Graham McIntire
58be26fe48
K8s pods have IPv4-only egress; without :inet in the gen_tcp opts, BEAM was picking mqtt.pskreporter.info's AAAA record and the kernel's connect() returned EINVAL, surfacing as :einval and a 30-second retry loop.
288 lines
10 KiB
Elixir
288 lines
10 KiB
Elixir
defmodule Microwaveprop.Pskr.Client do
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@moduledoc """
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MQTT 3.1.1 client for the PSK Reporter live spot firehose.
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Connects to `mqtt.pskreporter.info:1883` over plain TCP (the
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broker doesn't expose TLS), subscribes to a curated set of
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topics, and forwards every PUBLISH payload to
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`Pskr.Aggregator.ingest/2`. Each topic anchors on USA (DXCC 291)
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on either the sender or receiver side so the broker pre-filters
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out the bulk of the firehose before it reaches us — the
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alternative would be subscribing to `pskr/filter/v2/#` and
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dropping ~95% client-side.
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## No external MQTT library
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We talk to the broker with `:gen_tcp` and the codec in
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`Microwaveprop.Pskr.Mqtt`. emqtt's transitive `quicer` dep was a
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CMake/native-build mess in our slim Debian builder image; the
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alternative pure-Elixir client (tortoise311) bundles a
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gen_state_machine + retry/inflight stack we don't use because
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we're subscribe-only at QoS 0. Implementing the wire protocol
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inline is ~150 lines of binary parsing — less code than the
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dependency-management overhead of either choice.
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## Cluster singleton
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All replicas start this GenServer; **only one across the cluster
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actually connects to MQTT**. We elect a leader via
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`:global.register_name/2` (atomic across the BEAM cluster, which
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libcluster gives us). The losing nodes stay in `:standby` mode:
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no socket, no DB writes, just an idle process watching for the
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leader's `nodedown` to re-run election.
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Handover loses at most one flush cycle (~60 s) of in-flight
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aggregates from the old leader's Aggregator — acceptable, since
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the upsert-on-conflict logic in `Pskr.Aggregator` merges any
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overlapping path-hours additively.
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## Bands
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Subscribes to **VHF and up** by default (6m, 2m, 70cm, 23cm). HF
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spots are dominated by ionospheric propagation, which isn't what
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this project models. Microwave bands are listed too but spots
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there are vanishingly rare (FT8 activity is mostly 144 MHz /
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432 MHz / 1296 MHz).
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## Off in dev/test
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`:microwaveprop, :pskr_mqtt_enabled` defaults to `false` in
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dev/test so `mix test` doesn't open an outbound connection. Prod
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flips it on via runtime.exs.
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"""
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use GenServer
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alias Microwaveprop.Pskr.Aggregator
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alias Microwaveprop.Pskr.Mqtt
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require Logger
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@broker_host ~c"mqtt.pskreporter.info"
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@broker_port 1883
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@keepalive_seconds 60
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@keepalive_ms @keepalive_seconds * 1000
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# USA = 291 (continental). PSK Reporter splits Alaska (6) and
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# Hawaii (110) as separate DXCCs but neither is currently in the
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# HRRR domain; HRDPS will eventually add Canada (1).
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@us_dxcc 291
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@default_bands ~w(6m 2m 70cm 23cm 13cm 9cm 6cm 3cm 1.25cm)
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@spec start_link(keyword()) :: GenServer.on_start()
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def start_link(opts \\ []) do
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GenServer.start_link(__MODULE__, opts, name: Keyword.get(opts, :name, __MODULE__))
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end
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@impl true
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def init(opts) do
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Process.flag(:trap_exit, true)
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# `:net_kernel.monitor_nodes/1` lands `{:nodeup, node}` /
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# `{:nodedown, node}` in our mailbox — that's what tells a
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# standby client the leader vanished and election should
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# re-run.
