[Go] Google API 基本運用

程式語言：Go

Package：

Google APIs

google-api-go-client

功能：運用 google 各種服務

申請 API Key

1. 進入 Google APIs
2. 上方：新增專案
3. 資訊頁面：點選 啟用 API 和服務
4. 憑證頁面：依需求建立憑證

基本用法

1. 建立 client，內建已含認證方式，自定義 client 可在 Transport 實作
2. service.New(client) 建立 service 呼叫 API
3. service.apiService.apiCall(...) 建立 call
4. call.parameter(...) 設定各種參數
5. call.Do() 送出 request

範例：

package main

import (
    "fmt"
    "google.golang.org/api/drive/v3"
)

func main() {
    auth := NewAuth(redirectURL)
    client := auth.GetClient(clientsecretPath, "drive-go.json")

    service, err := drive.New(client)
    if err != nil {
        panic(err)
    }

    call := service.Files.List()
    call = call.PageSize(2)

    response, err := call.Do()
    if err != nil {
        panic(err)
    }
}

oauth2 範例

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "log"
    "net"
    "net/http"
    "net/url"
    "os"
    "os/user"
    "path/filepath"

    "github.com/pkg/errors"
    "golang.org/x/net/context"
    "golang.org/x/oauth2"
)

// This variable indicates whether the script should launch a web server to
// initiate the authorization flow or just display the URL in the terminal
// window. Note the following instructions based on this setting:
// * launchWebServer = true
//   1. Use OAuth2 credentials for a web application
//   2. Define authorized redirect URIs for the credential in the Google APIs
//      Console and set the RedirectURL property on the config object to one
//      of those redirect URIs. For example:
//      config.RedirectURL = "http://localhost:8090"
//   3. In the startWebServer function below, update the URL in this line
//      to match the redirect URI you selected:
//         listener, err := net.Listen("tcp", "localhost:8090")
//      The redirect URI identifies the URI to which the user is sent after
//      completing the authorization flow. The listener then captures the
//      authorization code in the URL and passes it back to this script.
// * launchWebServer = false
//   1. Use OAuth2 credentials for an installed application. (When choosing
//      the application type for the OAuth2 client ID, select "Other".)
//   2. Set the redirect URI to "urn:ietf:wg:oauth:2.0:oob", like this:
//      config.RedirectURL = "urn:ietf:wg:oauth:2.0:oob"
//   3. When running the script, complete the auth flow. Then copy the
//      authorization code from the browser and enter it on the command line.
const launchWebServer = true

const missingClientSecretsMessage = `
Please configure OAuth 2.0
To make this sample run, you need to populate the client_secrets.json file
found at:
   %v
with information from the {{ Google Cloud Console }}{{ https://cloud.google.com/console }}For more information about the client_secrets.json file format, please visit:
https://developers.google.com/api-client-library/python/guide/aaa_client_secrets
`

// Auth for oauth2
type Auth struct {
    redirectURL *url.URL
    config      *oauth2.Config

    useTLS          bool
    tlsCert, tlsKey string
}

// NewAuth create Auth
func NewAuth(redirectURL string) *Auth {
    a := &Auth{}
    var err error
    a.redirectURL, err = url.Parse(redirectURL)
    if err != nil {
        log.Fatal(err)
    }

    return a
}

// SetTLS when redirectURL is TLS, it should be setted
func (a *Auth) SetTLS(TLSCertPath, TLSKeyPath string) {
    a.tlsCert = TLSCertPath
    a.tlsKey = TLSKeyPath
    a.useTLS = true
}

// GetClient generate a Client. It returns the generated Client.
// clientsecret file format reference to client_secret.json.sample
func (a *Auth) GetClient(clientsecretPath, tokenFile string) *http.Client {
    ctx := context.Background()

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

    // If modifying the scope, delete your previously saved credentials
    // at ~/.credentials/tokenFile
    err = a.configFromJSON(b)
    if err != nil {
        log.Fatalf("Unable to parse client secret file to config: %v", err)
    }

    // Use a redirect URI like this for a web app. The redirect URI must be a
    // valid one for your OAuth2 credentials.
    a.config.RedirectURL = a.redirectURL.String()
    // Use the following redirect URI if launchWebServer=false in oauth2.go
    // config.RedirectURL = "urn:ietf:wg:oauth:2.0:oob"

    cacheFile, err := a.tokenCacheFile(tokenFile)
    if err != nil {
        log.Fatalf("Unable to get path to cached credential file. %v", err)
    }
    token, err := a.tokenFromFile(cacheFile)
    if err != nil {
        if launchWebServer {
            fmt.Println("Trying to get token from web")
            token, err = a.getTokenFromWeb()
        } else {
            fmt.Println("Trying to get token from prompt")
            token, err = a.getTokenFromPrompt()
        }
        if err == nil {
            a.saveToken(cacheFile, token)
        }
    }
    return a.config.Client(ctx, token)
}

