feat(tonic-types): add ability to extract rich error details from google.rpc.Status

[kyle-mccarthy]

Motivation

The tonic-types crate allows for extracting rich error details from a tonic::Status through the StatusExt trait. It does this by decoding the bytes returned by tonic::Status into a google.rpc.Status. However, it does not allow for extracting the error details directly from a google.rpc.Status instance.

This can present a problem if a message contains an internal google.rpc.Status value, which seems to be fairly common on some GCP bidi streams. Example message:

message AppendRowsResponse {
  message AppendResult {
    // ..
  }

  oneof response {
    AppendResult append_result = 1;
    google.rpc.Status error = 2;
  }
  // ..
}

Solution

• Provide From impls for converting between types defined in "std_messages" and the generated protobuf types.
• Add trait that implements a subset of the StatusExt functionality for pb::Status
• Update existing code to leverage conversions