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Add :telemetry_prefix option to Tesla.Middleware.Telemetry #390

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Add :telemetry_prefix option to Tesla.Middleware.Telemetry #390

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bc7659b
adds telemetry_prefix config w/ tests
keatz55 Jun 12, 2020
ac2e14e
adds better configuration options and docs
keatz55 Jun 12, 2020
619f19c
makes requested changes
keatz55 Jun 15, 2020
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90 changes: 58 additions & 32 deletions lib/tesla/middleware/telemetry.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,34 @@ if Code.ensure_loaded?(:telemetry) do
end)
```

## Options
- `:telemetry_prefix` - replaces default `[:tesla]` with desired Telemetry event prefix (see below)
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Since this option is passed directly to telemetry middleware I don't think we need to include the telemetry_ prefix in the prefix name (🥁)

I'd go with just :prefix .

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Sounds good. Will update.

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Just updated. Let me know if that works.


## Custom Telemetry Prefix

All events will use a `:telemetry_prefix` which defaults to `[:tesla]`.

You can customize events by providing your own `:telemetry_prefix` locally:

```
defmodule MyClient do
use Tesla

plug Tesla.Middleware.Telemetry, telemetry_prefix: [:custom, :prefix]

end

:telemetry.attach("my-tesla-telemetry", [:custom, :prefix, :request, :stop], fn event, measurements, meta, config ->
# Do something with the event
end)
```

You can configure `:telemetry_prefix` globally in your config, but if set the `:telemetry_prefix` option will override:

```
config :tesla, Tesla.Middleware.Telemetry, telemetry_prefix: [:custom, :prefix]
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I don't think this is a good idea - it would override this all clients from all dependencies.

Since the use case comes from building API clients as packages I think it would be better to hide tesla from end user and use this instead.

# config/config.exs
config :myclient, telemetry_prefix: [...]

# myclient.ex

defmodule Myclient do
  use Tesla
  @compile_config Application.compile_env(:myclient, :telemetry_prefix, [])
  plug Tesla.Middleware.Telemetry, prefix: Keyword.get(@compile_config, :prefix, [:myclient])
  # ...
end

# or top provide runtime configuration

defmodule Myclient do
  def new do
    config = Application.get_env(:myclient, :telemetry_prefix, [])
    middleware = [
      # ...
      {Tesla.Middleware.Telemetry, prefix: Keyword.get(@compile_config, :prefix, [:myclient])}
    ]

    Tesla.client(middleware, adapter)
  end
end

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That makes sense. I kept going back and forth on globalizing. Will remove and update.

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Just updated. Let me know if that works.

```

## Telemetry Events

* `[:tesla, :request, :start]` - emitted at the beginning of the request.
Expand Down Expand Up @@ -46,11 +74,14 @@ if Code.ensure_loaded?(:telemetry) do

@behaviour Tesla.Middleware

@default_telemetry_prefix [:tesla]

@impl Tesla.Middleware
def call(env, next, _opts) do
def call(env, next, opts) do
start_time = System.monotonic_time()
prefix = telemetry_prefix(opts)

emit_start(%{env: env})
emit_start(%{env: env}, prefix)

try do
Tesla.run(env, next)
Expand All @@ -59,62 +90,57 @@ if Code.ensure_loaded?(:telemetry) do
stacktrace = System.stacktrace()
duration = System.monotonic_time() - start_time

emit_exception(duration, %{kind: kind, reason: reason, stacktrace: stacktrace})
emit_exception(duration, %{kind: kind, reason: reason, stacktrace: stacktrace}, prefix)

:erlang.raise(kind, reason, stacktrace)
else
{:ok, env} = result ->
duration = System.monotonic_time() - start_time

emit_stop(duration, %{env: env})
emit_legacy_event(duration, result)
emit_stop(duration, %{env: env}, prefix)
emit_legacy_event(duration, result, prefix)

result

{:error, reason} = result ->
duration = System.monotonic_time() - start_time

emit_stop(duration, %{env: env, error: reason})
emit_legacy_event(duration, result)
emit_stop(duration, %{env: env, error: reason}, prefix)
emit_legacy_event(duration, result, prefix)

result
end
end

defp emit_start(metadata) do
:telemetry.execute(
[:tesla, :request, :start],
%{system_time: System.system_time()},
metadata
)
defp config, do: Application.get_env(:tesla, __MODULE__, [])

defp telemetry_prefix(opts) do
with nil <- Keyword.get(opts, :telemetry_prefix) do
Keyword.get(config(), :telemetry_prefix, @default_telemetry_prefix)
end
end

defp emit_start(metadata, prefix) do
event = prefix ++ [:request, :start]
:telemetry.execute(event, %{system_time: System.system_time()}, metadata)
end

defp emit_stop(duration, metadata) do
:telemetry.execute(
[:tesla, :request, :stop],
%{duration: duration},
metadata
)
defp emit_stop(duration, metadata, prefix) do
event = prefix ++ [:request, :stop]
:telemetry.execute(event, %{duration: duration}, metadata)
end

defp emit_legacy_event(duration, result) do
defp emit_legacy_event(duration, result, prefix) do
if !@disable_legacy_event do
event = prefix ++ [:request]
duration_µs = System.convert_time_unit(duration, :native, :microsecond)

:telemetry.execute(
[:tesla, :request],
%{request_time: duration_µs},
%{result: result}
)
:telemetry.execute(event, %{request_time: duration_µs}, %{result: result})
end
end

defp emit_exception(duration, metadata) do
:telemetry.execute(
[:tesla, :request, :exception],
%{duration: duration},
metadata
)
defp emit_exception(duration, metadata, prefix) do
event = prefix ++ [:request, :exception]
:telemetry.execute(event, %{duration: duration}, metadata)
end
end
end
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