Azure 存储的断点续传与 MD5 校验-ESG跨境

Azure 存储的断点续传与 MD5 校验

Azure 存储的断点续传与 MD5 校验

问题分析

首先关于 Azure 存储中 MD5 的描述，我们已经有相关的介绍文档，如果对于存储中 MD5 的描述不熟悉，可以先参考 Azure Blob 存储基于 MD5 的完整性检查的内容。

如果直接将文件上传到 Blob 中可以在上传的方法中配置 BlobRequestOptions 类，将该类的 StoreBlobContentMD5 参数设置为 true，即可在上传时自动计算 MD5 值并将此值写入到请求头部（ContentMD5）中（可以参考 BlobRequestOptions.StoreBlobContentMD5 Property 此文档的描述）。 但是如果使用断点续传的方法，是将文件分为多个块上传，之后通过 PubBlockList 请求完成组合，那么想要上传 MD5 值，需要在 PubBlockList 请求的头部添加 xmsblobcontentmd5 参数，但是在 sdk 相关的方法中，BlobRequestOptions 中并没有关于该参数的属性，所以如果使用断点续传，采用 sdk 的 PubBlockList() 方法无法将 MD5 值上传上去，本篇文档即要解决如何在断点续传时上传 MD5 值的问题。

解决方案

可以通过使用 REST API 的方式来解决此问题:

1.首先我们需要计算出文件的 MD5 值：

string contentHash = md5()(File.ReadAllBytes(sourcePath));

2.将文件分块上传：

public async Task PutBlobAsync(String containerName, String blobName, byte[] blobContent, String blobid, bool error = false)

{

  String requestMethod = PUT;

  String urlPath = String.Format({0}/{1}, containerName, blobName) +  comp=blockblockid= + blobid;

  String storageServiceVersion = 20150221;

  String dateInRfc1123Format = DateTime.UtcNow.ToString(R, CultureInfo.InvariantCulture);

  Int32 blobLength = blobContent.Length;

  //headers

  String canonicalizedHeaders = String.Format(

    \nxmsdate:{0}\nxmsversion:{1},

    dateInRfc1123Format,

    storageServiceVersion);

  //resources

  String canonicalizedResource = String.Format(/{0}/{1}, AzureConstants.Account, String.Format({0}/{1}, containerName, blobName) + \nblockid: + blobid + \ncomp:block);

  String stringToSign = String.Format(

  {0}\n\n\n{1}\n\n\n\n\n\n\n\n{2}\n{3},

  requestMethod,

  blobLength,

  canonicalizedHeaders,

  canonicalizedResource);

  string authorizationHeader = CreateAuthorizationHeader(stringToSign);

  //上传url

  Uri uri = new Uri(BlobEndPoint + urlPath);

  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);

  request.Method = requestMethod;

  request.Headers[xmsdate] = dateInRfc1123Format;

  request.Headers[xmsversion] = storageServiceVersion;

  request.Headers[Authorization] = authorizationHeader;

  request.ContentLength = blobLength;

  try {

    using (Stream requestStream = await request.GetRequestStreamAsync()) {

      requestStream.Write(blobContent, 0, blobLength);

    }

    using (HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync()) {

      String ETag = response.Headers[ETag];

      System.Console.WriteLine(ETag);

    }

    error = false;

  }

  catch (WebException ex) {

    System.Console.WriteLine(An error occured. Status code: + ((HttpWebResponse)ex.Response).StatusCode);

    System.Console.WriteLine(Error information:);

    error = true;

    using (Stream stream = ex.Response.GetResponseStream()) {

      using (StreamReader sr = new StreamReader(stream)) {

        var s = sr.ReadToEnd();

        System.Console.WriteLine(s);

      }

    }

  }

}

3.在 PutBlobListAsync() 方法中将 MD5 值和 xmsblobcontentmd5 写入到请求头中：

public async Task PutBlobListAsync(String containerName, String blobName, Liststring blobIdList, string md5, bool error = false)

{

  String requestMethod = PUT;

  String urlPath = String.Format({0}/{1}, containerName, blobName) + ?comp=blocklist;

  String storageServiceVersion = 20150221;

  String dateInRfc1123Format = DateTime.UtcNow.ToString(R, CultureInfo.InvariantCulture);

  String canonicalizedHeaders = String.Format(

    \nxmsblobcontentmd5:{0}\nxmsdate:{1}\nxmsversion:{2},

    md5,

    dateInRfc1123Format,

    storageServiceVersion);

  StringBuilder stringbuilder = new StringBuilder();

  stringbuilder.Append(BlockList);

  foreach (string item in blobIdList) {

    stringbuilder.Append( Latest + item + /Latest);

  }

  stringbuilder.Append(/BlockList);

  byte[] data = Encoding.UTF8.GetBytes(stringbuilder.ToString());

  Int32 blobLength = data.Length;

  String canonicalizedResource = String.Format(/{0}/{1}, AzureConstants.Account, String.Format({0}/{1}, containerName, blobName) + \ncomp:blocklist);

  String stringToSign = String.Format(

    {0}\n\n\n{1}\n\n\n\n\n\n\n\n{2}\n{3},

    requestMethod,

    blobLength,

    canonicalizedHeaders,

    canonicalizedResource);

  String authorizationHeader = CreateAuthorizationHeader(stringToSign);

  Uri uri = new Uri(BlobEndPoint + urlPath);

  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);

  request.Method = requestMethod;

  request.Headers[xmsblobcontentmd5] = md5;

  request.Headers[xmsdate] = dateInRfc1123Format;

  request.Headers[xmsversion] = storageServiceVersion;

  request.Headers[Authorization] = authorizationHeader;

  request.ContentLength = blobLength;

  try {

    using (Stream requestStream = await request.GetRequestStreamAsync()) {

      requestStream.Write(data, 0, blobLength);

    }

    using (HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync()) {

      String ETag = response.Headers[ETag];

      System.Console.WriteLine(ETag);

    }

    error = false;

  }

  catch (WebException ex) {

    System.Console.WriteLine(An error occured. Status code: + ((HttpWebResponse)ex.Response).StatusCode);

    System.Console.WriteLine(Error information:);

    error = true;

    using (Stream stream = ex.Response.GetResponseStream()) {

      using (StreamReader sr = new StreamReader(stream)) {

        var s = sr.ReadToEnd();

        System.Console.WriteLine(s);

      }

    }

  }

}

完整示例请参考示例代码。

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