How to add inline images to HTML emails as MIME attachments in Go?

To add inline images to HTML emails as MIME attachments in Go, you can follow these steps:

Import the required packages:

import (
    "encoding/base64"
    "net/mail"
    "net/smtp"
    "path/filepath"
    "strings"
)

Create a function to encode the image file as base64:

func encodeBase64Image(imagePath string) (string, error) {
    data, err := ioutil.ReadFile(imagePath)
    if err != nil {
        return "", err
    }
    encoded := base64.StdEncoding.EncodeToString(data)
    mimetype := mime.TypeByExtension(filepath.Ext(imagePath))
    return fmt.Sprintf("data:%s;base64,%s", mimetype, encoded), nil
}

Create a function to send the HTML email with inline images:

func sendHTMLEmailWithInlineImages(to, subject, htmlMessage, imagePath string) error {
    // Get the base64 encoded image
    inlineImage, err := encodeBase64Image(imagePath)
    if err != nil {
        return err
    }

    // Create the HTML email multipart message
    message := mail.NewMultipartMessage("mixed", nil)

    // Create the HTML part with inline image
    htmlPart := &mail.InlineHTML{HTML: htmlMessage}
    htmlPart.AddInline(imagePath, strings.NewReader(inlineImage))
    message.AddPart(htmlPart)

    // Set the email addresses
    message.SetHeader("From", "[email protected]")
    message.SetHeader("To", to)

    // Set the subject
    message.SetHeader("Subject", subject)

    // Send the email
    smtp.SendMail("mailserver:port", nil, "[email protected]", []string{to}, message.Bytes())

    return nil
}

Call the function with the appropriate parameters:

to := "[email protected]"
subject := "Example Subject"
htmlMessage := "<html><body><img src=\"cid:example.png\"></body></html>"
imagePath := "path/to/example.png"

err := sendHTMLEmailWithInlineImages(to, subject, htmlMessage, imagePath)
if err != nil {
    log.Fatal(err)
}

Make sure to replace "mailserver:port", "[email protected]", "[email protected]", "Example Subject", "example.png", "path/to/example.png" with the actual values for your email server, sender, recipient, subject, and image file.

Note: This code assumes you're using the built-in net/smtp package for sending emails. You may need to adjust the email sending code if you're using a different SMTP package.

Also, consider error handling and any additional customization you require for your specific email needs.