MimeKit.MimeMessage到浏览器可渲染的HTML

您的解决方案类似于我在MimeKit的MessageReader示例中使用的逻辑，但现在MimeKit提供了一个更好的解决方案:

/// <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 ();
        }
        string text = entity.Text;
        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);
    }
}

然后使用这个自定义的HtmlPreviewVisitor类，你会有一个类似这样的方法:

void Render (WebBrowser browser, MimeMessage message)
{
    var tmpDir = Path.Combine (Path.GetTempPath (), message.MessageId);
    var visitor = new HtmlPreviewVisitor (tmpDir);
    Directory.CreateDirectory (tmpDir);
    message.Accept (visitor);
    browser.DocumentText = visitor.HtmlBody;
}

我知道这看起来像是很多代码，但它涵盖的不仅仅是简单的情况。您会注意到，如果HTML不可用，它还可以处理text/plain和text/plain; format=flowed主体的渲染。它还正确地只使用封装multipart/related树的一部分的映像。

修改这段代码的一种方法是将图像嵌入到img标记中，而不是使用临时目录。要做到这一点，您需要将SaveImage方法修改为如下内容(注意，下一段代码未经过测试):

string SaveImage (MimePart image, string url)
{
    using (var output = new MemoryStream ()) {
        image.ContentObject.DecodeTo (output);
        var buffer = output.GetBuffer ();
        int length = (int) output.Length;
        return string.Format ("data:{0};base64,{1}", image.ContentType.MimeType, Convert.ToBase64String (buffer, 0, length));
    }
}