1 files changed, 70 insertions, 0 deletions
diff --git a/devtools/shared/network-observer/NetworkOverride.sys.mjs b/devtools/shared/network-observer/NetworkOverride.sys.mjs
new file mode 100644
index 0000000000..1b9ef6c873
--- /dev/null
+++ b/devtools/shared/network-observer/NetworkOverride.sys.mjs
@@ -0,0 +1,70 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This modules focuses on redirecting requests to a particular local file.
+ */
+
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+import { NetUtil } from "resource://gre/modules/NetUtil.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+});
+
+XPCOMUtils.defineLazyServiceGetter(
+  lazy,
+  "mimeService",
+  "@mozilla.org/mime;1",
+  "nsIMIMEService"
+);
+
+function readFile(file) {
+  const fstream = Cc["@mozilla.org/network/file-input-stream;1"].createInstance(
+    Ci.nsIFileInputStream
+  );
+  fstream.init(file, -1, 0, 0);
+  const data = NetUtil.readInputStreamToString(fstream, fstream.available());
+  fstream.close();
+  return data;
+}
+
+/**
+ * Given an in-flight channel, we will force to replace the content of this request
+ * with the content of a local file.
+ *
+ * @param {nsIHttpChannel} channel
+ *        The request to replace content for.
+ * @param {String} path
+ *        The absolute path to the local file to read content from.
+ */
+function overrideChannelWithFilePath(channel, path) {
+  // For JS it isn't important, but for HTML we ought to set the right content type on the data URI.
+  let mimeType = "";
+  try {
+    // getTypeFromURI will throw if there is no extension at the end of the URI
+    mimeType = lazy.mimeService.getTypeFromURI(channel.URI);
+  } catch (e) {}
+
+  // Redirect to a data: URI as we can't redirect to file:// URI
+  // without many security issues. We are leveraging the `allowInsecureRedirectToDataURI`
+  // attribute used by WebExtension.
+  const file = lazy.FileUtils.File(path);
+  const data = readFile(file);
+  const redirectURI = Services.io.newURI(
+    `data:${mimeType};base64,${btoa(data)}`
+  );
+
+  channel.redirectTo(redirectURI);
+
+  // Prevents having CORS exception and various issues because of redirecting to data: URI.
+  channel.loadInfo.allowInsecureRedirectToDataURI = true;
+}
+
+export const NetworkOverride = {
+  overrideChannelWithFilePath,
+};