HTTP for images between client and server sends empty stream - rest

Question

I am trying to send a stream (containing an image file) from a WASM client to a backend .NET Core 5 server. In the WASM app, I start with a MemoryStream that contains the file data. In order to send the data contained in this MemoryStream using HttpClient.PostAsync, I seem to have to convert it to a StreamContent object:
StreamContent streamContent = new StreamContent(imageMemoryStream);
I use the debugger to verify that the length of the content of streamContent is not zero at this point. So far so good.
I then use HttpClient.PostAsync to send this stream to the server:
var response = await Http.PostAsync("api/HttpStreamReceiver", streamContent);
On the server side, I have a controller that receives HTTP messages:
[Route("api/[controller]")]
[ApiController]
public class HttpStreamReceiverController : ControllerBase
{
[HttpPost]
public async Task<ActionResult> Get()
{
Stream imageStream;
try
{
imageStream = Request.Body;
}
catch (Exception)
{
return new BadRequestObjectResult("Error saving file");
}
}
}
Here, it seems that Request.Body is empty. Trying to evaluate the length of either Request.Body or of imageStream on the server side results in a System.NotSupportedException, and
await imageStream.ReadAsync(buffer);
leaves buffer blank. What am I doing wrong here?

Answer 1

The image file cannot be transmitted through the body unless it is serialized. I suggest you use MultipartFormDataContent to pass the file.
This is an example.
class Program
{
static async Task Main(string[] args)
{
string filePath = #"D:\upload\images\1.png";
HttpClient _httpClient = new HttpClient();
string _url = "https://localhost:44324/api/HttpStreamReceiver/";
if (string.IsNullOrWhiteSpace(filePath))
{
throw new ArgumentNullException(nameof(filePath));
}
if (!File.Exists(filePath))
{
throw new FileNotFoundException($"File [{filePath}] not found.");
}
//Create form
using var form = new MultipartFormDataContent();
FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.ReadWrite);
byte[] buffur = new byte[fs.Length];
BinaryWriter bw = new BinaryWriter(fs);
bw.Write(buffur);
//var bytefile = AuthGetFileData(filePath);
var fileContent = new ByteArrayContent(buffur);
fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("multipart/form-data");
form.Add(fileContent, "image", Path.GetFileName(filePath));
//the other data in form
var response = await _httpClient.PostAsync($"{_url}", form);
response.EnsureSuccessStatusCode();
var responseContent = await response.Content.ReadAsStringAsync();
bw.Close();
}
}
Web api.
[Route("api/[controller]")]
[ApiController]
public class HttpStreamReceiverController: ControllerBase
{
[HttpPost]
public async Task<ActionResult> Get(IFormFile image)
{
//...
return Ok("get");
}
}
Result: