runtime: enforce minimal node version to 6.9.0

Etherpad 1.6.6 does not run on node <= 5 already.
Node 6.9 is the first LTS release in the 6 series, and comes with npm 3.10.8.

Declarations in package.json are advisory unless the user has set
`engine-strict` config flag.

Updated the docs accordingly.

README.md

@@ -8,6 +8,9 @@ Etherpad is a really-real time collaborative editor scalable to thousands of sim
 
 # Installation
 
+## Requirements
+- `nodejs` >= **6.9.0**
+
 ## Uber-Quick Ubuntu
 ```
 curl -sL https://deb.nodesource.com/setup_9.x | sudo -E bash -
@@ -21,7 +24,7 @@ You'll need gzip, git, curl, libssl develop libraries, python and gcc.
 - *For Fedora/CentOS*: `yum install gzip git curl python openssl-devel && yum groupinstall "Development Tools"`
 - *For FreeBSD*: `portinstall node, npm, curl, git (optional)`
 
-Additionally, you'll need [node.js](https://nodejs.org) installed.
+Additionally, you'll need [node.js](https://nodejs.org) installed (minimum required Node version: **6.9.0**).
 Ideally, the latest stable version is preferred. Please note that the packages offered on some operating systems are outdated. In those cases, we recommend installing nodejs from official archives or compiling it from source (avoiding yum/apt).
 
 **As any user (we recommend creating a separate user called etherpad):**

doc/plugins.md

@@ -99,7 +99,7 @@ Your plugin must also contain a [package definition file](https://docs.npmjs.com
   "author": "USERNAME (REAL NAME) <MAIL@EXAMPLE.COM>",
   "contributors": [],
   "dependencies": {"MODULE": "0.3.20"},
-  "engines": { "node": ">= 0.6.0"}
+  "engines": { "node": ">= 6.9.0"}
 }
 ```
 

src/node/server.js

@@ -24,6 +24,7 @@
 var log4js = require('log4js')
   , async = require('async')
   , stats = require('./stats')
+  , NodeVersion = require('./utils/NodeVersion')
   ;
 
 log4js.replaceConsole();
@@ -39,6 +40,11 @@ var settings
 var npm = require("npm/lib/npm.js");
 
 async.waterfall([
+  function(callback)
+  {
+    NodeVersion.enforceMinNodeVersion('6.9.0', callback);
+  },
+
   // load npm
   function(callback) {
     npm.load({}, function(er) {

src/node/utils/NodeVersion.js

@@ -0,0 +1,37 @@
+/**
+ * Checks related to Node runtime version
+ */
+
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Quits if Etherpad is not running on a given minimum Node version
+ *
+ * @param  {String}     minNodeVersion   Minimum required Node version
+ * @param  {Function}   callback         Standard callback function
+ */
+exports.enforceMinNodeVersion = function(minNodeVersion, callback) {
+  const semver = require('semver');
+  const currentNodeVersion = process.version;
+
+  // we cannot use template literals, since we still do not know if we are
+  // running under Node >= 4.0
+  if (semver.lt(currentNodeVersion, minNodeVersion)) {
+    console.error('Running Etherpad on Node ' + currentNodeVersion + ' is not supported. Please upgrade at least to Node ' + minNodeVersion);
+  } else {
+    console.debug('Running on Node ' + currentNodeVersion + ' (minimum required Node version: ' + minNodeVersion + ')');
+    callback();
+  }
+};

src/package.json

@@ -67,8 +67,8 @@
     "wd": "1.6.1"
   },
   "engines": {
-    "node": ">=0.10.0",
-    "npm": ">=1.0"
+    "node": ">=6.9.0",
+    "npm": ">=3.10.8"
   },
   "repository": {
     "type": "git",