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:ok = :net_kernel.monitor_nodes(true)
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state = %{
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role: :standby,
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socket: nil,
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buffer: <<>>,
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bands: Keyword.get(opts, :bands, @default_bands),
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aggregator: Keyword.get(opts, :aggregator, Aggregator),
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client_id: Keyword.get(opts, :client_id, default_client_id()),
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received: 0,
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ping_timer: nil
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}
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{:ok, state, {:continue, :elect}}
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end
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@impl true
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def handle_continue(:elect, state) do
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case :global.register_name(__MODULE__, self()) do
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:yes ->
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Logger.info("Pskr.Client elected leader on #{node()} — connecting to MQTT")
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{:noreply, %{state | role: :active}, {:continue, :connect}}
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:no ->
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Logger.info("Pskr.Client standby on #{node()} (leader: #{inspect(:global.whereis_name(__MODULE__))})")
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{:noreply, state}
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end
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end
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def handle_continue(:connect, state) do
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case do_connect(state) do
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{:ok, socket, ping_timer} ->
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{:noreply, %{state | socket: socket, ping_timer: ping_timer}}
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{:error, reason} ->
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Logger.error("Pskr.Client connect failed: #{inspect(reason)} — retrying in 30s")
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Process.send_after(self(), :reconnect, 30_000)
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{:noreply, state}
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end
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end
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@impl true
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def handle_info(:reconnect, state), do: {:noreply, state, {:continue, :connect}}
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def handle_info(:ping, %{socket: socket} = state) when is_port(socket) do
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case :gen_tcp.send(socket, Mqtt.pingreq()) do
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:ok ->
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{:noreply, %{state | ping_timer: schedule_ping()}}
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{:error, reason} ->
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Logger.warning("Pskr.Client PINGREQ send failed: #{inspect(reason)}")
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{:noreply, drop_socket(state), {:continue, :connect}}
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end
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end
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def handle_info(:ping, state), do: {:noreply, state}
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# Standby clients re-run election on any cluster topology change.
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# Active leaders ignore — their registration stays valid until
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# *their* node disappears.
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def handle_info({event, _node}, %{role: :standby} = state) when event in [:nodeup, :nodedown] do
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{:noreply, state, {:continue, :elect}}
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end
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def handle_info({event, _node}, state) when event in [:nodeup, :nodedown], do: {:noreply, state}
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def handle_info({:tcp, socket, data}, %{socket: socket} = state) do
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:inet.setopts(socket, active: :once)
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{:noreply, process_buffer(%{state | buffer: state.buffer <> data})}
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end
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def handle_info({:tcp_closed, socket}, %{socket: socket} = state) do
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Logger.warning("Pskr.Client TCP closed (received #{state.received} so far) — reconnecting in 5s")
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Process.send_after(self(), :reconnect, 5_000)
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{:noreply, drop_socket(state)}
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end
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def handle_info({:tcp_error, socket, reason}, %{socket: socket} = state) do
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Logger.warning("Pskr.Client TCP error #{inspect(reason)} — reconnecting in 5s")
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Process.send_after(self(), :reconnect, 5_000)
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{:noreply, drop_socket(state)}
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end
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def handle_info(_other, state), do: {:noreply, state}
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@impl true
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def terminate(_reason, %{socket: socket}) when is_port(socket) do
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_ = :gen_tcp.send(socket, Mqtt.disconnect())
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_ = :gen_tcp.close(socket)
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:ok
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end
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def terminate(_reason, _state), do: :ok
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# ---------- Connection setup ----------
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defp do_connect(state) do
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# `:inet` forces IPv4 resolution + an IPv4 socket. Without
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# this, BEAM can pick the broker's AAAA record while our K8s
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# pod has IPv4-only egress, and `:gen_tcp.connect/4` fails
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# with `:einval` from the kernel `connect()` syscall.
