feat(helpers): Add helpers for reading/parsing JSON

This is boilerplate that can easily be provided to users of the library.

src/helper.rs

@@ -0,0 +1,34 @@
+#![allow(dead_code)]
+
+//! Helper functions allowing you to avoid writing boilerplate code for common operations, such as
+//! parsing JSON or reading files.
+
+// Copyright (c) 2016 Google Inc ([email protected]).
+//
+// Refer to the project root for licensing information.
+
+use serde_json;
+use std::io;
+use std::fs;
+
+use types::ApplicationSecret;
+
+pub fn read_application_secret(file: &String) -> io::Result<ApplicationSecret> {
+    use std::io::Read;
+
+    let mut secret = String::new();
+    let mut file = try!(fs::OpenOptions::new().read(true).open(file));
+    try!(file.read_to_string(&mut secret));
+
+    parse_application_secret(&secret)
+}
+
+pub fn parse_application_secret(secret: &String) -> io::Result<ApplicationSecret> {
+    match serde_json::from_str(secret) {
+        Err(e) => {
+            Err(io::Error::new(io::ErrorKind::InvalidData,
+                               format!("Bad application secret: {}", e)))
+        }
+        Ok(decoded) => Ok(decoded),
+    }
+}