Move CSP logic to new file, Fix boolean config examples

Not sure why I was quoting these in the first place

lib/csp.js

@@ -0,0 +1,80 @@
+var config = require('./config')
+var uuid = require('uuid')
+
+var CspStrategy = {}
+
+var defaultDirectives = {
+  defaultSrc: ['\'self\''],
+  scriptSrc: ['\'self\'', 'vimeo.com', 'https://gist.github.com', 'www.slideshare.net', 'https://query.yahooapis.com', 'https://*.disqus.com', '\'unsafe-eval\''],
+  // ^ TODO: Remove unsafe-eval - webpack script-loader issues https://github.com/hackmdio/hackmd/issues/594
+  imgSrc: ['*'],
+  styleSrc: ['\'self\'', '\'unsafe-inline\'', 'https://assets-cdn.github.com'], // unsafe-inline is required for some libs, plus used in views
+  fontSrc: ['\'self\'', 'https://public.slidesharecdn.com'],
+  objectSrc: ['*'], // Chrome PDF viewer treats PDFs as objects :/
+  childSrc: ['*'],
+  connectSrc: ['*']
+}
+
+var cdnDirectives = {
+  scriptSrc: ['https://cdnjs.cloudflare.com', 'https://cdn.mathjax.org'],
+  styleSrc: ['https://cdnjs.cloudflare.com', 'https://fonts.googleapis.com'],
+  fontSrc: ['https://cdnjs.cloudflare.com', 'https://fonts.gstatic.com']
+}
+
+CspStrategy.computeDirectives = function () {
+  var directives = {}
+  mergeDirectives(directives, config.csp.directives)
+  mergeDirectivesIf(config.csp.addDefaults, directives, defaultDirectives)
+  mergeDirectivesIf(config.usecdn, directives, cdnDirectives)
+  if (!areAllInlineScriptsAllowed(directives)) {
+    addInlineScriptExceptions(directives)
+  }
+  addUpgradeUnsafeRequestsOptionTo(directives)
+  return directives
+}
+
+function mergeDirectives (existingDirectives, newDirectives) {
+  for (var propertyName in newDirectives) {
+    var newDirective = newDirectives[propertyName]
+    if (newDirective) {
+      var existingDirective = existingDirectives[propertyName] || []
+      existingDirectives[propertyName] = existingDirective.concat(newDirective)
+    }
+  }
+}
+
+function mergeDirectivesIf (condition, existingDirectives, newDirectives) {
+  if (condition) {
+    mergeDirectives(existingDirectives, newDirectives)
+  }
+}
+
+function areAllInlineScriptsAllowed (directives) {
+  return directives.scriptSrc.indexOf('\'unsafe-inline\'') !== -1
+}
+
+function addInlineScriptExceptions (directives) {
+  directives.scriptSrc.push(getCspNonce)
+  // TODO: This is the SHA-256 hash of the inline script in build/reveal.js/plugins/notes/notes.html
+  // Any more clean solution appreciated.
+  directives.scriptSrc.push('\'sha256-EtvSSxRwce5cLeFBZbvZvDrTiRoyoXbWWwvEVciM5Ag=\'')
+}
+
+function getCspNonce (req, res) {
+  return "'nonce-" + res.locals.nonce + "'"
+}
+
+function addUpgradeUnsafeRequestsOptionTo (directives) {
+  if (config.csp.upgradeInsecureRequests === 'auto' && config.usessl) {
+    directives.upgradeInsecureRequests = true
+  } else if (config.csp.upgradeInsecureRequests === true) {
+    directives.upgradeInsecureRequests = true
+  }
+}
+
+CspStrategy.addNonceToLocals = function (req, res, next) {
+  res.locals.nonce = uuid.v4()
+  next()
+}
+
+module.exports = CspStrategy