create backend

lib/mound_hunters_web/plugs/request_logger.ex

@@ -0,0 +1,101 @@
+defmodule MoundHuntersWeb.Plugs.RequestLogger do
+  @moduledoc """
+  Logs each HTTP request as a single JSON line in combined log format plus custom fields.
+  
+  Log format includes:
+  - Standard combined log fields: remote_ip, timestamp, method, path, status, bytes, referer, user_agent
+  - Custom fields: request_id, duration_ms, query_params, lat, lng, tile_id, lookup_id, error
+  """
+  import Plug.Conn
+  require Logger
+
+  def init(opts), do: opts
+
+  def call(conn, _opts) do
+    start_time = System.monotonic_time(:microsecond)
+    request_id = generate_request_id()
+
+    conn =
+      conn
+      |> put_private(:request_start_time, start_time)
+      |> put_private(:request_id, request_id)
+
+    register_before_send(conn, fn conn ->
+      log_request(conn, start_time, request_id)
+      conn
+    end)
+  end
+
+  defp log_request(conn, start_time, request_id) do
+    end_time = System.monotonic_time(:microsecond)
+    duration_ms = (end_time - start_time) / 1000.0
+
+    log_entry = %{
+      # Standard combined log format fields
+      remote_ip: format_remote_ip(conn.remote_ip),
+      timestamp: DateTime.utc_now() |> DateTime.to_iso8601(),
+      method: conn.method,
+      path: conn.request_path,
+      query_string: conn.query_string,
+      status: conn.status,
+      bytes_sent: get_resp_header(conn, "content-length") |> List.first() || "-",
+      referer: get_req_header(conn, "referer") |> List.first() || "-",
+      user_agent: get_req_header(conn, "user-agent") |> List.first() || "-",
+      
+      # Custom fields
+      request_id: request_id,
+      duration_ms: Float.round(duration_ms, 2),
+      
+      # Tile-specific fields (if present)
+      lat: get_query_param(conn, "lat"),
+      lng: get_query_param(conn, "lng"),
+      tile_id: get_private_field(conn, :tile_id),
+      lookup_id: get_private_field(conn, :lookup_id),
+      
+      # Error information
+      error: get_private_field(conn, :error_message)
+    }
+
+    # Remove nil values for cleaner logs
+    log_entry = Enum.reject(log_entry, fn {_k, v} -> is_nil(v) end) |> Map.new()
+
+    # Log to file as JSON line
+    json_line = Jason.encode!(log_entry)
+    Logger.info(json_line, logger: :request_log)
+
+    # Also log summary to console
+    console_msg = 
+      "#{conn.method} #{conn.request_path} - #{conn.status} - #{Float.round(duration_ms, 2)}ms"
+    Logger.info(console_msg)
+  end
+
+  defp format_remote_ip({a, b, c, d}) do
+    "#{a}.#{b}.#{c}.#{d}"
+  end
+
+  defp format_remote_ip({a, b, c, d, e, f, g, h}) do
+    parts = [a, b, c, d, e, f, g, h]
+    parts
+    |> Enum.map(&Integer.to_string(&1, 16))
+    |> Enum.join(":")
+  end
+
+  defp get_query_param(conn, key) do
+    case conn.query_params do
+      %{^key => value} when value != "" -> value
+      _ -> nil
+    end
+  end
+
+  defp get_private_field(conn, key) do
+    case conn.private do
+      %{^key => value} -> value
+      _ -> nil
+    end
+  end
+
+  defp generate_request_id do
+    :crypto.strong_rand_bytes(8)
+    |> Base.url_encode64(padding: false)
+  end
+end