Change the parseQueryString function to return a Map rather than an Object (issue 13829)

Even though the code as-is *should* be safe, given that we're using an Object with a `null` prototype, it cannot hurt to change this to a Map to prevent any issues (since we're parsing unknown and potentially unsafe data).

Overall I also think that these changes improve the `parseQueryString` call-sites, since we now have a proper way of checking for the existence of a particular key (and don't have to use `in` which stringifies the keys in the Object).

This patch also changes the default, when no `value` exists, from `null` to an empty string since the use of `decodeURIComponent` currently can modify the value in a somewhat surprising way (at least to me).
Note how `decodeURIComponent(null) === "null"` which is unlikely to be what you actually want, whereas `decodeURIComponent("") === ""` which seems much more helpful.

web/app.js

@@ -329,35 +329,38 @@ const PDFViewerApplication = {
     if (!hash) {
       return undefined;
     }
-    const hashParams = parseQueryString(hash),
+    const params = parseQueryString(hash),
       waitOn = [];
 
-    if ("disableworker" in hashParams && hashParams.disableworker === "true") {
+    if (params.get("disableworker") === "true") {
       waitOn.push(loadFakeWorker());
     }
-    if ("disablerange" in hashParams) {
-      AppOptions.set("disableRange", hashParams.disablerange === "true");
+    if (params.has("disablerange")) {
+      AppOptions.set("disableRange", params.get("disablerange") === "true");
     }
-    if ("disablestream" in hashParams) {
-      AppOptions.set("disableStream", hashParams.disablestream === "true");
+    if (params.has("disablestream")) {
+      AppOptions.set("disableStream", params.get("disablestream") === "true");
     }
-    if ("disableautofetch" in hashParams) {
+    if (params.has("disableautofetch")) {
       AppOptions.set(
         "disableAutoFetch",
-        hashParams.disableautofetch === "true"
+        params.get("disableautofetch") === "true"
       );
     }
-    if ("disablefontface" in hashParams) {
-      AppOptions.set("disableFontFace", hashParams.disablefontface === "true");
+    if (params.has("disablefontface")) {
+      AppOptions.set(
+        "disableFontFace",
+        params.get("disablefontface") === "true"
+      );
     }
-    if ("disablehistory" in hashParams) {
-      AppOptions.set("disableHistory", hashParams.disablehistory === "true");
+    if (params.has("disablehistory")) {
+      AppOptions.set("disableHistory", params.get("disablehistory") === "true");
     }
-    if ("verbosity" in hashParams) {
-      AppOptions.set("verbosity", hashParams.verbosity | 0);
+    if (params.has("verbosity")) {
+      AppOptions.set("verbosity", params.get("verbosity") | 0);
     }
-    if ("textlayer" in hashParams) {
-      switch (hashParams.textlayer) {
+    if (params.has("textlayer")) {
+      switch (params.get("textlayer")) {
         case "off":
           AppOptions.set("textLayerMode", TextLayerMode.DISABLE);
           break;
@@ -365,24 +368,24 @@ const PDFViewerApplication = {
         case "shadow":
         case "hover":
           const viewer = this.appConfig.viewerContainer;
-          viewer.classList.add("textLayer-" + hashParams.textlayer);
+          viewer.classList.add(`textLayer-${params.get("textlayer")}`);
           break;
       }
     }
-    if ("pdfbug" in hashParams) {
+    if (params.has("pdfbug")) {
       AppOptions.set("pdfBug", true);
       AppOptions.set("fontExtraProperties", true);
 
