Fiddler with dotnet-isolated Az Function - Error starting gRPC call

Question

I have a C# dotnet 5 Azure Function in VS2019 configured with "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated".

If I run the function in the dev environment (ctrl + F5) while Fiddler is running then I get the following error:

Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: Requesting HTTP version 2.0 with version policy RequestVersionOrHigher while HTTP/2 is not enabled.

The function will run fine if Fiddler is not running.

Anyone know how to resolve this?

Answer 1

I recommend to install Fiddler Everywhere which has HTTP/2 and gRPC support.

To setup Fiddler Everywhere make sure

1. 'Ignore server certificate errors' is checked (Settings -> HTTPS)
2. Enabled HTTP/2 support (Settings -> Connections)
3. Bypass Fiddler for URLs that start with 127.0.0.1 (Settings -> Connections)

https://www.telerik.com/blogs/introduction-grpc-fiddler-everywhere

Answer 2

I've made Fiddler work with an Azure Function project with two additions to the standard setup:

1. Add 127.0.0.1 to the bypass list
2. Add tls1.1 and tls1.2 to the supported protocols and skip decryption for 127.0.0.1