C# HttpClient POST Request with Custom Headers sends incorrect Content-Type header field

Question

I have sample code written in C# in Visual Studio on Windows 10 that attempts to send a POST request with custom headers to a service running at http://localhost:9998 which is failing.

When I look at the request the Content-Type header field is being sent as ContentType (no hyphen).

httpRequestMessage:Method: POST, RequestUri: 'http://localhost:9998/', Version: 1.1, Content: System.Net.Http.ByteArrayContent, Headers: {
ContentType: application/vnd.com.documents4j.any-msword Accept: application/pdf Converter-Job-Priority: 1000 }response:StatusCode: 500, ReasonPhrase: 'Request failed.', Version: 1.1, Content: System.Net.Http.StreamContent, Headers: { Connection: close Date: Sat, 10 Apr 2021 22:39:24 GMT Content-Length: 1031 Content-Type: text/html; charset=ISO-8859-1 }Press any key to continue. . .

I am wondering if this is the cause of the problem?

I have code written in C# that uses RestSharp and that sends Content-Type correctly and returns a successful result. I have code written in Java that also sends Content-Type correctly and returns a successful result.

Sample Code 1 [Problem sending Content-Type as ContentType]

using System;
using System.Net;
using System.IO;
using System.Net.Http;

namespace HttpPOST10
{
    class Program
    {
        public static string MyUri { get; private set; }
        static void Main(string[] args)
        {
//            string url = "http://localhost:9998";
            string url = "http://localhost:8888"; // Fiddler
            Uri myUri = new Uri(url);
            string srcFilename = @"C:\temp2\Sample.doc";
            string destFileName = @"C:\temp3\Sample-HttpPOST10.pdf";

            UploadFile(url, srcFilename, destFileName);
        }
        private static bool UploadFile(string url, string srcFilename, string destFileName)
        {
            HttpClient httpClient = new HttpClient();
            byte[] data;
            data = File.ReadAllBytes(srcFilename);
            var httpRequestMessage = new HttpRequestMessage
            {
                Method = HttpMethod.Post,
                RequestUri = new Uri(url),
                Headers = {
                    { HttpRequestHeader.ContentType.ToString(), "application/vnd.com.documents4j.any-msword" },
                    { HttpRequestHeader.Accept.ToString(), "application/pdf" },
                    { "Converter-Job-Priority", "1000" },
//                    {"User-Agent",  "RestSharp/106.11.8.0" }
                },
                Content = new ByteArrayContent(data)
            };
            Console.Write("httpRequestMessage:" + httpRequestMessage);
            var response = httpClient.SendAsync(httpRequestMessage).Result;
            Console.Write("response:" + response);

            return true;
        }
    }
}

Answer 1

Thank you Jimi - have now got a successful response.

httpRequestMessage:Method: POST, RequestUri: 'http://localhost:9998/', Version: 1.1, Content: System.Net.Http.ByteArrayContent, Headers: {
ContentType: application/vnd.com.documents4j.any-msword Accept: application/pdf Converter-Job-Priority: 1000 Content-Type: application/vnd.com.documents4j.any-msword }response:StatusCode: 200, ReasonPhrase: 'OK', Version: 1.1, Content: System.Net.Http.StreamContent, Headers: { Vary: Accept-Encoding
Transfer-Encoding: chunked Date: Mon, 12 Apr 2021 03:04:14 GMT
Content-Type: application/pdf

The code change was:

private static bool UploadFile(string url, string srcFilename, string destFileName)
{
    HttpClient httpClient = new HttpClient();
    byte[] data;
    data = File.ReadAllBytes(srcFilename);

    HttpContent content = new ByteArrayContent(data);
    content.Headers.Add("Content-Type", "application/vnd.com.documents4j.any-msword");

    var httpRequestMessage = new HttpRequestMessage
    {
        Method = HttpMethod.Post,
        RequestUri = new Uri(url),
        Headers = {
            { HttpRequestHeader.ContentType.ToString(), "application/vnd.com.documents4j.any-msword" },
            { HttpRequestHeader.Accept.ToString(), "application/pdf" },
            { "Converter-Job-Priority", "1000" },
        },
        Content = content
    };

    Console.Write("httpRequestMessage:" + httpRequestMessage);
                var response = httpClient.SendAsync(httpRequestMessage).Result;
    Console.Write("response:" + response);

    return true;
}