Add support for removal of response headers

The syntax to remove response header is a special case
of HTML filtering, whereas the response headers are
targeted, rather than the response body:

  example.com##^responseheader(header-name)

Where `header-name` is the name of the header to
remove, and must always be lowercase.

The removal of response headers can only be applied to
document resources, i.e. main- or sub-frames.

Only a limited set of headers can be targeted for
removal:

  location
  refresh
  report-to
  set-cookie

This limitation is to ensure that uBO never lowers the
security profile of web pages, i.e. we wouldn't want to
remove `content-security-policy`.

Given that the header removal occurs at onHeaderReceived
time, this new ability works for all browsers.

The motivation for this new filtering ability is instance
of website using a `refresh` header to redirect a visitor
to an undesirable destination after a few seconds.

src/background.html

@@ -34,6 +34,7 @@
 <script src="js/cosmetic-filtering.js"></script>
 <script src="js/scriptlet-filtering.js"></script>
 <script src="js/html-filtering.js"></script>
+<script src="js/httpheader-filtering.js"></script>
 <script src="js/hnswitches.js"></script>
 <script src="js/ublock.js"></script>
 <script src="js/storage.js"></script>

src/css/logger-ui.css

@@ -260,11 +260,11 @@ body.colorBlind #netFilteringDialog > .panes > .details > div[data-status="2"] {
 #vwRenderer .logEntry > div[data-tabid="-1"] {
     text-shadow: 0 0.2em 0.4em #aaa;
     }
-#vwRenderer .logEntry > div.cosmeticRealm,
+#vwRenderer .logEntry > div.extendedRealm,
 #vwRenderer .logEntry > div.redirect {
     background-color: rgba(255, 255, 0, 0.1);
     }
-body.colorBlind #vwRenderer .logEntry > div.cosmeticRealm,
+body.colorBlind #vwRenderer .logEntry > div.extendedRealm,
 body.colorBlind #vwRenderer .logEntry > div.redirect {
     background-color: rgba(0, 19, 110, 0.1);
     }
@@ -324,13 +324,13 @@ body[dir="rtl"] #vwRenderer .logEntry > div > span:first-child {
 #vwRenderer .logEntry > div.messageRealm[data-type="tabLoad"] > span:nth-of-type(2) {
     text-align: center;
     }
-#vwRenderer .logEntry > div.cosmeticRealm > span:nth-of-type(2) > span:first-of-type {
+#vwRenderer .logEntry > div.extendedRealm > span:nth-of-type(2) > span:first-of-type {
     display: none;
     }
-#vwRenderer .logEntry > div.cosmeticRealm > span:nth-of-type(2) > span:last-of-type {
+#vwRenderer .logEntry > div.extendedRealm > span:nth-of-type(2) > span:last-of-type {
     pointer-events: none;
     }
-#vwRenderer .logEntry > div.cosmeticRealm.isException > span:nth-of-type(2) > span:last-of-type {
+#vwRenderer .logEntry > div.extendedRealm.isException > span:nth-of-type(2) > span:last-of-type {
     text-decoration: line-through rgba(0,0,255,0.7);
     }
 #vwRenderer .logEntry > div > span:nth-of-type(3) {
@@ -615,12 +615,12 @@ body[dir="rtl"] #netFilteringDialog > .headers > .tools {
 #netFilteringDialog > .headers > .tools > span:hover {
     background-color: #eee;
     }
-#netFilteringDialog.cosmeticRealm > .headers > .dynamic,
+#netFilteringDialog.extendedRealm > .headers > .dynamic,
-#netFilteringDialog.cosmeticRealm > .panes > .dynamic {
+#netFilteringDialog.extendedRealm > .panes > .dynamic {
     display: none;
     }
-#netFilteringDialog.cosmeticRealm > .headers > .static,
+#netFilteringDialog.extendedRealm > .headers > .static,
-#netFilteringDialog.cosmeticRealm > .panes > .static {
+#netFilteringDialog.extendedRealm > .panes > .static {
     display: none;
     }
 #netFilteringDialog > div.panes {

