Simplified Python gRPC Interceptors¶
The primary aim of this project is to make Python gRPC interceptors simple.
The Python grpc
package provides service interceptors, but they’re a bit hard to
use because of their flexibility. The grpc
interceptors don’t have direct access
to the request and response objects, or the service context. Access to these are often
desired, to be able to log data in the request or response, or set status codes on the
context.
The secondary aim of this project is to keep the code small and simple. Code you can
read through and understand quickly gives you confidence and helps debug issues. When
you install this package, you also don’t want a bunch of other packages that might
cause conflicts within your project. Too many dependencies also slow down installation
as well as runtime (fresh imports take time). Hence, a goal of this project is to keep
dependencies to a minimum. The only dependency is the grpc
package.
The grpc_interceptor
package provides the following:
An
Interceptor
base class, to make it easy to define your own service interceptors.An
ExceptionToStatusInterceptor
interceptor, so your service can raise exceptions that set the gRPC status code correctly (rather than the default of every exception resulting in anUNKNOWN
status code). This is something for which pretty much any service will have a use.
Installation¶
$ pip install grpc-interceptor
Usage¶
To define your own interceptor (we can use ExceptionToStatusInterceptor
as an example):
from grpc_interceptor.base import Interceptor
class ExceptionToStatusInterceptor(Interceptor):
def intercept(
self,
method: Callable,
request: Any,
context: grpc.ServicerContext,
method_name: str,
) -> Any:
"""Override this method to implement a custom interceptor.
You should call method(request, context) to invoke the
next handler (either the RPC method implementation, or the
next interceptor in the list).
Args:
method: The next interceptor, or method implementation.
request: The RPC request, as a protobuf message.
context: The ServicerContext pass by gRPC to the service.
method_name: A string of the form
"/protobuf.package.Service/Method"
Returns:
This should generally return the result of
method(request, context), which is typically the RPC
method response, as a protobuf message. The interceptor
is free to modify this in some way, however.
"""
try:
return method(request, context)
except GrpcException as e:
context.set_code(e.status_code)
context.set_details(e.details)
raise
Then inject your interceptor when you create the grpc
server:
interceptors = [ExceptionToStatusInterceptor()]
server = grpc.server(
futures.ThreadPoolExecutor(max_workers=10),
interceptors=interceptors
)
To use ExceptionToStatusInterceptor
:
from grpc_interceptor.exceptions import NotFound
class MyService(my_pb2_grpc.MyServiceServicer):
def MyRpcMethod(
self, request: MyRequest, context: grpc.ServicerContext
) -> MyResponse:
thing = lookup_thing()
if not thing:
raise NotFound("Sorry, your thing is missing")
...
This results in the gRPC status status code being set to NOT_FOUND
,
and the details "Sorry, your thing is missing"
. This saves you the hassle of
catching exceptions in your service handler, or passing the context down into
helper functions so they can call context.abort
or context.set_code
. It allows
the more Pythonic approach of just raising an exception from anywhere in the code,
and having it be handled automatically.
Limitations¶
These are the current limitations, although supporting these is possible. Contributions or requests are welcome.
Interceptor
currently only supports unary-unary RPCs.The package only provides service interceptors.