How to send attachments in golang

With the rapid development of the Internet, email has become an indispensable part of people's daily life and work. In emails, emails containing attachments are becoming more and more common, such as sending resumes, contracts, pictures, etc. Golang is a fast, simple, and secure programming language that more and more people are using to develop email sending applications. In this article, we will explain how to send emails with attachments using Golang.

First, we need to use an email sending library to send emails. I recommend using the popular gomail library. It is a simple and easy-to-use email sending library that supports SMTP and sending attachments. We need to install it using the go get command:

go get gopkg.in/gomail.v2

Next, we need to create an email with an attachment. To achieve this, we need to create a multipart message for the email body and attachments. This is a standard format for email content and attachments. Let's take a look at how to create a multipart message with attachments:

func createMessage(to []string, subject string, body string, attachmentPath string) *gomail.Message {
    //create a new message
    message := gomail.NewMessage()
    //set the receiver
    message.SetHeader("To", to...)
    //set the subject
    message.SetHeader("Subject", subject)

    //create a multipart message
    multipart := gomail.NewMultipart("mixed")
    message.SetBody("text/html", body)

    //create and add attachment
    attachment := gomail.NewMessagePart()
    attachment.SetHeader("Content-Type", "application/octet-stream")
    attachment.SetHeader("Content-Disposition", fmt.Sprintf("attachment; filename=%s", attachmentPath))
    attachment.SetBodyFile(attachmentPath)
    multipart.AddPart(attachment)

    //add multipart message to the main message
    message.SetBody(multipart)
    return message
}

In the above code, we first create a new message, and then set the recipients and subject. Next, we create a multipart message containing body and attachments. Finally, we add the multipart message to the main message and return that message.

In the above code, we use NewMessage to construct an email instance, and then set the recipient's email address and email subject. Next, we created a multipart instance and added it to the theme. A multipart instance contains text content and attachments with file paths. The attachment's content type and file name are set in the multipart instance and added to the created multipart instance. Finally, we set the multipart instance to be the body of the email instance.

Now that we have created the email with the attachment, the next step is to send the email to the intended recipient using the SMTP protocol. The following code demonstrates how to use the popular gomail library to send emails:

func sendEmail(to []string, subject string, body string, attachmentPath string) {
    //create a new message
    message := createMessage(to, subject, body, attachmentPath)

    //create a new SMTP dialer
    dialer := gomail.NewDialer("smtp.gmail.com", 587, "yourEmail@gmail.com", "yourPassword")

    //send the message using the SMTP dialer
    if err := dialer.DialAndSend(message); err != nil {
        log.Fatalf("Failed to send email: %v", err)
    }
}

In the above code, we first call the createMessage function to create an email message, and then create a Dialer object, which is used to establish a connection to the SMTP server. We need to set the Dialer's server address, port number, email address and password of the email sender. Here we take Gmail's SMTP server as an example.

Finally, we send the email to the target recipient through the DialAndSend method. If an error is encountered when sending an email, a non-nil error will be returned. We can use the error handling mechanism to handle exceptions.

Summary:

In this article, we introduced how to send emails with attachments using Golang. We used the gomail library to send the email, created a multipart message, added the body and attachments, and sent the email to the recipient using SMTP. Through this article, you will learn how to use the email sending library in Golang to send emails with attachments.

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