ui,tunnel: support DNS search domains

wg-quick has supported this for a while, but not the config layer, and
not the Go backend, so wire this all up.

Requested-by: Alexis Geoffrey <alexis.geoffrey97@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 49 insertions, 2 deletions

diff --git a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
index dfe217a3..701b0715 100644
--- a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -274,6 +274,9 @@ public final class GoBackend implements Backend {
             for (final InetAddress addr : config.getInterface().getDnsServers())
                 builder.addDnsServer(addr.getHostAddress());
 
+            for (final String dnsSearchDomain : config.getInterface().getDnsSearchDomains())
+                builder.addSearchDomain(dnsSearchDomain);
+
             boolean sawDefaultRoute = false;
             for (final Peer peer : config.getPeers()) {
                 for (final InetNetwork addr : peer.getAllowedIps()) {
diff --git a/tunnel/src/main/java/com/wireguard/config/InetAddresses.java b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
index 573c522d..32a8be9e 100644
--- a/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
+++ b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
@@ -23,6 +23,7 @@ import androidx.annotation.Nullable;
 public final class InetAddresses {
     @Nullable private static final Method PARSER_METHOD;
     private static final Pattern WONT_TOUCH_RESOLVER = Pattern.compile("^(((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:)))(%.+)?)|((?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))$");
+    private static final Pattern VALID_HOSTNAME = Pattern.compile("^(?=.{1,255}$)[0-9A-Za-z](?:(?:[0-9A-Za-z]|-){0,61}[0-9A-Za-z])?(?:\\.[0-9A-Za-z](?:(?:[0-9A-Za-z]|-){0,61}[0-9A-Za-z])?)*\\.?$");
 
     static {
         Method m = null;
@@ -39,6 +40,16 @@ public final class InetAddresses {
     }
 
     /**
+     * Determines whether input is a valid DNS hostname.
+     *
+     * @param maybeHostname a string that is possibly a DNS hostname
+     * @return whether or not maybeHostname is a valid DNS hostname
+     */
+    public static boolean isHostname(final CharSequence maybeHostname) {
+        return VALID_HOSTNAME.matcher(maybeHostname).matches();
+    }
+
+    /**
      * Parses a numeric IPv4 or IPv6 address without performing any DNS lookups.
      *
      * @param address a string representing the IP address
diff --git a/tunnel/src/main/java/com/wireguard/config/Interface.java b/tunnel/src/main/java/com/wireguard/config/Interface.java
index 01bb3699..1ece3b10 100644
--- a/tunnel/src/main/java/com/wireguard/config/Interface.java
+++ b/tunnel/src/main/java/com/wireguard/config/Interface.java
@@ -40,6 +40,7 @@ public final class Interface {
 
     private final Set<InetNetwork> addresses;
     private final Set<InetAddress> dnsServers;
+    private final Set<String> dnsSearchDomains;
     private final Set<String> excludedApplications;
     private final Set<String> includedApplications;
     private final KeyPair keyPair;
@@ -50,6 +51,7 @@ public final class Interface {
         // Defensively copy to ensure immutability even if the Builder is reused.
         addresses = Collections.unmodifiableSet(new LinkedHashSet<>(builder.addresses));
         dnsServers = Collections.unmodifiableSet(new LinkedHashSet<>(builder.dnsServers));
+        dnsSearchDomains = Collections.unmodifiableSet(new LinkedHashSet<>(builder.dnsSearchDomains));
         excludedApplications = Collections.unmodifiableSet(new LinkedHashSet<>(builder.excludedApplications));
         includedApplications = Collections.unmodifiableSet(new LinkedHashSet<>(builder.includedApplications));
         keyPair = Objects.requireNonNull(builder.keyPair, "Interfaces must have a private key");
@@ -108,6 +110,7 @@ public final class Interface {
         final Interface other = (Interface) obj;
         return addresses.equals(other.addresses)
                 && dnsServers.equals(other.dnsServers)
+                && dnsSearchDomains.equals(other.dnsSearchDomains)
                 && excludedApplications.equals(other.excludedApplications)
                 && includedApplications.equals(other.includedApplications)
                 && keyPair.equals(other.keyPair)
@@ -136,6 +139,16 @@ public final class Interface {
     }
 
     /**
+     * Returns the set of DNS search domains associated with the interface.
+     *
+     * @return a set of strings
+     */
+    public Set<String> getDnsSearchDomains() {
+        // The collection is already immutable.
+        return dnsSearchDomains;
+    }
+
+    /**
      * Returns the set of applications excluded from using the interface.
      *
      * @return a set of package names
@@ -222,6 +235,7 @@ public final class Interface {
             sb.append("Address = ").append(Attribute.join(addresses)).append('\n');
         if (!dnsServers.isEmpty()) {
             final List<String> dnsServerStrings = dnsServers.stream().map(InetAddress::getHostAddress).collect(Collectors.toList());
+            dnsServerStrings.addAll(dnsSearchDomains);
             sb.append("DNS = ").append(Attribute.join(dnsServerStrings)).append('\n');
         }
         if (!excludedApplications.isEmpty())
@@ -254,6 +268,8 @@ public final class Interface {
         // Defaults to an empty set.
         private final Set<InetAddress> dnsServers = new LinkedHashSet<>();
         // Defaults to an empty set.
+        private final Set<String> dnsSearchDomains = new LinkedHashSet<>();
+        // Defaults to an empty set.
         private final Set<String> excludedApplications = new LinkedHashSet<>();
         // Defaults to an empty set.
         private final Set<String> includedApplications = new LinkedHashSet<>();
@@ -284,6 +300,16 @@ public final class Interface {
             return this;
         }
 
+        public Builder addDnsSearchDomain(final String dnsSearchDomain) {
+            dnsSearchDomains.add(dnsSearchDomain);
+            return this;
+        }
+
+        public Builder addDnsSearchDomains(final Collection<String> dnsSearchDomains) {
+            this.dnsSearchDomains.addAll(dnsSearchDomains);
+            return this;
+        }
+
         public Interface build() throws BadConfigException {
             if (keyPair == null)
                 throw new BadConfigException(Section.INTERFACE, Location.PRIVATE_KEY,
@@ -326,8 +352,15 @@ public final class Interface {
 
         public Builder parseDnsServers(final CharSequence dnsServers) throws BadConfigException {
             try {
-                for (final String dnsServer : Attribute.split(dnsServers))
-                    addDnsServer(InetAddresses.parse(dnsServer));
+                for (final String dnsServer : Attribute.split(dnsServers)) {
+                    try {
+                        addDnsServer(InetAddresses.parse(dnsServer));
+                    } catch (final ParseException e) {
+                        if (e.getParsingClass() != InetAddress.class || !InetAddresses.isHostname(dnsServer))
+                            throw e;
+                        addDnsSearchDomain(dnsServer);
+                    }
+                }
                 return this;
             } catch (final ParseException e) {
                 throw new BadConfigException(Section.INTERFACE, Location.DNS, e);