Update docs

Author: crbelaus

guides/Getting Started.md

@@ -133,12 +133,19 @@ This is completely optional, and you can find more information about it in the `
 
 ## Notifications
 
-We currently do not support notifications out of the box.
+Currently ErrorTracker does not support notifications out of the box.
 
-However, we provideo some detailed Telemetry events that you may use to implement your own notifications following your custom rules and notification channels.
+However, it provides some detailed Telemetry events that you may use to implement your own notifications following your custom rules and notification channels.
 
 If you want to take a look at the events you can attach to, take a look at `ErrorTracker.Telemetry` module documentation.
 
+## Ignoring errors
+
+ErrorTracker tracks every error by default. In certain cases some errors may be expected or just not interesting to track.
+ErrorTracker provides functionality that allows you to ignore errors based on their attributes and context.
+
+Take a look at the `ErrorTracker.Ignorer` behaviour for more information about how to implement your own ignorer.
+
 ## Pruning resolved errors
 
 By default errors are kept in the database indefinitely. This is not ideal for production

lib/error_tracker.ex

@@ -107,12 +107,14 @@ defmodule ErrorTracker do
     {kind, reason} = normalize_exception(exception, stacktrace)
     {:ok, stacktrace} = ErrorTracker.Stacktrace.new(stacktrace)
     {:ok, error} = Error.new(kind, reason, stacktrace)
-
     context = Map.merge(get_context(), given_context)
 
-    {_error, occurrence} = upsert_error!(error, stacktrace, context, reason)
+    ignorer = Application.get_env(:error_tracker, :ignorer)
 
-    occurrence
+    if ignorer && !ignorer.ignore?(error, context) do
+      {_error, occurrence} = upsert_error!(error, stacktrace, context, reason)
+      occurrence
+    end
   end
 
   @doc """

lib/error_tracker/ignorer.ex

@@ -0,0 +1,39 @@
+defmodule ErrorTracker.Ignorer do
+  @moduledoc """
+  Behaviour for ignoring errors.
+
+  The ErrorTracker tracks every error that happens in your application. In certain cases you may
+  want to ignore some errors and don't track them. To do so you can implement this behaviour.
+
+      defmodule MyApp.ErrorIgnorer do
+        @behaviour ErrorTracker.Ignorer
+
+        @impl true
+        def ignore?(error = %ErrorTracker.Error{}, context) do
+          # return true if the error should be ignored
+        end
+      end
+
+  Once implemented, include it in the ErrorTracker configuration:
+
+      config :error_tracker, ignorer: MyApp.ErrorIgnorer
+
+  With this configuration in place, the ErrorTracker will call `MyApp.ErrorIgnorer.ignore?/2` before
+  tracking errors. If the function returns `true` the error will be ignored and won't be tracked.
+
+  > #### A note on performance {: .warning}
+  >
+  > Keep in mind that the `ignore?/2` will be called in the context of the ErrorTracker itself.
+  > Slow code will have a significant impact in the ErrorTracker performance. Buggy code can bring
+  > the ErrorTracker process down.
+  """
+
+  @doc """
+  Decide wether the given error should be ignored or not.
+
+  This function receives both the current Error and context and should return a boolean indicating
+  if it should be ignored or not. If the function returns true the error will be ignored, otherwise
+  it will be tracked.
+  """
+  @callback ignore?(error :: ErrorTracker.Error.t(), context :: map()) :: boolean
+end

test/error_tracker/ignorer_test.exs

@@ -0,0 +1,21 @@
+defmodule ErrorTracker.IgnorerTest do
+  use ErrorTracker.Test.Case
+
+  setup_all do
+    Application.put_env(:error_tracker, :ignorer, ErrorTracker.EveryErrorIgnorer)
+  end
+
+  test "ignores errors" do
+    refute report_error(fn -> raise "[IGNORE] Sample error" end)
+    assert report_error(fn -> raise "Sample error" end)
+  end
+end
+
+defmodule ErrorTracker.EveryErrorIgnorer do
+  @behaviour ErrorTracker.Ignorer
+
+  @impl true
+  def ignore?(error, _context) do
+    String.contains?(error.reason, "[IGNORE]")
+  end
+end