SendAsync() returning 422 Unprocessable Entity

Question

I wrote a function using GetAsync() which works fine, but now i'd like to expand on it using SendAsync() instead [for POSTing and sofourth]; however my SendAsync() version is not working as expected, it returns a 422 unprocessible entity. (no IDE atm; sorry for minor typos)

init

var Client = new HttpClient{
    BaseAddress = "https://example.com"
}
Client.DefaultRequestHeaders.UserAgent.ParseAdd("Project/1.0 (blah blah)");

...

Working GetAsync()

public async Task<string> GetResponse(string user, string pass){
    var uri = $"/user/login.json?name={user}&password={pass}";
    var req = await Client.GetAsync(uri);
    return req.Content.Request.Content.ReasStringAsync();
}

non working SendAsync()

public async Task<string> GetResponse(string page, Dictionary<string, string> args){
//assume page = "/user/login.json" and args == {"username", "user"},{"password", "pass"}
try{
    var req = new HttpRequestMessage
    {
        Method = HttpMethod.Get,
        RequestUri = new Uri(page),
        Content = new FormUrlEncodedContent(args),
    }

    var response = await Client.SendAsync(req);
    if(response.IsSuccessStatusCode){
        return await response.Content.ReasStringAsync();
    return null;
}
catch{ return null }
}

note: along with the 422, the response still contains json which states "invalid Auth Token!"

What is GetAsync() doing that SendAsync() is not?

Answer 1

Your Send included content in the BODY of a HTTP GET request.

HTTP GET requests should not have a BODY and there are servers that wont process such requests.

Convert the dictionary to a QueryString and include it in the URI.

public async Task<string> GetResponse(string page, Dictionary<string, string> args) {
    //assume page = "/user/login.json" and args == {"username", "user"},{"password", "pass"}
    try {
        QueryString queryString = QueryString.Create(args);
        var uri = new Uri(page + queryString.ToString());
        var request = new HttpRequestMessage(HttpMethod.Get, uri);
        var response = await Client.SendAsync(request);
        if(response.IsSuccessStatusCode){
            return await response.Content.ReadAsStringAsync();
        return string.Empty;
    } catch { return string.Empty; }
}