如何解决C# .NET Framework 4.8无法向Pub/Sub模拟器发消息问题

问题背景 #

在.NET Framework 4.8环境下向Google Pub/Sub模拟器发送消息时失败，但生产环境中代码可正常运行，且相同代码在.NET 8.0环境下配合gcloud模拟器能正常工作。两者使用相同的NuGet包和gcloud版本。

环境信息 #

• 使用的NuGet包：
  Google.Api.Gax = 4.4.0
Google.Cloud.PubSub.V1 = 3.8.0
• gcloud版本：

  >gcloud version
  Google Cloud SDK 455.0.0
  beta 2023.11.10
  bq 2.0.98
  core 2023.11.10
  gsutil 5.27
  pubsub-emulator 0.8.10
  

• 模拟器启动命令：
  gcloud beta emulators pubsub start --project=my-project --host-port=localhost:8085
• 环境变量设置：
  setx PUBSUB_EMULATOR_HOST "localhost:8085"

.NET Framework 4.8 原代码示例 #

using Google.Api.Gax;
using Google.Cloud.PubSub.V1;
using System;
using System.Threading.Tasks;

namespace PubSubDotNetTest
{
    internal class Program
    {
        static void Main(string[] args)
        {
            AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2Support", true);

            Subscriber().GetAwaiter().GetResult();
        }

        static async Task Subscriber()
        {
            Console.WriteLine("Starting publisher...");

            var projectId = "my-project";
            var topicId = "my-topic";

            PublisherServiceApiClient publisherService = await new PublisherServiceApiClientBuilder
            {
                EmulatorDetection = EmulatorDetection.EmulatorOrProduction
            }.BuildAsync();

            TopicName topicName = new TopicName(projectId, topicId);

            PublisherClient publisher = await new PublisherClientBuilder
            {
                TopicName = topicName,
                EmulatorDetection = EmulatorDetection.EmulatorOrProduction
            }.BuildAsync();

            await publisher.PublishAsync("Hello, Pubsub1");
            await publisher.ShutdownAsync(TimeSpan.FromSeconds(15));
        }   
    }
}

错误信息 #

代码抛出异常 #

Unhandled Exception: Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Bad gRPC response. Response protocol downgraded to HTTP/1.1.")
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Google.Api.Gax.Grpc.ApiCallRetryExtensions.<>c__DisplayClass0_0`2.<WithRetry>b__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Google.Cloud.PubSub.V1.Tasks.ForwardingAwaiter`1.GetResult() in /_/apis/Google.Cloud.PubSub.V1/Google.Cloud.PubSub.V1/Tasks/ForwardingAwaiter.cs:line 41
   at Google.Cloud.PubSub.V1.Tasks.Extensions.<>c__DisplayClass5_0`1.<ConfigureAwaitHideErrors>g__Inner|0.MoveNext() in /_/apis/Google.Cloud.PubSub.V1/Google.Cloud.PubSub.V1/Tasks/TaskHelper.cs:line 174
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Google.Cloud.PubSub.V1.Tasks.ForwardingAwaiter`1.GetResult() in /_/apis/Google.Cloud.PubSub.V1/Google.Cloud.PubSub.V1/Tasks/ForwardingAwaiter.cs:line 41
   at Google.Cloud.PubSub.V1.PublisherClientImpl.<PublishAsync>d__32.MoveNext() in /_/apis/Google.Cloud.PubSub.V1/Google.Cloud.PubSub.V1/PublisherClientImpl.cs:line 247
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at PubSubDotNetTest.Program.<Subscriber>d__1.MoveNext() in C:\MyPath\Program.cs:line 37
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at PubSubDotNetTest.Program.Main(String[] args) in C:\MyPath\Program.cs:line 12

模拟器控制台日志 #

[pubsub] Nov 21, 2023 10:37:46 AM io.gapi.emulators.netty.HttpVersionRoutingHandler channelRead
[pubsub] INFO: Detected non-HTTP/2 connection.
[pubsub] Nov 21, 2023 10:37:46 AM io.gapi.emulators.netty.NotFoundHandler handleRequest
[pubsub] INFO: Unknown request URI: /google.pubsub.v1.Publisher/Publish
[pubsub] Nov 21, 2023 10:37:46 AM io.gapi.emulators.netty.NotFoundHandler handleRequest
[pubsub] INFO: Unknown request URI: /google.pubsub.v1.Publisher/Publish
[pubsub] Nov 21, 2023 10:37:46 AM io.gapi.emulators.netty.NotFoundHandler handleRequest
[pubsub] INFO: Unknown request URI: /google.pubsub.v1.Publisher/Publish
[pubsub] Nov 21, 2023 10:37:47 AM io.gapi.emulators.netty.NotFoundHandler handleRequest
[pubsub] INFO: Unknown request URI: /google.pubsub.v1.Publisher/Publish
[pubsub] Nov 21, 2023 10:37:52 AM io.gapi.emulators.netty.NotFoundHandler handleRequest
[pubsub] INFO: Unknown request URI: /google.pubsub.v1.Publisher/Publish

尝试过的无效方案 #

• 添加AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true);
• 手动指定模拟器Endpoint和无安全凭证连接

解决方案 #

.NET Framework 4.8中，默认的gRPC传输层无法正确支持未加密的HTTP/2连接，需要强制使用Grpc.Core的原生通道而非基于SocketsHttpHandler的实现。修改后的代码如下：

using Google.Api.Gax;
using Google.Cloud.PubSub.V1;
using Grpc.Core;
using System;
using System.Threading.Tasks;

namespace PubSubDotNetTest
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // 禁用SocketsHttpHandler，强制使用Grpc.Core原生通道
            AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);
            // 开启未加密HTTP/2支持
            AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true);

            Subscriber().GetAwaiter().GetResult();
        }

        static async Task Subscriber()
        {
            Console.WriteLine("Starting publisher...");

            var projectId = "my-project";
            var topicId = "my-topic";

            PublisherClient publisher = await new PublisherClientBuilder
            {
                TopicName = new TopicName(projectId, topicId),
                EmulatorDetection = EmulatorDetection.EmulatorOrProduction,
                // 显式配置无加密凭证
                ChannelCredentials = ChannelCredentials.Insecure
            }.BuildAsync();

            await publisher.PublishAsync("Hello, Pubsub1");
            await publisher.ShutdownAsync(TimeSpan.FromSeconds(15));
        }   
    }
}

关键修改点 #

1. 禁用SocketsHttpHandler：添加AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);，强制gRPC使用Grpc.Core的原生TCP通道，该通道对未加密HTTP/2的支持更稳定。
2. 保留未加密HTTP/2开关：确保环境允许未加密的HTTP/2连接。
3. 显式指定无加密凭证：配合模拟器的无加密连接要求，避免自动加密逻辑干扰。

另外，也可以尝试将Google.Cloud.PubSub.V1版本降级到3.5.0等早期版本，部分用户反馈旧版本在.NET Framework下对模拟器的兼容性更好，但优先推荐上述通道配置方案。

内容的提问来源于stack exchange，提问作者juanespty