func (a *Auth) configFromJSON(jsonKey []byte, scope ...string) error {
    type cred struct {
        ClientID     string   `json:"client_id,omitempty"`
        ClientSecret string   `json:"client_secret,omitempty"`
        RedirectURIs []string `json:"redirect_uris,omitempty"`
        AuthURI      string   `json:"auth_uri,omitempty"`
        TokenURI     string   `json:"token_uri,omitempty"`
    }
    var j struct {
        Web       *cred `json:"web,omitempty"`
        Installed *cred `json:"installed,omitempty"`
    }
    if err := json.Unmarshal(jsonKey, &j); err != nil {
        return err
    }
    var c *cred
    switch {
    case j.Web != nil:
        c = j.Web
    case j.Installed != nil:
        c = j.Installed
    default:
        return fmt.Errorf("oauth2: no credentials found")
    }
    if len(c.RedirectURIs) < 1 {
        return errors.New("oauth2: missing redirect URL in the client_credentials.json")
    }
    a.config = &oauth2.Config{
        ClientID:     c.ClientID,
        ClientSecret: c.ClientSecret,
        RedirectURL:  c.RedirectURIs[0],
        Scopes:       scope,
        Endpoint: oauth2.Endpoint{
            AuthURL:  c.AuthURI,
            TokenURL: c.TokenURI,
        },
    }

    return nil
}

// startWebServer starts a web server that listens on http://localhost:8080.
// The webserver waits for an oauth code in the three-legged auth flow.
func (a *Auth) startWebServer() (codeCh chan string, err error) {
    listener, err := net.Listen("tcp", a.redirectURL.Host)
    if err != nil {
        return nil, errors.Wrapf(err, "net.Listen")
    }
    codeCh = make(chan string)

    handFunc := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        code := r.FormValue("code")
        codeCh <- code // send code to OAuth flow
        listener.Close()
        w.Header().Set("Content-Type", "text/plain")
        fmt.Fprintf(w, "Received code: %v\r\nYou can now safely close this browser window.", code)
    })
    if a.useTLS {
        log.Printf("create TLS Server\n")
        log.Printf("certPath: %s\n", a.tlsCert)
        log.Printf("keyPath: %s\n", a.tlsKey)
        go http.ServeTLS(listener, handFunc, a.tlsCert, a.tlsKey)
    } else {
        go http.Serve(listener, handFunc)
    }

    return codeCh, nil
}

// Exchange the authorization code for an access token
func (a *Auth) exchangeToken(code string) (*oauth2.Token, error) {
    // set access_type offline for refresh token
    token, err := a.config.Exchange(oauth2.NoContext, code, oauth2.AccessTypeOffline)
    if err != nil {
        log.Fatalf("Unable to retrieve token %v", err)
    }
    return token, nil
}

// getTokenFromPrompt uses Config to request a Token and prompts the user
// to enter the token on the command line. It returns the retrieved Token.
func (a *Auth) getTokenFromPrompt() (*oauth2.Token, error) {
    authURL := a.config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)

    var code string
    fmt.Printf("Go to the following link in your browser. After completing "+
        "the authorization flow, enter the authorization code on the command "+
        "line: \n%v\n", authURL)

    if _, err := fmt.Scan(&code); err != nil {
        log.Fatalf("Unable to read authorization code %v", err)
    }

    fmt.Println(authURL)
    return a.exchangeToken(code)
}

// getTokenFromWeb uses Config to request a Token.
// It returns the retrieved Token.
func (a *Auth) getTokenFromWeb() (*oauth2.Token, error) {
    codeCh, err := a.startWebServer()
    if err != nil {
        fmt.Printf("Unable to start a web server. %s", err)
        return nil, errors.Wrapf(err, "a.startWebServer")
    }

    authURL := a.config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
    err = openURL(authURL)
    if err != nil {
        log.Fatalf("Unable to open authorization URL in web server: %v", err)
    } else {
        fmt.Println("Your browser has been opened to an authorization URL.",
            "This program will resume once authorization has been provided.")
        fmt.Println(authURL)
    }

    // Wait for the web server to get the code.
    code := <-codeCh
    return a.exchangeToken(code)
}

// tokenCacheFile generates credential file path/filename.
// It returns the generated credential path/filename.
func (a *Auth) 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 (a *Auth) 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 (a *Auth) saveToken(file string, token *oauth2.Token) {
    fmt.Println("trying to save 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)
}

參考

取得 Google API Key(金鑰) 流程，啟用服務 + 瞭解配額限制
google 官方 oauth2 範例
Go實戰--golang中OAuth2.0的使用(使用google賬號進行登陸驗證)