. Pin three-part. Maturity is per endpoint — read capabilities/0, not this banner.

Everything general is in dp_exchange_core's usage rules. This file is only what is specific to Webull.

Credentials are required for market data

There is no anonymous endpoint on this venue. Every OpenAPI call is signed, including the ones that look public, so get_price/2 needs credentials that the same call on Coinbase or Gemini does not:

{:ok, quote} = DpExchange.Webull.get_price("BTC-USD", credentials: %{
  app_key: "…", app_secret: "…"
})

capabilities/0 declares credential_benefit: :required — the only venue in the family that does. Branch on that rather than assuming market data is free; the alternative is finding out from a 401.

You keep the credentials. This package signs one request with them and holds nothing.

Start it, and it brings its own rate limiter

children = [{DpExchange.Webull, credentials: my_credentials()}]

Passing credentials at start is what lets the package replay your subscriptions after a reconnect — see below. Without them, a reconnect cannot re-subscribe.

Subscribing is two protocols, and you see neither

Market data arrives over MQTT on a WebSocket. Subscriptions are HTTP calls. They are joined by a session identifier this package generates and gives to both.

:ok = DpExchange.Webull.subscribe(["BTC-USD"], credentials: creds, to: self())

The venue does not restore subscriptions after a reconnect. This package replays them for you, which is the whole reason you never have to notice a reconnect. That replay uses the credentials you supplied — at start, or on the subscribe call.

Coverage means delivering, not accepted

On this venue there are three different moments: you asked, the HTTP subscribe returned 200, and data is arriving. coverage/1 reports only the third. A 200 on the subscribe does not mean the stream is flowing.

The venue's connection budget shapes what you can ask for

This package opens one connection and never exposes sockets, so you cannot cause a sixth. The one-minute retention is why reconnect backoff matters: reconnecting immediately after hitting the limit fails until the venue ages the old sessions out.

If two instances ever shared a session id, the venue would disconnect whichever connected first — each instance looking healthy in isolation. The id is generated per feed, so this cannot happen unless you pass one explicitly.

UAT has REST but no stream

{:ok, quote} = DpExchange.Webull.get_price("BTC-USD", environment: :uat, credentials: creds)

environment: :uat gives authenticated REST against test data. There is no UAT broker — the hostname does not resolve — so:

DpExchange.Webull.subscribe(["BTC-USD"], environment: :uat)
#=> {:error, {:streaming_unavailable, :uat}}

It refuses rather than falling back to production, because a consumer testing against UAT that received production prices would be reading real market data believing it was fake.

Ask first if you need to branch:

if DpExchange.Webull.streaming?(environment: :uat), do: …

Production and UAT can run side by side — supervisor, feed and limiter names all derive from the environment, so the two neither collide nor share a rate-limit bucket.

:production is the default and a typo raises. environment: :uatt is an ArgumentError, not a quiet fallback: meaning UAT and getting production sends a real order to a real broker.

There is no trade volume, anywhere

Not on the bars, not on the snapshot, not on the stream. volume is nil, never 0 — zero would look like a real measurement of no trading. capabilities/0 says reports_trade_volume: false, so route volume-dependent work to another venue rather than reading a column of nils.

Eight candle widths, and 1w is deliberately not one

1m 5m 15m 30m 1h 2h 4h 1d.

The venue does serve a weekly bar. It is excluded because a weekly boundary depends on which weekday the venue starts its week, Core.Timeframe models no alignment rule for it, and a bar whose boundary cannot be verified is a bar that should not be stored.

Asking for a width outside that list is an error, never the nearest one.

Timestamps come from the venue, or the call fails

A bar or quote the venue did not date returns {:error, :missing_venue_timestamp}. The local clock is never substituted — an undated bar stamped with your own clock is indistinguishable from a real one, which is how a gap becomes invisible.

What this package does not do yet

Order placement, balances, accounts, fees, transfers, trade history, the order book and the market overview are all :unsupported in this release. That is a statement about this package, not about the venue — Webull serves all of them, and they have not been ported. Read capabilities/0 rather than assuming.