Auto merge of #20840 - fabricedesre:save-localstorage, r=Manishearth

Save local storage at every change and not just on shutdown

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Currently local storage is saved to `local_data.json` only at shutdown when the storage thread receives the `StorageThreadMsg::Exit` message. This is not reliable enough in any case, and especially problematic for a young engine like Servo. Data loss ensues...

I kept the exit message in the storage thread even if we are not doing work anymore. I can remove it if needed but it should be useful once we move to a better storage backend than a json file.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because we don't have tests for that persistence layer.

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1 files changed, 13 insertions, 6 deletions

diff --git a/components/net/storage_thread.rs b/components/net/storage_thread.rs
index 88726d5702b..5a336d2ea7a 100644
--- a/components/net/storage_thread.rs
+++ b/components/net/storage_thread.rs
@@ -67,21 +67,22 @@ impl StorageManager {
                     self.keys(sender, url, storage_type)
                 }
                 StorageThreadMsg::SetItem(sender, url, storage_type, name, value) => {
-                    self.set_item(sender, url, storage_type, name, value)
+                    self.set_item(sender, url, storage_type, name, value);
+                    self.save_state()
                 }
                 StorageThreadMsg::GetItem(sender, url, storage_type, name) => {
                     self.request_item(sender, url, storage_type, name)
                 }
                 StorageThreadMsg::RemoveItem(sender, url, storage_type, name) => {
-                    self.remove_item(sender, url, storage_type, name)
+                    self.remove_item(sender, url, storage_type, name);
+                    self.save_state()
                 }
                 StorageThreadMsg::Clear(sender, url, storage_type) => {
-                    self.clear(sender, url, storage_type)
+                    self.clear(sender, url, storage_type);
+                    self.save_state()
                 }
                 StorageThreadMsg::Exit(sender) => {
-                    if let Some(ref config_dir) = self.config_dir {
-                        resource_thread::write_json_to_file(&self.local_data, config_dir, "local_data.json");
-                    }
+                    // Nothing to do since we save localstorage set eagerly.
                     let _ = sender.send(());
                     break
                 }
@@ -89,6 +90,12 @@ impl StorageManager {
         }
     }
 
+    fn save_state(&self) {
+        if let Some(ref config_dir) = self.config_dir {
+            resource_thread::write_json_to_file(&self.local_data, config_dir, "local_data.json");
+        }
+    }
+
     fn select_data(&self, storage_type: StorageType)
                    -> &HashMap<String, (usize, BTreeMap<String, String>)> {
         match storage_type {