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L41-node-server-async-bind.md

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Asynchronous port binding method in Node Server API

Abstract

Add a method to the Node gRPC Server class that binds a port as an asynchronous operation.

Background

In the initial development of the Node gRPC library, the Server class method to bind a port, called bind, was implemented as a synchronous operation because it was available as a synchronous operation in the underlying core library. In contrast, in the Node built in net module, the Server class's listen method, which performs a similar function, is asynchronous. In the new pure JavaScript Node gRPC library, the underlying network operations use the net module, so it is impossible to implement the bind method as a synchronous operation.

Proposal

We would add a method called bindAsync to the Server class that implements the same functionality as bind, but provides the result asynchronously. The specific function signature would be as follows:

class Server {

  // ...

  /**
   * @param port The port that the server should bind on, in the format "address:port"
   * @param creds Server credentials object to be used for SSL.
   * @param callback Callback to be called asynchronously with the result of binding the port
   */
  bindAsync(port: string, creds: ServerCredentials, callback: (error: Error, port: number)=>void): void;
}

The semantics of the arguments are exactly the same as with the existing bind method, and the semantics of the port passed to the callback are identical to the semantics of the return value of the existing bind method: a negative number indicates failure, and a positive number indicates success binding to that port number. An error will also be passed to the callback if port is negative.

Rationale

The semantics of bindAsync would be identical to the semantics of bind except it is asynchronous, so the name communicates that. Keeping the semantics and API as similar as possible minimizes the work need to transition between the two. The semantically redundant error is passed to the callback for greater consistency with other Node APIs, so that it can be used with functions such as util.promisify(). We could also implement the asynchrony using promises, but a callback based API is more consistent with the rest of the existing API. In the future, promise support could be added, perhaps by returning a promise when no callback is provided.

Implementation

I (@murgatroid99) will implement this in the grpc library as soon as this proposal is accepted, and in the @grpc/grpc-js library as part of the server implementation.