Question

我想多次发送完全相同的请求，例如：

HttpClient client = new HttpClient();
HttpRequestMessage req = new HttpRequestMessage(HttpMethod.Get, "http://example.com");

await client.SendAsync(req, HttpCompletionOption.ResponseContentRead);
await client.SendAsync(req, HttpCompletionOption.ResponseContentRead);

第二次发送请求会抛出一条消息：

请求消息已发送。无法发送相同的请求多次留言。

他们是否可以“克隆”请求，以便我可以再次发送？

我的真实代码在HttpRequestMessage上设置的变量多于上例中的变量，如标题和请求方法等变量。

Answer 1

我编写了以下扩展方法来克隆请求。

public static HttpRequestMessage Clone(this HttpRequestMessage req)
{
    HttpRequestMessage clone = new HttpRequestMessage(req.Method, req.RequestUri);

    clone.Content = req.Content;
    clone.Version = req.Version;

    foreach (KeyValuePair<string, object> prop in req.Properties)
    {
        clone.Properties.Add(prop);
    }

    foreach (KeyValuePair<string, IEnumerable<string>> header in req.Headers)
    {
        clone.Headers.TryAddWithoutValidation(header.Key, header.Value);
    }

    return clone;
}

Answer 2

这是对@drahcir提出的扩展方法的改进。改进是确保克隆请求的内容以及请求本身：

public static HttpRequestMessage Clone(this HttpRequestMessage request)
{
    var clone = new HttpRequestMessage(request.Method, request.RequestUri)
    {
        Content = request.Content.Clone(),
        Version = request.Version
    };
    foreach (KeyValuePair<string, object> prop in request.Properties)
    {
        clone.Properties.Add(prop);
    }
    foreach (KeyValuePair<string, IEnumerable<string>> header in request.Headers)
    {
        clone.Headers.TryAddWithoutValidation(header.Key, header.Value);
    }

    return clone;
}

public static HttpContent Clone(this HttpContent content)
{
    if (content == null) return null;

    var ms = new MemoryStream();
    content.CopyToAsync(ms).Wait();
    ms.Position = 0;

    var clone = new StreamContent(ms);
    foreach (KeyValuePair<string, IEnumerable<string>> header in content.Headers)
    {
        clone.Headers.Add(header.Key, header.Value);
    }
    return clone;
}

编辑05/02/18 ：此处的异步版

public static Task<HttpRequestMessage> CloneAsync(this HttpRequestMessage request)
{
    var clone = new HttpRequestMessage(request.Method, request.RequestUri)
    {
        Content = await request.Content.CloneAsync().ConfigureAwait(false),
        Version = request.Version
    };
    foreach (KeyValuePair<string, object> prop in request.Properties)
    {
        clone.Properties.Add(prop);
    }
    foreach (KeyValuePair<string, IEnumerable<string>> header in request.Headers)
    {
        clone.Headers.TryAddWithoutValidation(header.Key, header.Value);
    }

    return clone;
}

public static Task<HttpContent> CloneAsync(this HttpContent content)
{
    if (content == null) return null;

    var ms = new MemoryStream();
    await content.CopyToAsync(ms).ConfigureAwait(false);
    ms.Position = 0;

    var clone = new StreamContent(ms);
    foreach (KeyValuePair<string, IEnumerable<string>> header in content.Headers)
    {
        clone.Headers.Add(header.Key, header.Value);
    }
    return clone;
}

Answer 3

我正在传递Func<HttpRequestMessage>的实例，而不是HttpRequestMessage的实例。函数指向工厂方法，因此每次调用时都会收到一条全新的消息，而不是重新使用。

Answer 4

我有类似的问题并以黑客方式解决它，反思。

感谢开源！通过阅读源代码，结果发现_sendStatus类中存在私有字段HttpRequestMessage，我所做的是在重用请求消息之前将其重置为0。它适用于.NET Core，我希望微软永远不会重命名或删除它。：P

// using System.Reflection;
// using System.Net.Http;
// private const string SEND_STATUS_FIELD_NAME = "_sendStatus";
private void ResetSendStatus(HttpRequestMessage request)
{
    TypeInfo requestType = request.GetType().GetTypeInfo();
    FieldInfo sendStatusField = requestType.GetField(SEND_STATUS_FIELD_NAME, BindingFlags.Instance | BindingFlags.NonPublic);
    if (sendStatusField != null)
        sendStatusField.SetValue(request, 0);
    else
        throw new Exception($"Failed to hack HttpRequestMessage, {SEND_STATUS_FIELD_NAME} doesn't exist.");
}

Answer 5

AFAIK，HttpClient只是'HttpWebRequest'的包装器，它使用流来发送/接收数据，这使得无法重新使用请求，尽管它应该非常简单地克隆它/在循环中制作它。

重新发送HttpRequestMessage - 异常

5 个答案: