如何使用MimeKit获取电子邮件的WYSIWYG正文

时间:2016-01-24 19:09:39

标签: c# email mailkit mimekit

我使用名为EAgetmail的库来检索指定电子邮件的正文,但它运行良好,但我现在正在使用Mailkit。问题是EAgetmail相当于message.body返回主体,因为用户在电子邮件客户端中看到它,但在mailkit中它返回了许多不同的数据。

这是相关代码:

using (var client = new ImapClient())
{
    client.Connect(emailServer, 993, true);
    client.AuthenticationMechanisms.Remove("XOAUTH2");
    client.Authenticate(username, password);
    var inbox = client.Inbox;
    inbox.Open(FolderAccess.ReadOnly);
    SearchQuery query;
    if (checkBox.IsChecked == false)
    {
        query = SearchQuery.DeliveredBefore((DateTime)dateEnd).And(
            SearchQuery.DeliveredAfter((DateTime)dateStart)).And(
            SearchQuery.SubjectContains("Subject to find"));
    }
    else
    {
        query = SearchQuery.SubjectContains("Subject to find");
    }
    foreach (var uid in inbox.Search(query))
    {
        var message = inbox.GetMessage(uid);
        formEmails.Add(message.TextBody);
        messageDate.Add(message.Date.LocalDateTime);
    }
    client.Disconnect(true);
}

我还尝试了message.Body.ToString()并在消息部分中搜索纯文本,但都没有工作。 我的问题是如何使用Mailkit复制EAgetmail的.body属性的效果(只返回纯文本中的正文内容,如用户所见)?

2 个答案:

答案 0 :(得分:11)

对电子邮件的一个常见误解是,有一个明确定义的邮件正文,然后是一个附件列表。实际情况并非如此。实际情况是MIME是内容的树结构,就像文件系统一样。

幸运的是,MIME确实为邮件客户端如何解释MIME部分的树结构定义了一套通用规则。 Content-Disposition标题旨在向接收客户端提供关于哪些部分要作为消息正文的一部分显示以及哪些部分应被解释为附件的提示。

Content-Disposition标题通常包含以下两个值之一:inlineattachment

这些价​​值观的含义应该相当明显。如果值是attachment,则所述MIME部分的内容意味着被呈现为与核心消息分开的文件附件。但是,如果值为inline,则该MIME部分的内容应在邮件客户端呈现核心邮件正文中内联显示。如果Content-Disposition标头不存在,则应将其视为值为inline

从技术上讲,缺少Content-Disposition标题或标记为inline的每个部分都是核心邮件正文的一部分。

但是还有更多的东西。

现代MIME邮件通常包含multipart/alternative MIME容器,该容器通常包含发件人编写的文本的text/plaintext/html版本。 text/html版本的格式通常与发件人在其WYSIWYG编辑器中看到的格式更接近于text/plain版本。

以两种格式发送消息文本的原因是并非所有邮件客户端都能够显示HTML。

接收客户端应仅显示multipart/alternative容器中包含的备用视图之一。由于备选视图按照最忠实于最忠实的顺序列出发件人在其所见即所得编辑器中看到的内容,因此接收客户端应该从最后开始的备用视图列表中进行操作并向后工作,直到找到它的一部分为止能够显示。

示例:

multipart/alternative
  text/plain
  text/html

如上例所示,text/html部分列在最后,因为它最忠实于发件人在撰写邮件时在其所见即所得编辑器中看到的内容。

为了使问题更复杂,有时现代邮件客户端将使用multipart/related MIME容器而不是简单的text/html部分,以便在HTML中嵌入图像和其他多媒体内容。

示例:

multipart/alternative
  text/plain
  multipart/related
    text/html
    image/jpeg
    video/mp4
    image/png

在上面的示例中,其中一个备用视图是multipart/related容器,其中包含引用兄弟视频和图像的消息体的HTML版本。

现在您已经大致了解了消息的结构以及如何解释各种MIME实体,我们可以开始弄清楚如何按预期实际呈现消息。

使用MimeVisitor(呈现消息的最准确方式)

MimeKit包含一个MimeVisitor类,用于访问MIME树结构中的每个节点。例如,以下MimeVisitor子类可用于生成由浏览器控件(例如WebBrowser)呈现的HTML:

/// <summary>
/// Visits a MimeMessage and generates HTML suitable to be rendered by a browser control.
/// </summary>
class HtmlPreviewVisitor : MimeVisitor
{
    List<MultipartRelated> stack = new List<MultipartRelated> ();
    List<MimeEntity> attachments = new List<MimeEntity> ();
    readonly string tempDir;
    string body;

    /// <summary>
    /// Creates a new HtmlPreviewVisitor.
    /// </summary>
    /// <param name="tempDirectory">A temporary directory used for storing image files.</param>
    public HtmlPreviewVisitor (string tempDirectory)
    {
        tempDir = tempDirectory;
    }

    /// <summary>
    /// The list of attachments that were in the MimeMessage.
    /// </summary>
    public IList<MimeEntity> Attachments {
        get { return attachments; }
    }

    /// <summary>
    /// The HTML string that can be set on the BrowserControl.
    /// </summary>
    public string HtmlBody {
        get { return body ?? string.Empty; }
    }

    protected override void VisitMultipartAlternative (MultipartAlternative alternative)
    {
        // walk the multipart/alternative children backwards from greatest level of faithfulness to the least faithful
        for (int i = alternative.Count - 1; i >= 0 && body == null; i--)
            alternative[i].Accept (this);
    }

    protected override void VisitMultipartRelated (MultipartRelated related)
    {
        var root = related.Root;

        // push this multipart/related onto our stack
        stack.Add (related);

        // visit the root document
        root.Accept (this);

        // pop this multipart/related off our stack
        stack.RemoveAt (stack.Count - 1);
    }

    // look up the image based on the img src url within our multipart/related stack
    bool TryGetImage (string url, out MimePart image)
    {
        UriKind kind;
        int index;
        Uri uri;

        if (Uri.IsWellFormedUriString (url, UriKind.Absolute))
            kind = UriKind.Absolute;
        else if (Uri.IsWellFormedUriString (url, UriKind.Relative))
            kind = UriKind.Relative;
        else
            kind = UriKind.RelativeOrAbsolute;

        try {
            uri = new Uri (url, kind);
        } catch {
            image = null;
            return false;
        }

        for (int i = stack.Count - 1; i >= 0; i--) {
            if ((index = stack[i].IndexOf (uri)) == -1)
                continue;

            image = stack[i][index] as MimePart;
            return image != null;
        }

        image = null;

        return false;
    }

    // Save the image to our temp directory and return a "file://" url suitable for
    // the browser control to load.
    // Note: if you'd rather embed the image data into the HTML, you can construct a
    // "data:" url instead.
    string SaveImage (MimePart image, string url)
    {
        string fileName = url.Replace (':', '_').Replace ('\\', '_').Replace ('/', '_');

        string path = Path.Combine (tempDir, fileName);

        if (!File.Exists (path)) {
            using (var output = File.Create (path))
                image.ContentObject.DecodeTo (output);
        }

        return "file://" + path.Replace ('\\', '/');
    }

    // Replaces <img src=...> urls that refer to images embedded within the message with
    // "file://" urls that the browser control will actually be able to load.
    void HtmlTagCallback (HtmlTagContext ctx, HtmlWriter htmlWriter)
    {
        if (ctx.TagId == HtmlTagId.Image && !ctx.IsEndTag && stack.Count > 0) {
            ctx.WriteTag (htmlWriter, false);

            // replace the src attribute with a file:// URL
            foreach (var attribute in ctx.Attributes) {
                if (attribute.Id == HtmlAttributeId.Src) {
                    MimePart image;
                    string url;

                    if (!TryGetImage (attribute.Value, out image)) {
                        htmlWriter.WriteAttribute (attribute);
                        continue;
                    }

                    url = SaveImage (image, attribute.Value);

                    htmlWriter.WriteAttributeName (attribute.Name);
                    htmlWriter.WriteAttributeValue (url);
                } else {
                    htmlWriter.WriteAttribute (attribute);
                }
            }
        } else if (ctx.TagId == HtmlTagId.Body && !ctx.IsEndTag) {
            ctx.WriteTag (htmlWriter, false);

            // add and/or replace oncontextmenu="return false;"
            foreach (var attribute in ctx.Attributes) {
                if (attribute.Name.ToLowerInvariant () == "oncontextmenu")
                    continue;

                htmlWriter.WriteAttribute (attribute);
            }

            htmlWriter.WriteAttribute ("oncontextmenu", "return false;");
        } else {
            // pass the tag through to the output
            ctx.WriteTag (htmlWriter, true);
        }
    }

    protected override void VisitTextPart (TextPart entity)
    {
        TextConverter converter;

        if (body != null) {
            // since we've already found the body, treat this as an attachment
            attachments.Add (entity);
            return;
        }

        if (entity.IsHtml) {
            converter = new HtmlToHtml {
                HtmlTagCallback = HtmlTagCallback
            };
        } else if (entity.IsFlowed) {
            var flowed = new FlowedToHtml ();
            string delsp;

            if (entity.ContentType.Parameters.TryGetValue ("delsp", out delsp))
                flowed.DeleteSpace = delsp.ToLowerInvariant () == "yes";

            converter = flowed;
        } else {
            converter = new TextToHtml ();
        }

        body = converter.Convert (entity.Text);
    }

    protected override void VisitTnefPart (TnefPart entity)
    {
        // extract any attachments in the MS-TNEF part
        attachments.AddRange (entity.ExtractAttachments ());
    }

    protected override void VisitMessagePart (MessagePart entity)
    {
        // treat message/rfc822 parts as attachments
        attachments.Add (entity);
    }

    protected override void VisitMimePart (MimePart entity)
    {
        // realistically, if we've gotten this far, then we can treat this as an attachment
        // even if the IsAttachment property is false.
        attachments.Add (entity);
    }
}

您使用此访问者的方式可能如下所示:

void Render (MimeMessage message)
{
    var tmpDir = Path.Combine (Path.GetTempPath (), message.MessageId);
    var visitor = new HtmlPreviewVisitor (tmpDir);

    Directory.CreateDirectory (tmpDir);

    message.Accept (visitor);

    DisplayHtml (visitor.HtmlBody);
    DisplayAttachments (visitor.Attachments);
}

使用TextBodyHtmlBody属性(最简单的方式)

为了简化获取邮件文本的常见任务,MimeMessage包含两个属性,可帮助您获取邮件正文的text/plaintext/html版本。它们分别是TextBodyHtmlBody

但请记住,至少使用HtmlBody属性,可能是HTML部分是multipart/related的子项,允许它引用图像和其他类型的媒体它也包含在multipart/related实体中。这个属性实际上只是一个方便的属性,并不是自己遍历MIME结构的真正好的替代品,因此您可以正确地解释相关内容。

答案 1 :(得分:0)

旧帖子,但相关,可以使用内置的 MimeKit 将正文作为文本获取:

string body = mimeMessage.GetTextBody(MimeKit.Text.TextFormat.Plain);