CDPEx.Telemetry (CDPEx v0.4.0)

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The :telemetry events CDPEx emits.

CDPEx is silent by default: it emits these events but attaches no handlers. Attach your own with :telemetry.attach/4 (or a reporter like Telemetry.Metrics) to record them. Emitting with no handler attached is a cheap no-op.

Handlers run synchronously in the process that emits the event — including the CDPEx.Browser / CDPEx.Connection GenServers, where error events fire immediately before that process stops. Keep handlers fast (offload slow work to a Task or a queue); a slow handler delays the emitting process and, for error events, Chrome teardown.

Events

[:cdp_ex, :launch, :start | :stop | :exception]

A span around CDPEx.launch/1 — Chrome spawn, WebSocket connect, and bootstrap. :stop carries the span :duration (in :native time units); its metadata is %{} on success or %{error: reason} when the launch failed. A failed launch still completes through :stop (the browser never started); only a raised exception emits :exception.

[:cdp_ex, :navigate, :start | :stop | :exception]

A span around CDPEx.Page.navigate/3.

  • :start metadata — %{url: url}
  • :stop metadata — %{url, status, final_url} plus :error when the navigation failed. status and final_url are nil unless the call used response: true (see CDPEx.Page.navigate/3) — nil means "not requested", not "unknown". A navigation error tuple flows through :stop (with :error in the metadata), not :exception.

Both spans' metadata also carry :telemetry_span_context (injected by :telemetry.span/3 to correlate :start/:stop/:exception).

[:cdp_ex, :page, :start] and [:cdp_ex, :page, :stop]

Emitted when a page is opened (CDPEx.new_page/2) and closed (CDPEx.close_page/2).

  • measurements — %{system_time: System.system_time()}
  • metadata — %{target_id, transport} where transport is :dedicated or :session

:stop fires only on an explicit close_page/2. A page that dies any other way (a Chrome crash, the browser connection going down) emits [:cdp_ex, :error] instead of :stop — so a gauge built by pairing :start/:stop should also decrement on those errors, or use a counter.

[:cdp_ex, :error]

A genuine fault — a page's WebSocket closed unexpectedly, the browser connection went down, or Chrome exited.

  • measurements — %{system_time: System.system_time()}
  • metadata — %{reason, context}:
    • :chrome_exited — reason is the integer OS exit status
    • :browser_connection_down — reason is the connection's exit reason
    • :ws_closed — reason is the WebSocket close reason (e.g. :closed, or a {code, binary} peer close)

One fault can emit several events

A single Chrome death surfaces as one :ws_closed per live connection (each dedicated page's, plus the browser's) and one :browser_connection_down, racing with :chrome_exited (whichever the browser observes first). Treat them as one incident per browser, not one fault each. A clean CDPEx.stop/1 or close_page/2 emits no error event.

Example

:telemetry.attach(
  "log-cdp-navigate",
  [:cdp_ex, :navigate, :stop],
  fn _event, %{duration: dur}, %{url: url, status: status}, _config ->
    ms = System.convert_time_unit(dur, :native, :millisecond)
    IO.puts("navigated #{url} -> #{inspect(status)} in #{ms}ms")
  end,
  nil
)

Summary

Types

span_name()

The CDPEx operations wrapped in a :telemetry span.

Types

span_name()

(since 0.4.0) 
@type span_name() :: :launch | :navigate

The CDPEx operations wrapped in a :telemetry span.