Why do I get a 404 trying to post a large file to a Core Web API

Question

I am very new to file transfer between HttpClient and a Web API, so please excuse any ignorance and guesswork in my code. I have been trying to post a file created with System.IO.Compression.ZipFile to my web API now for about a day, and always I get a 404 response. If I post with an empty stream, the API action method is invoked, so I know the 404 is due to content and not the URI.

This method is in the client WPF application that attempts to post the file:

public async Task PostDirAsync(string localDirPath, string serverDir)
{
    var sourcePath = Path.Combine("Temp", Guid.NewGuid() + ".zip");
    ZipFile.CreateFromDirectory(localDirPath, sourcePath, CompressionLevel.Fastest, true);
    StreamContent streamContent;
    using (var fs = File.Open(sourcePath, FileMode.Open))
    {
        var outStream = new MemoryStream();
        await fs.CopyToAsync(outStream);
        outStream.Position = 0;
        streamContent = new StreamContent(outStream);
    }
    streamContent.Headers.Add("Content-Type", "application/octet-stream");
    var resp = await _client.PostAsync("api/File/PostDir?serverPath={WebUtility.UrlEncode(serverDir)}", streamContent);
}

And this is the action method in the Web API that receives the post, but only if I don't do the outStream.Position = 0; before attempting to post:

[HttpPost("PostDir")]
[DisableRequestSizeLimit]
public async Task<IActionResult> PostDir(string serverPath)
{           
    var zipName = Path.Combine(_config["QuickDrive:TempDir"], Guid.NewGuid() + ".zip");
    using (var ms = new MemoryStream())
    using (var fileStream = System.IO.File.Create(zipName))
    {
        await Request.Body.CopyToAsync(ms);
        ms.Position = 0;
        await ms.CopyToAsync(fileStream);
    }
    return Ok();
}

The action method is invoked and runs without error with an empty stream, but is pretty useless as it writes an empty file. What am I doing wrong?

Answer 1

As mentioned in the comments, your first problem was that the Stream instances involved in the file copying were not being reset using Stream.Position = 0 . I know you've made these changes already, but I just want to emphasise that this is a two-part solution.

So, the second part:

In your example code, you've added the [DisableRequestSizeLimit] annotation in order to bypass the default ASP.NET Core 2.0+ Kestrel request limits. However, there's also a limit that's imposed by IIS, which is 30MB by default. When this size limit is exceeded, IIS itself generates a 404 response, which is what you're seeing.

This answer explains how to change this limit using a custom Web.config (included below for completeness):

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <security>
      <requestFiltering>
        <!-- 1 GB -->
        <requestLimits maxAllowedContentLength="1073741824" />
      </requestFiltering>
    </security>
  </system.webServer>
</configuration>

---

As somewhat of a side note:

Unless you have a specific reason to do so, you can avoid the use of MemoryStream in your code and just pass fs directly into new StreamContent(...) . You can do something similar with the Request.Body stream and copy that directly into the output FileStream . This would end up with:

public async Task PostDirAsync(string localDirPath, string serverDir)
{
    var sourcePath = Path.Combine("Temp", Guid.NewGuid() + ".zip");
    ZipFile.CreateFromDirectory(localDirPath, sourcePath, CompressionLevel.Fastest, true);

    var streamContent = new StreamContent(File.Open(sourcePath, FileMode.Open));
    streamContent.Headers.Add("Content-Type", "application/octet-stream");
    var resp = await _client.PostAsync("api/File/PostDir?serverPath={WebUtility.UrlEncode(serverDir)}", streamContent);
}

And with:

[HttpPost("PostDir")]
[DisableRequestSizeLimit]
public async Task<IActionResult> PostDir(string serverPath)
{           
    var zipName = Path.Combine(_config["QuickDrive:TempDir"], Guid.NewGuid() + ".zip");
    using (var fileStream = System.IO.File.Create(zipName))
        await Request.Body.CopyToAsync(fileStream );
    return Ok();
}