Amazon S3 examples using SDK for .NET (v4)

Create a presigned POST URL.

    /// <summary>
    /// Create a presigned POST URL with conditions.
    /// </summary>
    /// <param name="s3Client">The Amazon S3 client.</param>
    /// <param name="bucketName">The name of the bucket.</param>
    /// <param name="objectKey">The object key (path) where the uploaded file will be stored.</param>
    /// <param name="expires">When the presigned URL expires.</param>
    /// <param name="fields">Dictionary of fields to add to the form.</param>
    /// <param name="conditions">List of conditions to apply.</param>
    /// <returns>A CreatePresignedPostResponse object with URL and form fields.</returns>
    public async Task<CreatePresignedPostResponse> CreatePresignedPostAsync(
        IAmazonS3 s3Client,
        string bucketName,
        string objectKey,
        DateTime expires,
        Dictionary<string, string>? fields = null,
        List<S3PostCondition>? conditions = null)
    {
        var request = new CreatePresignedPostRequest
        {
            BucketName = bucketName,
            Key = objectKey,
            Expires = expires
        };

        // Add custom fields if provided
        if (fields != null)
        {
            foreach (var field in fields)
            {
                request.Fields.Add(field.Key, field.Value);
            }
        }

        // Add conditions if provided
        if (conditions != null)
        {
            foreach (var condition in conditions)
            {
                request.Conditions.Add(condition);
            }
        }

        return await s3Client.CreatePresignedPostAsync(request);
    }

Create and use presigned POST URLs for direct browser uploads.

/// <summary>
/// Scenario demonstrating the complete workflow for presigned POST URLs:
/// 1. Create an S3 bucket
/// 2. Create a presigned POST URL
/// 3. Upload a file using the presigned POST URL
/// 4. Clean up resources
/// </summary>
public class CreatePresignedPostBasics
{
    public static ILogger<CreatePresignedPostBasics> _logger = null!;
    public static S3Wrapper _s3Wrapper = null!;
    public static UiMethods _uiMethods = null!;
    public static IHttpClientFactory _httpClientFactory = null!;
    public static bool _isInteractive = true;
    public static string? _bucketName;
    public static string? _objectKey;

    /// <summary>
    /// Set up the services and logging.
    /// </summary>
    /// <param name="host">The IHost instance.</param>
    public static void SetUpServices(IHost host)
    {
        var loggerFactory = LoggerFactory.Create(builder =>
        {
            builder.AddConsole();
        });
        _logger = new Logger<CreatePresignedPostBasics>(loggerFactory);

        _s3Wrapper = host.Services.GetRequiredService<S3Wrapper>();
        _httpClientFactory = host.Services.GetRequiredService<IHttpClientFactory>();
        _uiMethods = new UiMethods();
    }

    /// <summary>
    /// Perform the actions defined for the Amazon S3 Presigned POST scenario.
    /// </summary>
    /// <param name="args">Command line arguments.</param>
    /// <returns>A Task object.</returns>
    public static async Task Main(string[] args)
    {
        _isInteractive = !args.Contains("--non-interactive");

        // Set up dependency injection for Amazon S3
        using var host = Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder(args)
            .ConfigureServices((_, services) =>
                services.AddAWSService<IAmazonS3>()
                    .AddTransient<S3Wrapper>()
                    .AddHttpClient()
            )
            .Build();

        SetUpServices(host);

        try
        {
            // Display overview
            _uiMethods.DisplayOverview();
            _uiMethods.PressEnter(_isInteractive);

            // Step 1: Create bucket
            await CreateBucketAsync();
            _uiMethods.PressEnter(_isInteractive);

            // Step 2: Create presigned URL
            _uiMethods.DisplayTitle("Step 2: Create presigned POST URL");
            var response = await CreatePresignedPostAsync();
            _uiMethods.PressEnter(_isInteractive);

            // Step 3: Display URL and fields
            _uiMethods.DisplayTitle("Step 3: Presigned POST URL details");
            DisplayPresignedPostFields(response);
            _uiMethods.PressEnter(_isInteractive);

            // Step 4: Upload file
            _uiMethods.DisplayTitle("Step 4: Upload test file using presigned POST URL");
            await UploadFileAsync(response);
            _uiMethods.PressEnter(_isInteractive);

            // Step 5: Verify file exists
            await VerifyFileExistsAsync();
            _uiMethods.PressEnter(_isInteractive);

            // Step 6: Cleanup
            _uiMethods.DisplayTitle("Step 6: Clean up resources");
            await CleanupAsync();

            _uiMethods.DisplayTitle("S3 Presigned POST Scenario completed successfully!");
            _uiMethods.PressEnter(_isInteractive);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error in scenario");
            Console.WriteLine($"Error: {ex.Message}");

            // Attempt cleanup if there was an error
            if (!string.IsNullOrEmpty(_bucketName))
            {
                _uiMethods.DisplayTitle("Cleaning up resources after error");
                await _s3Wrapper.DeleteBucketAsync(_bucketName);
                Console.WriteLine($"Cleaned up bucket: {_bucketName}");
            }
        }
    }

    /// <summary>
    /// Create an S3 bucket for the scenario.
    /// </summary>
    private static async Task CreateBucketAsync()
    {
        _uiMethods.DisplayTitle("Step 1: Create an S3 bucket");

        // Generate a default bucket name for the scenario
        var defaultBucketName = $"presigned-post-demo-{DateTime.Now:yyyyMMddHHmmss}".ToLower();

        // Prompt user for bucket name or use default in non-interactive mode
        _bucketName = _uiMethods.GetUserInput(
            $"Enter S3 bucket name (or press Enter for '{defaultBucketName}'): ",
            defaultBucketName,
            _isInteractive);

