Add debug log feature (#39)

example/main.go

@@ -73,6 +73,7 @@ Then set the following options:`)
 		LocalServerReadyChan: ready,
 		LocalServerCertFile:  o.localServerCert,
 		LocalServerKeyFile:   o.localServerKey,
+		Logf:                 log.Printf,
 	}
 
 	ctx := context.Background()

oauth2cli.go

@@ -89,6 +89,9 @@ type Config struct {
 	// A channel to send its URL when the local server is ready. Default to none.
 	LocalServerReadyChan chan<- string
 
+	// Logger function for debug.
+	Logf func(format string, args ...interface{})
+
 	// DEPRECATED: this will be removed in the future release.
 	// Use LocalServerBindAddress instead.
 	// Address which the local server binds to.
@@ -123,6 +126,9 @@ func (c *Config) validateAndSetDefaults() error {
 	if c.LocalServerSuccessHTML == "" {
 		c.LocalServerSuccessHTML = DefaultLocalServerSuccessHTML
 	}
+	if c.Logf == nil {
+		c.Logf = func(string, ...interface{}) {}
+	}
 	return nil
 }
 
@@ -150,16 +156,17 @@ func (c *Config) populateDeprecatedFields() {
 // 	5. Exchange the code and a token.
 // 	6. Return the code.
 //
-func GetToken(ctx context.Context, config Config) (*oauth2.Token, error) {
-	if err := config.validateAndSetDefaults(); err != nil {
+func GetToken(ctx context.Context, c Config) (*oauth2.Token, error) {
+	if err := c.validateAndSetDefaults(); err != nil {
 		return nil, fmt.Errorf("invalid config: %w", err)
 	}
-	config.populateDeprecatedFields()
-	code, err := receiveCodeViaLocalServer(ctx, &config)
+	c.populateDeprecatedFields()
+	code, err := receiveCodeViaLocalServer(ctx, &c)
 	if err != nil {
 		return nil, fmt.Errorf("authorization error: %w", err)
 	}
-	token, err := config.OAuth2Config.Exchange(ctx, code, config.TokenRequestOptions...)
+	c.Logf("oauth2cli: exchanging the code and token")
+	token, err := c.OAuth2Config.Exchange(ctx, code, c.TokenRequestOptions...)
 	if err != nil {
 		return nil, fmt.Errorf("could not exchange the code and token: %w", err)
 	}

server.go

@@ -33,32 +33,40 @@ func receiveCodeViaLocalServer(ctx context.Context, c *Config) (string, error) {
 			select {
 			case received, ok := <-respCh:
 				if !ok {
+					c.Logf("oauth2cli: response channel has been closed")
 					return nil // channel is closed (after the server is stopped)
 				}
 				if resp == nil {
 					resp = received // pick only the first response
 				}
+				c.Logf("oauth2cli: shutting down the server at %s", l.Addr())
 				if err := server.Shutdown(ctx); err != nil {
 					return fmt.Errorf("could not shutdown the local server: %w", err)
 				}
 			case <-ctx.Done():
+				c.Logf("oauth2cli: context cancelled: %s", ctx.Err())
+				c.Logf("oauth2cli: shutting down the server at %s", l.Addr())
 				if err := server.Shutdown(ctx); err != nil {
 					return fmt.Errorf("could not shutdown the local server: %w", err)
 				}
-				return fmt.Errorf("context done while waiting for authorization response: %w", ctx.Err())
+				return fmt.Errorf("context cancelled while waiting for authorization response: %w", ctx.Err())
 			}
 		}
 	})
 	eg.Go(func() error {
 		defer close(respCh)
 		if c.LocalServerCertFile != "" && c.LocalServerKeyFile != "" {
+			c.Logf("oauth2cli: starting HTTPS server at %s", l.Addr())
 			if err := server.ServeTLS(l, c.LocalServerCertFile, c.LocalServerKeyFile); err != nil && err != http.ErrServerClosed {
-				return fmt.Errorf("could not start a local TLS server: %w", err)
+				return fmt.Errorf("could not start HTTPS server: %w", err)
 			}
+			c.Logf("oauth2cli: stopped HTTPS server at %s", l.Addr())
 		} else {
+			c.Logf("oauth2cli: starting HTTP server at %s", l.Addr())
 			if err := server.Serve(l); err != nil && err != http.ErrServerClosed {
-				return fmt.Errorf("could not start a local server: %w", err)
+				return fmt.Errorf("could not start HTTP server: %w", err)
 			}
+			c.Logf("oauth2cli: stopped HTTP server at %s", l.Addr())
 		}
 		return nil
 	})
@@ -109,6 +117,7 @@ func (h *localServerHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 func (h *localServerHandler) handleIndex(w http.ResponseWriter, r *http.Request) {
 	authCodeURL := h.config.OAuth2Config.AuthCodeURL(h.config.State, h.config.AuthCodeOptions...)
+	h.config.Logf("oauth2cli: sending redirect to %s", authCodeURL)
 	http.Redirect(w, r, authCodeURL, 302)
 }