Send email with attachments in golang

Here is the code:

package main
import (
"encoding/json"
"fmt"
"log"
"net/http"
"net/url"
"os"
"os/user"
"path/filepath"
"golang.org/x/net/context"
"golang.org/x/oauth2"
"golang.org/x/oauth2/google"
"google.golang.org/api/gmail/v1"
"encoding/base64"
"io/ioutil"
)
// getClient uses a Context and Config to retrieve a Token
// then generate a Client. It returns the generated Client.
func getClient(ctx context.Context, config *oauth2.Config, configFileName string) *http.Client {
cacheFile, err := tokenCacheFile(configFileName)
if err != nil {
log.Fatalf("Unable to get path to cached credential file. %v", err)
}
tok, err := tokenFromFile(cacheFile)
if err != nil {
tok = getTokenFromWeb(config)
saveToken(cacheFile, tok)
}
return config.Client(ctx, tok)
}
// getTokenFromWeb uses Config to request a Token.
// It returns the retrieved Token.
func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
fmt.Printf("Go to the following link in your browser then type the " +
"authorization code: \n%v\n", authURL)
var code string
if _, err := fmt.Scan(&code); err != nil {
log.Fatalf("Unable to read authorization code %v", err)
}
tok, err := config.Exchange(oauth2.NoContext, code)
if err != nil {
log.Fatalf("Unable to retrieve token from web %v", err)
}
return tok
}
// tokenCacheFile generates credential file path/filename.
// It returns the generated credential path/filename.
func tokenCacheFile(filename string) (string, error) {
usr, err := user.Current()
if err != nil {
return "", err
}
tokenCacheDir := filepath.Join(usr.HomeDir, ".credentials")
os.MkdirAll(tokenCacheDir, 0700)
return filepath.Join(tokenCacheDir,
url.QueryEscape(filename)), err
}
// tokenFromFile retrieves a Token from a given file path.
// It returns the retrieved Token and any read error encountered.
func tokenFromFile(file string) (*oauth2.Token, error) {
f, err := os.Open(file)
if err != nil {
return nil, err
}
t := &oauth2.Token{}
err = json.NewDecoder(f).Decode(t)
defer f.Close()
return t, err
}
// saveToken uses a file path to create a file and store the
// token in it.
func saveToken(file string, token *oauth2.Token) {
fmt.Printf("Saving credential file to: %s\n", file)
f, err := os.Create(file)
if err != nil {
log.Fatalf("Unable to cache oauth token: %v", err)
}
defer f.Close()
json.NewEncoder(f).Encode(token)
}
func main() {
// Use oauth2.NoContext if there isn't a good context to pass in.
//ctx := context.TODO()
ctx := context.Background()
b, err := ioutil.ReadFile("client_secret.json")
if err != nil {
log.Fatalf("Unable to read client secret file: %v", err)
}
// If modifying these scopes, delete your previously saved credentials
// at ~/.credentials/gmail-go-quickstart.json
sendConfig, err := google.ConfigFromJSON(b, gmail.GmailSendScope)
if err != nil {
log.Fatalf("Unable to parse client secret file to config: %v", err)
}
sendClient := getClient(ctx, sendConfig, "send.json")
sendService, err := gmail.New(sendClient)
if err != nil {
log.Fatalf("Unable to retrieve gmail Client %v", err)
}
if err := SendEmail(ctx, sendService, "jane1988@gmail.com"); err != nil {
log.Fatalf("failed to send email: %v", err)
}
}
func SendEmail(ctx context.Context, svc *gmail.Service, email string) error {
header := make(map[string]string)
header["To"] = email
header["Subject"] = "hello there"
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\n", k, v)
}
msg += "\n" + "Hello, Gmail!"
gmsg := gmail.Message{
Raw: encodeWeb64String([]byte(msg)),
}
_, err := svc.Users.Messages.Send("me", &gmsg).Do()
return err
}
func encodeWeb64String(b []byte) string {
s := base64.URLEncoding.EncodeToString(b)
var i = len(s) - 1
for s[i] == '=' {
i--
}
return s[0 : i + 1]
}

This works perfectly, but without attachments. How can I attach files to the mail?

Maybe you can try change the header Content-Type to multipart/mixed (RFC 2046, Section 5.1.3) or multipart/alternative (RFC 2046, Section 5.1.4) and check how to use Content-Disposition: attachment; filename=<your file here.ext>.