Example of Polly retry policy on gRPC client

Program.cs

using DemoGrpc.Domain.Entities;
using DemoGrpc.Protobufs;
using Grpc.Core;
using Microsoft.Extensions.DependencyInjection;
using Polly;
using System;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;
using static DemoGrpc.Protobufs.CountryService;
using System.Net;
using Microsoft.Extensions.Logging;

namespace ConsoleAppGRPC
{
    class Program
    {
        static async Task Main(string[] args)
        {
            // DI
            var services = new ServiceCollection();

            var loggerFactory = LoggerFactory.Create(logging =>
            {
                logging.AddConsole();
                logging.SetMinimumLevel(LogLevel.Debug);
            });

            var serverErrors = new HttpStatusCode[] { 
                HttpStatusCode.BadGateway, 
                HttpStatusCode.GatewayTimeout, 
                HttpStatusCode.ServiceUnavailable, 
                HttpStatusCode.InternalServerError, 
                HttpStatusCode.TooManyRequests, 
                HttpStatusCode.RequestTimeout 
            };

            var gRpcErrors = new StatusCode[] {
                StatusCode.DeadlineExceeded,
                StatusCode.Internal,
                StatusCode.NotFound,
                StatusCode.ResourceExhausted,
                StatusCode.Unavailable,
                StatusCode.Unknown
            };

            Func<HttpRequestMessage, IAsyncPolicy<HttpResponseMessage>> retryFunc = (request) =>
            {
                return Policy.HandleResult<HttpResponseMessage>(r => {
                    
                    var grpcStatus = StatusManager.GetStatusCode(r);
                    var httpStatusCode = r.StatusCode;

                    return (grpcStatus == null && serverErrors.Contains(httpStatusCode)) || // if the server send an error before gRPC pipeline
                           (httpStatusCode == HttpStatusCode.OK && gRpcErrors.Contains(grpcStatus.Value)); // if gRPC pipeline handled the request (gRPC always answers OK)
                })
                .WaitAndRetryAsync(3, (input) => TimeSpan.FromSeconds(3 + input), (result, timeSpan, retryCount, context) =>
                                    {
                                        var grpcStatus = StatusManager.GetStatusCode(result.Result);
                                        Console.WriteLine($"Request failed with {grpcStatus}. Retry");
                                    });
            };

            services.AddGrpcClient<CountryServiceClient>(o =>
            {
                o.Address = new Uri("https://localhost:5001");
            }).AddPolicyHandler(retryFunc);

            var provider = services.BuildServiceProvider();
            var client = provider.GetRequiredService<CountryServiceClient>();

            try
            {
                var countries = (await client.GetAllAsync(new EmptyRequest())).Countries.Select(x => new Country
                {
                    CountryId = x.Id,
                    Description = x.Description,
                    CountryName = x.Name
                }).ToList();

                Console.WriteLine("Found countries");
                countries.ForEach(x => Console.WriteLine($"Found country {x.CountryName} ({x.CountryId}) {x.Description}"));

            }
            catch (RpcException e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}