Repository: elastic/apm-agent-python

Issue:
No-Code-Changes Instrumentation: Starlette/FastAPI
Write an instrumentation for Starlett/FastAPI to for use with the no-code-changes wrapper script + sitecustomize.py

[Meta](https://github.com/elastic/apm-agent-python/issues/1600)


Discussion:

Resolving patch:
diff --git a/elasticapm/instrumentation/packages/starlette.py b/elasticapm/instrumentation/packages/starlette.py
new file mode 100644
--- /dev/null
+++ b/elasticapm/instrumentation/packages/starlette.py
@@ -0,0 +1,55 @@
+#  BSD 3-Clause License
+#
+#  Copyright (c) 2022, Elasticsearch BV
+#  All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer.
+#
+#  * Redistributions in binary form must reproduce the above copyright notice,
+#    this list of conditions and the following disclaimer in the documentation
+#    and/or other materials provided with the distribution.
+#
+#  * Neither the name of the copyright holder nor the names of its
+#    contributors may be used to endorse or promote products derived from
+#    this software without specific prior written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+#  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+#  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+#  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+#  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+#  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+#  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+#  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import weakref
+from typing import TYPE_CHECKING
+
+from elasticapm.instrumentation.packages.base import AbstractInstrumentedModule
+
+if TYPE_CHECKING:
+    from starlette.applications import Starlette
+
+
+class StarletteInstrumentation(AbstractInstrumentedModule):
+    name = "starlette"
+
+    instrument_list = [("starlette.applications", "Starlette.build_middleware_stack")]
+
+    instrumented_apps = []
+
+    creates_transactions = True
+
+    def call(self, module, method, wrapped, instance: "Starlette", args, kwargs):
+        from elasticapm.contrib.starlette import ElasticAPM
+
+        if ElasticAPM not in instance.user_middleware:
+            instance.add_middleware(ElasticAPM, client=None)
+            self.instrumented_apps.append(weakref.ref(instance))
+        return wrapped(*args, **kwargs)
diff --git a/elasticapm/instrumentation/register.py b/elasticapm/instrumentation/register.py
--- a/elasticapm/instrumentation/register.py
+++ b/elasticapm/instrumentation/register.py
@@ -101,6 +101,7 @@
 _wrapper_register = {
     "elasticapm.instrumentation.packages.flask.FlaskInstrumentation",
     "elasticapm.instrumentation.packages.django.DjangoAutoInstrumentation",
+    "elasticapm.instrumentation.packages.starlette.StarletteInstrumentation",
 }
 
 


Test patch:
diff --git a/tests/instrumentation/starlette_tests.py b/tests/instrumentation/starlette_tests.py
new file mode 100644
--- /dev/null
+++ b/tests/instrumentation/starlette_tests.py
@@ -0,0 +1,62 @@
+#  BSD 3-Clause License
+#
+#  Copyright (c) 2023, Elasticsearch BV
+#  All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer.
+#
+#  * Redistributions in binary form must reproduce the above copyright notice,
+#    this list of conditions and the following disclaimer in the documentation
+#    and/or other materials provided with the distribution.
+#
+#  * Neither the name of the copyright holder nor the names of its
+#    contributors may be used to endorse or promote products derived from
+#    this software without specific prior written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+#  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+#  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+#  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+#  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+#  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+#  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+#  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import pytest  # isort:skip
+
+pytest.importorskip("starlette")  # isort:skip
+
+from starlette.applications import Starlette
+from starlette.responses import PlainTextResponse
+from starlette.routing import Route
+from starlette.testclient import TestClient
+
+from elasticapm import async_capture_span
+from elasticapm.conf import constants
+from elasticapm.contrib.starlette import ElasticAPM
+
+
+def test_starlette_app_instrumented(wrapper_instrument, elasticapm_client):
+    async def hi(request):
+        body = await request.body()
+        with async_capture_span("test"):
+            pass
+        return PlainTextResponse(str(len(body)))
+
+    routes = [Route("/", hi)]
+    app = Starlette(routes=routes)
+    test_client = TestClient(app)
+
+    app.build_middleware_stack()
+    assert any(middleware.cls is ElasticAPM for middleware in app.user_middleware)
+    test_client.get("/")
+    transaction = elasticapm_client.events[constants.TRANSACTION][0]
+    assert transaction["name"] == "GET /"
+    assert transaction["result"] == "HTTP 2xx"
+    assert transaction["outcome"] == "success"