src/js/background.js

@@ -166,6 +166,7 @@ const µBlock = (( ) => { // jshint ignore:line
         compiledCosmeticSection: 200,
         compiledScriptletSection: 300,
         compiledHTMLSection: 400,
+        compiledHTTPHeaderSection: 500,
         compiledSentinelSection: 1000,
         compiledBadSubsection: 1,
 

src/js/codemirror/ubo-static-filtering.js

@@ -549,6 +549,23 @@ const initHints = function() {
 
     const getExtSelectorHints = function(cursor, line) {
         const beg = cursor.ch;
+        // Special selector case: `^responseheader`
+        {
+            const match = /#\^([a-z]+)$/.exec(line.slice(0, beg));
+            if (
+                match !== null &&
+                'responseheader'.startsWith(match[1]) &&
+                line.slice(beg) === ''
+            ) {
+                return pickBestHints(
+                    cursor,
+                    match[1],
+                    '',
+                    [ 'responseheader()' ]
+                );
+            }
+        }
+        // Procedural operators
         const matchLeft = /#\^?.*:([^:]*)$/.exec(line.slice(0, beg));
         const matchRight = /^([a-z-]*)\(?/.exec(line.slice(beg));
         if ( matchLeft === null || matchRight === null ) { return; }
@@ -561,6 +578,18 @@ const initHints = function() {
         return pickBestHints(cursor, matchLeft[1], matchRight[1], hints);
     };
 
+    const getExtHeaderHints = function(cursor, line) {
+        const beg = cursor.ch;
+        const matchLeft = /#\^responseheader\((.*)$/.exec(line.slice(0, beg));
+        const matchRight = /^([^)]*)/.exec(line.slice(beg));
+        if ( matchLeft === null || matchRight === null ) { return; }
+        const hints = [];
+        for ( const hint of parser.removableHTTPHeaders ) {
+            hints.push(hint);
+        }
+        return pickBestHints(cursor, matchLeft[1], matchRight[1], hints);
+    };
+
     const getExtScriptletHints = function(cursor, line) {
         const beg = cursor.ch;
         const matchLeft = /#\+\js\(([^,]*)$/.exec(line.slice(0, beg));
@@ -607,10 +636,12 @@ const initHints = function() {
             let hints;
             if ( cursor.ch <= parser.slices[parser.optionsAnchorSpan.i+1] ) {
                 hints = getOriginHints(cursor, line);
+            } else if ( parser.hasFlavor(parser.BITFlavorExtScriptlet) ) {
+                hints = getExtScriptletHints(cursor, line);
+            } else if ( parser.hasFlavor(parser.BITFlavorExtResponseHeader) ) {
+                hints = getExtHeaderHints(cursor, line);
             } else {
-                hints = parser.hasFlavor(parser.BITFlavorExtScriptlet)
+                hints = getExtSelectorHints(cursor, line);
-                    ? getExtScriptletHints(cursor, line)
-                    : getExtSelectorHints(cursor, line);
             }
             return hints;
         }

src/js/cosmetic-filtering.js

@@ -540,6 +540,15 @@ FilterContainer.prototype.compileSpecificSelector = function(
 
 /******************************************************************************/
 
+FilterContainer.prototype.compileTemporary = function(parser) {
+    return {
+        session: this.sessionFilterDB,
+        selector: parser.result.compiled,
+    };
+};
+
+/******************************************************************************/
+
 FilterContainer.prototype.fromCompiledContent = function(reader, options) {
     if ( options.skipCosmetic ) {
         this.skipCompiledContent(reader);

src/js/html-filtering.js

@@ -237,12 +237,12 @@
         µBlock.filteringContext
             .duplicate()
             .fromTabId(details.tabId)
-            .setRealm('cosmetic')
+            .setRealm('extended')
             .setType('dom')
             .setURL(details.url)
             .setDocOriginFromURL(details.url)
             .setFilter({
-                source: 'cosmetic',
+                source: 'extended',
                 raw: `${exception === 0 ? '##' : '#@#'}^${selector}`
             })
             .toLogger();
@@ -322,6 +322,13 @@
         }
     };
 
