New static network filter option urlskip=

Related issue:
uBlockOrigin/uBlock-issues#3206

The main purpose is to bypass URLs designed to track whether a user
visited a specific URL, typically used in click-tracking links.

The `urlskip=` option ...

- ... is valid only when used in a trusted filter list
- ... is enforced only on top documents
- ... is enforced on both blocked and non-blocked documents
- ... is a modifier, i.e. it cannot be used along with other
      modifier options in a single filter

The syntax is `urlskip=[steps]`, where steps is a space-separated
list of extraction directives detailing what action to perform on
the current URL.

The only supported directive in this first commit is `?name`,
which purpose is to extract the value of a named URL parameter
and use the result as the new URL. Example:

  ||example.com/path/to/tracker$urlskip=?url

The above filter will cause navigation to

  https://example.com/path/to/tracker?url=https://example.org/

to automatically bypass navigation to `example.com` and navigate
directly to

  https://example.org/

It is possible to recursively extract URL parameters by using
more than one directive, example:

  ||example.com/path/to/tracker$urlskip=?url ?to

More extraction capabilities may be added in the future.

src/js/filtering-context.js

@@ -163,6 +163,9 @@ export const FilteringContext = class {
         this.stype = a;
     }
 
+    isRootDocument() {
+        return (this.itype & MAIN_FRAME) !== 0;
+    }
     isDocument() {
         return (this.itype & FRAME_ANY) !== 0;
     }

src/js/logger-ui.js

@@ -331,7 +331,7 @@ const processLoggerEntries = function(response) {
             parsed.type === 'main_frame' &&
             parsed.aliased === false && (
                 parsed.filter === undefined ||
-                parsed.filter.modifier !== true
+                parsed.filter.modifier !== true && parsed.filter.source !== 'redirect'
             )
         ) {
             const separator = createLogSeparator(parsed, unboxed.url);

src/js/pagestore.js

@@ -933,26 +933,34 @@ const PageStore = class {
     }
 
     redirectNonBlockedRequest(fctxt) {
-        const transformDirectives = staticNetFilteringEngine.transformRequest(fctxt);
-        const pruneDirectives = fctxt.redirectURL === undefined &&
-            staticNetFilteringEngine.hasQuery(fctxt) &&
-            staticNetFilteringEngine.filterQuery(fctxt) ||
-            undefined;
-        if ( transformDirectives === undefined && pruneDirectives === undefined ) { return; }
-        if ( logger.enabled !== true ) { return; }
-        if ( transformDirectives !== undefined ) {
-            fctxt.pushFilters(transformDirectives.map(a => a.logData()));
-        }
-        if ( pruneDirectives !== undefined ) {
-            fctxt.pushFilters(pruneDirectives.map(a => a.logData()));
+        const directives = [];
+        staticNetFilteringEngine.transformRequest(fctxt, directives);
+        if ( staticNetFilteringEngine.hasQuery(fctxt) ) {
+            staticNetFilteringEngine.filterQuery(fctxt, directives);
         }
+        if ( directives.length === 0 ) { return; }
+        if ( logger.enabled !== true ) { return; }
+        fctxt.pushFilters(directives.map(a => a.logData()));
         if ( fctxt.redirectURL === undefined ) { return; }
         fctxt.pushFilter({
             source: 'redirect',
             raw: fctxt.redirectURL
         });
     }
 
+    skipMainDocument(fctxt) {
+        const directives = staticNetFilteringEngine.urlSkip(fctxt);
+        if ( directives === undefined ) { return; }
+        if ( logger.enabled !== true ) { return; }
+        fctxt.pushFilters(directives.map(a => a.logData()));
+        if ( fctxt.redirectURL !== undefined ) {
+            fctxt.pushFilter({
+                source: 'redirect',
+                raw: fctxt.redirectURL
+            });
+        }
+    }
+
     filterCSPReport(fctxt) {
         if (
             sessionSwitches.evaluateZ(

src/js/static-filtering-parser.js

@@ -191,6 +191,7 @@ export const NODE_TYPE_NET_OPTION_NAME_REPLACE      = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_SCRIPT       = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_SHIDE        = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_TO           = iota++;
+export const NODE_TYPE_NET_OPTION_NAME_URLSKIP      = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_URLTRANSFORM = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_XHR          = iota++;
 export const NODE_TYPE_NET_OPTION_NAME_WEBRTC       = iota++;
@@ -274,6 +275,7 @@ export const nodeTypeFromOptionName = new Map([
     [ 'shide', NODE_TYPE_NET_OPTION_NAME_SHIDE ],
     /* synonym */ [ 'specifichide', NODE_TYPE_NET_OPTION_NAME_SHIDE ],
     [ 'to', NODE_TYPE_NET_OPTION_NAME_TO ],
+    [ 'urlskip', NODE_TYPE_NET_OPTION_NAME_URLSKIP ],
     [ 'uritransform', NODE_TYPE_NET_OPTION_NAME_URLTRANSFORM ],
     [ 'xhr', NODE_TYPE_NET_OPTION_NAME_XHR ],
     /* synonym */ [ 'xmlhttprequest', NODE_TYPE_NET_OPTION_NAME_XHR ],
@@ -1441,6 +1443,7 @@ export class AstFilterParser {
             case NODE_TYPE_NET_OPTION_NAME_REDIRECT:
             case NODE_TYPE_NET_OPTION_NAME_REDIRECTRULE:
             case NODE_TYPE_NET_OPTION_NAME_REPLACE:
+            case NODE_TYPE_NET_OPTION_NAME_URLSKIP:
             case NODE_TYPE_NET_OPTION_NAME_URLTRANSFORM:
                 realBad = isNegated || (isException || hasValue) === false ||
                     modifierType !== 0;
@@ -1519,6 +1522,21 @@ export class AstFilterParser {
             }
             break;
         }
+        case NODE_TYPE_NET_OPTION_NAME_URLSKIP: {
+            realBad = abstractTypeCount || behaviorTypeCount || unredirectableTypeCount;
+            if ( realBad ) { break; }
+            if ( requiresTrustedSource() ) {
+                this.astError = AST_ERROR_UNTRUSTED_SOURCE;
+                realBad = true;
+                break;
+            }
+            const value = this.getNetOptionValue(NODE_TYPE_NET_OPTION_NAME_URLSKIP);
+            if ( value.startsWith('?') === false || value.length < 2 ) {
+                this.astError = AST_ERROR_OPTION_BADVALUE;
+                realBad = true;
+            }
+            break;
+        }
         case NODE_TYPE_NET_OPTION_NAME_URLTRANSFORM: {
             realBad = abstractTypeCount || behaviorTypeCount || unredirectableTypeCount;
             if ( realBad ) { break; }
@@ -3139,6 +3157,7 @@ export const netOptionTokenDescriptors = new Map([
     [ 'shide', { } ],
     /* synonym */ [ 'specifichide', { } ],
     [ 'to', { mustAssign: true } ],
+    [ 'urlskip', { mustAssign: true } ],
     [ 'uritransform', { mustAssign: true } ],
     [ 'xhr', { canNegate: true } ],
     /* synonym */ [ 'xmlhttprequest', { canNegate: true } ],