Asp.Net Web Api File Upload And Download Via Web Api Complete Guide

ASP.NET Web API File Upload and Download via Web API

ASP.NET Web API is a framework that facilitates the construction of HTTP-based services for connecting clients like browsers, phones, and tablets to the data of your web application or service. It's part of the broad .NET technology suite and provides robust functionality for handling various types of data, including file uploads and downloads.

File Upload in ASP.NET Web API

Uploading files over HTTP can be quite challenging due to the limitations and quirks associated with handling binary data. ASP.NET Web API simplifies this process with built-in functionalities specifically designed to manage file uploads efficiently.

Enabling Multipart Support

In ASP.NET Web API, file uploads often use multipart/form-data encoding. To handle such requests, you need to make sure your API controller is set up properly to parse multipart content.

• MultipartMemoryStreamProvider: This is used for small files and stores uploaded files temporarily in memory.
• MultipartFormDataStreamProvider: Suitable for larger files, it stores files on disk.

public class FileUploadController : ApiController
{
    [HttpPost]
    [Route("api/uploadfile")]
    public async Task<IHttpActionResult> Upload()
    {
        if (!Request.Content.IsMimeMultipartContent())
        {
            return BadRequest("Unsupported Media Type.");
        }

        var streamProvider = new MultipartFormDataStreamProvider("UploadedFiles");
        await Request.Content.ReadAsMultipartAsync(streamProvider);

        foreach (var fileData in streamProvider.FileData)
        {
            string fileName = Path.GetFileName(fileData.LocalFileName);
            // Additional file validation and processing can be added here
        }

        return Ok(streamProvider.FileData.Select(fd => fd.LocalFileName));
    }
}

Handling Large Files

For large files, consider using MultipartFileStreamProvider. This provider allows you to upload chunks of the file at a time, reducing memory consumption and improving efficiency.

public class MultipartFileStreamProvider : MultipartStreamProvider
{
    private readonly string _rootPath;

    public MultipartFileStreamProvider(string rootPath)
    {
        if (string.IsNullOrWhiteSpace(rootPath))
        {
            throw new ArgumentException("File root path must not be null.", nameof(rootPath));
        }

        this._rootPath = rootPath;
    }

    public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
    {
        var name = headers.ContentDisposition.FileName.Trim('"');
        name = Path.ChangeExtension(Path.GetFileNameWithoutExtension(Path.GetRandomFileName()), Path.GetExtension(name));
        return new FileStream(Path.Combine(this._rootPath, name), FileMode.Create);
    }
    
    public override string ContentDispositionHeaderValueFileName
    {
        get { return "attachment"; }
        set { /* No action */ }
    }

    public override string ContentTypeHeaderValue
    {
        get { return "application/octet-stream"; }
        set { /* No action */ }
    }
}

[HttpPost]
[Route("api/UploadLargeFile")]
public async Task<IHttpActionResult> UploadLargeFile()
{
    if (!Request.Content.IsMimeMultipartContent())
    {
        return BadRequest("Unsupported Media Type.");
    }

    var streamProvider = new MultipartFileStreamProvider("UploadedFiles");
    await Request.Content.ReadAsMultipartAsync(streamProvider);

    foreach (var fileData in streamProvider.FileData)
    {
        string fileName = Path.GetFileName(fileData.LocalFileName);
        // Process each file here...
    }

    return Ok(new { success = true });
}

File Download from ASP.NET Web API

Downloading files involves sending file content along with HTTP response headers from the server back to the client. The Web API response message can be configured to carry the file name and other relevant details.

Returning Binary Content

This example shows how to send a file as binary content. Ensure appropriate MIME type is set in the response header.

public class FileDownloadController : ApiController
{
    [HttpGet]
    [Route("api/DownloadFile")]
    public IHttpActionResult DownloadFile(string name)
    {
        string filePath = $"UploadedFiles/{name}";
        if (!System.IO.File.Exists(filePath))
        {
            return NotFound();
        }

        var fileInfo = new FileInfo(filePath);
        var stream = fileInfo.OpenRead();

        return new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StreamContent(stream)
            {
                Headers =
                {
                    ContentType = new MediaTypeHeaderValue(MimeMapping.GetMimeMapping(fileInfo.Name)),
                    ContentLength = fileInfo.Length,
                    ContentDisposition = new ContentDispositionHeaderValue("attachment")
                    {
                        FileName = fileInfo.Name
                    }
                }
            }
        };
    }
}

Error Handling and Validation

Implementing comprehensive error handling and input validation is crucial to ensure a smooth and secure file upload/download operation. Validate file types, sizes, and names to prevent any malicious activities.

• Content-Type: Check if the uploaded file has an appropriate MIME type.
• File Size: Set maximum file size limits to avoid excessive memory allocation.
• File Name: Sanitize file names to prevent potential directory traversal attacks.

public class FileUploadController : ApiController
{
    private const int MaxFileSize = 1048576; // 1MB

    [HttpPost]
    [Route("api.UploadWithValidation")]
    public async Task<IHttpActionResult> UploadWithValidation()
    {
        if (!Request.Content.IsMimeMultipartContent())
        {
            return BadRequest("Unsupported media type.");
        }

        var multipartStreamProvider = new MultiPartFormDataStreamProvider(filePath);

        try
        {
            await Request.Content.ReadAsMultipartAsync(multipartStreamProvider);
            
            foreach (var fileData in multipartStreamProvider.FileData)
            {
                string fileName = Path.GetFileName(fileData.Headers.ContentDisposition.FileName.Trim('"'));
                
                if(fileData.Headers.ContentType.MediaType != "image/jpeg" && 
                   fileData.Headers.ContentType.MediaType != "application/pdf" ||
                   fileData.Headers.ContentLength.Value > MaxFileSize)
                {
                    return BadRequest("File type or size not supported.");
                }

                // Proceed with further file processing...
            }
        }
        catch (Exception e)
        {
            return InternalServerError(e);
        }

        return Ok("Files uploaded successfully.");
    }
}

Security Considerations

Always prioritize security when dealing with file uploads and downloads:

• Authentication & Authorization: Secure endpoints by implementing authentication mechanisms. Ensure only authorized users can upload or download files.
• Antivirus Scanning: Integrate server-side antivirus scanning to check files for malware before they're processed or stored.
• Rate Limiting: Prevent abuse and DOS attacks by limiting the number of uploads/downloads per user/IP.
• Audit Logs: Maintain audit logs to track who uploaded/downloaded what files when.
• Storage Management: Store uploaded files outside of the web application root to prevent direct access via HTTP.

Conclusion

ASP.NET Web API offers powerful tools and methods for managing file uploads and downloads. Through proper implementation, including handling multipart content, validating inputs, and addressing security concerns, developers can create reliable and secure services for file operations within their applications.

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