+    api.compileTemporary = function(parser) {
+        return {
+            session: sessionFilterDB,
+            selector: parser.result.compiled,
+        };
+    };
+
     api.fromCompiledContent = function(reader) {
         // Don't bother loading filters if stream filtering is not supported.
         if ( µb.canFilterResponseData === false ) { return; }
@@ -348,15 +355,6 @@
     api.retrieve = function(details) {
         const hostname = details.hostname;
 
-        // https://github.com/gorhill/uBlock/issues/2835
-        //   Do not filter if the site is under an `allow` rule.
-        if (
-            µb.userSettings.advancedUserEnabled &&
-            µb.sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2
-        ) {
-            return;
-        }
-
         const plains = new Set();
         const procedurals = new Set();
         const exceptions = new Set();
@@ -379,6 +377,15 @@
     
         if ( plains.size === 0 && procedurals.size === 0 ) { return; }
 
+        // https://github.com/gorhill/uBlock/issues/2835
+        //   Do not filter if the site is under an `allow` rule.
+        if (
+            µb.userSettings.advancedUserEnabled &&
+            µb.sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2
+        ) {
+            return;
+        }
+
         const out = { plains, procedurals };
 
         if ( exceptions.size === 0 ) {

src/js/logger-ui.js

@@ -29,6 +29,9 @@
 
 /******************************************************************************/
 
+// TODO: fix the inconsistencies re. realm vs. filter source which have
+//       accumulated over time.
+
 const messaging = vAPI.messaging;
 const logger = self.logger = { ownerId: Date.now() };
 const logDate = new Date();
@@ -341,6 +344,11 @@ const processLoggerEntries = function(response) {
 /******************************************************************************/
 
 const parseLogEntry = function(details) {
+    // Patch realm until changed all over codebase to make this unecessary
+    if ( details.realm === 'cosmetic' ) {
+        details.realm = 'extended';
+    }
+
     const entry = new LogEntry(details);
 
     // Assemble the text content, i.e. the pre-built string which will be
@@ -441,6 +449,8 @@ const viewPort = (( ) => {
     const vwLogEntryTemplate = document.querySelector('#logEntryTemplate > div');
     const vwEntries = [];
 
+    const detailableRealms = new Set([ 'network', 'extended' ]);
+
     let vwHeight = 0;
     let lineHeight = 0;
     let wholeHeight = 0;
@@ -672,7 +682,7 @@ const viewPort = (( ) => {
             return div;
         }
 
-        if ( details.realm === 'network' || details.realm === 'cosmetic' ) {
+        if ( detailableRealms.has(details.realm) ) {
             divcl.add('canDetails');
         }
 
@@ -685,13 +695,13 @@ const viewPort = (( ) => {
             }
             if ( filteringType === 'static' ) {
                 divcl.add('canLookup');
-                if ( filter.modifier === true ) {
+            } else if ( details.realm === 'extended' ) {
-                    div.setAttribute('data-modifier', '');
-                }
-            } else if ( filteringType === 'cosmetic' ) {
                 divcl.add('canLookup');
                 divcl.toggle('isException', filter.raw.startsWith('#@#'));
             }
+            if ( filter.modifier === true ) {
+                div.setAttribute('data-modifier', '');
+            }
         }
         span = div.children[1];
         if ( renderFilterToSpan(span, cells[1]) === false ) {
@@ -1575,7 +1585,7 @@ const reloadTab = function(ev) {
                 rawFilter: rawFilter,
             });
             handleResponse(response);
-        } else if ( targetRow.classList.contains('cosmeticRealm') ) {
+        } else if ( targetRow.classList.contains('extendedRealm') ) {
             const response = await messaging.send('loggerUI', {
                 what: 'listsFromCosmeticFilter',
                 url: targetRow.children[6].textContent,
@@ -1583,7 +1593,7 @@ const reloadTab = function(ev) {
             });
             handleResponse(response);
         }
-    } ;
+    };
 
