Decoding grpc-status-details-bin ?

[jscti]

Hi there

Server side, we send an error withDetails (in GO) :

st2 := status.New(codes.Aborted, "failed to map")
    st2.WithDetails(&Error{
        Code:     1,
        Message: "error",
    })

Client side (js / typescript), we need to retrieve these details somehow but all we receive is a serialized string (trailers.get('grpc-status-details-bin') ) .. how can we decode it ?

Thanks

[johanbrandhorst]

Go encodes the metadata as base64 after marshalling the proto message, so you should be able to base64 decode followed by a unmarshalling of the data into a google.rpc.Status type.

[johanbrandhorst]

See https://github.com/grpc/grpc-go/blob/ca62c6b92c334f52c7e48b7cbf624f3b877fb092/internal/transport/http_util.go#L317 for how its done in Go clients. Should be very applicable to JS clients too. We may need to add some convenience function for this, but for now this is what you will need.

[jscti]

Thanks for the (very) quick reply.

DIdn't recognize a base64 string, but yeah, decoded it this way and it's OK ;)

Thanks

[jscti]

Struggling for a few hours now, I can't figure out how to parse the base64decoded string.
Nothing seems related on node_modules/grpc or node_modules/grpc_web_client. Can't find either any grpc/status look-alike file.

If you have any clue ^^

Server side :

st2 := status.New(st, "test")
    st2, _ = st2.WithDetails(&gateway_public.Error{
        ErrorType: gateway_public.ErrorType_SPONSORSHIPCODE_CAPTCHA_VERIFICATION_FAILED,
        Message:   "A",
    }, &gateway_public.Error{
        ErrorType: gateway_public.ErrorType_SPONSORSHIPCODE_CAPTCHA_VERIFICATION_FAILED,
        Message:   "B",
    }, &gateway_public.Error{
        ErrorType: gateway_public.ErrorType_SPONSORSHIPCODE_CAPTCHA_VERIFICATION_FAILED,
        Message:   "C",
    })

Client side, I receive :

test1
(type.googleapis.com/gateway.public.ErrorA1
(type.googleapis.com/gateway.public.ErrorB1
(type.googleapis.com/gateway.public.ErrorC

[johanbrandhorst]

Yeah that looks right, but you still need to parse the any.Any details in your status.Status type. You need to switch over the typeURL (e.g. type.googleapis.com/gateway.public.Error) and unmarshal the value into the correct type.

[jscti]

You totally lost me there
grpc-web-client doesn't have a Status class/object to load the entire response in one go.
Do I have to parse the response as a string ? Split over line-break, remove last numeric char if it exists ? (wtf?).

[johanbrandhorst]

OK I thought you had parsed this into a status type already, but I assume this string is just what you go from base64 decoding the trailer then? Here's what you need to do:

1. You need to generate a JS type for the google.rpc.Status type (https://github.com/googleapis/googleapis/blob/master/google/rpc/status.proto). I don't know if this exists pre-generated anywhere.
2. Importing from the previously generated file, you need to create a Status instance by marshalling from the decoded base64 string. I can't remember the exact method names, but it should be obvious.
3. Now that you have a Status type, you will see that it has 3 fields: Message, Code and Details. Details is an array of any.Any types.
4. For each element in the Details field of your status message, you will need to find the correct pre-generated type based on the typeURL field (for example, type.googleapis.com/gateway.public.Error means you should use the pre-generated type for this error).
5. Once you've found the type, you again need to marshal this message from the value field in the any.Any element in the details array.

That will give you your 3 error details marshalled into JS types.

[jscti]

Thanks for the help !

Stuck at step 2 :D

Tried :

const str = atob(metadataa.get('grpc-status-details-bin')[0]);
const bytes = new Uint8Array(Math.ceil(str.length / 2));
for (let i = 0; i < bytes.length; i++) {
    bytes[i] = str.charCodeAt(i);
}
const status = Status.deserializeBinary(bytes);

But decoder triggers an error ... "Failure: Decoder hit an error"
Can't find a proper string to base64 helper ..

[johanbrandhorst]

You still need to base64 decode it first. What does atob do?

[johanbrandhorst]

You should be able to get a Uint8Array from a base64 decoder of the original string.

[jscti]

atob returns a string :/

[johanbrandhorst]

Does creating a Uint8Array from the string work? Anyway, that issue is clearly outside the scope of this issue. I think we can definitely do some work to make this easier for users, but I've given the basic instructions.

[jscti]

So, I got it working with a (not-so-pretty) double deserialization (grpc-go can only send any[] as details and not ErrorStatus[]) :

onEnd: (code: grpc.Code, message, responseMetadata: grpc.Metadata) => {
    if (responseMetadata.has('grpc-status-details-bin')) {
        try {
            const errDetails = atob(responseMetadata.get('grpc-status-details-bin')[0]);

            details = ErrorStatus.deserializeBinary(stringToUint8Array(errDetails))
                .getDetailsList()
                .map(detail => ErrorStatusDetail.deserializeBinary(detail.getValue_asU8()));
        } catch (error) {}
    }
[...]
}

function stringToUint8Array(str): Uint8Array {
    const buf = new ArrayBuffer(str.length);
    const bufView = new Uint8Array(buf);
    for (let i = 0; i < str.length; i++) {
        bufView[i] = str.charCodeAt(i);
    }
    return bufView;
}

and proto :

message ErrorStatusDetail {
  ErrorStatusDetailType type = 1;
  string message = 2;
}

message ErrorStatus {
  int32 code = 1;
  string message = 2;
  repeated google.protobuf.Any details = 3;
}

Thanks for your help

[johanbrandhorst]

Nice work! Just a little clarification - the double marshalling is a consequence of using any.Any - not a limitation in grpc-go.

[jscti]

Yep but when using directly ErrorStatusDetail in the proto + single marshalling, I get a "Assertion failed" error