Azure Blob Storage

Azure Storage 是微软 Azure 云提供的云端存储解决方案，当前支持的存储类型有 Blob、Queue、File 和 Table。

Blob Storage 是什么？

Azure Blob Storage 是用来存放大量的像文本、图片、视频等非结构化数据的存储服务。我们可以在任何地方通过互联网协议 http 或者 https 访问 Blob Storage。简单说，就是把文件放在云上，给它一个 URL，通过这个 URL 来访问文件。这就涉及到一个问题：如何控制访问权限？答案是我们可以根据自己的需要，设置 Blob 对象是只能被自己访问，还是可以被所有人访问。

下面是 Blog Storage 典型的应用场景：

1. 存储图片和文档，这些文件可以直接通过浏览器访问。
2. 支持分布式访问，主要用于 cdn。
3. 提供视频、音频流。
4. 存储基本的文件备份和归档文件。

Azure Blob Storage 的结构

下图描述了 Blob Storage 的基本组织结构：

• Azure Storage Account:

Storage Account 是用来管理 Azure Storage 的一个命名空间，主要用来控制存储数据的访问权限和计费。对于 Blob、Queue、File 和 Table 这些 Azure 提供的存储服务的访问控制，都是通过 Storage Account 来进行的，所以要想使用 Blob Storage，首先需要创建你的 Storage Account。

• Container：

Container 中包含一组资源，所有的 Blob 都必须存在于Container中。一个 Storage Account 中可以包含无限个 Container，每个Container中也可以包含无限个Blob。需要注意的是 Container 的名字必须全部小写。

• Blob：

一个Blob 就代表一个文件。为了区分应用的场景及提升不同应用场景下存储的性能，又为 Blob 划分了不同的类型：block blobs， page blobs，append blobs。

1. Block blobs 主要用来存储静态的文件，比如图片、电影和文档。
2. Append blobs 与 block blobs 类似，但优化了 append 操作，主要的应用场景是存储日志文件。
3. Page blobs 针对频繁的读写操作做了优化，如 Azure 上虚拟机的磁盘，就是使用的 page blobs

示例代码

//------------------------------------------------------------------------------
//MIT License

//Copyright(c) 2017 Microsoft Corporation. All rights reserved.

//Permission is hereby granted, free of charge, to any person obtaining a copy
//of this software and associated documentation files (the "Software"), to deal
//in the Software without restriction, including without limitation the rights
//to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//copies of the Software, and to permit persons to whom the Software is
//furnished to do so, subject to the following conditions:

//The above copyright notice and this permission notice shall be included in all
//copies or substantial portions of the Software.

//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//SOFTWARE.
//------------------------------------------------------------------------------


namespace storage_blobs_dotnet_quickstart
{
    using Microsoft.WindowsAzure.Storage;
    using Microsoft.WindowsAzure.Storage.Blob;
    using System;
    using System.IO;
    using System.Threading.Tasks;

    /// <summary>
    /// Azure Storage Quickstart Sample - Demonstrate how to upload, list, download, and delete blobs. 
    ///
    /// Note: This sample uses the .NET asynchronous programming model to demonstrate how to call Blob storage using the 
    /// storage client library's asynchronous API's. When used in production applications, this approach enables you to improve the 
    /// responsiveness of your application. Calls to Blob storage are prefixed by the await keyword. 
    /// 
    /// Documentation References: 
    /// - Azure Storage client library for .NET - https://docs.microsoft.com/dotnet/api/overview/azure/storage?view=azure-dotnet
    /// - Asynchronous Programming with Async and Await - http://msdn.microsoft.com/library/hh191443.aspx
    /// </summary>

    public static class Program
    {
        public static void Main()
        {
            Console.WriteLine("Azure Blob storage - .NET Quickstart sample");
            Console.WriteLine();
            ProcessAsync().GetAwaiter().GetResult();

            Console.WriteLine("Press any key to exit the sample application.");
            Console.ReadLine();
        }

        private static async Task ProcessAsync()
        {
            CloudStorageAccount storageAccount = null;
            CloudBlobContainer cloudBlobContainer = null;
            string sourceFile = null;
            string destinationFile = null;

