Унарные вызовы и потоковая передача от сервера

Типы RPC в gRPC

Унарный RPC: основной шаблон

// .proto definition
service OrderService {
  rpc GetOrder (GetOrderRequest) returns (OrderResponse);
}

message GetOrderRequest { int32 id = 1; }
message OrderResponse   { int32 id = 1; string status = 2; double total = 3; }

Реализация унарного RPC

public class OrderService : OrderService.OrderServiceBase
{
    private readonly IOrderRepository _repo;
    public OrderService(IOrderRepository repo) => _repo = repo;

    public override async Task<OrderResponse> GetOrder(
        GetOrderRequest request,
        ServerCallContext context)
    {
        var order = await _repo.GetByIdAsync(request.Id, context.CancellationToken);
        if (order is null)
            throw new RpcException(new Status(StatusCode.NotFound, "Order not found"));

        return new OrderResponse
        {
            Id     = order.Id,
            Status = order.Status.ToString(),
            Total  = (double)order.Total
        };
    }
}

Вызов унарного RPC с клиента

var client = new OrderService.OrderServiceClient(channel);

// Async call with cancellation
var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
var reply = await client.GetOrderAsync(
    new GetOrderRequest { Id = 42 },
    cancellationToken: cts.Token);

Console.WriteLine($"Order {reply.Id}: {reply.Status} - ${reply.Total}");

Потоковая передача от сервера: определение Proto

service StockService {
  // Client sends one symbol, server streams price updates
  rpc WatchStock (WatchRequest) returns (stream StockUpdate);
}

message WatchRequest  { string symbol = 1; }
message StockUpdate   { string symbol = 1; double price = 2; int64 timestamp = 3; }

Реализация потоковой передачи от сервера

public override async Task WatchStock(
    WatchRequest request,
    IServerStreamWriter<StockUpdate> responseStream,
    ServerCallContext context)
{
    while (!context.CancellationToken.IsCancellationRequested)
    {
        var price = await _market.GetPriceAsync(request.Symbol);

        await responseStream.WriteAsync(new StockUpdate
        {
            Symbol    = request.Symbol,
            Price     = price,
            Timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
        });

        await Task.Delay(1000, context.CancellationToken);
    }
}

Получение потока от сервера на клиенте

using var call = client.WatchStock(
    new WatchRequest { Symbol = "MSFT" });

await foreach (var update in call.ResponseStream.ReadAllAsync())
{
    Console.WriteLine($"{update.Symbol}: ${update.Price:F2}");
}
// Continues until server closes the stream or client cancels

Отмена потока от сервера

var cts = new CancellationTokenSource();

// Cancel after 30 seconds
cts.CancelAfter(TimeSpan.FromSeconds(30));

using var call = client.WatchStock(
    new WatchRequest { Symbol = "AAPL" },
    cancellationToken: cts.Token);

try
{
    await foreach (var update in
        call.ResponseStream.ReadAllAsync(cts.Token))
    {
        Console.WriteLine($"Price: {update.Price}");
    }
}
catch (OperationCanceledException)
{
    Console.WriteLine("Stream cancelled.");
}

Метаданные: заголовки запроса и завершающие заголовки

// Server: send initial metadata
await context.WriteResponseHeadersAsync(new Metadata
{
    { "x-correlation-id", Guid.NewGuid().ToString() }
});

// Server: set trailing metadata
context.ResponseTrailers.Add("x-total-count", "1500");

// Client: read headers
var headers  = await call.ResponseHeadersAsync;
var trailerId = headers.GetValue("x-correlation-id");

gRPC для браузерных клиентов

// dotnet add package Grpc.AspNetCore.Web

app.UseGrpcWeb();
app.MapGrpcService<GreeterService>().EnableGrpcWeb();

// Blazor client:
var handler = new GrpcWebHandler(GrpcWebMode.GrpcWeb,
    new HttpClientHandler());
using var channel = GrpcChannel.ForAddress(
    "https://localhost:7042",
    new GrpcChannelOptions { HttpHandler = handler });

Практический пример: служба потоковой передачи журналов

public override async Task StreamLogs(
    LogStreamRequest request,
    IServerStreamWriter<LogEntry> responseStream,
    ServerCallContext context)
{
    await foreach (var log in _logChannel.Reader.ReadAllAsync(
        context.CancellationToken))
    {
        if (log.Level >= request.MinLevel)
        {
            await responseStream.WriteAsync(new LogEntry
            {
                Level   = log.Level.ToString(),
                Message = log.Message,
                Timestamp = Timestamp.FromDateTime(log.Timestamp)
            });
        }
    }
}

Быстрая проверка

Итоги: унарные RPC и потоковая передача от сервера