我试图设置一个HttpClient对象的Content-Type头作为我调用的API所要求的。

我试着像下面这样设置内容类型:

using (var httpClient = new HttpClient())
{
    httpClient.BaseAddress = new Uri("http://example.com/");
    httpClient.DefaultRequestHeaders.Add("Accept", "application/json");
    httpClient.DefaultRequestHeaders.Add("Content-Type", "application/json");
    // ...
}

它允许我添加Accept头,但当我尝试添加Content-Type时,它会抛出以下异常:

误用头名称。确保请求头与一起使用 HttpRequestMessage,带有HttpResponseMessage的响应头,以及 内容头与HttpContent对象。

如何在HttpClient请求中设置内容类型报头?


当前回答

我用RestSharp得到了答案:

        private async Task<string> GetAccessTokenAsync()
        {
            var client = new RestClient(_baseURL);

            var request = new RestRequest("auth/v1/login", Method.POST, DataFormat.Json);

            request.AddHeader("Content-Type", "application/json");
            request.AddHeader("x-api-key", _apiKey);
            request.AddHeader("Accept-Language", "br");
            request.AddHeader("x-client-tenant", "1");
        
            ...
        }

这对我很管用。

其他回答

尝试使用HttpClientFactory

services.AddSingleton<WebRequestXXX>()
        .AddHttpClient<WebRequestXXX>("ClientX", config =>
        {
           config.BaseAddress = new System.Uri("https://jsonplaceholder.typicode.com");
           config.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
           config.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "application/json; charset=utf-8");
        });

======================

public class WebRequestXXXX
{
    private readonly IHttpClientFactory _httpClientFactory;

    public WebRequestXXXX(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory;
    }

    public List<Posts> GetAllPosts()
    {
        using (var _client = _httpClientFactory.CreateClient("ClientX"))
        {
            var response = _client.GetAsync("/posts").Result;

            if (response.IsSuccessStatusCode)
            {
                var itemString = response.Content.ReadAsStringAsync().Result;
                var itemJson = System.Text.Json.JsonSerializer.Deserialize<List<Posts>>(itemString, 
                    new System.Text.Json.JsonSerializerOptions 
                    {
                        PropertyNameCaseInsensitive = true
                    });

                return itemJson;
            }
            else
            {
                return new List<Posts>();
            }
        }
    }
}
var content = new JsonContent();
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
content.Headers.ContentType.Parameters.Add(new NameValueHeaderValue("charset", "utf-8"));
content.Headers.ContentType.Parameters.Add(new NameValueHeaderValue("IEEE754Compatible", "true"));

这就是你所需要的。

使用Newtonsoft。Json,如果你需要一个内容为Json字符串。

public class JsonContent : HttpContent
   {
    private readonly MemoryStream _stream = new MemoryStream();
    ~JsonContent()
    {
        _stream.Dispose();
    }

    public JsonContent(object value)
    {
        Headers.ContentType = new MediaTypeHeaderValue("application/json");
        using (var contexStream = new MemoryStream())
        using (var jw = new JsonTextWriter(new StreamWriter(contexStream)) { Formatting = Formatting.Indented })
        {
            var serializer = new JsonSerializer();
            serializer.Serialize(jw, value);
            jw.Flush();
            contexStream.Position = 0;
            contexStream.WriteTo(_stream);
        }
        _stream.Position = 0;

    }

    private JsonContent(string content)
    {
        Headers.ContentType = new MediaTypeHeaderValue("application/json");
        using (var contexStream = new MemoryStream())
        using (var sw = new StreamWriter(contexStream))
        {
            sw.Write(content);
            sw.Flush();
            contexStream.Position = 0;
            contexStream.WriteTo(_stream);
        }
        _stream.Position = 0;
    }

    protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)
    {
        return _stream.CopyToAsync(stream);
    }

    protected override bool TryComputeLength(out long length)
    {
        length = _stream.Length;
        return true;
    }

    public static HttpContent FromFile(string filepath)
    {
        var content = File.ReadAllText(filepath);
        return new JsonContent(content);
    }
    public string ToJsonString()
    {
        return Encoding.ASCII.GetString(_stream.GetBuffer(), 0, _stream.GetBuffer().Length).Trim();
    }
}

你可以用这个,它会工作!

HttpRequestMessage msg = new HttpRequestMessage(HttpMethod.Get,"URL");
msg.Content = new StringContent(string.Empty, Encoding.UTF8, "application/json");

HttpResponseMessage response = await _httpClient.SendAsync(msg);
response.EnsureSuccessStatusCode();

string json = await response.Content.ReadAsStringAsync();

诀窍在于你可以设置各种标题,比如:

HttpRequestMessage request = new HttpRequestMessage();
request.Headers.Add("Accept-Language", "en"); //works OK

但不是任何标题。例如:

request.Headers.Add("Content-Type", "application/json");//wrong

将引发运行时异常“误用头名”。这似乎是可行的:

request.Headers.Add(
   HttpRequestHeader.ContentType.ToString(), //useless
   "application/json"
);

但是这样会产生一个名为ContentType的无用头,没有连字符。标头名称不区分大小写,但对连字符非常敏感。

解决方案是在将body添加到http请求的Content部分时声明body的编码和类型:

string Body = "...";
request.Content =
   new StringContent(Body, Encoding.UTF8, "application/json");

只有这样,适用的http头才会自动添加到请求中:

Content-Type: application/json; charset=utf-8

在一台没有代理服务器的机器上,使用Fiddler很难发现这一点。Visual Studio曾经有一个网络工具,你可以在其中检查所有的头文件,但只能在版本2015,而不是在更新的版本2017或2022。如果使用调试器检查请求。头文件,你不会发现由StringContent()自动添加的头文件。

对于我的场景,第三方API正在创建HttpRequestMessage,因此我无法使用投票最多的答案来解决这个问题。我不喜欢干扰反射的想法所以其他答案也不成立。

相反,我从AndroidMessageHandler扩展,并使用这个新类作为HttpClient的参数。AndroidMessageHandler包含SendAsync方法,可以在HttpRequestMessage对象发送之前重写该方法。如果您没有访问Android Xamarin库的权限,您可以使用HttpMessageHandler来解决一些问题。

public class XamarinHttpMessageHandler : global::Xamarin.Android.Net.AndroidMessageHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // Here I make check that I'm only modifying a specific request
        // and not all of them.
        if (request.RequestUri != null && request.RequestUri.AbsolutePath.EndsWith("download") && request.Content != null)
        {
            request.Content.Headers.Add("Content-Type", "text/plain");
        }
        return base.SendAsync(request, cancellationToken);
    }
}

然后使用:

var client = new HttpClient(new XamarinHttpMessageHandler());