技術メモ

const string sendFIleName = @"C:\Users\FileI\source\repos\ClientProject\ClientProject\Test.txt";

byte[] bs = File.ReadAllBytes(sendFIleName);
string base64String = Convert.ToBase64String(bs);

var entity = new FileSample();
entity.fileName = Path.GetFileName(sendFIleName);
entity.fileData = base64String;

var json = JsonConvert.SerializeObject(entity);

const string targetUrl = "https://localhost:7189/Home/Test2";
try
{
using (var client = new HttpClient())
{
var content = new StringContent(json, Encoding.UTF8, "application/json");
var task = client.PostAsync(targetUrl, content);
var result = task.GetAwaiter().GetResult();
MessageBox.Show(result.Content.ReadAsStringAsync().GetAwaiter().GetResult());
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}