# `PhoenixMicro.Transport.BroadwayProducer`
[🔗](https://github.com/iamkanishka/phoenix_micro/blob/v1.0.0/lib/phoenix_micro/transport/broadway_producer.ex#L1)

A GenStage `Producer` that bridges any `PhoenixMicro.Transport` into a
Broadway pipeline.

This module implements the `Broadway.Producer` behaviour and sits at the
head of every `PhoenixMicro.Pipeline`. It:

1. Subscribes to the configured transport topic on `init`.
2. Buffers incoming `PhoenixMicro.Message` structs in an internal queue.
3. Drains the queue **on demand** — Broadway's processors pull messages,
   so the producer never pushes faster than downstream can handle (true
   backpressure).
4. Emits Telemetry demand/buffer events for operational visibility.
5. Re-subscribes automatically if the transport subscription is lost.

## How demand works

Broadway calls `handle_demand/2` whenever a processor slot becomes free.
`BroadwayProducer` dispatches up to `demand` buffered messages as
`Broadway.Message` structs. If the buffer is empty it stores the pending
demand and dispatches messages as they arrive via `handle_info/2`.

This creates the classic GenStage pull model:

    Transport broker
          │  (push — unbounded)
          ▼
    BroadwayProducer buffer  ←── demand ── Broadway processors
          │  (pull — demand-driven)
          ▼
    Broadway processors

The buffer size is capped by `:max_demand` (default 1000) to prevent
unbounded memory growth. When the buffer is full, incoming messages are
nacked so the broker can redeliver them later.

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*Consult [api-reference.md](api-reference.md) for complete listing*