Initial commit, part 1

pkg/oauthhandler/oauth2_handler.go

@@ -0,0 +1,107 @@
+package oauthhandler
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os/exec"
+	"runtime"
+
+	"github.com/facebookincubator/go-belt/tool/logger"
+)
+
+type OAuth2Handler struct {
+	authURL      string
+	exchangeFn   func(code string) error
+	receiverAddr string
+}
+
+func NewOAuth2Handler(
+	authURL string,
+	exchangeFn func(code string) error,
+	receiverAddr string,
+) *OAuth2Handler {
+	return &OAuth2Handler{
+		authURL:      authURL,
+		exchangeFn:   exchangeFn,
+		receiverAddr: receiverAddr,
+	}
+}
+
+// it is guaranteed exchangeFn was called if error is nil.
+func (h *OAuth2Handler) Handle(ctx context.Context) error {
+	if h.receiverAddr != "" {
+		err := h.handleViaBrowser()
+		if err == nil {
+			return nil
+		}
+		logger.Errorf(ctx, "unable to authenticate automatically: %v", err)
+	}
+	return h.handleViaCLI()
+}
+
+func (h *OAuth2Handler) handleViaCLI() error {
+	fmt.Printf(
+		"It is required to get an oauth2 token. "+
+			"Please open the link below in the browser:\n\n\t%s\n\n",
+		h.authURL,
+	)
+
+	fmt.Printf("Enter the code: ")
+	var code string
+	if _, err := fmt.Scan(&code); err != nil {
+		log.Fatalf("Unable to read authorization code %v", err)
+	}
+	return h.exchangeFn(code)
+}
+
+func (h *OAuth2Handler) handleViaBrowser() error {
+	codeCh, err := h.newCodeReceiver()
+	if err != nil {
+		return err
+	}
+
+	err = launchBrowser(h.authURL)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Your browser has been launched (URL: %s).\nPlease approve the permissions.\n", h.authURL)
+
+	// Wait for the web server to get the code.
+	code := <-codeCh
+	return h.exchangeFn(code)
+}
+
+func (h *OAuth2Handler) newCodeReceiver() (codeCh chan string, err error) {
+	// this function was mostly borrowed from https://developers.google.com/youtube/v3/code_samples/go#authorize_a_request
+	listener, err := net.Listen("tcp", h.receiverAddr)
+	if err != nil {
+		return nil, err
+	}
+	codeCh = make(chan string)
+
+	go http.Serve(listener, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		code := r.FormValue("code")
+		codeCh <- code
+		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)
+	}))
+
+	return codeCh, nil
+}
+
+func launchBrowser(url string) error {
+	switch runtime.GOOS {
+	case "darwin":
+		return exec.Command("open", url).Start()
+	case "linux":
+		return exec.Command("xdg-open", url).Start()
+	case "windows":
+		return exec.Command("rundll32", "url.dll,FileProtocolHandler", url).Start()
+	}
+	return fmt.Errorf("unsupported platform: <%s>", runtime.GOOS)
+}