imp: accept any string-like parameter

Use the power of the `AsRef` trait to take generic parameters for
several API functions. This makes the API more ergonomic because the
callers may pass in static `str` slices or references to owned `String`s
or even more exotic things like a `Cow`, all based on their particular
situation.

Update the tests and examples to use the most natural types they have
available.

Fixes #77. No existing code should break, as `&String` implements
`AsRef<str>` and `AsRef<Path>`

examples/drive_example/src/main.rs

@@ -34,7 +34,7 @@ fn main() {
     let authenticator = Authenticator::new(&secret,
                                            DefaultAuthenticatorDelegate,
                                            client,
-                                           DiskTokenStorage::new(&"token_store.json".to_string())
+                                           DiskTokenStorage::new("token_store.json")
                                                .unwrap(),
                                            Some(FlowType::InstalledInteractive));
     let client = hyper::Client::with_connector(

examples/service_account/src/main.rs

@@ -165,7 +165,7 @@ fn publish_stuff(methods: &PubsubMethods, message: &str) {
 // If called as '.../service_account pub', act as publisher; if called as '.../service_account
 // sub', act as subscriber.
 fn main() {
-    let client_secret = oauth::service_account_key_from_file(&"pubsub-auth.json".to_string())
+    let client_secret = oauth::service_account_key_from_file("pubsub-auth.json")
         .unwrap();
     let client = hyper::Client::with_connector(HttpsConnector::new(NativeTlsClient::new().unwrap()));
     let mut access = oauth::ServiceAccountAccess::new(client_secret, client);

src/authenticator.rs

@@ -238,8 +238,7 @@ where
                                     }
                                 }
                                 RefreshResult::RefreshError(ref err_str, ref err_description) => {
-                                    self.delegate
-                                        .token_refresh_failed(&err_str, &err_description);
+                                    self.delegate.token_refresh_failed(err_str, err_description);
                                     let storage_err =
                                         match self.storage.set(scope_key, &scopes, None) {
                                             Ok(_) => String::new(),

src/authenticator_delegate.rs

@@ -90,7 +90,11 @@ pub trait AuthenticatorDelegate {
     /// Called if we could not acquire a refresh token for a reason possibly specified
     /// by the server.
     /// This call is made for the delegate's information only.
-    fn token_refresh_failed(&mut self, error: &String, error_description: &Option<String>) {
+    fn token_refresh_failed<S: AsRef<str>>(
+        &mut self,
+        error: S,
+        error_description: &Option<String>,
+    ) {
         {
             let _ = error;
         }
@@ -136,7 +140,11 @@ pub trait AuthenticatorDelegate {
     /// We need the user to navigate to a URL using their browser and potentially paste back a code
     /// (or maybe not). Whether they have to enter a code depends on the InstalledFlowReturnMethod
     /// used.
-    fn present_user_url(&mut self, url: &String, need_code: bool) -> Option<String> {
+    fn present_user_url<S: AsRef<str> + fmt::Display>(
+        &mut self,
+        url: S,
+        need_code: bool,
+    ) -> Option<String> {
         if need_code {
             println!(
                 "Please direct your browser to {}, follow the instructions and enter the \

src/device.rs

@@ -314,7 +314,7 @@ pub mod tests {
     fn working_flow() {
         use crate::helper::parse_application_secret;
 
-        let appsecret = parse_application_secret(&TEST_APP_SECRET.to_string()).unwrap();
+        let appsecret = parse_application_secret(TEST_APP_SECRET).unwrap();
         let mut flow = DeviceFlow::new(
             hyper::Client::with_connector(<MockGoogleAuth as Default>::default()),
             &appsecret,

src/helper.rs

@@ -28,8 +28,9 @@ pub fn read_application_secret(path: &Path) -> io::Result<ApplicationSecret> {
 }
 
 /// Read an application secret from a JSON string.
-pub fn parse_application_secret(secret: &String) -> io::Result<ApplicationSecret> {
-    let result: serde_json::Result<ConsoleApplicationSecret> = serde_json::from_str(secret);
+pub fn parse_application_secret<S: AsRef<str>>(secret: S) -> io::Result<ApplicationSecret> {
+    let result: serde_json::Result<ConsoleApplicationSecret> =
+        serde_json::from_str(secret.as_ref());
     match result {
         Err(e) => Err(io::Error::new(
             io::ErrorKind::InvalidData,
@@ -52,7 +53,7 @@ pub fn parse_application_secret(secret: &String) -> io::Result<ApplicationSecret
 
 /// Read a service account key from a JSON file. You can download the JSON keys from the Google
 /// Cloud Console or the respective console of your service provider.
-pub fn service_account_key_from_file(path: &String) -> io::Result<ServiceAccountKey> {
+pub fn service_account_key_from_file<S: AsRef<Path>>(path: S) -> io::Result<ServiceAccountKey> {
     let mut key = String::new();
     let mut file = fs::OpenOptions::new().read(true).open(path)?;
     file.read_to_string(&mut key)?;

src/refresh.rs

@@ -166,7 +166,7 @@ mod tests {
 
     #[test]
     fn refresh_flow() {
-        let appsecret = parse_application_secret(&TEST_APP_SECRET.to_string()).unwrap();
+        let appsecret = parse_application_secret(TEST_APP_SECRET).unwrap();
 
         let mut c = hyper::Client::with_connector(<MockGoogleRefresh as Default>::default());
         let mut flow = RefreshFlow::new(&mut c);

src/service_account.rs

@@ -351,7 +351,7 @@ mod tests {
     //#[test]
     #[allow(dead_code)]
     fn test_service_account_e2e() {
-        let key = service_account_key_from_file(&TEST_PRIVATE_KEY_PATH.to_string()).unwrap();
+        let key = service_account_key_from_file(TEST_PRIVATE_KEY_PATH).unwrap();
         let client =
             hyper::Client::with_connector(HttpsConnector::new(NativeTlsClient::new().unwrap()));
         let mut acc = ServiceAccountAccess::new(key, client);
@@ -364,7 +364,7 @@ mod tests {
 
     #[test]
     fn test_jwt_initialize_claims() {
-        let key = service_account_key_from_file(&TEST_PRIVATE_KEY_PATH.to_string()).unwrap();
+        let key = service_account_key_from_file(TEST_PRIVATE_KEY_PATH).unwrap();
         let scopes = vec!["scope1", "scope2", "scope3"];
         let claims = super::init_claims_from_key(&key, &scopes);
 
@@ -384,7 +384,7 @@ mod tests {
 
     #[test]
     fn test_jwt_sign() {
-        let key = service_account_key_from_file(&TEST_PRIVATE_KEY_PATH.to_string()).unwrap();
+        let key = service_account_key_from_file(TEST_PRIVATE_KEY_PATH).unwrap();
         let scopes = vec!["scope1", "scope2", "scope3"];
         let claims = super::init_claims_from_key(&key, &scopes);
         let jwt = super::JWT::new(claims);

src/storage.rs

@@ -132,9 +132,9 @@ pub struct DiskTokenStorage {
 }
 
 impl DiskTokenStorage {
-    pub fn new(location: &String) -> Result<DiskTokenStorage, io::Error> {
+    pub fn new<S: AsRef<str>>(location: S) -> Result<DiskTokenStorage, io::Error> {
         let mut dts = DiskTokenStorage {
-            location: location.clone(),
+            location: location.as_ref().to_owned(),
             tokens: HashMap::new(),
         };