Upload/Download/Delete Files From AWS S3 Using .NET Core API

public async Task<byte[]> DownloadFileAsync(string file)
{
	MemoryStream ms = null;

	try
	{
		GetObjectRequest getObjectRequest = new GetObjectRequest
		{
			BucketName = _bucketName,
			Key = file
		};
			
		using (var response = await _awsS3Client.GetObjectAsync(getObjectRequest))
		{
			if (response.HttpStatusCode == HttpStatusCode.OK)
			{
				using (ms = new MemoryStream())
				{
					await response.ResponseStream.CopyToAsync(ms);
				}
			}
		}

		if (ms is null || ms.ToArray().Length < 1)
			throw new FileNotFoundException(string.Format("The document '{0}' is not found", file));

		return ms.ToArray();
	}
	catch (Exception)
	{
		throw;
	}
}

Upload File to S3

Create UploadDocumentToS3 action (POST method) in the AwsS3Controller controller and pass the actual file (type is IFormFile) as parameter. The different results of the UploadDocumentToS3 action method are,

1. If the file is null or empty, then Bad Request(400) error response will be returned to the user.
2. If the file is valid then uploaded the file to S3 (status code is 200).

AwsS3Controller.cs

[HttpPost]
public IActionResult UploadDocumentToS3(IFormFile file)
{
	try
	{
		if (file is null || file.Length <= 0)
			return ReturnMessage("file is required to upload", (int)HttpStatusCode.BadRequest);

		_aws3Services = new Aws3Services(appConfiguration.AwsAccessKey, appConfiguration.AwsSecretAccessKey, appConfiguration.AwsSessionToken, appConfiguration.Region, appConfiguration.BucketName);

		var result = _aws3Services.UploadFileAsync(file);

		return ReturnMessage(string.Empty, (int)HttpStatusCode.Created);
	}
	catch (Exception ex)
	{
		return ReturnMessage(ex.Message, (int)HttpStatusCode.InternalServerError);
	}
}

Create a new function UploadFileAsync in the Aws3Services class. We are going to use TransferUtility for uploading the file to S3.

TransferUtility provides a simple API for uploading content to or downloading content from Amazon S3. Please refer to the link for more details about TransferUtility.

Create TransferUtilityUploadRequest object, which has details of the bucket and the file to be uploaded. Pass the TransferUtilityUploadRequest object to TransferUtility's UploadAsync method to upload the file.

Aws3Services .cs

public async Task<bool> UploadFileAsync(IFormFile file)
{
	try
	{
		using (var newMemoryStream = new MemoryStream())
		{
			file.CopyTo(newMemoryStream);

			var uploadRequest = new TransferUtilityUploadRequest
			{
				InputStream = newMemoryStream,
				Key = file.FileName,
				BucketName = _bucketName,
				ContentType = file.ContentType
			};

			var fileTransferUtility = new TransferUtility(_awsS3Client);

			await fileTransferUtility.UploadAsync(uploadRequest);

			return true;
		}
	}
	catch (Exception)
	{
		throw;
	}
}

Delete Files in the S3

Create DeletetDocumentFromS3 action (DELETE method) in the AwsS3Controller controller and pass the filename as parameter. The different results of the UploadDocumentToS3 action method are,

1. If the filename parameter is null or empty, then Bad Request(400) error response will be returned to the user.
2. If the file is available in the S3 then deleted the file and return the success response (status code is 200).
3. If the file is not available in the S3 then Not Found (404) error response will be returned.

AwsS3Controlle.cs

[HttpDelete("{documentName}")]
public IActionResult DeletetDocumentFromS3(string documentName)
{
	try
	{
		if (string.IsNullOrEmpty(documentName))
			return ReturnMessage("The 'documentName' parameter is required", (int)HttpStatusCode.BadRequest);

		_aws3Services = new Aws3Services(appConfiguration.AwsAccessKey, appConfiguration.AwsSecretAccessKey, appConfiguration.AwsSessionToken, appConfiguration.Region, appConfiguration.BucketName);

		_aws3Services.DeleteFileAsync(documentName);

		return ReturnMessage(string.Format("The document '{0}' is deleted successfully", documentName));
	}
	catch (Exception ex)
	{
		return ValidateException(ex);
	}
}

Create a new function called DeleteFileAsync in the Aws3Services class. File name and the version id (If S3 bucket is enabled versioning, then pass version id else pass empty) are parameter for this function.

