Async-ify.

README.md

Index: README.md
diff --git a/README.md b/README.md
index 52b724c9d5bf6125bf4bf2bf69a1f2414392dbd4..23be5ff2047324bf4312934f7b6612152f3996b5 100644
--- a/README.md
+++ b/README.md
@@ -48,53 +48,60 @@ final secret = "my client secret";
 // query parameters.
 final redirectUrl = Uri.parse("http://my-site.com/oauth2-redirect");
 
-var credentialsFile = new File("~/.myapp/credentials.json");
-return credentialsFile.exists().then((exists) {
-  // If the OAuth2 credentials have already been saved from a previous
-  // run, we just want to reload them.
+/// A file in which the users credentials are stored persistently. If the server
+/// issues a refresh token allowing the client to refresh outdated credentials,
+/// these may be valid indefinitely, meaning the user never has to
+/// re-authenticate.
+final credentialsFile = new File("~/.myapp/credentials.json");
+
+/// Either load an OAuth2 client from saved credentials or authenticate a new
+/// one.
+Future<oauth2.Client> getClient() async {
+  var exists = await credentialsFile.exists();
+
+  // If the OAuth2 credentials have already been saved from a previous run, we
+  // just want to reload them.
   if (exists) {
-    return credentialsFile.readAsString().then((json) {
-      var credentials = new oauth2.Credentials.fromJson(json);
-      return new oauth2.Client(identifier, secret, credentials);
-    });
+    var credentials = new oauth2.Credentials.fromJson(
+        await credentialsFile.readAsString());
+    return new oauth2.Client(identifier, secret, credentials);
   }
 
-  // If we don't have OAuth2 credentials yet, we need to get the
-  // resource owner to authorize us. We're assuming here that we're a
-  // command-line application.
+  // If we don't have OAuth2 credentials yet, we need to get the resource owner
+  // to authorize us. We're assuming here that we're a command-line application.
   var grant = new oauth2.AuthorizationCodeGrant(
       identifier, secret, authorizationEndpoint, tokenEndpoint);
 
-  // Redirect the resource owner to the authorization URL. This will be
-  // a URL on the authorization server (authorizationEndpoint with some
-  // additional query parameters). Once the resource owner has
-  // authorized, they'll be redirected to `redirectUrl` with an
-  // authorization code.
+  // Redirect the resource owner to the authorization URL. This will be a URL on
+  // the authorization server (authorizationEndpoint with some additional query
+  // parameters). Once the resource owner has authorized, they'll be redirected
+  // to `redirectUrl` with an authorization code.
   //
   // `redirect` is an imaginary function that redirects the resource
   // owner's browser.
-  return redirect(grant.getAuthorizationUrl(redirectUrl)).then((_) {
-    // Another imaginary function that listens for a request to
-    // `redirectUrl`.
-    return listen(redirectUrl);
-  }).then((request) {
-    // Once the user is redirected to `redirectUrl`, pass the query
-    // parameters to the AuthorizationCodeGrant. It will validate them
-    // and extract the authorization code to create a new Client.
-    return grant.handleAuthorizationResponse(request.uri.queryParameters);
-  })
-}).then((client) {
-  // Once you have a Client, you can use it just like any other HTTP
-  // client.
-  return client.read("http://example.com/protected-resources.txt")
-      .then((result) {
-    // Once we're done with the client, save the credentials file. This
-    // ensures that if the credentials were automatically refreshed
-    // while using the client, the new credentials are available for the
-    // next run of the program.
-    return credentialsFile.open(FileMode.WRITE).then((file) {
-      return file.writeString(client.credentials.toJson());
-    }).then((file) => file.close()).then((_) => result);
-  });
-}).then(print);
+  await redirect(grant.getAuthorizationUrl(redirectUrl));
+  
+  // Another imaginary function that listens for a request to `redirectUrl`.
+  var request = await listen(redirectUrl);
+
+  // Once the user is redirected to `redirectUrl`, pass the query parameters to
+  // the AuthorizationCodeGrant. It will validate them and extract the
+  // authorization code to create a new Client.
+  return await grant.handleAuthorizationResponse(request.uri.queryParameters);
+}
+
+main() async {
+  var client = await loadClient();
+
+  // Once you have a Client, you can use it just like any other HTTP client.
+  var result = client.read("http://example.com/protected-resources.txt");
+
+  // Once we're done with the client, save the credentials file. This ensures
+  // that if the credentials were automatically refreshed while using the
+  // client, the new credentials are available for the next run of the
+  // program.
+  await credentialsFile.writeAsString(client.credentials.toJson());
+
+  print(result);
+}
 ```