我有一个异步函数,用于向服务器发送请求消息。功能如下:
class http
{
public async Task<string> HttpRequest()
{
HttpRequestMessage request = GetHttpRequestMessage();
var str1 = await ExecuteRequest(request);
return str1;
}
private async Task<string> ExecuteRequest(HttpRequestMessage request)
{
string result = string.Empty;
try
{
using (HttpClient client = new HttpClient())
{
var responses = await client.SendAsync(request);
responses.EnsureSuccessStatusCode();
result = await responses.Content.ReadAsStringAsync();
}
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
return result;
}
private const string _DataTypeJson = @"application/json";
private HttpRequestMessage GetHttpRequestMessage()
{
Dictionary<string, string> headers = GetHeadersUsedForToken();
string str = "https://test.com//tokens";
Uri uri = new Uri(str);
HttpRequestMessage request = new HttpRequestMessage
{
RequestUri = uri,
};
if (null != headers)
{
foreach (string key in headers.Keys)
{
request.Headers.Add(key, headers[key]);
}
}
// Hard code Accpt type is Json
request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue(_DataTypeJson));
request.Method = HttpMethod.Get;
return request;
}
private Dictionary<string, string> GetHeadersUsedForToken()
{
return new Dictionary<string, string>
{
{ "id", "abc" },
{ "secret", "***" }
};
}
}
此功能在控制台项目中运行正常,但当我尝试将此功能移至WCF服务,并尝试在服务中调用HttpRequest()
功能时,
[ServiceContract]
public interface IService1
{
[OperationContract]
Task<string> GetData();
}
public class Service1 : IService1
{
public Task<string> GetData()
{
http test = new http();
return test.HttpRequest();
}
}
抛出异常:
Message An error occurred while sending the request.
InnerException {"The underlying connection was closed: An unexpected error occurred on a send."}
答案 0 :(得分:1)
使用async / await,你需要让它始终保持异步。
使服务成为基于任务的异步服务
[ServiceContract]
public interface IService1 {
[OperationContract]
Task<string> GetData();
}
通过这种方式,可以使其余的代码始终保持异步。
public class http {
public async Task<string> HttpRequestAsync() {
var request = GetHttpRequestMessage();
string str1 = await ExecuteRequest(request);
Console.WriteLine(str1);
return str1;
}
//...code removed for brevity as they are already Task-based
}
现在应该允许在服务实现中使用该函数
public class Service1 : IService1 {
public Task<string> GetData() {
http test = new http();
return test.HttpRequestAsync();
}
}
在原始示例中,提供的代码是混合异步和阻塞调用.Result
,这可能会导致死锁
参考Async/Await - Best Practices in Asynchronous Programming
我还建议让HttpClient
静态并重用它,而不是创建多个实例并处理它们。
更新:
另一种可能性是被调用的URL是HTTPS。
在通过HttpClient
//Handle TLS protocols
System.Net.ServicePointManager.SecurityProtocol =
System.Net.SecurityProtocolType.Tls
| System.Net.SecurityProtocolType.Tls11
| System.Net.SecurityProtocolType.Tls12;