将 .jpg 图像（base64 字符串表示）嵌入到电子邮件正文中 (System.Net.Mail)

Question

我能够正确地将 jpg 图像转换为 base64String。但是我无法使用转换后的图像字符串和 LinkedResource 将其嵌入电子邮件正文中。该图像在电子邮件正文中显示为未找到图像图标。任何帮助将不胜感激。

我已经按照 link 中的示例进行操作：

我正在使用 HtmlAgilityPack（nuget 包）通过以下代码定位 img 元素。

private string embedImageInMail(string html)
       {
            HtmlAgilityPack.HtmlDocument doc = new 
HtmlAgilityPack.HtmlDocument();
            doc.LoadHtml(html);
            doc.DocumentNode.Descendants("img").Where(e =>
            {
                string src = e.GetAttributeValue("src", null) ?? "";
                return !string.IsNullOrEmpty(src) && src.StartsWith("data:image");
            })
            .ToList()
            .ForEach(x =>
            {
                string currentSrcValue = x.GetAttributeValue("src", null);
                currentSrcValue = currentSrcValue.Split(',')[1];    //Base64 part of string
                byte[] imageData = Convert.FromBase64String(currentSrcValue);
                string contentId = Guid.NewGuid().ToString();
                using (MemoryStream ms = new MemoryStream(imageData))
                {
                    LinkedResource inline = new LinkedResource(ms, "image/jpeg");
                    inline.ContentId = contentId;
                    inline.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;
                    x.SetAttributeValue("src", "cid:" + inline.ContentId);
                }
            });

        return doc.DocumentNode.OuterHtml; 
    }

传递给函数的html参数包含一个img标签，其src等于图像的base64编码。从此函数返回的内容将分配给电子邮件的 message.body。

Answer 1

已按照其他 post 中的解决方案解决。如果其他人正在尝试做同样的事情并且遇到了像我一样的麻烦，我将在下面 post 编写代码。

基本上我必须将 html 中的 LinkedResource（图像）保存到一个列表，然后遍历该列表并将所有图像添加到 foreach 循环之外的 AlternateView。

 // Embeds image to properly show in Email. Image element to show in html will not work in Email body. 
                        // 
                        // XmlAgilityPack gets used here to parse html string. 
                        List<LinkedResource> linkedResources = new List<LinkedResource>(); 
                        HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
                        int increment = 0; 
                        doc.LoadHtml(tempMsg);
                        doc.DocumentNode.Descendants("img").Where(z =>
                            {
                                string src = z.GetAttributeValue("src", null) ?? "";
                                return !string.IsNullOrEmpty(src) && src.StartsWith("data:image");
                            })
                            .ToList()
                            .ForEach(x =>
                            {
                                string currentSrcValue = x.GetAttributeValue("src", null);
                                currentSrcValue = currentSrcValue.Split(',')[1];    //Base64 part of string
                                byte[] imageData = Convert.FromBase64String(currentSrcValue);
                                string id = Guid.NewGuid().ToString();
                                increment++;

                                LinkedResource inlineImage = new LinkedResource(new MemoryStream(imageData), System.Net.Mime.MediaTypeNames.Image.Jpeg);
                                inlineImage.ContentType.Name = "img " + increment; 
                                inlineImage.ContentId = id;
                                inlineImage.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;
                                x.SetAttributeValue("src", "cid:" + inlineImage.ContentId);
                                linkedResources.Add(inlineImage);
                            });

                        // Append multiple images from template to email message.
                        // 
                        // Write html to message.body 
                        AlternateView altView = AlternateView.CreateAlternateViewFromString(doc.DocumentNode.OuterHtml, null, "text/html");
                        linkedResources.ForEach(x=>altView.LinkedResources.Add(x));
                        message.AlternateViews.Add(altView);

                        String[] attachments = txtAttachFiles.Text.Split(';');
                        foreach (String filename in attachments)
                        {
                            if (File.Exists(filename))
                            {
                                Attachment attachment = new Attachment(filename);
                                message.Attachments.Add(attachment);
                            }
                        }

                        // loop is set to 1 in the app.config file so technically this for loop is not needed, but will keep this loop just in case. 
                        for (int loop = 0; loop < Convert.ToInt32(ConfigurationManager.AppSettings["loop"]); loop++)
                        {
                            SmtpClient smtp = new SmtpClient();
                            smtp.Host = ConfigurationManager.AppSettings["mailHost"];
                            smtp.Port = Int32.Parse(ConfigurationManager.AppSettings["mailPort"]);
                            smtp.UseDefaultCredentials = Convert.ToBoolean(ConfigurationManager.AppSettings["mailDefaultCredentials"]);
                            smtp.Send(message);
                        }
                    }

将 .jpg 图像（base64 字符串表示）嵌入到电子邮件正文中 (System.Net.Mail)

Embedding .jpg image (base64 string representation) into email message body (System.Net.Mail)

c#

base64

image-processing

system.net.mail