add replacement logic & improve description

src/scriptlets/trusted-replace-fetch-response.js

@@ -22,63 +22,55 @@ import {
 /**
  * @scriptlet trusted-replace-fetch-response
  *
- * @description // FIXME
- * Prevents `fetch` calls if **all** given parameters match
- *
- * Related UBO scriptlet:
- * https://github.com/gorhill/uBlock/wiki/Resources-Library#no-fetch-ifjs-
+ * @description
+ * Replaces response text content of `fetch` requests if **all** given parameters match.
  *
  * **Syntax**
  * ```
- * example.org#%#//scriptlet('prevent-fetch'[, propsToMatch[, responseBody]])
+ * example.org#%#//scriptlet('trusted-replace-fetch-response'[, pattern, replacement[, propsToMatch]])
  * ```
  *
+ * - pattern - optional, argument for matching contents of responseText that should be replaced. If set, `replacement` is required;
+ * possible values:
+ *   - '*' to match all text content
+ *   - string
+ *   - regular expression
+ * - replacement — optional, should be set if `pattern` is set. String to replace matched content with. Empty string to remove content.
  * - `propsToMatch` - optional, string of space-separated properties to match; possible props:
  *   - string or regular expression for matching the URL passed to fetch call; empty string, wildcard `*` or invalid regular expression will match all fetch calls
  *   - colon-separated pairs `name:value` where
  *     - `name` is [`init` option name](https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#parameters)
  *     - `value` is string or regular expression for matching the value of the option passed to fetch call; invalid regular expression will cause any value matching
- * - responseBody - optional, string for defining response body value, defaults to `emptyObj`. Possible values:
- *    - `emptyObj` - empty object
- *    - `emptyArr` - empty array
+ *
  * > Usage with no arguments will log fetch calls to browser console;
- * which is useful for debugging but permitted for production filter lists.
+ * which is useful for debugging but only allowed for production filter lists.
+ *
+ * > Scriptlet does nothing if response body can't be converted to text.
  *
  * **Examples**
  * 1. Log all fetch calls
  *     ```
  *     example.org#%#//scriptlet('prevent-fetch')
  *     ```
  *
- * 2. Prevent all fetch calls
+ * 2. Replace response text content of fetch requests with specific url
  *     ```
- *     example.org#%#//scriptlet('prevent-fetch', '*')
- *     OR
- *     example.org#%#//scriptlet('prevent-fetch', '')
+ *     example.org#%#//scriptlet('trusted-replace-fetch-response', 'adb_detect:true', 'adb_detect:false', 'example.org')
+ *     example.org#%#//scriptlet('trusted-replace-fetch-response', '/#EXT-X-VMAP-AD-BREAK[\s\S]*?/', '#EXT-X-ENDLIST', 'example.org')
  *     ```
  *
- * 3. Prevent fetch call for specific url
+ * 3. Remove all text content of fetch responses with specific request method
  *     ```
- *     example.org#%#//scriptlet('prevent-fetch', '/url\\.part/')
+ *     example.org#%#//scriptlet('trusted-replace-fetch-response', '*', '', 'method:GET')
  *     ```
  *
- * 4. Prevent fetch call for specific request method
+ * 4. Replace response text content of fetch requests matching by URL regex and request methods
  *     ```
- *     example.org#%#//scriptlet('prevent-fetch', 'method:HEAD')
+ *     example.org#%#//scriptlet('trusted-replace-fetch-response', '/#EXT-X-VMAP-AD-BREAK[\s\S]*?/', '#EXT-X-ENDLIST', '/\.m3u8/ method:/GET|HEAD/')
  *     ```
- *
- * 5. Prevent fetch call for specific url and request method
+ * 5. Remove text content of all fetch responses for example.com
  *     ```
- *     example.org#%#//scriptlet('prevent-fetch', '/specified_url_part/ method:/HEAD|GET/')
- *     ```
- *
- * 6. Prevent fetch call and specify response body value
- *     ```
- *     ! Specify response body for fetch call to a specific url
- *     example.org#%#//scriptlet('prevent-fetch', '/specified_url_part/ method:/HEAD|GET/', 'emptyArr')
- *
- *     ! Specify response body for all fetch calls
- *     example.org#%#//scriptlet('prevent-fetch', '', 'emptyArr')
+ *     example.org#%#//scriptlet('trusted-replace-fetch-response', '*', '', 'example.com')
  *     ```
  */
 /* eslint-enable max-len */
@@ -98,12 +90,12 @@ export function trustedReplaceFetchResponse(source, pattern = '', replacement =
 
     // eslint-disable-next-line no-console
     const log = console.log.bind(console);
-    const nativeFetch = window.fetch;
+    const nativeFetch = fetch;
 
     let shouldPrevent = false;
     let fetchData;
 
-    const handlerWrapper = (target, thisArg, args) => {
+    const handlerWrapper = async (target, thisArg, args) => {
         fetchData = getFetchData(args);
 
         if (typeof propsToMatch === 'undefined') {
@@ -131,14 +123,65 @@ export function trustedReplaceFetchResponse(source, pattern = '', replacement =
             }
         }
 
-        if (shouldPrevent) {
-            // REPLACE CONTENT HERE
+        if (!shouldPrevent) {
+            return Reflect.apply(target, thisArg, args);
+        }
 
-
-            hit(source);
+        // Send original request to retrieve response data
+        let response;
+        try {
+            response = await nativeFetch(...args);
+        } catch {
+            return Reflect.apply(target, thisArg, args);
         }
 
-        return Reflect.apply(target, thisArg, args);
+        // Try to convert response body to text
+        let bodyText;
+        try {
+            bodyText = await response.text();
+        } catch {
+            // log if response body can't be converted to a string
+            const fetchDataStr = objectToString(fetchData);
+            const logMessage = `log: Response body can't be converted to text: ${fetchDataStr}`;
+            log(source, logMessage);
+            return Reflect.apply(target, thisArg, args);
+        }
+
+        const {
+            bodyUsed,
+            headers,
+            ok,
+            redirected,
+            status,
+            statusText,
+            type,
+            url,
+        } = response;
+
+        const patternRegexp = pattern === getWildcardSymbol()
+            ? toRegExp
+            : toRegExp(pattern);
+
+        const modifiedContent = bodyText.replace(patternRegexp, replacement);
+
+        // eslint-disable-next-line compat/compat
+        const fiddledResponse = new Response(modifiedContent, {
+            status,
+            statusText,
+            headers,
+        });
+
+        // Manually set properties which can't be set by Response constructor
+        Object.defineProperties(fiddledResponse, {
+            url: { value: url },
+            type: { value: type },
+            ok: { value: ok },
+            bodyUsed: { value: bodyUsed },
+            redirected: { value: redirected },
+        });
+
+        hit(source);
+        return fiddledResponse;
     };
 
     const fetchHandler = {