Add json-prune.js scriptlet

The scriptlet will trap calls to JSON.parse, and
if the result of the parsing is an Object, it
will remove specified properties from the result
before returning to the caller.

Usage:

    ##+js(json-prune, arg1, [arg2])

Where:

- arg1: a list of space-separated properties to remove

- arg2: optional, a list of space-separated properties
        which must be all present for the pruning to
        occur

Example:

    ##+js(json-prune, enabled, adpath config)

A property in a list of properties can be a chain
of properties, example: adpath.url.first

Author: gorhill

assets/resources/scriptlets.js

@@ -236,6 +236,61 @@
 })();
 
 
+/// json-prune.js
+(function() {
+    const log = console.log.bind(console);
+    const rawPrunePaths = '{{1}}';
+    const rawNeedlePaths = '{{2}}';
+    const prunePaths = rawPrunePaths !== '{{1}}' && rawPrunePaths !== ''
+        ? rawPrunePaths.split(/ +/)
+        : [];
+    const needlePaths = rawNeedlePaths !== '{{2}}' && rawNeedlePaths !== ''
+        ? rawNeedlePaths.split(/ +/)
+        : [];
+    const findOwner = function(root, path) {
+        let owner = root;
+        let chain = path;
+        for (;;) {
+            if ( owner instanceof Object === false ) { return; }
+            const pos = chain.indexOf('.');
+            if ( pos === -1 ) {
+                return owner.hasOwnProperty(chain)
+                    ? [ owner, chain ]
+                    : undefined;
+            }
+            const prop = chain.slice(0, pos);
+            if ( owner.hasOwnProperty(prop) === false ) { return; }
+            owner = owner[prop];
+            chain = chain.slice(pos + 1);
+        }
+    };
+    const mustProcess = function(root) {
+        for ( const needlePath of needlePaths ) {
+            const details = findOwner(root, needlePath);
+            if ( details === undefined ) { return false; }
+        }
+        return true;
+    };
+    JSON.parse = new Proxy(JSON.parse, {
+        apply: function() {
+            const r = Reflect.apply(...arguments);
+            if ( prunePaths.length === 0 ) {
+                log(location.hostname, r);
+                return r;
+            }
+            if ( mustProcess(r) === false ) { return r; }
+            for ( const path of prunePaths ) {
+                const details = findOwner(r, path);
+                if ( details !== undefined ) {
+                    delete details[0][details[1]];
+                }
+            }
+            return r;
+        },
+    });
+})();
+
+
 // Imported from:
 // https://github.com/NanoAdblocker/NanoFilters/blob/1f3be7211bb0809c5106996f52564bf10c4525f7/NanoFiltersSource/NanoResources.txt#L126
 //