LookupServer: Modernize load_etc_hosts()

This reworks the LookupServer::load_etc_hosts() method to use the
IPv4Address APIs instead of trying to parse an IPv4 address itself.

It also adds a few error checks for invalid entries in /etc/hosts,
trims away leading and trailing whitespace from lines and tries to use
StringView over String.

Userland/Services/LookupServer/LookupServer.cpp

@@ -25,6 +25,8 @@
 namespace LookupServer {
 
 static LookupServer* s_the;
+// NOTE: This is the TTL we return for the hostname or answers from /etc/hosts.
+static constexpr u32 s_static_ttl = 86400;
 
 LookupServer& LookupServer::the()
 {
@@ -66,48 +68,51 @@ LookupServer::LookupServer()
 
 void LookupServer::load_etc_hosts()
 {
- // The TTL we return for static data from /etc/hosts.
- // The value here is 1 day.
- static constexpr u32 static_ttl = 86400;
-
  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()) {
  m_etc_hosts.set(name, {});
  it = m_etc_hosts.find(name);
  }
- it->value.empend(name, record_type, DNSRecordClass::IN, static_ttl, data, false);
+ it->value.empend(name, record_type, DNSRecordClass::IN, s_static_ttl, data, false);
  };
 
  auto file = Core::File::construct("/etc/hosts");
- if (!file->open(Core::OpenMode::ReadOnly))
+ if (!file->open(Core::OpenMode::ReadOnly)) {
+ dbgln("Failed to open '/etc/hosts'");
  return;
+ }
+
+ u32 line_number = 0;
  while (!file->eof()) {
- auto line = file->read_line(1024);
- if (line.is_empty())
+ auto original_line = file->read_line(1024);
+ ++line_number;
+ if (original_line.is_empty())
  break;
- auto fields = line.split('\t');
-
- auto sections = fields[0].split('.');
- IPv4Address addr {
- (u8)atoi(sections[0].characters()),
- (u8)atoi(sections[1].characters()),
- (u8)atoi(sections[2].characters()),
- (u8)atoi(sections[3].characters()),
- };
- auto raw_addr = addr.to_in_addr_t();
+ auto trimmed_line = original_line.view().trim_whitespace();
+ auto fields = trimmed_line.split_view('\t', false);
+
+ if (fields.size() < 2) {
+ dbgln("Failed to parse line {} from '/etc/hosts': '{}'", line_number, original_line);
+ continue;
+ }
 
- DNSName name = fields[1];
+ if (fields.size() > 2)
+ dbgln("Line {} from '/etc/hosts' ('{}') has more than two parts, only the first two are used.", line_number, original_line);
+
+ auto maybe_address = IPv4Address::from_string(fields[0]);
+ if (!maybe_address.has_value()) {
+ dbgln("Failed to parse line {} from '/etc/hosts': '{}'", line_number, original_line);
+ continue;
+ }
+
+ auto raw_addr = maybe_address->to_in_addr_t();
+
+ DNSName name { fields[1] };
  add_answer(name, DNSRecordType::A, String { (const char*)&raw_addr, sizeof(raw_addr) });
 
- IPv4Address reverse_addr {
- (u8)atoi(sections[3].characters()),
- (u8)atoi(sections[2].characters()),
- (u8)atoi(sections[1].characters()),
- (u8)atoi(sections[0].characters()),
- };
  StringBuilder builder;
- builder.append(reverse_addr.to_string());
+ builder.append(maybe_address->to_string_reversed());
  builder.append(".in-addr.arpa");
  add_answer(builder.to_string(), DNSRecordType::PTR, name.as_string());
  }