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tcp_opts = [:binary, :inet, active: :once, packet: :raw, keepalive: true]
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with {:ok, socket} <- :gen_tcp.connect(@broker_host, @broker_port, tcp_opts, 10_000),
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:ok <- :gen_tcp.send(socket, Mqtt.connect(state.client_id, @keepalive_seconds)),
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{:ok, :connected, rest} <- await_connack(socket, <<>>),
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:ok <- :gen_tcp.send(socket, subscribe_packet(state.bands)) do
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Logger.info("Pskr.Client connected as #{state.client_id}, subscribed to #{length(state.bands)} bands")
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# `rest` holds anything the broker sent piggybacked after
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# CONNACK — feed it back into the buffer so we don't lose
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# the SUBACK or an early PUBLISH.
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send(self(), {:tcp, socket, rest})
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{:ok, socket, schedule_ping()}
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end
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end
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# CONNACK arrives synchronously right after CONNECT, so a small
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# blocking read here keeps the state machine simple. If we don't
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# get it within 10s, treat the connection as dead.
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defp await_connack(socket, buffer) do
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case Mqtt.parse(buffer) do
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{:ok, {:connack, 0, _}, rest} ->
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{:ok, :connected, rest}
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{:ok, {:connack, code, _}, _} ->
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{:error, {:connack_refused, code}}
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{:incomplete, buf} ->
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case :gen_tcp.recv(socket, 0, 10_000) do
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{:ok, chunk} -> await_connack(socket, buf <> chunk)
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{:error, _} = err -> err
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end
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{:error, _} = err ->
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err
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end
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end
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defp subscribe_packet(bands) do
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topics =
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Enum.flat_map(bands, fn band ->
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[{topic_for(band, :sender_us), 0}, {topic_for(band, :receiver_us), 0}]
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end)
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Mqtt.subscribe(1, topics)
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end
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# Topic order (from the broker's landing page):
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# pskr/filter/v2/<band>/<mode>/<sc>/<rc>/<sl>/<rl>/<sa>/<ra>
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defp topic_for(band, :sender_us), do: "pskr/filter/v2/#{band}/+/+/+/+/+/#{@us_dxcc}/+"
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defp topic_for(band, :receiver_us), do: "pskr/filter/v2/#{band}/+/+/+/+/+/+/#{@us_dxcc}"
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# ---------- Inbound dispatch ----------
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defp process_buffer(state) do
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case Mqtt.parse(state.buffer) do
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{:ok, {:publish, _topic, payload}, rest} ->
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Aggregator.ingest(state.aggregator, payload)
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process_buffer(%{state | buffer: rest, received: state.received + 1})
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{:ok, {:suback, _id, results}, rest} ->
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if Enum.any?(results, &(&1 == 0x80)) do
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Logger.warning("Pskr.Client SUBACK contains failures: #{inspect(results)}")
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end
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process_buffer(%{state | buffer: rest})
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{:ok, :pingresp, rest} ->
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process_buffer(%{state | buffer: rest})
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{:ok, _other, rest} ->
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process_buffer(%{state | buffer: rest})
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{:incomplete, buffer} ->
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%{state | buffer: buffer}
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{:error, reason} ->
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Logger.error("Pskr.Client parse error: #{inspect(reason)} — dropping connection")
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Process.send_after(self(), :reconnect, 1_000)
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drop_socket(state)
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end
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end
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defp drop_socket(state) do
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if state.ping_timer, do: Process.cancel_timer(state.ping_timer)
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if is_port(state.socket), do: :gen_tcp.close(state.socket)
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%{state | socket: nil, buffer: <<>>, ping_timer: nil}
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end
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defp schedule_ping, do: Process.send_after(self(), :ping, @keepalive_ms)
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# ---------- Client ID ----------
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defp default_client_id do
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suffix = 4 |> :crypto.strong_rand_bytes() |> Base.encode16(case: :lower)
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"microwaveprop-#{node_short()}-#{suffix}"
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end
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defp node_short do
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case System.get_env("POD_IP") do
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nil -> node() |> to_string() |> String.replace(["@", "."], "-")
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ip -> String.replace(ip, ".", "-")
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end
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end
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end
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