Fix agent API protobuf support and Mix.env runtime error

Fixed two critical issues preventing agent communication:

1. Fix Mix.env() runtime error in production
   - Replace Mix.env() with Application.get_env(:towerops, :env)
   - Add :env config to test.exs
   - Mix module not available in production releases

2. Add Protocol Buffers support to agent API endpoints
   - GET /api/v1/agent/config now accepts application/x-protobuf
   - POST /api/v1/agent/heartbeat now accepts application/x-protobuf
   - Added conversion functions for config/equipment/sensors/interfaces
   - Maintains JSON backward compatibility as fallback

All agent controller tests passing (14 tests, 0 failures)

CLAUDE.md

@@ -452,4 +452,5 @@ end)
 - Use `ConnCase` for controller/LiveView tests
 - Use `async: true` for tests that can run in parallel (most unit tests)
 - Use `async: false` for tests with shared state (supervisor tests, integration tests)
-- never open the test coverage html files
+- never open the test coverage html files
+- remember when working in rust to always run cargo fmt before committing

config/test.exs

@@ -43,6 +43,9 @@ config :towerops, ToweropsWeb.Endpoint,
   secret_key_base: "XDSSqVUtRXUjEfzxefIAaPIzBfonpNMOrCRyP1a0kjPzzyOpVNSRmMBVae/bwTqj",
   server: false
 
+# Set environment identifier for runtime checks
+config :towerops, :env, :test
+
 # Use mocks for testing
 config :towerops,
   ping_module: Towerops.Monitoring.PingMock,

lib/towerops_web/controllers/api/agent_controller.ex

@@ -10,6 +10,9 @@ defmodule ToweropsWeb.Api.AgentController do
 
   use ToweropsWeb, :controller
 
+  alias Towerops.Agent.AgentConfig
+  alias Towerops.Agent.HeartbeatMetadata
+  alias Towerops.Agent.HeartbeatResponse
   alias Towerops.Agent.MetricBatch
   alias Towerops.Agents
   alias Towerops.Snmp
@@ -20,6 +23,8 @@ defmodule ToweropsWeb.Api.AgentController do
   Returns polling configuration for all equipment that should be polled by this agent.
   This includes directly assigned equipment plus equipment that inherits the agent
   from site or organization defaults.
+
+  Supports both JSON and Protocol Buffers response formats based on Accept header.
   """
   def get_config(conn, _params) do
     agent_token = conn.assigns.current_agent_token
@@ -31,7 +36,21 @@ defmodule ToweropsWeb.Api.AgentController do
       equipment: Enum.map(equipment_list, &build_equipment_config/1)
     }
 
-    json(conn, config)
+    # Check Accept header for protobuf support
+    case get_req_header(conn, "accept") do
+      ["application/x-protobuf" | _] ->
+        # Convert to protobuf and send
+        proto_config = convert_config_to_proto(config)
+        binary = AgentConfig.encode(proto_config)
+
+        conn
+        |> put_resp_content_type("application/x-protobuf")
+        |> send_resp(200, binary)
+
+      _ ->
+        # Default to JSON
+        json(conn, config)
+    end
   end
 
   @doc """
@@ -68,21 +87,51 @@ defmodule ToweropsWeb.Api.AgentController do
   POST /api/v1/agent/heartbeat
 
   Updates the agent's last_seen_at timestamp and metadata.
+  Supports both JSON and Protocol Buffers formats.
   """
   def heartbeat(conn, params) do
     agent_token = conn.assigns.current_agent_token
     ip = to_string(:inet_parse.ntoa(conn.remote_ip))
 
