Merge pull request #176 from getsentry/sampling

sample_rate configuration

Author: mitchellhenke

README.md

@@ -73,6 +73,7 @@ config :sentry,
 | `hackney_pool_timeout` | False  | 5000 | |
 | `before_send_event` | False | | |
 | `after_send_event` | False | | |
+| `sample_rate` | False | 1.0 | |
 | `enable_source_code_context` | True | | |
 | `root_source_code_path` | Required if `enable_source_code_context` is enabled | | Should generally be set to `File.cwd!`|
 | `context_lines` | False  | 3 | |

docs/config.rst

@@ -89,6 +89,10 @@ Optional settings
 
   This option allows performing arbitrary operations after attempting to send an event.  Accepts an anonymous function or a {module, function} tuple, and the event will be passed as the first argument, and the result of sending the event will be passed as the second argument.
 
+.. describe:: sample_rate
+
+  The sampling factor to apply to events.  A value of 0.0 will deny sending any events, and a value of 1.0 will send 100% of events.
+
 .. describe:: context_lines
 
   The number of lines of source code before and after the line that caused the exception to be included.  Defaults to ``3``.

lib/sentry/client.ex

@@ -41,6 +41,7 @@ defmodule Sentry.Client do
   @type get_dsn :: {String.t, String.t, Integer.t}
   @sentry_version 5
   @max_attempts 4
+  @default_sample_rate 1.0
   @hackney_pool_name :sentry_pool
 
   quote do
@@ -54,12 +55,23 @@ defmodule Sentry.Client do
 
   ### Options
   * `:result` - Allows specifying how the result should be returned. Options include `:sync`, `:none`, and `:async`.  `:sync` will make the API call synchronously, and return `{:ok, event_id}` if successful.  `:none` sends the event from an unlinked child process under `Sentry.TaskSupervisor` and will return `{:ok, ""}` regardless of the result.  `:async` will start an unlinked task and return a tuple of `{:ok, Task.t}` on success where the Task can be awaited upon to receive the result asynchronously.  When used in an OTP behaviour like GenServer, the task will send a message that needs to be matched with `GenServer.handle_info/2`.  See `Task.Supervisor.async_nolink/2` for more information.  `:async` is the default.
+  * `:sample_rate` - The sampling factor to apply to events.  A value of 0.0 will deny sending any events, and a value of 1.0 will send 100% of events.
   """
-  @spec send_event(Event.t) :: {:ok, Task.t | String.t} | :error
+  @spec send_event(Event.t) :: {:ok, Task.t | String.t} | :error | :unsampled
   def send_event(%Event{} = event, opts \\ []) do
     result = Keyword.get(opts, :result, :async)
+    sample_rate = Keyword.get(opts, :sample_rate) || Application.get_env(:sentry, :sample_rate, @default_sample_rate)
 
     event = maybe_call_before_send_event(event)
+
+    if sample_event?(sample_rate) do
+      encode_and_send(event, result)
+    else
+      :unsampled
+    end
+  end
+
+  defp encode_and_send(event, result) do
     case Poison.encode(event) do
       {:ok, body} ->
         do_send_event(event, body, result)
@@ -225,4 +237,12 @@ defmodule Sentry.Client do
     |> Kernel.round()
     |> :timer.sleep()
   end
+
+  defp sample_event?(1), do: true
+  defp sample_event?(1.0), do: true
+  defp sample_event?(0), do: false
+  defp sample_event?(0.0), do: false
+  defp sample_event?(sample_rate) do
+    :rand.uniform < sample_rate
+  end
 end

test/client_test.exs

@@ -156,4 +156,46 @@ defmodule Sentry.ClientTest do
         end) =~ "AFTER_SEND_EVENT"
     end
   end
+
+  test "sends event with sample_rate of 1" do
+    bypass = Bypass.open
+    Bypass.expect bypass, fn conn ->
+      {:ok, _body, conn} = Plug.Conn.read_body(conn)
+      Plug.Conn.resp(conn, 200, ~s<{"id": "340"}>)
+    end
+
+    modify_env(:sentry, [dsn: "http://public:secret@localhost:#{bypass.port}/1",
+                         client: Sentry.Client
+                       ]
+    )
+
+    try do
+      Event.not_a_function
+    rescue
+      e ->
+        {:ok, _} = Sentry.capture_exception(e, result: :sync, sample_rate: 1)
+    end
+  end
+
+  test "does not send event with sample_rate of 0" do
+    bypass = Bypass.open
+    Bypass.expect bypass, fn conn ->
+      {:ok, _body, conn} = Plug.Conn.read_body(conn)
+      Plug.Conn.resp(conn, 200, ~s<{"id": "340"}>)
+    end
+
+    modify_env(:sentry, [dsn: "http://public:secret@localhost:#{bypass.port}/1",
+                         client: Sentry.Client
+                       ]
+    )
+
+    try do
+      Event.not_a_function
+    rescue
+      e ->
+        {:ok, _} = Sentry.capture_exception(e, result: :sync, sample_rate: 1)
+        Bypass.down(bypass)
+        :unsampled = Sentry.capture_exception(e, result: :sync, sample_rate: 0.0)
+    end
+  end
 end