add config.freeze()

Author: Raynos

README.md

@@ -65,6 +65,7 @@ zero-config := (dirname: String, opts?: {
     get: (keypath?: Keypath) => Any,
     set: ((keypath: Keypath, value: Any) => void) &
         (value: Any) => void,
+    freeze: () => void,
     getRemote: (keypath?: Keypath) => Any,
     setRemote: ((keypath: Keypath, value: Any) => void) &
         (value: Any) => void
@@ -224,6 +225,19 @@ Note you can also call `config.set(entireObject)` to merge an
   deep extend to set all the key / value pairs in `entireObject`
   onto the config instance.
 
+#### `config.freeze()`
+
+Since the `config` object is supposed to represent a set of
+  static, immutable configuration that's loaded at process
+  startup time it would be useful to enforce this.
+
+Once you are ready to stop mutating `config` you can call
+  `.freeze()`. Any future calls to `.set()` will throw a 
+  config frozen exception.
+
+Note that you can always call `config.setRemote()` as that is
+  not effected by `.freeze()`
+
 #### `var value = config.getRemote(keypath)`
 
 The same as `config.get()` but gets from a different in memory

config-wrapper.js

@@ -7,9 +7,12 @@ var errors = require('./errors.js');
 module.exports = ConfigWrapper;
 
 function ConfigWrapper(configObject) {
+    var frozen = false;
+
     return {
         get: getKey,
-        set: setKey
+        set: setKey,
+        freeze: freeze
     };
 
     function getKey(keyPath) {
@@ -21,6 +24,14 @@ function ConfigWrapper(configObject) {
     }
 
     function setKey(keyPath, value) {
+        if (frozen) {
+            throw errors.SetFrozenObject({
+                keyPath: keyPath,
+                valueStr: JSON.stringify(value),
+                value: value
+            });
+        }
+
         if (arguments.length === 1) {
             return multiSet(keyPath);
         }
@@ -42,6 +53,10 @@ function ConfigWrapper(configObject) {
         return putPath(configObject, keyPath, v);
     }
 
+    function freeze() {
+        frozen = true;
+    }
+
     function multiSet(obj) {
         if (obj === null || typeof obj !== 'object') {
             throw errors.InvalidMultiSetArgument({

errors.js

@@ -50,11 +50,25 @@ var InvalidMultiSetArgument = TypedError({
     obj: null
 });
 
+var SetFrozenObject = TypedError({
+    type: 'set.frozen.object',
+    message: 'Cannot `config.set(key, value)`. Config is ' +
+        'frozen.\n' +
+        'expected `config.set()` not to be called. Instead ' +
+        'it was called with {keyPath} and {valueStr}.\n' +
+        'SUGGESTED FIX: Do not call `config.set()` it was ' +
+        'frozen by someone else.\n',
+    keyPath: null,
+    valueStr: null,
+    value: null
+});
+
 module.exports = {
     InvalidDirname: InvalidDirname,
     MissingDatacenter: MissingDatacenter,
     DatacenterRequired: DatacenterRequired,
     DatacenterFileRequired: DatacenterFileRequired,
     InvalidKeyPath: InvalidKeyPath,
-    InvalidMultiSetArgument: InvalidMultiSetArgument
+    InvalidMultiSetArgument: InvalidMultiSetArgument,
+    SetFrozenObject: SetFrozenObject
 };

index.js

@@ -39,6 +39,7 @@ function fetchConfigSync(dirname, opts) {
 
     config.get = localConfigWrapper.get;
     config.set = localConfigWrapper.set;
+    config.freeze = localConfigWrapper.freeze;
     config.getRemote = remoteConfigWrapper.get;
     config.setRemote = remoteConfigWrapper.set;
 

test/index.js

@@ -370,3 +370,23 @@ test('config.setRemote()', function t(assert) {
 
     assert.end();
 });
+
+test('config.freeze()', function t(assert) {
+    var config = fetchConfig(__dirname);
+
+    config.set('foo', 'bar');
+
+    assert.equal(config.get('foo'), 'bar');
+
+    config.freeze();
+
+    assert.throws(function () {
+        config.set('foo', 'baz');
+    }, /Config is frozen/);
+
+    assert.throws(function () {
+        config.set('bar', 'baz');
+    }, /Config is frozen/);
+
+    assert.end();
+});