process: add allowedNodeEnvironmentFlags property

`process.allowedNodeEnvironmentFlags` provides an API to validate and
list flags as specified in `NODE_OPTIONS` from user code.

Refs: https://github.com/nodejs/node/issues/17740
Signed-off-by: Christopher Hiller <boneskull@boneskull.com>

PR-URL: https://github.com/nodejs/node/pull/19335
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Sam Ruby <rubys@intertwingly.net>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

1 files changed, 89 insertions, 0 deletions

diff --git a/lib/internal/bootstrap/node.js b/lib/internal/bootstrap/node.js
index e4748602f3..c98ea20798 100644
--- a/lib/internal/bootstrap/node.js
+++ b/lib/internal/bootstrap/node.js
@@ -185,6 +185,8 @@
 
     perf.markMilestone(NODE_PERFORMANCE_MILESTONE_BOOTSTRAP_COMPLETE);
 
+    setupAllowedFlags();
+
     // There are various modes that Node can run in. The most common two
     // are running from a script and running the REPL - but there are a few
     // others like the debugger or running --eval arguments. Here we decide
@@ -635,5 +637,92 @@
     new vm.Script(source, { displayErrors: true, filename });
   }
 
+  function setupAllowedFlags() {
+    // This builds process.allowedNodeEnvironmentFlags
+    // from data in the config binding
+
+    const replaceDashesRegex = /-/g;
+    const leadingDashesRegex = /^--?/;
+    const trailingValuesRegex = /=.*$/;
+
+    // Save references so user code does not interfere
+    const replace = Function.call.bind(String.prototype.replace);
+    const has = Function.call.bind(Set.prototype.has);
+    const test = Function.call.bind(RegExp.prototype.test);
+
+    const {
+      allowedV8EnvironmentFlags,
+      allowedNodeEnvironmentFlags
+    } = process.binding('config');
+
+    const trimLeadingDashes = (flag) => replace(flag, leadingDashesRegex, '');
+
+    // Save these for comparison against flags provided to
+    // process.allowedNodeEnvironmentFlags.has() which lack leading dashes.
+    // Avoid interference w/ user code by flattening `Set.prototype` into
+    // each object.
+    const [nodeFlags, v8Flags] = [
+      allowedNodeEnvironmentFlags, allowedV8EnvironmentFlags
+    ].map((flags) => Object.defineProperties(
+      new Set(flags.map(trimLeadingDashes)),
+      Object.getOwnPropertyDescriptors(Set.prototype))
+    );
+
+    class NodeEnvironmentFlagsSet extends Set {
+      constructor(...args) {
+        super(...args);
+
+        // the super constructor consumes `add`, but
+        // disallow any future adds.
+        this.add = () => this;
+      }
+
+      delete() {
+        // noop, `Set` API compatible
+        return false;
+      }
+
+      clear() {
+        // noop
+      }
+
+      has(key) {
+        // This will return `true` based on various possible
+        // permutations of a flag, including present/missing leading
+        // dash(es) and/or underscores-for-dashes in the case of V8-specific
+        // flags.  Strips any values after `=`, inclusive.
+        if (typeof key === 'string') {
+          key = replace(key, trailingValuesRegex, '');
+          if (test(leadingDashesRegex, key)) {
+            return has(this, key) ||
+                  has(v8Flags,
+                      replace(
+                        replace(
+                          key,
+                          leadingDashesRegex,
+                          ''
+                        ),
+                        replaceDashesRegex,
+                        '_'
+                      )
+                  );
+          }
+          return has(nodeFlags, key) ||
+                has(v8Flags, replace(key, replaceDashesRegex, '_'));
+        }
+        return false;
+      }
+    }
+
+    Object.freeze(NodeEnvironmentFlagsSet.prototype.constructor);
+    Object.freeze(NodeEnvironmentFlagsSet.prototype);
+
+    process.allowedNodeEnvironmentFlags = Object.freeze(
+      new NodeEnvironmentFlagsSet(
+        allowedNodeEnvironmentFlags.concat(allowedV8EnvironmentFlags)
+      )
+    );
+  }
+
   startup();
 });