Protobuf to
C#.

// Client/PaymentsService.cs
using System.Net.Http;
using System.Text.Json;
using Example.Payments.Models;

namespace Example.Payments.Client;

public class PaymentsService : BaseHttpClient
{
    public PaymentsService(
        HttpClient httpClient,
        string baseUrl,
        JsonSerializerOptions? jsonOptions)
        : base(httpClient, baseUrl, jsonOptions) { }

    public async Task<Payment> GetPaymentAsync(
        GetPaymentRequest requestBody,
        CancellationToken cancellationToken = default)
    {
        return await ExecuteConnectAsync<Payment>(
            "/payments.v1.PaymentsService/GetPayment",
            requestBody,
            cancellationToken).ConfigureAwait(false);
    }

    public async Task<Payment> CreatePaymentAsync(
        CreatePaymentRequest requestBody,
        CancellationToken cancellationToken = default)
    {
        return await ExecuteConnectAsync<Payment>(
            "/payments.v1.PaymentsService/CreatePayment",
            requestBody,
            cancellationToken).ConfigureAwait(false);
    }
}

// Client/BaseHttpClient.cs (shared)
public abstract class BaseHttpClient
{
    protected readonly HttpClient _httpClient;
    protected readonly string _baseUrl;
    protected readonly JsonSerializerOptions? _jsonOptions;

    public BaseHttpClient(
        HttpClient httpClient,
        string baseUrl,
        JsonSerializerOptions? jsonOptions = null)
    {
        _httpClient = httpClient;
        _baseUrl = baseUrl.TrimEnd('/');
        _jsonOptions = jsonOptions;
    }

    protected async Task<TResponse> ExecuteConnectAsync<TResponse>(
        string path, object? body, CancellationToken cancellationToken)
    {
        var requestUrl = $"{_baseUrl}{path}";
        using var request = new HttpRequestMessage(HttpMethod.Post, requestUrl);
        request.Content = new StringContent(
            body is null ? "{}" : JsonSerializer.Serialize(body, _jsonOptions),
            Encoding.UTF8,
            "application/json");
        request.Headers.TryAddWithoutValidation(
            "Connect-Protocol-Version", "1");
        using var response = await _httpClient
            .SendAsync(request, cancellationToken)
            .ConfigureAwait(false);
        response.EnsureSuccessStatusCode();
        var content = await response.Content
            .ReadAsStringAsync()
            .ConfigureAwait(false);
        return JsonSerializer.Deserialize<TResponse>(content, _jsonOptions)!;
    }

    // For server-stream RPCs (`stream` return type),
    // a sibling helper returns IAsyncEnumerable<T> and
    // reads NDJSON line-by-line from the response body.
    protected async IAsyncEnumerable<TResponse> ExecuteServerStreamAsync<TResponse>(
        string path, object? body,
        [EnumeratorCancellation] CancellationToken cancellationToken)
    { /* NDJSON loop over the response stream */ }
}