     const fillSummaryPane = function() {
         const rows = dialog.querySelectorAll('.pane.details > div');
@@ -1595,7 +1605,7 @@ const reloadTab = function(ev) {
         text = filterFromTargetRow();
         if (
             (text !== '') &&
-            (trcl.contains('cosmeticRealm') || trcl.contains('networkRealm'))
+            (trcl.contains('extendedRealm') || trcl.contains('networkRealm'))
         ) {
             toSummaryPaneFilterNode(rows[0], text);
         } else {
@@ -1607,7 +1617,7 @@ const reloadTab = function(ev) {
             (
                 trcl.contains('dynamicHost') ||
                 trcl.contains('dynamicUrl') ||
-                trcl.contains('switch')
+                trcl.contains('switchRealm')
             )
         ) {
             rows[2].children[1].textContent = text;
@@ -1677,7 +1687,9 @@ const reloadTab = function(ev) {
 
     // Fill dynamic URL filtering pane
     const fillDynamicPane = function() {
-        if ( targetRow.classList.contains('cosmeticRealm') ) { return; }
+        if ( targetRow.classList.contains('extendedRealm') ) {
+            return;
+        }
 
         // https://github.com/uBlockOrigin/uBlock-issues/issues/662#issuecomment-509220702
         if ( targetType === 'doc' ) { return; }
@@ -1712,8 +1724,6 @@ const reloadTab = function(ev) {
         }
 
         colorize();
-
-        uDom('#modalOverlayContainer [data-pane="dynamic"]').removeClass('hide');
     };
 
     const fillOriginSelect = function(select, hostname, domain) {
@@ -1733,7 +1743,9 @@ const reloadTab = function(ev) {
 
     // Fill static filtering pane
     const fillStaticPane = function() {
-        if ( targetRow.classList.contains('cosmeticRealm') ) { return; }
+        if ( targetRow.classList.contains('extendedRealm') ) {
+            return;
+        }
 
         const template = vAPI.i18n('loggerStaticFilteringSentence');
         const rePlaceholder = /\{\{[^}]+?\}\}/g;
@@ -1842,8 +1854,8 @@ const reloadTab = function(ev) {
             }
         );
         dialog.classList.toggle(
-            'cosmeticRealm',
+            'extendedRealm',
-            targetRow.classList.contains('cosmeticRealm')
+            targetRow.classList.contains('extendedRealm')
         );
         targetDomain = domains[0];
         targetPageDomain = domains[1];
@@ -2403,10 +2415,10 @@ const popupManager = (( ) => {
 // Filter hit stats' MVP ("minimum viable product")
 //
 const loggerStats = (( ) => {
+    const enabled = false;
     const filterHits = new Map();
     let dialog;
     let timer;
-
     const makeRow = function() {
         const div = document.createElement('div');
         div.appendChild(document.createElement('span'));
@@ -2470,6 +2482,7 @@ const loggerStats = (( ) => {
 
     return {
         processFilter: function(filter) {
+            if ( enabled !== true ) { return; }
             if ( filter.source !== 'static' && filter.source !== 'cosmetic' ) {
                 return;
             }

src/js/messaging.js

@@ -1440,21 +1440,14 @@ const getURLFilteringData = function(details) {
 const compileTemporaryException = function(filter) {
     const parser = new vAPI.StaticFilteringParser();
     parser.analyze(filter);
-    if ( parser.shouldDiscard() ) { return {}; }
+    if ( parser.shouldDiscard() ) { return; }
-    let selector = parser.result.compiled;
+    return µb.staticExtFilteringEngine.compileTemporary(parser);
-    let session;
-    if ( (parser.flavorBits & parser.BITFlavorExtScriptlet) !== 0 ) {
-        session = µb.scriptletFilteringEngine.getSession();
-    } else if ( (parser.flavorBits & parser.BITFlavorExtHTML) !== 0 ) {
-        session = µb.htmlFilteringEngine.getSession();
-    } else {
-        session = µb.cosmeticFilteringEngine.getSession();
-    }
-    return { session, selector };
 };
 
 const toggleTemporaryException = function(details) {
-    const { session, selector } = compileTemporaryException(details.filter);
+    const result = compileTemporaryException(details.filter);
+    if ( result === undefined ) { return false; }
+    const { session, selector } = result;
     if ( session.has(1, selector) ) {
         session.remove(1, selector);
         return false;
@@ -1464,7 +1457,9 @@ const toggleTemporaryException = function(details) {
 };
 
