ConfigServer: Monitor opened config files for changes

After opening a domain configuration and putting into our configuration
cache, we now monitor the underlying file for changes and send out
notifications to monitoring clients as needed.

This patch has three FIXME's:

- We create a new Core::FileWatcher for each domain.
- We don't yet detect removed keys.
- We don't know the type of key, so we assume everything is a string.

There are a number of ways we can solve those problems but let's not
hold up this patch while we wait for solutions. :^)

2 files changed, 28 insertions, 1 deletions

diff --git a/Userland/Services/ConfigServer/ClientConnection.cpp b/Userland/Services/ConfigServer/ClientConnection.cpp
index 246a95e10f..6a2e0194b6 100644
--- a/Userland/Services/ConfigServer/ClientConnection.cpp
+++ b/Userland/Services/ConfigServer/ClientConnection.cpp
@@ -7,6 +7,7 @@
 #include "ClientConnection.h"
 #include <ConfigServer/ConfigClientEndpoint.h>
 #include <LibCore/ConfigFile.h>
+#include <LibCore/FileWatcher.h>
 
 namespace ConfigServer {
 
@@ -15,6 +16,7 @@ static HashMap<int, RefPtr<ClientConnection>> s_connections;
 struct CachedDomain {
     String domain;
     NonnullRefPtr<Core::ConfigFile> config;
+    RefPtr<Core::FileWatcher> watcher;
 };
 
 static HashMap<String, NonnullOwnPtr<CachedDomain>> s_cache;
@@ -26,7 +28,30 @@ static Core::ConfigFile& ensure_domain_config(String const& domain)
         return *it->value->config;
 
     auto config = Core::ConfigFile::open_for_app(domain, Core::ConfigFile::AllowWriting::Yes);
-    auto cache_entry = make<CachedDomain>(domain, config);
+    // FIXME: Use a single FileWatcher with multiple watches inside.
+    auto watcher_or_error = Core::FileWatcher::create(InodeWatcherFlags::Nonblock);
+    VERIFY(!watcher_or_error.is_error());
+    auto result = watcher_or_error.value()->add_watch(config->filename(), Core::FileWatcherEvent::Type::ContentModified);
+    VERIFY(!result.is_error());
+    watcher_or_error.value()->on_change = [config, domain](auto&) {
+        auto new_config = Core::ConfigFile::open(config->filename());
+        // FIXME: Detect removed keys.
+        // FIXME: Detect type of keys.
+        for (auto& group : new_config->groups()) {
+            for (auto& key : new_config->keys(group)) {
+                auto old_value = config->read_entry(group, key);
+                auto new_value = new_config->read_entry(group, key);
+                if (old_value != new_value) {
+                    for (auto& it : s_connections) {
+                        if (it.value->is_monitoring_domain(domain)) {
+                            it.value->async_notify_changed_string_value(domain, group, key, new_value);
+                        }
+                    }
+                }
+            }
+        }
+    };
+    auto cache_entry = make<CachedDomain>(domain, config, watcher_or_error.release_value());
     s_cache.set(domain, move(cache_entry));
     return *config;
 }
diff --git a/Userland/Services/ConfigServer/ClientConnection.h b/Userland/Services/ConfigServer/ClientConnection.h
index 55bd3ebb9c..026f17ff81 100644
--- a/Userland/Services/ConfigServer/ClientConnection.h
+++ b/Userland/Services/ConfigServer/ClientConnection.h
@@ -20,6 +20,8 @@ public:
 
     virtual void die() override;
 
+    bool is_monitoring_domain(String const& domain) const { return m_monitored_domains.contains(domain); }
+
 private:
     explicit ClientConnection(NonnullRefPtr<Core::LocalSocket>, int client_id);