Accept any IO object for credentials

lib/fcm.rb

@@ -320,10 +320,18 @@ def validate_condition_topics?(condition)
   def jwt_token
     scope = "https://www.googleapis.com/auth/firebase.messaging"
     authorizer = Google::Auth::ServiceAccountCredentials.make_creds(
-      json_key_io: File.open(@json_key_path),
+      json_key_io: json_key,
       scope: scope,
     )
     token = authorizer.fetch_access_token!
     token["access_token"]
   end
+
+  def json_key
+    @json_key ||= if @json_key_path.respond_to?(:read)
+                    @json_key_path
+                  else
+                    File.open(@json_key_path)
+                  end
+  end
 end

spec/fcm_spec.rb

@@ -498,4 +498,16 @@
   describe "subscribing to a topic" do
     # TODO
   end
+
+  describe "credentials path" do
+    it "can be a path to a file" do
+      fcm = FCM.new("test", "README.md")
+      expect(fcm.__send__(:json_key).class).to eq(File)
+    end
+
+    it "can be an IO object" do
+      fcm = FCM.new("test", StringIO.new("hey"))
+      expect(fcm.__send__(:json_key).class).to eq(StringIO)
+    end
+  end
 end