Preload safe debug shim (#29)

In https://github.com/ferdium/ferdium-app/pull/23 we removed usages of
the debug package due to an electron bug.

This patch aims to restore some debug functionality by introducing a
shim. The shim detect whether if it is being introduced in a preload
script where the electron but would be triggered, and falls back to a
simple replacement for debug. However, in the main and renderer
processes, where a preload script is not being used, we still get full
debug functionality.

In this way, a module can be used both in a preload script and outside
of it, while still preserving debug functionality whenever possible.

Signed-off-by: Kristóf Marussy <kristof@marussy.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/preload-safe-debug.ts b/src/preload-safe-debug.ts
new file mode 100644
index 000000000..d96ea9017
--- /dev/null
+++ b/src/preload-safe-debug.ts
@@ -0,0 +1,29 @@
+/*
+  eslint-disable global-require --
+  This file contains a workaround for situations were global require is problematic.
+*/
+
+/**
+ * Make sure we don't try to load `debug` in the preload script.
+ *
+ * Doing so would trigger the bug https://github.com/electron/electron/issues/31689
+ * because `debug` will try to access `localStorage` to save the log level:
+ * https://www.npmjs.com/package/debug#user-content-browser-support
+ *
+ * We check for the presence of `ipcRenderer`, a render-only electron API,
+ * to detect whether we're in the renderer process.
+ * We serve the user interface from the `file://` origin, so any different origin
+ * must be a preload script.
+ */
+module.exports = function debug(namespace: string): (...params: any[]) => void {
+  if ('ipcRenderer' in require('electron') && window.origin !== 'file://') {
+    // Only output debug messages to the console if debugging is requested.
+    // We don't reimplement the matching algorithm from `debug` and just dump all
+    // messages to the console if some form of `Ferdium` debugging is enabled.
+    if (process.env.DEBUG?.startsWith('Ferdium:')) {
+      return (...params) => console.debug(`[${namespace}]`, ...params);
+    }
+    return () => { };
+  }
+  return require('debug')(namespace);
+}