大家使用C#同步邮件的时候，会不会遇到一件头疼的事情，C#只支持POP协议（只能获取收件箱的邮件，其他文件夹获取不到），Imap需要用第三方的来，而常见的几个第三方的类库，在同步大附件的时候，总是会超时。迫于无奈，我只好自己写一个Imap协议获取邮件。通过不断调试，获取大附件再也不会超时了，下面就跟大家分享一下。
程序原理就是利用TCP请求邮件服务器，然后发送IMAP命令执行一系列操作。
a01 xxx@126.com password
结果：a01 OK LOGIN completed
a02 list "" *
结果：
LIST () “/” “INBOX”
LIST (\Drafts) “/” “&g0l6P3ux-”
LIST (\Sent) “/” “&XfJT0ZAB-”
LIST (\Trash) “/” “&XfJSIJZk-”
LIST (\Junk) “/” “&V4NXPpCuTvY-”
LIST () “/” “&dcVr0pCuTvY-”
LIST () “/” “&Xn9USpCuTvY-”
LIST () “/” “&i6KWBZCuTvY-”
LIST () “/” “&YhF2hGWHaGM-”
LIST () “/” “java”
LIST () “/” “&bUuL1WWHTvZZOQ-”
LIST () “/” “&Y6hef5CuTvY-”
LIST () “/” “test”
LIST () “/” “folder”
a02 OK LIST Completed
a03 select inbox
结果：
2918 EXISTS
458 RECENT
OK [UIDVALIDITY 1] UIDs valid
FLAGS (\Answered \Seen \Deleted \Draft \Flagged)
OK [PERMANENTFLAGS (\Answered \Seen \Deleted \Draft \Flagged)] Limited
a03 OK [READ-WRITE] SELECT completed
a04 SEARCH SINCE 日-月-年
其中月为英文缩写，如Jan，Feb
b01 fetch body[header] //邮件头
b01 fetch body[1] //邮件主体
具体命令大家可自行百度学习，这边就不过多讲解。
public void Connection(string serveraddress, int port)
{
try
{
tcpclient.Connect(serveraddress, port);
sslstream = new SslStream(tcpclient.GetStream());
sslstream.AuthenticateAsClient(serveraddress);
bool flag = sslstream.IsAuthenticated;
if (!flag)
{
throw new Exception("sslstream IsAuthenticated return false");
}
}
catch (Exception ex)
{
throw ex;
}
}
构造imap命令，使用StreamWriter写入命令，StreamReader逐行获取，判断失败返回的关键字
public void login(string username, string password)
{
sw = new StreamWriter(sslstream);
// Assigned reader to stream
reader = new StreamReader(sslstream);
sw.WriteLine("a01 LOGIN " + username + " " + password);
sw.Flush();
try
{
string strTemp = string.Empty;
while ((strTemp = reader.ReadLine()) != null)
{
if (strTemp.IndexOf("OK LOGIN completed") != -1)
{
break;
}
else if (strTemp.IndexOf("NO LOGIN failed") != -1)
{
throw new Exception("NO LOGIN failed");
}
}
}
catch (Exception ex)
{
throw ex;
}
}
同理提交查看文件夹的命令，循环读取返回内容，直到"OK LIST completed"结束
public string FoldersList()
{
sw.WriteLine("a02 list \"\" *");
sw.Flush();
string str = string.Empty;
try
{
string strTemp = string.Empty;
while ((strTemp = reader.ReadLine()) != null)
{
if (strTemp.IndexOf("OK LIST completed") != -1)
{
break;
}
str += strTemp + "\r";
}
}
catch (Exception ex)
{
return "error:" + ex.Message;
}
return str;
}
存在"SELECT completed"返回True，否则False
public bool SelectFolder(string folder)
{
sw.WriteLine("a03 select " + folder);
sw.Flush();
try
{
string strTemp = string.Empty;
while ((strTemp = reader.ReadLine()) != null)
{
if (strTemp.IndexOf("NO SELECT failed") != -1)
{
return false;
}
if (strTemp.IndexOf("SELECT completed") != -1)
{
return true;
}
}
}
catch (Exception ex)
{
return false;
}
return false;
}
使用"SEARCH SINCE 日期"命令获取某天开始的邮件，ToSearchDt()方法会将日期转成IMAP命令需要的格式，返回的是uid数组
public string[] Search(DateTime dateTime, bool isReverse = true)
{
string strDateTime = ToSearchDt(dateTime);
sw.WriteLine("a04 SEARCH SINCE " + strDateTime);