-    metadata = %{
-      "version" => Map.get(params, "version"),
-      "hostname" => Map.get(params, "hostname"),
-      "uptime_seconds" => Map.get(params, "uptime_seconds")
-    }
+    # Parse metadata based on content type
+    metadata =
+      case get_req_header(conn, "content-type") do
+        ["application/x-protobuf" | _] ->
+          # Decode protobuf
+          {:ok, body, _conn} = Plug.Conn.read_body(conn)
+          proto_metadata = HeartbeatMetadata.decode(body)
+
+          %{
+            "version" => proto_metadata.version,
+            "hostname" => proto_metadata.hostname,
+            "uptime_seconds" => proto_metadata.uptime_seconds
+          }
+
+        _ ->
+          # JSON format (fallback)
+          %{
+            "version" => Map.get(params, "version"),
+            "hostname" => Map.get(params, "hostname"),
+            "uptime_seconds" => Map.get(params, "uptime_seconds")
+          }
+      end
 
     # Update synchronously in the heartbeat endpoint
     Agents.update_agent_token_heartbeat(agent_token.id, ip, metadata)
 
-    json(conn, %{status: "ok"})
+    # Return response in appropriate format
+    case get_req_header(conn, "content-type") do
+      ["application/x-protobuf" | _] ->
+        proto_response = %HeartbeatResponse{status: "ok"}
+        binary = HeartbeatResponse.encode(proto_response)
+
+        conn
+        |> put_resp_content_type("application/x-protobuf")
+        |> send_resp(200, binary)
+
+      _ ->
+        json(conn, %{status: "ok"})
+    end
   end
 
   # Private helpers
@@ -209,4 +258,59 @@ defmodule ToweropsWeb.Api.AgentController do
       _ -> DateTime.truncate(DateTime.utc_now(), :second)
     end
   end
+
+  # Convert internal config format to protobuf
+  defp convert_config_to_proto(config) do
+    %AgentConfig{
+      version: config.version,
+      poll_interval_seconds: config.poll_interval_seconds,
+      equipment: Enum.map(config.equipment, &convert_equipment_to_proto/1)
+    }
+  end
+
+  defp convert_equipment_to_proto(eq) do
+    %Towerops.Agent.Equipment{
+      id: eq.id,
+      name: eq.name,
+      ip_address: eq.ip_address,
+      snmp: convert_snmp_to_proto(eq.snmp),
+      poll_interval_seconds: eq.poll_interval_seconds,
+      sensors: Enum.map(eq.sensors, &convert_sensor_to_proto/1),
+      interfaces: Enum.map(eq.interfaces, &convert_interface_to_proto/1)
+    }
+  end
+
+  defp convert_snmp_to_proto(snmp) do
+    %Towerops.Agent.SnmpConfig{
+      enabled: snmp.enabled,
+      version: snmp.version,
+      community: snmp.community,
+      port: snmp.port
+    }
+  end
+
+  defp convert_sensor_to_proto(sensor) do
+    %Towerops.Agent.Sensor{
+      id: sensor.id,
+      type: sensor.type,
+      oid: sensor.oid,
+      divisor: sensor.divisor || 0.0,
+      unit: sensor.unit || "",
+      metadata: convert_metadata_to_proto(sensor.metadata)
+    }
+  end
+
+  defp convert_interface_to_proto(interface) do
+    %Towerops.Agent.Interface{
+      id: interface.id,
+      if_index: interface.if_index,
+      if_name: interface.if_name
+    }
+  end
+
+  defp convert_metadata_to_proto(nil), do: %{}
+
+  defp convert_metadata_to_proto(metadata) when is_map(metadata) do
+    Map.new(metadata, fn {k, v} -> {to_string(k), to_string(v)} end)
+  end
 end

lib/towerops_web/plugs/agent_auth.ex

@@ -46,7 +46,7 @@ defmodule ToweropsWeb.Plugs.AgentAuth do
 
     # In test environment, update synchronously to avoid DB ownership issues
     # In production, update asynchronously for better performance
-    if Mix.env() == :test do
+    if Application.get_env(:towerops, :env) == :test do
       _ = Agents.update_agent_token_heartbeat(agent_token.id, ip)
     else
       update_heartbeat_async(agent_token.id, ip)