Go Quickstart

Complete the steps described in the rest of this page to create a simple Go command-line application that makes requests to the Drive API.

Prerequisites

To run this quickstart, you need the following prerequisites:

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

Step 1: Turn on the Drive API

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

Enable the Drive 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 Drive API Go client library and OAuth2 package using the following commands:
go get -u google.golang.org/api/drive/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:

drive/quickstart/quickstart.go
package main

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

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

// Retrieve a token, saves the token, then returns the generated client.
func getClient(config *oauth2.Config) *http.Client {
	// The file token.json stores the user's access and refresh tokens, and is
	// created automatically when the authorization flow completes for the first
	// time.
	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(context.TODO(), 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)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	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)
	if err != nil {
		log.Fatalf("Unable to cache oauth token: %v", err)
	}
	defer f.Close()
	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, drive.DriveMetadataReadonlyScope)
	if err != nil {
		log.Fatalf("Unable to parse client secret file to config: %v", err)
	}
	client := getClient(config)

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

	r, err := srv.Files.List().PageSize(10).
		Fields("nextPageToken, files(id, name)").Do()
	if err != nil {
		log.Fatalf("Unable to retrieve files: %v", err)
	}
	fmt.Println("Files:")
	if len(r.Files) == 0 {
		fmt.Println("No files found.")
	} else {
		for _, i := range r.Files {
			fmt.Printf("%s (%s)\n", i.Name, i.Id)
		}
	}
}

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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