We are going to use AmazonS3Client's DeleteObjectAsync method to delete the file in the S3. Please refer to the link for more details about DeleteObjectAsync.

Create DeleteObjectRequest object, which has details of S3 bucket and file name. Pass the DeleteObjectRequest to DeleteObjectAsync method to perform a delete operation.

Note: Before going to delete, we need to check if the file is available or not. If not, then return "Not Found" exception otherwise delete the file. To check the file availability is an optional one. Depending on the use case, we can add this functionality to it.

Aws3Services.cs

[HttpDelete("{documentName}")]
public IActionResult DeletetDocumentFromS3(string documentName)
{
	try
	{
		if (string.IsNullOrEmpty(documentName))
			return ReturnMessage("The 'documentName' parameter is required", (int)HttpStatusCode.BadRequest);

		_aws3Services = new Aws3Services(appConfiguration.AwsAccessKey, appConfiguration.AwsSecretAccessKey, appConfiguration.AwsSessionToken, appConfiguration.Region, appConfiguration.BucketName);

		_aws3Services.DeleteFileAsync(documentName);

		return ReturnMessage(string.Format("The document '{0}' is deleted successfully", documentName));
	}
	catch (Exception ex)
	{
		return ValidateException(ex);
	}
}

private async Task DeleteFile(string fileName, string versionId)
{
	DeleteObjectRequest request = new DeleteObjectRequest
	{
		BucketName = _bucketName,
		Key = fileName
	};

	if (!string.IsNullOrEmpty(versionId))
		request.VersionId = versionId;

	await _awsS3Client.DeleteObjectAsync(request);
}

public bool IsFileExists(string fileName, string versionId)
{
	try
	{
		GetObjectMetadataRequest request = new GetObjectMetadataRequest()
		{
			BucketName = _bucketName,
			Key = fileName,
			VersionId = !string.IsNullOrEmpty(versionId) ? versionId : null
		};

		var response = _awsS3Client.GetObjectMetadataAsync(request).Result;

		return true;
	}
	catch (Exception ex)
	{
		if (ex.InnerException != null && ex.InnerException is AmazonS3Exception awsEx)
		{
			if (string.Equals(awsEx.ErrorCode, "NoSuchBucket"))
				return false;

			else if (string.Equals(awsEx.ErrorCode, "NotFound"))
				return false;
		}

		throw;
	}
}

Test the Web API

Now let's run the application and test the above functionality through Swagger. Swagger (OpenAPI) is a language-agnostic specification for describing REST APIs. Swagger UI offers a web-based UI that provides information about the service, using the generated OpenAPI specification.

To enable the swagger we need to follow the below steps.

Step 1

Install Swashbuckle.AspNetCore package using the NuGet Package Manager

Step 2

Add the Swagger generator to the services collection in the Startup.ConfigureServices method.

public void ConfigureServices(IServiceCollection services)
{
	services
		.AddSingleton<IAppConfiguration, AppConfiguration>()
		.AddSwaggerGen()
		.AddControllers();
}

In the Startup.Configure method, enable the middleware for serving the generated JSON document and the Swagger UI.

app.UseSwagger();

app.UseSwaggerUI(c =>
{
	c.SwaggerEndpoint("/swagger/v1/swagger.json", "DotNet_AWS");
});

Step 3

Hit F5 to run the API locally and To launch the Swagger just hit the http://localhost:<port_number>/swagger/index.html URL in the browser. You will get the below Swagger UI.

Just expand the required operation and click "Try it out" button.

Enter the input values and click the "Execute" button.

Download the File (GET Method)

Upload the File (Post Method)

Delete the File (Delete Method)

Summary

In this article, you learned about how to implement the following functionality using .NET Core Web API.

1. Download the file from S3
2. Upload the file to S3
3. Delete the file in the S3