System.Net.Http.HttpRequestException

An HttpRequestException is thrown by HttpClient when a request fails. It can mean that the server could not be reached, that the name could not be resolved, that a certificate was not trusted, or, when you call EnsureSuccessStatusCode, that the server answered with an error status.

The message and the inner exception tell which one it is. From .NET 5, the StatusCode and HttpRequestError properties tell you without parsing the message.

Statistics

19

11

Common causes

The request did not give a successful response. The first thing to find out is whether the server ever answered.

using var client = new HttpClient();
var json = await client.GetStringAsync("http://localhost:1/prices");   // HttpRequestException: connection refused

using var client = new HttpClient();

try
{
    var json = await client.GetStringAsync("http://localhost:1/prices");
}
catch (HttpRequestException e) when (e.HttpRequestError == HttpRequestError.ConnectionError)
{
    logger.LogWarning(e, "The price service is not available");
}

using var client = new HttpClient();
var response = await client.GetAsync("https://api.example.com/prices");
response.EnsureSuccessStatusCode();   // HttpRequestException: Response status code does not indicate success: 404 (Not Found)

using var client = new HttpClient();
var response = await client.GetAsync("https://api.example.com/prices");

if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
{
    Console.WriteLine("No prices yet.");
}
else
{
    response.EnsureSuccessStatusCode();
}

How to fix it and prevent it

builder.Services.AddHttpClient<PriceClient>(client =>
{
    client.BaseAddress = new Uri("https://api.example.com");
});

builder.Services.AddHttpClient("prices").AddStandardResilienceHandler();

How to read the stack trace

The outer exception has the message, and the inner exception is the cause. Look at the inner exception first:

System.Net.Http.HttpRequestException: No connection could be made because the target machine actively refused it. (localhost:5001)
 ---> System.Net.Sockets.SocketException (10061): No connection could be made because the target machine actively refused it.
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource.GetResult(Int16 token)
   at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.InjectNewHttp11ConnectionAsync(QueueItem queueItem)
   at System.Threading.Tasks.TaskCompletionSourceWithCancellation`1.WaitWithCancellationAsync(CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.SocketsHttpHandler.<SendAsync>g__CreateHandlerAndSendAsync|115_0(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.GetStringAsyncCore(HttpRequestMessage request, CancellationToken cancellationToken)
   at Shop.Services.PriceClient.GetPrices(String url) in C:\src\Shop\Services\PriceClient.cs:line 12
   at Program.<Main>$(String[] args) in C:\src\Shop\Program.cs:line 5

The inner exception is a SocketException with the code 10061, so the server was reached but nothing was listening on the port (localhost:5001). The call that started it, line 12 of PriceClient.cs, is at the bottom of the trace. If the inner exception is missing, check the StatusCode property.

Should you catch it?

Yes. Remote calls fail for reasons you cannot control, so catching HttpRequestException around them is normal. Filter on StatusCode or HttpRequestError to handle the cases you know.

Do not retry on every error. A 400 or a 404 will fail again, and a connection error or a 503 may work the next time.

Related exceptions

• SocketException is the inner exception when the connection fails.
• TaskCanceledException is thrown when the request times out.
• WebException is the exception of the older WebRequest API.

Frequently asked questions

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claude mcp add --transport http --client-id claudecode elmahio https://mcp.elmah.io/mcp

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Further reading

YouTube videos

Answers from Stack Overflow

  ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

private const int NumberOfRetries = 3;
private const int DelayOnRetry = 1000;

public static async Task<HttpResponseMessage> GetFromUrlAsync(string url) {
    using (var client = new HttpClient()) {
        for (int i=1; i <= NumberOfRetries; ++i) {
            try {
                return await client.GetAsync(url); 
            }
            catch (Exception e) when (i < NumberOfRetries) {
                await Task.Delay(DelayOnRetry);
            }
        }
    }
}

try
{
    HttpResponseMessage response = await client.GetAsync("http://www.ajshdgasjhdgajdhgasjhdgasjdhgasjdhgas.tk/");
    response.EnsureSuccessStatusCode();    // Throw if not a success code.

    // ...
}
catch (HttpRequestException e)
{
    // Handle exception.
}

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

Source: Stack Overflow