-      const enabled = hashParams.pdfbug.split(",");
+      const enabled = params.get("pdfbug").split(",");
       waitOn.push(loadAndEnablePDFBug(enabled));
     }
     // It is not possible to change locale for the (various) extension builds.
     if (
       (typeof PDFJSDev === "undefined" ||
         PDFJSDev.test("!PRODUCTION || GENERIC")) &&
-      "locale" in hashParams
+      params.has("locale")
     ) {
-      AppOptions.set("locale", hashParams.locale);
+      AppOptions.set("locale", params.get("locale"));
     }
 
     if (waitOn.length === 0) {
@@ -2167,7 +2170,7 @@ function webViewerInitialized() {
   if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
     const queryString = document.location.search.substring(1);
     const params = parseQueryString(queryString);
-    file = "file" in params ? params.file : AppOptions.get("defaultUrl");
+    file = params.get("file") ?? AppOptions.get("defaultUrl");
     validateFileURL(file);
   } else if (PDFJSDev.test("MOZCENTRAL")) {
     file = window.location.href;

web/pdf_history.js

@@ -544,8 +544,8 @@ class PDFHistory {
     const hash = unescape(getCurrentHash()).substring(1);
     const params = parseQueryString(hash);
 
-    const nameddest = params.nameddest || "";
-    let page = params.page | 0;
+    const nameddest = params.get("nameddest") || "";
+    let page = params.get("page") | 0;
 
     if (!this._isValidPage(page) || (checkNameddest && nameddest.length > 0)) {
       page = null;
@@ -753,7 +753,7 @@ function isDestHashesEqual(destHash, pushHash) {
   if (destHash === pushHash) {
     return true;
   }
-  const { nameddest } = parseQueryString(destHash);
+  const nameddest = parseQueryString(destHash).get("nameddest");
   if (nameddest === pushHash) {
     return true;
   }

web/pdf_link_service.js

@@ -263,20 +263,20 @@ class PDFLinkService {
     let pageNumber, dest;
     if (hash.includes("=")) {
       const params = parseQueryString(hash);
-      if ("search" in params) {
+      if (params.has("search")) {
         this.eventBus.dispatch("findfromurlhash", {
           source: this,
-          query: params.search.replace(/"/g, ""),
-          phraseSearch: params.phrase === "true",
+          query: params.get("search").replace(/"/g, ""),
+          phraseSearch: params.get("phrase") === "true",
         });
       }
       // borrowing syntax from "Parameters for Opening PDF Files"
-      if ("page" in params) {
-        pageNumber = params.page | 0 || 1;
+      if (params.has("page")) {
+        pageNumber = params.get("page") | 0 || 1;
       }
-      if ("zoom" in params) {
+      if (params.has("zoom")) {
         // Build the destination array.
-        const zoomArgs = params.zoom.split(","); // scale,left,top
+        const zoomArgs = params.get("zoom").split(","); // scale,left,top
         const zoomArg = zoomArgs[0];
         const zoomArgNumber = parseFloat(zoomArg);
 
@@ -336,16 +336,16 @@ class PDFLinkService {
       } else if (pageNumber) {
         this.page = pageNumber; // simple page
       }
-      if ("pagemode" in params) {
+      if (params.has("pagemode")) {
         this.eventBus.dispatch("pagemode", {
           source: this,
-          mode: params.pagemode,
+          mode: params.get("pagemode"),
         });
       }
       // Ensure that this parameter is *always* handled last, in order to
       // guarantee that it won't be overridden (e.g. by the "page" parameter).
-      if ("nameddest" in params) {
-        this.goToDestination(params.nameddest);
+      if (params.has("nameddest")) {
+        this.goToDestination(params.get("nameddest"));
       }
     } else {
       // Named (or explicit) destination.

web/ui_utils.js

@@ -180,16 +180,18 @@ function watchScroll(viewAreaElement, callback) {
 }
 
 /**
- * Helper function to parse query string (e.g. ?param1=value&parm2=...).
+ * Helper function to parse query string (e.g. ?param1=value&param2=...).
+ * @param {string}
+ * @returns {Map}
  */
 function parseQueryString(query) {
   const parts = query.split("&");
-  const params = Object.create(null);
+  const params = new Map();
   for (let i = 0, ii = parts.length; i < ii; ++i) {
-    const param = parts[i].split("=");
-    const key = param[0].toLowerCase();
-    const value = param.length > 1 ? param[1] : null;
-    params[decodeURIComponent(key)] = decodeURIComponent(value);
+    const param = parts[i].split("="),
+      key = param[0].toLowerCase(),
+      value = param.length > 1 ? param[1] : "";
+    params.set(decodeURIComponent(key), decodeURIComponent(value));
   }
   return params;
 }