如何从Azure文件共享下载文件结尾

Question

此代码始终返回一个空字符串

        CloudFile cFile = fShare.getFile(subDir, rootDir, logFileName, AzureConstants.PATH);
        if (cFile.Exists())
        {

            using (var ms = new MemoryStream())
            {
                long?offset =Convert.ToInt64(cFile.Properties.Length * .8);
                long? length = Convert.ToInt64(cFile.Properties.Length * .20);


                cFile.DownloadRangeToStream(ms, offset, length);

                using (var sr = new StreamReader(ms))
                {
                    return sr.ReadToEnd();// this does run and it returns an empty string ""
                }
          }    
         }

我正在尝试读取文件的最后20％，而不是先下载整个内容，然后再阅读最后20％。甚至不需要最后20％的内容，只需阅读最后一行（它是一个文本文件）即可。这里是否缺少某些东西，或者我可以使用其他一些蔚蓝的方法来实现这一目标？

Answer 1

You forgot to set the memory stream's position to zero before use StreamReader.

Sample code as below:

using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Auth;
using Microsoft.WindowsAzure.Storage.File;
using System;
using System.IO;

namespace ConsoleApp19
{
    class Program
    {
        static void Main(string[] args)
        {
            string s1 = "";

            CloudStorageAccount storageAccount = new CloudStorageAccount(new StorageCredentials("your account", "your key"), true);
            CloudFileClient fileClient = storageAccount.CreateCloudFileClient();
            CloudFileShare share = fileClient.GetShareReference("t11");
            CloudFileDirectory rootDir = share.GetRootDirectoryReference();
            CloudFile file =rootDir.GetFileReference("test.txt");

            if (file.Exists())
            {
                using (var ms = new MemoryStream())
                {
                    long? offset = Convert.ToInt64(file.Properties.Length * .8);
                    long? length = Convert.ToInt64(file.Properties.Length * .20);

                    file.DownloadRangeToStream(ms, offset, length);

                    //set the position of memory stream to zero
                    ms.Position = 0;
                    using (var sr = new StreamReader(ms))
                    {
                        s1 = sr.ReadToEnd();
                    }

                    Console.WriteLine(s1);
                }

            }

            Console.WriteLine("---done---");
            Console.ReadLine();
        }
    }
} 

My test file:

And the test result: