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 Apps Script Execution API.

Prerequisites

To run this quickstart, you'll need:

  • Go, latest version recommended.
  • Git, latest version recommended.
  • Access to the internet and a web browser.
  • A Google account with Google Drive enabled.
  • A target Apps Script to call with the API.

Step 1: Turn on the Google Apps Script Execution API

  1. Open your target Apps Script in the editor and select Resources > Cloud Platform project.
  2. In the dialog that opens, click on the blue link (that starts with your script's name) at the top to open the console project associated with your script.
  3. The left sidebar should say API Manager. If it does not, click the icon in the upper-left to open a side panel and select API Manager. Select Library in the left sidebar.
  4. In the search bar under the Google APIs tab, enter "Google Apps Script Execution API". Click the same name in the list that appears. In the new tab that opens, click Enable API.
  5. Click Credentials in the left sidebar.
  6. Select the Credentials tab, click the Create credentials button and select OAuth client ID.
  7. Select the application type Other, enter the name "Google Apps Script Execution API Quickstart", and click the Create button.
  8. Click OK to dismiss the resulting dialog.
  9. Click the file_download (Download JSON) button to the right of the client ID.
  10. Move this file to your working directory and rename it client_secret.json.

Step 2: Prepare the workspace

  1. Set the GOPATH environment variable to your working directory.
  2. Get the Google Apps Script Execution API Go client library and OAuth2 package using the following commands:
go get -u google.golang.org/api/script/v1
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:



package main

import (
  "encoding/json"
  "fmt"
  "io/ioutil"
  "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/script/v1"
)

// 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) *http.Client {
  cacheFile, err := tokenCacheFile()
  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() (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("script-go-quickstart.json")), 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.OpenFile(file, 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() {
  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/script-go-quickstart.json
  config, err := google.ConfigFromJSON(b, "https://www.googleapis.com/auth/drive")
  if err != nil {
    log.Fatalf("Unable to parse client secret file to config: %v", err)
  }
  scriptId := "ENTER_YOUR_SCRIPT_ID_HERE"
  client := getClient(ctx, config)

  // Generate a service object.
  srv, err := script.New(client)
  if err != nil {
    log.Fatalf("Unable to retrieve script Client %v", err)
  }

  // Create an execution request object.
  req := script.ExecutionRequest{Function:"getFoldersUnderRoot"}

  // Make the API request.
  resp, err := srv.Scripts.Run(scriptId, &req).Do()
  if err != nil {
    // The API encountered a problem before the script started executing.
    log.Fatalf("Unable to execute Apps Script function. %v", err)
  }

  if resp.Error != nil {
    // The API executed, but the script returned an error.

    // Extract the first (and only) set of error details and cast as a map.
    // The values of this map are the script's 'errorMessage' and
    // 'errorType', and an array of stack trace elements (which also need to
    // be cast as maps).
    error := resp.Error.Details[0].(map[string]interface{})
    fmt.Printf("Script error message: %s\n", error["errorMessage"]);

    if (error["scriptStackTraceElements"] != nil) {
      // There may not be a stacktrace if the script didn't start executing.
      fmt.Printf("Script error stacktrace:\n")
      for _, trace := range error["scriptStackTraceElements"].([]interface{}) {
        t := trace.(map[string]interface{})
        fmt.Printf("\t%s: %d\n", t["function"], int(t["lineNumber"].(float64)))
      }
    }
  } else {
    // The result provided by the API needs to be cast into the correct type,
    // based upon what types the Apps Script function returns. Here, the
    // function returns an Apps Script Object with String keys and values, so
    // must be cast into a map (folderSet).
    r := resp.Response.(map[string]interface{})
    folderSet := r["result"].(map[string]interface{})
    if len(folderSet) == 0 {
      fmt.Printf("No folders returned!\n")
    } else {
      fmt.Printf("Folders under your root folder:\n")
      for id, folder := range folderSet {
        fmt.Printf("\t%s (%s)\n", folder, id)
      }
    }
  }

}
Be sure to also replace the placeholder ENTER_YOUR_SCRIPT_ID_HERE with the script ID of your target script.

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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