Go Quickstart

Complete the steps described in the rest of this page, and in about five minutes you'll have a simple Go command-line application that makes requests to the Google Calendar API.

Prerequisites

To run this quickstart, you'll need:

  • Go, latest version recommended.
  • Git, latest version recommended.
  • A Google account with Google Calendar enabled.

Step 1: Turn on the Google Calendar API

Click this button to create a new console project and automatically enable the Google Calendar API:

Enable the Google Calendar API

This opens a new dialog. In the dialog, do the following:

  1. Select + Create a new project.
  2. Download the configuration file.
  3. Move the downloaded file to your working directory and ensure it is named credentials.json.

Step 2: Prepare the workspace

  1. Set the GOPATH environment variable to your working directory.
  2. Get the Google Calendar API Go client library and OAuth2 package using the following commands:
go get -u google.golang.org/api/calendar/v3
go get -u golang.org/x/oauth2/...

Step 3: Set up the sample

Create a file named quickstart.go in your working directory and copy in the following code:

calendar/quickstart/quickstart.go
package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"time"

	"golang.org/x/net/context"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/calendar/v3"
)

// Retrieve a token, saves the token, then returns the generated client.
func getClient(config *oauth2.Config) *http.Client {
	tokFile := "token.json"
	tok, err := tokenFromFile(tokFile)
	if err != nil {
		tok = getTokenFromWeb(config)
		saveToken(tokFile, tok)
	}
	return config.Client(context.Background(), tok)
}

// Request a token from the web, then 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 authCode string
	if _, err := fmt.Scan(&authCode); err != nil {
		log.Fatalf("Unable to read authorization code: %v", err)
	}

	tok, err := config.Exchange(oauth2.NoContext, authCode)
	if err != nil {
		log.Fatalf("Unable to retrieve token from web: %v", err)
	}
	return tok
}

// Retrieves a token from a local file.
func tokenFromFile(file string) (*oauth2.Token, error) {
	f, err := os.Open(file)
	defer f.Close()
	if err != nil {
		return nil, err
	}
	tok := &oauth2.Token{}
	err = json.NewDecoder(f).Decode(tok)
	return tok, err
}

// Saves a token to a file path.
func saveToken(path string, token *oauth2.Token) {
	fmt.Printf("Saving credential file to: %s\n", path)
	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	defer f.Close()
	if err != nil {
		log.Fatalf("Unable to cache oauth token: %v", err)
	}
	json.NewEncoder(f).Encode(token)
}

func main() {
	b, err := ioutil.ReadFile("credentials.json")
	if err != nil {
		log.Fatalf("Unable to read client secret file: %v", err)
	}

	// If modifying these scopes, delete your previously saved token.json.
	config, err := google.ConfigFromJSON(b, calendar.CalendarReadonlyScope)
	if err != nil {
		log.Fatalf("Unable to parse client secret file to config: %v", err)
	}
	client := getClient(config)

	srv, err := calendar.New(client)
	if err != nil {
		log.Fatalf("Unable to retrieve Calendar client: %v", err)
	}

	t := time.Now().Format(time.RFC3339)
	events, err := srv.Events.List("primary").ShowDeleted(false).
		SingleEvents(true).TimeMin(t).MaxResults(10).OrderBy("startTime").Do()
	if err != nil {
		log.Fatalf("Unable to retrieve next ten of the user's events: %v", err)
	}
	fmt.Println("Upcoming events:")
	if len(events.Items) == 0 {
		fmt.Println("No upcoming events found.")
	} else {
		for _, item := range events.Items {
			date := item.Start.DateTime
			if date == "" {
				date = item.Start.Date
			}
			fmt.Printf("%v (%v)\n", item.Summary, date)
		}
	}
}

Step 4: Run the sample

Build and run the sample using the following command from your working directory:

go run quickstart.go

The first time you run the sample, it will prompt you to authorize access:

  1. Browse to the provided URL in your web browser.

    If you are not already logged into your Google account, you will be prompted to log in. If you are logged into multiple Google accounts, you will be asked to select one account to use for the authorization.

  2. Click the Accept button.
  3. Copy the code you're given, paste it into the command-line prompt, and press Enter.

Notes

  • Authorization information is stored on the file system, so subsequent executions will not prompt for authorization.
  • The authorization flow in this example is designed for a command-line application. For information on how to perform authorization in a web application, see Using OAuth 2.0 for Web Server Applications.

Further reading

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