Asp.Net核心HttpClient获得响应411长度所需的错误

Question

我正在尝试使用C＃HttpClient创建一个将一些数据发布到API端点的服务。代码如下。

public class HttpClientService : IHttpClientService
{
    static HttpClient client = new HttpClient();

    public HttpClientService()
    {
        client.BaseAddress = new Uri("http://xx.xx.xx.xx/");
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    }

    public async Task<Uri> MakeLogEntry(CnsLog log)
    {
        HttpResponseMessage response = await client.PostAsJsonAsync("api/logs", log);
        return response.Headers.Location;
    }

}

问题是终点返回错误411 Length Required。我发现这是因为我的请求没有内容长度标头集，我在使用Fiddler检查请求时发现这是真的。

我试图在构造函数中设置客户端上的内容长度标头，但之后代码不编译。我被困住了，不胜感激任何帮助。谢谢

Answer 1

您不希望在客户端上设置Content-Length标头，尤其是因为它是静态实例。您想根据个别请求进行设置。

PostAsJsonAsync是一个很好的快捷方式，从poco构建HttpContent，从该内容构建HttpRequestMessage，并发送POST请求。方便，但所有抽象都没有给你机会设置请求级标头。所以，你需要做更多的工作来构建/发送请求：

var json = JsonConvert.SerializeObject(log);
var content = new StringContent(json, Encoding.UTF8, "application/json");
content.Headers.ContentLength = json.Length;
var response = await client.PostAsync("api/logs", content);

Answer 2

或者你可以使用HttpWebRequest。

byte[] postBytes = Encoding.ASCII.GetBytes(log);
request.ContentLength = postBytes.Length;

HttpWebRequest的示例如下：

ASCIIEncoding encoder = new ASCIIEncoding();
byte[] data = encoder.GetBytes(serializedObject); // a json object, or xml, whatever...

HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.Method = "POST";
request.ContentType = "application/json";
request.ContentLength = data.Length;
request.Expect = "application/json";

request.GetRequestStream().Write(data, 0, data.Length);

HttpWebResponse response = request.GetResponse() as HttpWebResponse;