LookupServer: Watch /etc/hosts for changes during runtime

This adds a FileWatcher to the LookupServer which watches '/etc/hosts'
for changes during runtime and reloads its contents. If the file is
deleted, m_etc_hosts will be cleared.

Since we now need to access '/etc/hosts' later during runtime, it needs
to be unveiled with read permissions.

Userland/Services/LookupServer/LookupServer.cpp

@@ -45,6 +45,29 @@ LookupServer::LookupServer()
 
  load_etc_hosts();
 
+ auto maybe_file_watcher = Core::FileWatcher::create();
+ // NOTE: If this happens during startup, something is very wrong.
+ if (maybe_file_watcher.is_error()) {
+ dbgln("Core::FileWatcher::create(): {}", maybe_file_watcher.error());
+ VERIFY_NOT_REACHED();
+ }
+ m_file_watcher = maybe_file_watcher.release_value();
+
+ m_file_watcher->on_change = [this](auto&) {
+ dbgln("Reloading '/etc/hosts' because it was changed.");
+ load_etc_hosts();
+ };
+
+ auto result = m_file_watcher->add_watch("/etc/hosts", Core::FileWatcherEvent::Type::ContentModified | Core::FileWatcherEvent::Type::Deleted);
+ // NOTE: If this happens during startup, something is very wrong.
+ if (result.is_error()) {
+ dbgln("Core::FileWatcher::add_watch(): {}", result.error());
+ VERIFY_NOT_REACHED();
+ } else if (!result.value()) {
+ dbgln("Core::FileWatcher::add_watch(): {}", result.value());
+ VERIFY_NOT_REACHED();
+ }
+
  if (config->read_bool_entry("DNS", "EnableServer")) {
  m_dns_server = DNSServer::construct(this);
  // TODO: drop root privileges here.
@@ -68,6 +91,7 @@ LookupServer::LookupServer()
 
 void LookupServer::load_etc_hosts()
 {
+ m_etc_hosts.clear();
  auto add_answer = [this](const DNSName& name, DNSRecordType record_type, String data) {
  auto it = m_etc_hosts.find(name);
  if (it == m_etc_hosts.end()) {

Userland/Services/LookupServer/LookupServer.h

@@ -10,6 +10,7 @@
 #include "DNSPacket.h"
 #include "DNSServer.h"
 #include "MulticastDNS.h"
+#include <LibCore/FileWatcher.h>
 #include <LibCore/Object.h>
 
 namespace LookupServer {
@@ -35,6 +36,7 @@ class LookupServer final : public Core::Object {
  RefPtr<DNSServer> m_dns_server;
  RefPtr<MulticastDNS> m_mdns;
  Vector<String> m_nameservers;
+ RefPtr<Core::FileWatcher> m_file_watcher;
  HashMap<DNSName, Vector<DNSAnswer>, DNSName::Traits> m_etc_hosts;
  HashMap<DNSName, Vector<DNSAnswer>, DNSName::Traits> m_lookup_cache;
 };

Userland/Services/LookupServer/main.cpp

@@ -30,6 +30,11 @@ int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
  return 1;
  }
 
+ if (unveil("/etc/hosts", "r") < 0) {
+ perror("unveil");
+ return 1;
+ }
+
  if (unveil(nullptr, nullptr) < 0) {
  perror("unveil");
  return 1;