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c#postmanprotocol-buffersgrpc

Postman - "Could not load server reflection. Details: unknown error" when using GRPC server reflection

I am trying to use Postman on my GRPC service as described here: https://learn.microsoft.com/en-us/aspnet/core/grpc/test-tools?view=aspnetcore-6.0

Unfortunately, I am getting the error below:

Could not load server reflection.
Details: unknown error

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In Console I can see a bunch of info messages, no errors:

info: Microsoft.AspNetCore.Hosting.Diagnostics2 Request finished HTTP/2 POST http://localhost:5001/grpc.reflection.v1alpha.ServerReflection/ServerReflectionInfo application/grpc - - 200 - application/grpc 57.0449ms
info: Microsoft.AspNetCore.Hosting.Diagnostics2 Request finished HTTP/2 POST http://localhost:5001/grpc.reflection.v1alpha.ServerReflection/ServerReflectionInfo application/grpc - - 200 - application/grpc 158.2632ms
info: Microsoft.AspNetCore.Routing.EndpointMiddleware1
Executed endpoint 'gRPC - /grpc.reflection.v1alpha.ServerReflection/ServerReflectionInfo'

Not sure what can be done to investigate and fix.
If I import the proto files to Postman, I can execute an endpoint and it works OK.

Some details:

  • I am using http/2 over HTTP.
  • Postman Version 10.14.5
  • All grpc packages are version 2.50.0
  • I am tried a few ways of enabling http/2 as in this answer

Any help appreciated!

Solution

  • I have used https://github.com/fullstorydev/grpcurl instead of Postman to connect to the service. It immediately gave me meaningful error:

    Failed to resolve symbol "My.Service":
    Symbol not found: My.Service
    caused by: File not found: google/protobuf/Empty.proto

    It was a bit puzzling, especially that the service works OK.
    However, it turns out that my import definitions had an incorrect casing (see https://github.com/fullstorydev/grpcurl/issues/203).

    I had "google/protobuf/Empty.proto"; instead of import "google/protobuf/empty.proto";.

    After correcting it works fine both in Postman and Grpcurl.

    For the record - it's not that Grpcurl has better error handling than Postman.
    It depends - for example, when an incorrect protocol is used (HTTP 1 instead of HTTP 2), Grpcurl just says Failed to dial target host "localhost:5001": context deadline exceeded whereas Postman's error is more meaningful: INTERNAL: Received RST_STREAM with code 2 triggered by internal client error: Protocol error