sw.Flush();
string str = string.Empty;
try
{
string strTemp = string.Empty;
while ((strTemp = reader.ReadLine()) != null)
{
if (strTemp.IndexOf("SEARCH") != -1)
{
str = strTemp.Replace("SEARCH", "").Replace("*", "").Trim();
}
break;
}
}
catch (Exception ex)
{
;
}
if (string.IsNullOrEmpty(str)) return null;
string[] arr = System.Text.RegularExpressions.Regex.Split(str, @"\s+");
if (isReverse)
{
arr = arr.Reverse().ToArray();
}
return arr;
}
这边主要是做了一个判断是否附件的处理，如果是附件设置一次读取的大小，再循环读取。如果用行读取的话，附件太大的话会卡很久到超时。这边设置的是一次100K，这个值可以适当调整
private string fetch(int id, string data, bool line = false)
{
sw.WriteLine("b01 fetch " + id + " " + data);
sw.Flush();
string str = string.Empty;
try
{
System.Text.RegularExpressions.Regex reg1 = new System.Text.RegularExpressions.Regex(@"body\[[1-9][0-9]{0,1}\]");
bool ismatch = reg1.IsMatch(data);
if (ismatch && data != "body[1]")
{
//100k
var clen = 1024 * 100;
var read = new Char[clen];
var count = reader.Read(read, 0, clen);
while (count > 0)
{
var strTemp = new string(read, 0, count);
str += strTemp;
if (strTemp.IndexOf("OK FETCH completed") != -1)
break;
count = reader.Read(read, 0, clen);
}
var arr = str.Split('\r');
string[] b = new string[arr.Length - 3];
Array.Copy(arr, 1, b, 0, arr.Length - 3);
str = string.Join("\r", b).Replace("\r\n", "").Replace(")", "");
}
else
{
string strTemp = string.Empty;
while ((strTemp = reader.ReadLine()) != null)
{
if (strTemp.IndexOf("OK SEARCH completed") != -1 || strTemp.ToLower().IndexOf(data) != -1)
{
continue;
}
if (strTemp.IndexOf("OK FETCH completed") != -1 || strTemp.IndexOf("BAD invalid command or parameters") != -1)
{
break;
}
if (line)
{
str += strTemp;
}
else
{
str += strTemp + "\r";
}
}
}
}
catch (Exception ex)
{
;
}
return str;
}
这边主要讲解核心的方法，其余的是一些解析邮件内容的方法，大家可下载源码自行研究。
为何需要解析？因为获取下来的是一大串的文本，我们需要根据一些标识，获取到我们想要的东西，如发件时间、发送的邮箱、标题、主题和附件等。我解析的方法可能略显粗糙，希望大家有兴趣的话可以来优化一下。
这边举例获取收件箱的邮件，如果全部文件夹都需要则可以遍历list，
using (ImapClient client = new ImapClient())
{
try
{
client.Connection("imap.mxhichina.com", 993);
client.login("邮箱", "密码");
//获取邮箱文件夹
var list = client.FoldersList();
//获取指定文件夹
var hasFolder = client.SelectFolder("INBOX");
if (hasFolder)
{
//要查询的时间
var ids = client.Search(DateTime.Now.AddDays(-1));
if (ids != null)
{
foreach (var id in ids)
{
try
{
var ID = Convert.ToInt32(id);
//获取邮件头
var header = client.GetHeader(ID);
//获取邮件主体
var body = client.GetBody(ID);
//获取附件
var attachemnts = client.GetAttachments(ID);
foreach (var attachment in attachemnts)
{
byte[] bytes = Convert.FromBase64String(attachment.bs64);
string uploadDir = "img";
if (!Directory.Exists(uploadDir))
{
Directory.CreateDirectory(uploadDir);
}
using (Image img = Image.FromStream(new MemoryStream(bytes)))
{
var fileName = uploadDir += "/" + System.Guid.NewGuid().ToString() + ".jpg";
img.Save(uploadDir, ImageFormat.Jpeg);
}
}
}
catch (Exception ex)
{
Console.WriteLine("获取邮件异常，id:{0},异常{1}", id, ex.Message);
}
}
}
}
}
catch (Exception ex)
{
;
}
}