Sending the contents of a webpage with images as an HTML mail

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Introduction

Some time ago, I had written an ASP.NET website showing some reports generated from a database. The reports contained tables, as well as dynamically generated graphs. To get a larger number of people to read the reports, it seemed like a good idea to send them as a weekly email newsletter. To be able to re-read the newsletter in a later stage, it was necessary to include the images, since they are changing over time. Embedding the images makes it also possible to send the mail to people that do not have access to the website.

This article shows a way to retrieve images from a web server and embed them into your email message.

Usage

This is how you can send a web page with the mailer class provided in this article:

// The contents that will be sent
Uri uri = new Uri("http://about.com/");

// Configuration of the email message
Fmd.Mail.WebpageMailer mailer = new Fmd.Mail.WebpageMailer();
mailer.SmtpServerName = "mail.somesmptserver.com";
mailer.Delay = 0;
mailer.MailMessage.From = new MailAddress("noreply@somedomain.com");
mailer.MailMessage.To.Add(new MailAddress("recipient@somedomain.com"));
mailer.MailMessage.Subject = "Automatic Mail Message " + 
                             DateTime.Now.ToShortDateString();
mailer.MailMessage.Priority = MailPriority.Normal;

// Sending the webpage
mailer.SendMailMessage(uri);

The main methods of the class

Sending the mail message

SendMailMessage is the main method in the class. It retrieves the contents of the web page to be sent. Next, it retrieves the images to embed. These parts are inserted into a mail message which is sent in the end.

public void SendMailMessage(Uri uri)
{
    // Retrieve the contents
    string htmlbody = GetBody(uri);
    
    // See what images there are to embed
    string modifiedbody;            
    List<linkedResource> foundResources;
    ExtractLinkedResources(uri, htmlbody, out modifiedbody, 
                           out foundResources);
    
    // Write the html to a memory stream
    MemoryStream stream = new MemoryStream();
    byte[] bytes = System.Text.Encoding.ASCII.GetBytes(modifiedbody);
    stream.Write(bytes, 0, bytes.Length);            
    stream.Position = 0;

    // Configure the mail so it contains the html page
    _mailMessage.Body = "This is a html mail - use an" + 
                        " email client that can read it";
    AlternateView altView = new AlternateView(stream, 
                  System.Net.Mime.MediaTypeNames.Text.Html);

    // Embed the images into the mail
    foreach (LinkedResource linkedResource in foundResources)
    {
        altView.LinkedResources.Add(linkedResource);
    }
    _mailMessage.AlternateViews.Add(altView);
    
    // Send the mail
    SmtpClient client = new SmtpClient(_smptServerName);
    client.Send(_mailMessage);
}

Filling the LinkedResource

This code snippet from ExtractLinkedResources shows how the images are embedded:

// Fill the linked resource
LinkedResource data = new LinkedResource(imageStream);

// Determine a name and set the media type of the linked resource
string generatedName = null;
if (contentType.ToLower().IndexOf("image/gif") >= 0)
{
    data.ContentType.MediaType = System.Net.Mime.MediaTypeNames.Image.Gif;
    generatedName = "image" + imageID.ToString() + ".gif";
}
else if (contentType.ToLower().IndexOf("image/jpeg") >= 0)
{
    data.ContentType.MediaType = System.Net.Mime.MediaTypeNames.Image.Jpeg;
    generatedName = "image" + imageID.ToString() + ".jpeg";
}

// it is something that I don't handle yet
if (generatedName == null)
    continue;

// Generate the linked resource for the image being embedded
string generatedSrc = "cid:" + generatedName;
data.ContentType.Name = generatedName;
data.ContentId = generatedName;
data.ContentLink = new Uri(generatedSrc);
linkedResources.Add(data); 

Getting a web page

This downloads the HTML contents:

public static string GetBody(Uri uri)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
    
    // Set some reasonable limits on resources used by this request
    request.MaximumAutomaticRedirections = 4;
    request.MaximumResponseHeadersLength = 4;
    // Set credentials to use for this request.
    request.Credentials = CredentialCache.DefaultCredentials;
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    
    // Get the stream associated with the response.
    Stream receiveStream = response.GetResponseStream();

    // Pipes the stream to a higher level stream reader
    // with the required encoding format. 
    StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8);

    string body = readStream.ReadToEnd();
    readStream.Close();

    response.Close();
    return body;
}

Glueing everything together

To make everything work together, there are a few things that need to be tackled. Since the images may be in some virtual directory on the web server, different from the page itself, their relative paths need to be changed. The program follows these steps to get everything together:

1. Read the HTML body
2. Analyze the HTML body to extract what images need to be retrieved
3. Download the images, and make them available as a MemoryStream to embed into the mail message
4. Modify the HTML so the image URLs are relative to the mail message instead of being relative to the web page
5. Put everything into the mail message and send it away

Final remarks

This article can do two things for you. It can get you started when you want to send web pages as an email message, and the sample code may help you when you are struggling on how to embed images into a mail message. I hope you find it useful!