grpc-api.ts

import * as protos from "./protos";
import pb = protos.exemplar;

const HOST = "https://localhost:1234";
const PROTO_CONTENT_TYPE = "application/x-protobuf";

interface ResponseMessageBuilder<PropT, RespT> {
  new(properties?: PropT): RespT;
  encode(message: PropT, writer?: protobuf.Writer): protobuf.Writer;
  decode(reader: (protobuf.Reader | Uint8Array), length?: number): RespT;
}

enum HttpMethod {
  GET,
  POST,
  PUT,
  DELETE,
}

function doFetch<RespPropsT, RespT, RespBuilderT extends ResponseMessageBuilder<RespPropsT, RespT>, ReqT>
  (url: string, builder: RespBuilderT, method: HttpMethod = HttpMethod.GET, req?: ReqT):
  Promise<RespT> {
  const params: RequestInit = {
    headers: {
      "Accept": PROTO_CONTENT_TYPE,
      "Content-Type": PROTO_CONTENT_TYPE,
    },
  };

  if (method != HttpMethod.GET) {
    const encodedRequest = req.constructor().encode(req).finish();
    params.method = "POST";
    params.body = toArrayBuffer(encodedRequest);
  }

  return fetch(`${HOST}${url}`, params).then((res) => {
    if (!res.ok) {
      throw Error(res.statusText);
    }
    return res.arrayBuffer().then((buffer) => builder.decode(new Uint8Array(buffer)));
  });
}

function toArrayBuffer(encodedRequest: Uint8Array): ArrayBuffer {
  return encodedRequest.buffer.slice(encodedRequest.byteOffset, encodedRequest.byteOffset + encodedRequest.byteLength);
}

// Endpoint wrapper
export function getTodos(): Promise<pb.GetTodosResponse> {
  return doFetch(`/api/todos`, pb.GetTodosResponse);
}