email/email.go

//Email is designed to be a package providing an "email interface for humans."
//Designed to be robust and flexible, the email package aims to make sending email easy without getting in the way.
package email

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"log"
	"mime"
	"net/mail"
	"net/smtp"
	"net/textproto"
	"os"
	"path/filepath"
	"strings"
)

//Email is the type used for email messages
type Email struct {
	From        string
	To          []string
	Bcc         []string
	Cc          []string
	Subject     string
	Text        string //Plaintext message (optional)
	Html        string //Html message (optional)
	Headers     textproto.MIMEHeader
	Attachments map[string]*Attachment
}

//NewEmail creates an Email, and returns the pointer to it.
func NewEmail() *Email {
	return &Email{Attachments: make(map[string]*Attachment), Headers: make(textproto.MIMEHeader)}
}

//Attach is used to attach a file to the email.
//It attempts to open the file reference by filename and, if successful, creates an Attachment.
//This Attachment is then appended to the slice of Email.Attachments.
//The function will then return the Attachment for reference, as well as nil for the error if successful.
func (e *Email) Attach(filename string) (a *Attachment, err error) {
	//Check if the file exists, return any error
	if _, err := os.Stat(filename); os.IsNotExist(err) {
		log.Fatal("%s does not exist", filename)
		return nil, err
	}
	//Read the file, and set the appropriate headers
	buffer, _ := ioutil.ReadFile(filename)
	e.Attachments[filename] = &Attachment{
		Filename: filename,
		Header:   make(textproto.MIMEHeader),
		Content:  buffer}
	at := e.Attachments[filename]
	//Get the Content-Type to be used in the MIMEHeader
	ct := mime.TypeByExtension(filepath.Ext(filename))
	if ct != "" {
		at.Header.Set("Content-Type", ct)
	} else {
		//If the Content-Type is blank, set the Content-Type to "application/octet-stream"
		at.Header.Set("Content-Type", "application/octet-stream")
	}
	at.Header.Set("Content-Disposition", fmt.Sprintf("attachment;\r\n filename=%s", filename))
	return e.Attachments[filename], nil
}

//Bytes converts the Email object to a []byte representation of it, including all needed MIMEHeaders, boundaries, etc.
func (e *Email) Bytes() []byte {
	buff := bytes.Buffer{}
	//w := multipart.NewWriter(&buff)
	//Set the appropriate headers (overwriting any conflicts)
	//Leave out Bcc (only included in envelope headers)
	//TODO: Support wrapping on 76 characters (ref: MIME RFC)
	e.Headers.Set("To", strings.Join(e.To, ","))
	e.Headers.Set("Cc", strings.Join(e.Cc, ","))
	e.Headers.Set("From", e.From)
	e.Headers.Set("Subject", e.Subject)
	//Write the envelope headers (including any custom headers)

	return buff.Bytes()
}

//Send an email using the given host and SMTP auth (optional), returns any error thrown by smtp.SendMail
//This function merges the To, Cc, and Bcc fields and calls the smtp.SendMail function using the Email.Bytes() output as the message
func (e *Email) Send(addr string, a smtp.Auth) error {
	// Merge the To, Cc, and Bcc fields
	to := append(append(e.To, e.Cc...), e.Bcc...)
	from, err := mail.ParseAddress(e.From)
	if err != nil {
		return err
	}
	return smtp.SendMail(addr, a, from.Address, to, e.Bytes())
}

//Attachment is a struct representing an email attachment.
//Based on the mime/multipart.FileHeader struct, Attachment contains the name, MIMEHeader, and content of the attachment in question
type Attachment struct {
	Filename string
	Header   textproto.MIMEHeader
	Content  []byte
}