 const hasTemporaryException = function(details) {
-    const { session, selector } = compileTemporaryException(details.filter);
+    const result = compileTemporaryException(details.filter);
+    if ( result === undefined ) { return false; }
+    const { session, selector } = result;
     return session && session.has(1, selector);
 };
 

src/js/reverselookup.js

@@ -221,6 +221,7 @@ if (
                 // Generic exception
                 case 8:
                 // HTML filtering
+                // Response header filtering
                 case 64:
                     if ( exception !== ((fargs[2] & 0b001) !== 0) ) { break; }
                     isProcedural = (fargs[2] & 0b010) !== 0;

src/js/scriptlet-filtering.js

@@ -206,12 +206,12 @@
         µBlock.filteringContext
             .duplicate()
             .fromTabId(details.tabId)
-            .setRealm('cosmetic')
+            .setRealm('extended')
             .setType('dom')
             .setURL(details.url)
             .setDocOriginFromURL(details.url)
             .setFilter({
-                source: 'cosmetic',
+                source: 'extended',
                 raw: (isException ? '#@#' : '##') + `+js(${token})`
             })
             .toLogger();
@@ -263,6 +263,13 @@
         }
     };
 
+    api.compileTemporary = function(parser) {
+        return {
+            session: sessionScriptletDB,
+            selector: parser.result.compiled,
+        };
+    };
+
     // 01234567890123456789
     // +js(token[, arg[, ...]])
     //     ^                  ^
@@ -302,15 +309,6 @@
 
         const hostname = request.hostname;
 
-        // https://github.com/gorhill/uBlock/issues/2835
-        //   Do not inject scriptlets if the site is under an `allow` rule.
-        if (
-            µb.userSettings.advancedUserEnabled &&
-            µb.sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2
-        ) {
-            return;
-        }
-
         $scriptlets.clear();
         $exceptions.clear();
 
@@ -324,6 +322,15 @@
         scriptletDB.retrieve(entity, [ $scriptlets, $exceptions ], 1);
         if ( $scriptlets.size === 0 ) { return; }
 
+        // https://github.com/gorhill/uBlock/issues/2835
+        //   Do not inject scriptlets if the site is under an `allow` rule.
+        if (
+            µb.userSettings.advancedUserEnabled &&
+            µb.sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2
+        ) {
+            return;
+        }
+
         const loggerEnabled = µb.logger.enabled;
 
         // Wholly disable scriptlet injection?

src/js/static-ext-filtering.js

@@ -59,11 +59,13 @@
         get acceptedCount() {
             return µb.cosmeticFilteringEngine.acceptedCount +
                    µb.scriptletFilteringEngine.acceptedCount +
+                   µb.httpheaderFilteringEngine.acceptedCount +
                    µb.htmlFilteringEngine.acceptedCount;
         },
         get discardedCount() {
             return µb.cosmeticFilteringEngine.discardedCount +
                    µb.scriptletFilteringEngine.discardedCount +
+                   µb.httpheaderFilteringEngine.discardedCount +
                    µb.htmlFilteringEngine.discardedCount;
         },
     };
@@ -137,7 +139,7 @@
                     this.timer = undefined;
                     this.strToIdMap.clear();
                 },
-                { timeout: 10000 }
+                { timeout: 5000 }
             );
         }
 
@@ -181,6 +183,7 @@
         }
 
         fromSelfie(selfie) {
+            if ( selfie === undefined ) { return; }
             this.hostnameToSlotIdMap = new Map(selfie.hostnameToSlotIdMap);
             this.hostnameSlots = selfie.hostnameSlots;
             this.strSlots = selfie.strSlots;
@@ -239,12 +242,14 @@
     api.reset = function() {
         µb.cosmeticFilteringEngine.reset();
         µb.scriptletFilteringEngine.reset();
+        µb.httpheaderFilteringEngine.reset();
         µb.htmlFilteringEngine.reset();
     };
 
     api.freeze = function() {
         µb.cosmeticFilteringEngine.freeze();
         µb.scriptletFilteringEngine.freeze();
+        µb.httpheaderFilteringEngine.freeze();
         µb.htmlFilteringEngine.freeze();
     };
 