        // Basic validation to ensure bucket name is not empty
        if (string.IsNullOrWhiteSpace(_bucketName))
        {
            _bucketName = defaultBucketName;
        }

        Console.WriteLine($"Creating bucket: {_bucketName}");

        await _s3Wrapper.CreateBucketAsync(_bucketName);

        Console.WriteLine($"Successfully created bucket: {_bucketName}");
    }


    /// <summary>
    /// Create a presigned POST URL.
    /// </summary>
    private static async Task<CreatePresignedPostResponse> CreatePresignedPostAsync()
    {
        _objectKey = "example-upload.txt";
        var expiration = DateTime.UtcNow.AddMinutes(10); // Short expiration for the demo

        Console.WriteLine($"Creating presigned POST URL for {_bucketName}/{_objectKey}");
        Console.WriteLine($"Expiration: {expiration} UTC");

        var s3Client = _s3Wrapper.GetS3Client();

        var response = await _s3Wrapper.CreatePresignedPostAsync(
            s3Client, _bucketName!, _objectKey, expiration);

        Console.WriteLine("Successfully created presigned POST URL");
        return response;
    }

    /// <summary>
    /// Upload a file using the presigned POST URL.
    /// </summary>
    private static async Task UploadFileAsync(CreatePresignedPostResponse response)
    {

        // Create a temporary test file to upload
        string testFilePath = Path.GetTempFileName();
        string testContent = "This is a test file for the S3 presigned POST scenario.";

        await File.WriteAllTextAsync(testFilePath, testContent);
        Console.WriteLine($"Created test file at: {testFilePath}");

        // Upload the file using the presigned POST URL
        Console.WriteLine("\nUploading file using the presigned POST URL...");
        var uploadResult = await UploadFileWithPresignedPostAsync(response, testFilePath);

        // Display the upload result
        if (uploadResult.Success)
        {
            Console.WriteLine($"Upload successful! Status code: {uploadResult.StatusCode}");
        }
        else
        {
            Console.WriteLine($"Upload failed with status code: {uploadResult.StatusCode}");
            Console.WriteLine($"Error: {uploadResult.Response}");
            throw new Exception("File upload failed");
        }

        // Clean up the temporary file
        File.Delete(testFilePath);
        Console.WriteLine("Temporary file deleted");
    }

    /// <summary>
    /// Helper method to upload a file using a presigned POST URL.
    /// </summary>
    private static async Task<(bool Success, HttpStatusCode StatusCode, string Response)> UploadFileWithPresignedPostAsync(
        CreatePresignedPostResponse response,
        string filePath)
    {
        try
        {
            _logger.LogInformation("Uploading file {filePath} using presigned POST URL", filePath);

            using var httpClient = _httpClientFactory.CreateClient();
            using var formContent = new MultipartFormDataContent();

            // Add all the fields from the presigned POST response
            foreach (var field in response.Fields)
            {
                formContent.Add(new StringContent(field.Value), field.Key);
            }

            // Add the file content
            var fileStream = File.OpenRead(filePath);
            var fileName = Path.GetFileName(filePath);
            var fileContent = new StreamContent(fileStream);
            fileContent.Headers.ContentType = new MediaTypeHeaderValue("text/plain");
            formContent.Add(fileContent, "file", fileName);

            // Send the POST request
            var httpResponse = await httpClient.PostAsync(response.Url, formContent);
            var responseContent = await httpResponse.Content.ReadAsStringAsync();

            // Log and return the result
            _logger.LogInformation("Upload completed with status code {statusCode}", httpResponse.StatusCode);

            return (httpResponse.IsSuccessStatusCode, httpResponse.StatusCode, responseContent);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error uploading file");
            return (false, HttpStatusCode.InternalServerError, ex.Message);
        }
    }

    /// <summary>
    /// Verify that the uploaded file exists in the S3 bucket.
    /// </summary>
    private static async Task VerifyFileExistsAsync()
    {
        _uiMethods.DisplayTitle("Step 5: Verify uploaded file exists");

        Console.WriteLine($"Checking if file exists at {_bucketName}/{_objectKey}...");

        try
        {
            var metadata = await _s3Wrapper.GetObjectMetadataAsync(_bucketName!, _objectKey!);

            Console.WriteLine($"File verification successful! File exists in the bucket.");
            Console.WriteLine($"File size: {metadata.ContentLength} bytes");
            Console.WriteLine($"File type: {metadata.Headers.ContentType}");
            Console.WriteLine($"Last modified: {metadata.LastModified}");
        }
        catch (AmazonS3Exception ex) when (ex.StatusCode == System.Net.HttpStatusCode.NotFound)
        {
            Console.WriteLine($"Error: File was not found in the bucket.");
            throw;
        }
    }

    private static void DisplayPresignedPostFields(CreatePresignedPostResponse response)
    {
        Console.WriteLine($"Presigned POST URL: {response.Url}");
        Console.WriteLine("Form fields to include:");

        foreach (var field in response.Fields)
        {
            Console.WriteLine($"  {field.Key}: {field.Value}");
        }
    }

    /// <summary>
    /// Clean up resources created by the scenario.
    /// </summary>
    private static async Task CleanupAsync()
    {
        if (!string.IsNullOrEmpty(_bucketName))
        {
            Console.WriteLine($"Deleting bucket {_bucketName} and its contents...");
            bool result = await _s3Wrapper.DeleteBucketAsync(_bucketName);

            if (result)
            {
                Console.WriteLine("Bucket deleted successfully");
            }
            else
            {
                Console.WriteLine("Failed to delete bucket - it may have been already deleted");
            }
        }
    }
}