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@grpc/grpc-js server implementation signature issue

Status

Issue: Issue#79.

This one is fixed in version v5.1.0, and there should be some document to explain more.

Issue

If you are using this tool of version v5.0.1, you may have already noticed a signature issue here: examples/src/grpcjs/server.ts#L74-L75. Note the // @ts-ignore:

// @ts-ignore
server.addService(BookServiceService, new ServerImpl());

The signature of implementation class looks like:

export const BookServiceService: IBookServiceService;

export interface IBookServiceServer {
  getBook: grpc.handleUnaryCall<book_pb.GetBookRequest, book_pb.Book>;
  getBooksViaAuthor: grpc.handleServerStreamingCall<book_pb.GetBookViaAuthor, book_pb.Book>;
  getGreatestBook: handleClientStreamingCall<book_pb.GetBookRequest, book_pb.Book>;
  getBooks: grpc.handleBidiStreamingCall<book_pb.GetBookRequest, book_pb.Book>;
}

class ServerImpl implements IBookServiceServer {
}

The signature of addService is:

export class Server {
  addService(
    service: ServiceDefinition,
    implementation: UntypedServiceImplementation
  ): void {}
}

As you can see the type of implementation need to be UntypedServiceImplementation. So it's inconsistent.

Fixing

The way of fixing is to define IBookServiceServer to extends UntypedServiceImplementation.

export interface IBookServiceServer extends grpc.UntypedServiceImplementation {
}

Though this fixing solved the issue of signature issue here (the original one):

// @ts-ignore
server.addService(BookServiceService, new ServerImpl());

It brings the new issue.

Because UntypedServiceImplementation is defined like:

export interface UntypedServiceImplementation {
  [name: string]: UntypedHandleCall;
}

This means all the attributes inside the UntypedServiceImplementation (and any derived implementation, like class ServerImpl implements IBookServiceServer extends grpc.UntypedServiceImplementation) have to be type of UntypedHandleCall.

So when you define a class to implement IBookServiceServer, you have to add a line of code, like:

class Impl implements IBookServiceServer {
    [name: string]: grpc.UntypedHandleCall;
}

Otherwise, tsc would throw errors: Typescript: Index signature is missing in type.

Implementation

According to this breaking change, there could be two styles of server side implementation. One is Object style, the other is Class style.

Object Style

const Impl: IBookServiceServer = {
    getBook: (call: grpc.ServerUnaryCall<GetBookRequest, Book>, callback: sendUnaryData<Book>): void => {},

    getBooks: (call: grpc.ServerDuplexStream<GetBookRequest, Book>): void => {},

    getBooksViaAuthor: (call: grpc.ServerWritableStream<GetBookViaAuthor, Book>): void => {},

    getGreatestBook: (call: grpc.ServerReadableStream<GetBookRequest, Book>, callback: sendUnaryData<Book>): void => {},
};

const server = new grpc.Server();
server.addService(BookServiceService, Impl);

This style is recommended. Since you can append more attributes in the Impl object, though they are not defined in IBookServiceServer, and you don't need to add [name: string]: grpc.UntypedHandleCall in your codes.

Class Style

class Impl implements IBookServiceServer {
    [name: string]: grpc.UntypedHandleCall;

    public getBook(call: grpc.ServerUnaryCall<GetBookRequest, Book>, callback: sendUnaryData<Book>): void {}

    public getBooks(call: grpc.ServerDuplexStream<GetBookRequest, Book>) {}

    public getBooksViaAuthor(call: grpc.ServerWritableStream<GetBookViaAuthor, Book>) {}

    public getGreatestBook(call: grpc.ServerReadableStream<GetBookRequest, Book>, callback: sendUnaryData<Book>) {}
}

const server = new grpc.Server();
server.addService(BookServiceService, new Impl());

This style is NOT recommended. Since only those already defined in the IBookServiceServer can be existing in this Impl class, and [name: string]: grpc.UntypedHandleCall is required for Class style.