通过Web客户端返回400错误请求

Question

EDIT. The people who suggested fiddler were great. Turns out the API i was posting to freaked out because the c# application had no user-agent. So adding one to the header fixed it

I'm trying to use c# web client to to post to an api but seem to be running into a wall. I'm trying to use this code to post json to an api however all i get is 400 bad request and i'm not sure what is going on.

output = "{ \"id\": \"xxxxxx\", \"company\": \"test\", \"fname\": \"test\", \"lname\": \"test\", \"member_level\": \"Member\",\"status\": \"active\"}";

using (var client = new WebClient())
{
     client.Headers.Add("token", "validtoken");
     client.Headers.Add("Content-Type", "application/json");
     client.UploadString(new Uri("url"), "POST", output);
}

I was able to use powershell to successfully post using a webrequest so i know the url and auth token are valid. but for whatever reason i can't get c# to post correctly. This is the working powershell command

curl url -Method POST -H @{"token" = "token"} -ContentType "application/json" -Body '{ "id": "xxxxxx", "company": "test", "fname": "test", "lname": "test", "member_level": "test","status": "active"}'

Answer 1

instead of

client.UploadString(new Uri("url"), "POST", output);

use

client.UploadData(url, "POST", Encoding.UTF8.GetBytes(output));

Answer 2

Just use built-in features of C# to keep code clean. When possible create classes that describe contracts for API communication. Use HttpClient when there is no need for low-level control. HttpClient can send these objects as JSON and you usually do not need to care about serialization issues.

This code should make a POST after you replaced url parts. Since you do not send the TOKEN this should raise a 401 error - you are not authorized. Add your valid token, delete the comment and this request should work.

using System;
using System.Collections.Generic;
using System.Net.Http;

public class User
{
    public string Id { get; set; }
    public string Company { get; set; }
    public string FName { get; set; }
    public string LName { get; set; }
    public string MemberLevel { get; set; }
    public string Status { get; set; }
}

class Program
{
    static void CreateUser(User user)
    {
        using (var client = new HttpClient())
        {
            // posts to https://yourawesomewebsite.com/api/users
            client.BaseAddress = new Uri("https://yourawesomewebsite.com");             
            //client.Headers.Add("token", "validtoken");
            HttpResponseMessage response = client.PostAsJson("api/users", user);
            response.EnsureSuccessStatusCode();
        }
    }

    static void Main()
    {     
        // Create a new user
        User user = new User
        { 
            Id = "xxxxx",
            Company = "Test",
            FName = "Test",
            LName = "Test",
            MemberLevel = "Test",
            Status = "Active"
        };

        CreateUser(user);
    }
}

Reference

• Calling a Web API From a .NET Client (C#)
• HttpClient, the best of both worlds