@@ -267,6 +272,12 @@
             return true;
         }
 
+        // Response header filtering
+        if ( (parser.flavorBits & parser.BITFlavorExtResponseHeader) !== 0 ) {
+            µb.httpheaderFilteringEngine.compile(parser, writer);
+            return true;
+        }
+
         // HTML filtering
         // TODO: evaluate converting Adguard's `$$` syntax into uBO's HTML
         //       filtering syntax.
@@ -280,9 +291,23 @@
         return true;
     };
 
+    api.compileTemporary = function(parser) {
+        if ( (parser.flavorBits & parser.BITFlavorExtScriptlet) !== 0 ) {
+            return µb.scriptletFilteringEngine.compileTemporary(parser);
+        }
+        if ( (parser.flavorBits & parser.BITFlavorExtResponseHeader) !== 0 ) {
+            return µb.httpheaderFilteringEngine.compileTemporary(parser);
+        }
+        if ( (parser.flavorBits & parser.BITFlavorExtHTML) !== 0 ) {
+            return µb.htmlFilteringEngine.compileTemporary(parser);
+        }
+        return µb.cosmeticFilteringEngine.compileTemporary(parser);
+    };
+
     api.fromCompiledContent = function(reader, options) {
         µb.cosmeticFilteringEngine.fromCompiledContent(reader, options);
         µb.scriptletFilteringEngine.fromCompiledContent(reader, options);
+        µb.httpheaderFilteringEngine.fromCompiledContent(reader, options);
         µb.htmlFilteringEngine.fromCompiledContent(reader, options);
     };
 
@@ -292,7 +317,8 @@
             JSON.stringify({
                 cosmetic: µb.cosmeticFilteringEngine.toSelfie(),
                 scriptlets: µb.scriptletFilteringEngine.toSelfie(),
-                html: µb.htmlFilteringEngine.toSelfie()
+                httpHeaders: µb.httpheaderFilteringEngine.toSelfie(),
+                html: µb.htmlFilteringEngine.toSelfie(),
             })
         );
     };
@@ -307,6 +333,7 @@
             if ( selfie instanceof Object === false ) { return false; }
             µb.cosmeticFilteringEngine.fromSelfie(selfie.cosmetic);
             µb.scriptletFilteringEngine.fromSelfie(selfie.scriptlets);
+            µb.httpheaderFilteringEngine.fromSelfie(selfie.httpHeaders);
             µb.htmlFilteringEngine.fromSelfie(selfie.html);
             return true;
         });

src/js/static-filtering-parser.js

@@ -304,6 +304,20 @@ const Parser = class {
         }
         // ##^...
         if ( hasBits(this.slices[i], BITCaret) ) {
+            // ##^responseheader(...)
+            if (
+                selector.startsWith('^responseheader(') &&
+                selector.endsWith(')')
+            ) {
+                this.flavorBits |= BITFlavorExtResponseHeader;
+                this.result.raw = selector.slice(1);
+                const headerName = selector.slice(16, -1).trim().toLowerCase();
+                this.result.compiled = `responseheader(${headerName})`;
+                if ( this.removableHTTPHeaders.has(headerName) === false ) {
+                    this.flavorBits |= BITFlavorUnsupported;
+                }
+                return;
+            }
             this.flavorBits |= BITFlavorExtHTML;
             selector = selector.slice(1);
         }
@@ -1244,6 +1258,16 @@ const Parser = class {
 
 /******************************************************************************/
 
+Parser.removableHTTPHeaders = Parser.prototype.removableHTTPHeaders = new Set([
+    '',
+    'location',
+    'report-to',
+    'refresh',
+    'set-cookie',
+]);
+
+/******************************************************************************/
+
 // https://github.com/chrisaljoudi/uBlock/issues/1004
 //   Detect and report invalid CSS selectors.
 
