How to Send Emails Using the Gmail Go SDK: Solving the Message Object Creation Puzzle?

How to Send Email through Gmail Go SDK

Problem:

Sending emails using the Gmail Go SDK can be challenging, especially due to the lack of clear documentation for creating the required Message object. The Message type's fields primarily facilitate email parsing, leaving it unclear how to construct a valid payload for sending emails.

Solution:

Despite the API's complexity, here are steps to send emails through Gmail Go SDK:

1. Create a Message Object:

• Create a MessagePart instance (p) and add headers for "From," "To," and "Subject."
• Encode the email message (em) as a base64 string (emsg) and set it as the payload's raw value.

2. Initialize a Gmail Service:

• Acquire an OAuth token from the user and use it to initialize a Gmail client.

3. Send the Email:

• Invoke the Send method with the message object as an argument.

4. Encode Header Values:

• To comply with RFC 2047, encode header values for "From" and "Subject."

5. Encode the Message Body:

• Encode the message body using Web64 encoding.

Custom Code Snippet:

<code class="go">import (
    "encoding/base64"
    "encoding/json"
    "fmt"
    "log"
    "net/mail"
    "strings"

    gmail "google.golang.org/api/gmail/v1"
)

type Email struct {
    FromName, FromEmail, ToName, ToEmail, Subject string
    Message                                       string
}

func (em *Email) SendMessage(cl *Client) error {
    from := mail.Address{em.FromName, em.FromEmail}
    to := mail.Address{em.ToName, em.ToEmail}

    header := make(map[string]string)
    header["From"] = from.String()
    header["To"] = to.String()
    header["Subject"] = encodeRFC2047(em.Subject)
    header["MIME-Version"] = "1.0"
    header["Content-Type"] = "text/html; charset=\"utf-8\""
    header["Content-Transfer-Encoding"] = "base64"

    var msg string
    for k, v := range header {
        msg += fmt.Sprintf("%s: %s\r\n", k, v)
    }
    msg += "\r\n" + em.Message

    gmsg := gmail.Message{
        Raw: encodeWeb64String([]byte(msg)),
    }

    // Send the email using Gmail Service
    ...

    return nil
}

func encodeRFC2047(s string) string {
    // use mail's rfc2047 to encode any string
    addr := mail.Address{s, ""}
    return strings.Trim(addr.String(), " <>")
}

func encodeWeb64String(b []byte) string {
    s := base64.URLEncoding.EncodeToString(b)

    var i = len(s) - 1
    for s[i] == '=' {
        i--
    }

    return s[0 : i+1]
}</code>

By following these steps, you can construct a valid Message object and successfully send emails through the Gmail Go SDK.

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