Allow greater control over caching (#68)

* Improve the help message - add the flag documentation.

* Make the cache location a variable (exported to allow modification),
set to home dir by default during initialization.

* Add a flag to set the cache file location.

* Support empty cache location, to explicitly disable caching.

* add help message for disabling cache.

main.go

@@ -18,10 +18,11 @@ import (
 	"flag"
 	"fmt"
 	"io/ioutil"
+	"os"
 	"strings"
+
 	"github.com/google/oauth2l/sgauth"
 	"github.com/google/oauth2l/util"
-	"os"
 )
 
 var (
@@ -30,9 +31,10 @@ var (
 	cmds        = []string{"fetch", "header", "info", "test"}
 )
 
-func help() {
-	fmt.Println("Usage: oauth2l {fetch|header|info|test|reset} " +
-		"[--jwt] [--json] [--sso] [--ssocli] {scope|aud|email}")
+func help(f *flag.FlagSet) {
+	fmt.Println("Usage: oauth2l fetch|header|info|test|reset [flags]... [scope|aud|email]...")
+	f.PrintDefaults()
+	os.Exit(0)
 }
 
 func readJSON(file string) (string, error) {
@@ -69,11 +71,6 @@ func parseScopes(scopes []string) string {
 }
 
 func main() {
-	if len(os.Args) < 2 {
-		help()
-		return
-	}
-
 	// Configure the CLI
 	flagSet := flag.NewFlagSet("fetch", flag.ExitOnError)
 	helpFlag := flagSet.Bool("help", false, "Print help message.")
@@ -85,11 +82,16 @@ func main() {
 	jwtFlag := flagSet.Bool("jwt", false, "Use JWT auth flow")
 	ssoFlag := flagSet.Bool("sso", false, "Use SSO auth flow")
 	ssocli := flagSet.String("ssocli", "", "Path to SSO CLI")
+	flagSet.StringVar(&util.CacheLocation, "cache", util.CacheLocation, "Path to the credential cache file. Disables caching if set to empty.")
+
+	if len(os.Args) < 2 {
+		help(flagSet)
+	}
+
 	flagSet.Parse(os.Args[2:])
 
 	if *helpFlag {
-		help()
-		return
+		help(flagSet)
 	}
 
 	// Get the command keyword from the first argument.
@@ -128,9 +130,9 @@ func main() {
 				parseScopes(flagSet.Args()[1:]))
 		} else {
 			// OAuth flow
-			if (len(flagSet.Args()) < 1) {
-				fmt.Println("Missing scope for OAuth 2.0")
-				help()
+			if len(flagSet.Args()) < 1 {
+				fmt.Println("Missing scope argument for OAuth 2.0")
+				help(flagSet)
 				return
 			}
 
@@ -157,6 +159,6 @@ func main() {
 		util.Reset()
 	} else {
 		// Unknown command, print usage.
-		help()
+		help(flagSet)
 	}
 }

util/cache.go

@@ -15,18 +15,19 @@
 package util
 
 import (
-	"log"
-	"io/ioutil"
 	"encoding/json"
+	"io/ioutil"
+	"log"
 	"os"
-	"github.com/google/oauth2l/sgauth"
 	"path/filepath"
-)
 
-const (
-	cacheFileName = ".oauth2l"
+	"github.com/google/oauth2l/sgauth"
 )
 
+const CacheFileName = ".oauth2l"
+
+var CacheLocation string = filepath.Join(sgauth.GuessUnixHomeDir(), CacheFileName)
+
 // The key struct that used to identify an auth token fetch operation.
 type CacheKey struct {
 	// The JSON credentials content downloaded from Google Cloud Console.
@@ -40,6 +41,9 @@ type CacheKey struct {
 }
 
 func LookupCache(settings *sgauth.Settings) (*sgauth.Token, error) {
+	if CacheLocation == "" {
+		return nil, nil
+	}
 	var token sgauth.Token
 	var cache, err = loadCache()
 	if err != nil {
@@ -58,6 +62,9 @@ func LookupCache(settings *sgauth.Settings) (*sgauth.Token, error) {
 }
 
 func InsertCache(settings *sgauth.Settings, token *sgauth.Token) error {
+	if CacheLocation == "" {
+		return nil
+	}
 	var cache, err = loadCache()
 	if err != nil {
 		return err
@@ -75,33 +82,36 @@ func InsertCache(settings *sgauth.Settings, token *sgauth.Token) error {
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(cacheLocation(), data, 0666)
+	return ioutil.WriteFile(CacheLocation, data, 0666)
 }
 
 func ClearCache() error {
-	if _, err := os.Stat(cacheLocation()); os.IsNotExist(err) {
+	if CacheLocation == "" {
+		return nil
+	}
+	if _, err := os.Stat(CacheLocation); os.IsNotExist(err) {
 		// Noop if file does not exist.
 		return nil
 	}
-	return os.Remove(cacheLocation())
+	return os.Remove(CacheLocation)
 }
 
 func loadCache() (map[string][]byte, error) {
-	if _, err := os.Stat(cacheLocation()); os.IsNotExist(err) {
+	if _, err := os.Stat(CacheLocation); os.IsNotExist(err) {
 		// Create the cache file if not existing.
-		f, err := os.OpenFile(cacheLocation(), os.O_RDONLY|os.O_CREATE, 0666)
+		f, err := os.OpenFile(CacheLocation, os.O_RDONLY|os.O_CREATE, 0666)
 		if err != nil {
 			log.Fatal(err)
 			return nil, err
 		}
 		f.Close()
 	}
-	data, err := ioutil.ReadFile(cacheLocation())
+	data, err := ioutil.ReadFile(CacheLocation)
 	if err != nil {
 		log.Fatal(err)
 		return nil, err
 	}
-	m := map[string][]byte{}
+	m := make(map[string][]byte)
 	if len(data) > 0 {
 		err = json.Unmarshal(data, &m)
 		if err != nil {
@@ -112,16 +122,11 @@ func loadCache() (map[string][]byte, error) {
 	return m, nil
 }
 
-func cacheLocation() string {
-	return filepath.Join(sgauth.GuessUnixHomeDir(), cacheFileName)
-}
-
 func createKey(settings *sgauth.Settings) CacheKey {
 	return CacheKey{
 		CredentialsJSON: settings.CredentialsJSON,
-		Scope: settings.Scope,
-		Audience: settings.Audience,
-		APIKey: settings.APIKey,
+		Scope:           settings.Scope,
+		Audience:        settings.Audience,
+		APIKey:          settings.APIKey,
 	}
 }
-