@@ -1978,6 +2002,7 @@ const BITFlavorExtStrong         = 1 <<  8;
 const BITFlavorExtCosmetic       = 1 <<  9;
 const BITFlavorExtScriptlet      = 1 << 10;
 const BITFlavorExtHTML           = 1 << 11;
+const BITFlavorExtResponseHeader = 1 << 12;
 const BITFlavorIgnore            = 1 << 29;
 const BITFlavorUnsupported       = 1 << 30;
 const BITFlavorError             = 1 << 31;
@@ -2087,6 +2112,7 @@ Parser.prototype.BITFlavorExtStrong = BITFlavorExtStrong;
 Parser.prototype.BITFlavorExtCosmetic = BITFlavorExtCosmetic;
 Parser.prototype.BITFlavorExtScriptlet = BITFlavorExtScriptlet;
 Parser.prototype.BITFlavorExtHTML = BITFlavorExtHTML;
+Parser.prototype.BITFlavorExtResponseHeader = BITFlavorExtResponseHeader;
 Parser.prototype.BITFlavorIgnore = BITFlavorIgnore;
 Parser.prototype.BITFlavorUnsupported = BITFlavorUnsupported;
 Parser.prototype.BITFlavorError = BITFlavorError;

src/js/traffic.js

@@ -508,7 +508,8 @@ const onHeadersReceived = function(details) {
     // Keep in mind response headers will be modified in-place if needed, so
     // `details.responseHeaders` will always point to the modified response
     // headers.
-    const responseHeaders = details.responseHeaders;
+    const { responseHeaders } = details;
+    if ( Array.isArray(responseHeaders) === false ) { return; }
 
     if ( isRootDoc === false && µb.hiddenSettings.filterOnHeaders === true ) {
         const result = pageStore.filterOnHeaders(fctxt, responseHeaders);
@@ -540,10 +541,16 @@ const onHeadersReceived = function(details) {
 
     // At this point we have a HTML document.
     
-    const filteredHTML = µb.canFilterResponseData &&
+    const filteredHTML =
-                         filterDocument(pageStore, fctxt, details) === true;
+        µb.canFilterResponseData && filterDocument(fctxt, details) === true;
 
-    let modifiedHeaders = injectCSP(fctxt, pageStore, responseHeaders) === true;
+    let modifiedHeaders = false;
+    if ( µb.httpheaderFilteringEngine.apply(fctxt, responseHeaders) === true ) {
+        modifiedHeaders = true;
+    }
+    if ( injectCSP(fctxt, pageStore, responseHeaders) === true ) {
+        modifiedHeaders = true;
+    }
 
     // https://bugzilla.mozilla.org/show_bug.cgi?id=1376932
     //   Prevent document from being cached by the browser if we modified it,
@@ -552,7 +559,7 @@ const onHeadersReceived = function(details) {
     //   Use `no-cache` instead of `no-cache, no-store, must-revalidate`, this
     //   allows Firefox's offline mode to work as expected.
     if ( (filteredHTML || modifiedHeaders) && dontCacheResponseHeaders ) {
-        let cacheControl = µb.hiddenSettings.cacheControlForFirefox1376932;
+        const cacheControl = µb.hiddenSettings.cacheControlForFirefox1376932;
         if ( cacheControl !== 'unset' ) {
             let i = headerIndexFromName('cache-control', responseHeaders);
             if ( i !== -1 ) {
@@ -565,7 +572,7 @@ const onHeadersReceived = function(details) {
     }
 
     if ( modifiedHeaders ) {
-        return { responseHeaders: responseHeaders };
+        return { responseHeaders };
     }
 };
 
@@ -614,7 +621,7 @@ const normalizeBehindTheSceneResponseHeaders = function(details) {
 
 **/
 
-const filterDocument = (function() {
+const filterDocument = (( ) => {
     const µb = µBlock;
     const filterers = new Map();
     let domParser, xmlSerializer,
@@ -805,7 +812,7 @@ const filterDocument = (function() {
         filterers.delete(this);
     };
 
-    return function(pageStore, fctxt, extras) {
+    return function(fctxt, extras) {
         // https://github.com/gorhill/uBlock/issues/3478
         const statusCode = extras.statusCode || 0;
         if ( statusCode !== 0 && (statusCode < 200 || statusCode >= 300) ) {