            // Retrieve the connection string for use with the application. The storage connection string is stored
            // in an environment variable on the machine running the application called storageconnectionstring.
            // If the environment variable is created after the application is launched in a console or with Visual
            // Studio, the shell needs to be closed and reloaded to take the environment variable into account.
            string storageConnectionString = Environment.GetEnvironmentVariable("storageconnectionstring");

            // Check whether the connection string can be parsed.
            if (CloudStorageAccount.TryParse(storageConnectionString, out storageAccount))
            {
                try
                {
                    // Create the CloudBlobClient that represents the Blob storage endpoint for the storage account.
                    CloudBlobClient cloudBlobClient = storageAccount.CreateCloudBlobClient();

                    // Create a container called 'quickstartblobs' and append a GUID value to it to make the name unique. 
                    cloudBlobContainer = cloudBlobClient.GetContainerReference("quickstartblobs" + Guid.NewGuid().ToString());
                    await cloudBlobContainer.CreateAsync();
                    Console.WriteLine("Created container '{0}'", cloudBlobContainer.Name);
                    Console.WriteLine();

                    // Set the permissions so the blobs are public. 
                    BlobContainerPermissions permissions = new BlobContainerPermissions
                    {
                        PublicAccess = BlobContainerPublicAccessType.Blob
                    };
                    await cloudBlobContainer.SetPermissionsAsync(permissions);

                    // Create a file in your local MyDocuments folder to upload to a blob.
                    string localPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
                    string localFileName = "QuickStart_" + Guid.NewGuid().ToString() + ".txt";
                    sourceFile = Path.Combine(localPath, localFileName);
                    // Write text to the file.
                    File.WriteAllText(sourceFile, "Hello, World!");

                    Console.WriteLine("Temp file = {0}", sourceFile);
                    Console.WriteLine("Uploading to Blob storage as blob '{0}'", localFileName);
                    Console.WriteLine();

                    // Get a reference to the blob address, then upload the file to the blob.
                    // Use the value of localFileName for the blob name.
                    CloudBlockBlob cloudBlockBlob = cloudBlobContainer.GetBlockBlobReference(localFileName);
                    await cloudBlockBlob.UploadFromFileAsync(sourceFile);

                    // List the blobs in the container.
                    Console.WriteLine("Listing blobs in container.");
                    BlobContinuationToken blobContinuationToken = null;
                    do
                    {
                        var results = await cloudBlobContainer.ListBlobsSegmentedAsync(null, blobContinuationToken);
                        // Get the value of the continuation token returned by the listing call.
                        blobContinuationToken = results.ContinuationToken;
                        foreach (IListBlobItem item in results.Results)
                        {
                            Console.WriteLine(item.Uri);
                        }
                    } while (blobContinuationToken != null); // Loop while the continuation token is not null.
                    Console.WriteLine();

                    // Download the blob to a local file, using the reference created earlier. 
                    // Append the string "_DOWNLOADED" before the .txt extension so that you can see both files in MyDocuments.
                    destinationFile = sourceFile.Replace(".txt", "_DOWNLOADED.txt");
                    Console.WriteLine("Downloading blob to {0}", destinationFile);
                    Console.WriteLine();
                    await cloudBlockBlob.DownloadToFileAsync(destinationFile, FileMode.Create);
                }
                catch (StorageException ex)
                {
                    Console.WriteLine("Error returned from the service: {0}", ex.Message);
                }
                finally
                {
                    Console.WriteLine("Press any key to delete the sample files and example container.");
                    Console.ReadLine();
                    // Clean up resources. This includes the container and the two temp files.
                    Console.WriteLine("Deleting the container and any blobs it contains");
                    if (cloudBlobContainer != null)
                    {
                        await cloudBlobContainer.DeleteIfExistsAsync();
                    }
                    Console.WriteLine("Deleting the local source file and local downloaded files");
                    Console.WriteLine();
                    File.Delete(sourceFile);
                    File.Delete(destinationFile);
                }
            }
            else
            {
                Console.WriteLine(
                    "A connection string has not been defined in the system environment variables. " +
                    "Add a environment variable named 'storageconnectionstring' with your storage " +
                    "connection string as a value.");
            }
        }
    }
}