FastAPI: capture custom request response headers in span attributes

CHANGELOG.md

@@ -15,7 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#999])(https://github.com/open-telemetry/opentelemetry-python-contrib/pull/999)
 
 ### Added
-
+- `opentelemetry-instrumentation-fastapi` Capture custom request/response headers in span attributes
+  ([#1032])(https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1032)
 - `opentelemetry-instrumentation-django` Capture custom request/response headers in span attributes
   ([#1024])(https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1024)
 - `opentelemetry-instrumentation-asgi` Capture custom request/response headers in span attributes

instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py

@@ -91,6 +91,57 @@ def client_response_hook(span: Span, message: dict):
 
    OpenTelemetryMiddleware().(application, server_request_hook=server_request_hook, client_request_hook=client_request_hook, client_response_hook=client_response_hook)
 
+Capture HTTP request and response headers
+*****************************************
+You can configure the agent to capture predefined HTTP headers as span attributes, according to the `semantic convention <https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/http.md#http-request-and-response-headers>`_.
+
+Request headers
+***************
+To capture predefined HTTP request headers as span attributes, set the environment variable ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST``
+to a comma-separated list of HTTP header names.
+
+For example,
+
+::
+
+    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST="content-type,custom_request_header"
+
+will extract ``content-type`` and ``custom_request_header`` from request headers and add them as span attributes.
+
+It is recommended that you should give the correct names of the headers to be captured in the environment variable.
+Request header names in ASGI are case insensitive. So, giving header name as ``CUStom-Header`` in environment variable will be able capture header with name ``custom-header``.
+
+The name of the added span attribute will follow the format ``http.request.header.<header_name>`` where ``<header_name>`` being the normalized HTTP header name (lowercase, with - characters replaced by _ ).
+The value of the attribute will be single item list containing all the header values.
+
+Example of the added span attribute,
+``http.request.header.custom_request_header = ["<value1>,<value2>"]``
+
+Response headers
+****************
+To capture predefined HTTP response headers as span attributes, set the environment variable ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE``
+to a comma-separated list of HTTP header names.
+
+For example,
+
+::
+
+    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE="content-type,custom_response_header"
+
+will extract ``content-type`` and ``custom_response_header`` from response headers and add them as span attributes.
+
+It is recommended that you should give the correct names of the headers to be captured in the environment variable.
+Response header names captured in ASGI are case insensitive. So, giving header name as ``CUStomHeader`` in environment variable will be able capture header with name ``customheader``.
+
+The name of the added span attribute will follow the format ``http.response.header.<header_name>`` where ``<header_name>`` being the normalized HTTP header name (lowercase, with - characters replaced by _ ).
+The value of the attribute will be single item list containing all the header values.
+
+Example of the added span attribute,
+``http.response.header.custom_response_header = ["<value1>,<value2>"]``
+
+Note:
+    Environment variable names to caputre http headers are still experimental, and thus are subject to change.
+
 API
 ---
 """

instrumentation/opentelemetry-instrumentation-fastapi/src/opentelemetry/instrumentation/fastapi/__init__.py

@@ -74,6 +74,58 @@ def client_response_hook(span: Span, message: dict):
 
    FastAPIInstrumentor().instrument(server_request_hook=server_request_hook, client_request_hook=client_request_hook, client_response_hook=client_response_hook)
 
+
+Capture HTTP request and response headers
+*****************************************
+You can configure the agent to capture predefined HTTP headers as span attributes, according to the `semantic convention <https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/http.md#http-request-and-response-headers>`_.
+
+Request headers
+***************
+To capture predefined HTTP request headers as span attributes, set the environment variable ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST``
+to a comma-separated list of HTTP header names.
+
+For example,
+
+::
+
+    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_REQUEST="content-type,custom_request_header"
+
+will extract ``content-type`` and ``custom_request_header`` from request headers and add them as span attributes.
+
+It is recommended that you should give the correct names of the headers to be captured in the environment variable.
+Request header names in FastAPI are case insensitive. So, giving header name as ``CUStom-Header`` in environment variable will be able capture header with name ``custom-header``.
+
+The name of the added span attribute will follow the format ``http.request.header.<header_name>`` where ``<header_name>`` being the normalized HTTP header name (lowercase, with - characters replaced by _ ).
+The value of the attribute will be single item list containing all the header values.
+
+Example of the added span attribute,
+``http.request.header.custom_request_header = ["<value1>,<value2>"]``
+
+Response headers
+****************
+To capture predefined HTTP response headers as span attributes, set the environment variable ``OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE``
+to a comma-separated list of HTTP header names.
+
+For example,
+
+::
+
+    export OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE="content-type,custom_response_header"
+
+will extract ``content-type`` and ``custom_response_header`` from response headers and add them as span attributes.
+
+It is recommended that you should give the correct names of the headers to be captured in the environment variable.
+Response header names captured in FastAPI are case insensitive. So, giving header name as ``CUStomHeader`` in environment variable will be able capture header with name ``customheader``.
+
+The name of the added span attribute will follow the format ``http.response.header.<header_name>`` where ``<header_name>`` being the normalized HTTP header name (lowercase, with - characters replaced by _ ).
+The value of the attribute will be single item list containing all the header values.
+
+Example of the added span attribute,
+``http.response.header.custom_response_header = ["<value1>,<value2>"]``
+
+Note:
+    Environment variable names to caputre http headers are still experimental, and thus are subject to change.
+
 API
 ---
 """