doc(resources): Preferences, HstsPreloadList, RippyPNG (#33775)

* Set to default if Preferences and HstsPreloadList are empty

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Add documentation of Preferences, HstsPreloadList, RippyPNG

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Add warn log when setting prefs to default

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Add error log instead

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Add error log to HSTS preload list

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>

* Apply suggestions from code review

Address a couple wording nits

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

---------

Signed-off-by: Wu Yu Wei <yuweiwu@pm.me>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/config/prefs.rs

@@ -9,7 +9,7 @@ use std::sync::LazyLock;
 
 use embedder_traits::resources::{self, Resource};
 use gen::Prefs;
-use log::warn;
+use log::{error, warn};
 use serde_json::{self, Value};
 
 use crate::pref_util::Preferences;
@@ -17,7 +17,10 @@ pub use crate::pref_util::{PrefError, PrefValue};
 
 static PREFS: LazyLock<Preferences<'static, Prefs>> = LazyLock::new(|| {
     let def_prefs: Prefs = serde_json::from_str(&resources::read_string(Resource::Preferences))
-        .expect("Failed to initialize config preferences.");
+        .unwrap_or_else(|_| {
+            error!("Preference json file is invalid. Setting Preference to default values");
+            Prefs::default()
+        });
     let result = Preferences::new(def_prefs, &gen::PREF_ACCESSORS);
     for (key, value) in result.iter() {
         set_stylo_pref_ref(&key, &value);

components/net/hsts.rs

@@ -10,7 +10,7 @@ use base::cross_process_instant::CrossProcessInstant;
 use embedder_traits::resources::{self, Resource};
 use headers::{HeaderMapExt, StrictTransportSecurity};
 use http::HeaderMap;
-use log::info;
+use log::{error, info};
 use net_traits::pub_domains::reg_suffix;
 use net_traits::IncludeSubdomains;
 use serde::{Deserialize, Serialize};
@@ -88,7 +88,10 @@ impl HstsList {
 
     pub fn from_servo_preload() -> HstsList {
         let list = resources::read_string(Resource::HstsPreloadList);
-        HstsList::from_preload(&list).expect("Servo HSTS preload file is invalid")
+        HstsList::from_preload(&list).unwrap_or_else(|| {
+            error!("HSTS preload file is invalid. Setting HSTS list to default values");
+            HstsList::default()
+        })
     }
 
     pub fn is_host_secure(&self, host: &str) -> bool {

components/shared/embedder/resources.rs

@@ -55,9 +55,13 @@ pub fn sandbox_access_files_dirs() -> Vec<PathBuf> {
 }
 
 pub enum Resource {
+    /// A json file of [`Preferences`](servo_config::pref_util::Preferences) configuration.
+    /// It can be empty but lots of features will be disabled.
     Preferences,
     BluetoothBlocklist,
     DomainList,
+    /// A preloaded list of HTTP Strict Transport Security. It can be an empty list and
+    /// [`HstsList::default()`](net::hsts::HstsList) will be called.
     HstsPreloadList,
     BadCertHTML,
     NetErrorHTML,
@@ -65,6 +69,12 @@ pub enum Resource {
     ServoCSS,
     PresentationalHintsCSS,
     QuirksModeCSS,
+    /// A placeholder image to display if we couldn't get the requested image.
+    ///
+    /// ## Safety
+    ///
+    /// Servo will crash if this is an invalid image. Check `resources/rippy.png` in Servo codebase to see what
+    /// a default rippy png should look like.
     RippyPNG,
     MediaControlsCSS,
     MediaControlsJS,