读取ftp以base64返回到前端

• 需求：库中存放文件服务器的文件绝对路径文件（d:\abc\111\abc.pdf），搭建的ftp会指向d:\abc ，故ftp:/192.1.1.12:21/111/abc.pdf能取到文件。请用C#代码并base64格式返回到前端。

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Text;
using Newtonsoft.Json;
using System.Data.Common;
using System.IO;
using System.Net;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            var st = GetFileByPath();
            Console.Write(st);
            Console.ReadLine();
        }  
		
		public static string GetFileByPath()
        {
            var filePath = "D:\\test\\1410\\412\\ab.pdf";
            string oldDir = @"D:\test";
            var dicFtp = JsonConvert.DeserializeObject<Dictionary<string, string>>(oldFtp);
            var ftpPath = $"ftp://192.168.192.31:21/" + filePath.Replace(oldDir, "").Replace(@"\", @"/").TrimStart('/');
            var str = DownloadFtp(ftpPath.Trim(), "", "");
            WriteLog("111☆" + str);
            return str;
        }
		
        private static string DownloadFtp(string ftpPath, string ftpUserID, string ftpPassword)
        {
            FtpWebRequest reqFTP;
            try
            {
                MemoryStream mms = new MemoryStream();
                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(ftpPath));
                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
                reqFTP.UseBinary = true;
                reqFTP.KeepAlive = false;
                reqFTP.Credentials = new NetworkCredential(ftpUserID, ftpPassword);
                reqFTP.KeepAlive = false;
                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();
                Stream ftpStream = response.GetResponseStream();
                long cl = response.ContentLength;
                int bufferSize = 2048;
                int readCount;
                byte[] buffer = new byte[bufferSize];
                readCount = ftpStream.Read(buffer, 0, bufferSize);
                while (readCount > 0)
                {
                    mms.Write(buffer, 0, readCount);
                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                }
				/*若用mms.GetBuffer()转base64，有坑：得到的字节中包含已分配但未使用的字节。ToArray无此坑！！！
				* 资料：http://www.csref.cn/vs100/method/System-IO-MemoryStream-GetBuffer.html
				*/
                var res = Convert.ToBase64String(mms.ToArray());
                ftpStream.Close();
                mms.Close();
                response.Close();
                if (!string.IsNullOrWhiteSpace(res) && ftpPath.ToLower().EndsWith(".pdf"))
                {
                    return "data:application/pdf;base64," + res;//二进制转base64
                }
                else
                {
                    return res;
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
  
  
        public static void WriteLog(string content, string group = "方便归类")
        { 
            //一条日志：证书链 耗时（ms）：1  2019/7/12 19:36:05 
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("{0}：    {1}    {2}", group, content, DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"));
            string path = @"d:\";
            Directory.CreateDirectory(path);//创建目录(存在，不重建不报错）
            File.AppendAllText(path + DateTime.Now.ToString("yyyy-MM-dd") + ".txt", "\r\n" + sb.ToString(), Encoding.UTF8);
        } 

    } 
}