Migrate tunnel related classes to tunnel/ Gradle module

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

9 files changed, 1374 insertions, 0 deletions

diff --git a/tunnel/src/main/java/com/wireguard/config/Attribute.java b/tunnel/src/main/java/com/wireguard/config/Attribute.java
new file mode 100644
index 00000000..1e9e25f0
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Attribute.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.util.Iterator;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import java9.util.Optional;
+
+public final class Attribute {
+    private static final Pattern LINE_PATTERN = Pattern.compile("(\\w+)\\s*=\\s*([^\\s#][^#]*)");
+    private static final Pattern LIST_SEPARATOR = Pattern.compile("\\s*,\\s*");
+
+    private final String key;
+    private final String value;
+
+    private Attribute(final String key, final String value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public static String join(final Iterable<?> values) {
+        final Iterator<?> it = values.iterator();
+        if (!it.hasNext()) {
+            return "";
+        }
+        final StringBuilder sb = new StringBuilder();
+        sb.append(it.next());
+        while (it.hasNext()) {
+            sb.append(", ");
+            sb.append(it.next());
+        }
+        return sb.toString();
+    }
+
+    public static Optional<Attribute> parse(final CharSequence line) {
+        final Matcher matcher = LINE_PATTERN.matcher(line);
+        if (!matcher.matches())
+            return Optional.empty();
+        return Optional.of(new Attribute(matcher.group(1), matcher.group(2)));
+    }
+
+    public static String[] split(final CharSequence value) {
+        return LIST_SEPARATOR.split(value);
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public String getValue() {
+        return value;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/BadConfigException.java b/tunnel/src/main/java/com/wireguard/config/BadConfigException.java
new file mode 100644
index 00000000..6d41b065
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/BadConfigException.java
@@ -0,0 +1,118 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.crypto.KeyFormatException;
+
+public class BadConfigException extends Exception {
+    private final Location location;
+    private final Reason reason;
+    private final Section section;
+    @Nullable private final CharSequence text;
+
+    private BadConfigException(final Section section, final Location location,
+                               final Reason reason, @Nullable final CharSequence text,
+                               @Nullable final Throwable cause) {
+        super(cause);
+        this.section = section;
+        this.location = location;
+        this.reason = reason;
+        this.text = text;
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final Reason reason, @Nullable final CharSequence text) {
+        this(section, location, reason, text, null);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final KeyFormatException cause) {
+        this(section, location, Reason.INVALID_KEY, null, cause);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              @Nullable final CharSequence text,
+                              final NumberFormatException cause) {
+        this(section, location, Reason.INVALID_NUMBER, text, cause);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final ParseException cause) {
+        this(section, location, Reason.INVALID_VALUE, cause.getText(), cause);
+    }
+
+    public Location getLocation() {
+        return location;
+    }
+
+    public Reason getReason() {
+        return reason;
+    }
+
+    public Section getSection() {
+        return section;
+    }
+
+    @Nullable
+    public CharSequence getText() {
+        return text;
+    }
+
+    public enum Location {
+        TOP_LEVEL(""),
+        ADDRESS("Address"),
+        ALLOWED_IPS("AllowedIPs"),
+        DNS("DNS"),
+        ENDPOINT("Endpoint"),
+        EXCLUDED_APPLICATIONS("ExcludedApplications"),
+        LISTEN_PORT("ListenPort"),
+        MTU("MTU"),
+        PERSISTENT_KEEPALIVE("PersistentKeepalive"),
+        PRE_SHARED_KEY("PresharedKey"),
+        PRIVATE_KEY("PrivateKey"),
+        PUBLIC_KEY("PublicKey");
+
+        private final String name;
+
+        Location(final String name) {
+            this.name = name;
+        }
+
+        public String getName() {
+            return name;
+        }
+    }
+
+    public enum Reason {
+        INVALID_KEY,
+        INVALID_NUMBER,
+        INVALID_VALUE,
+        MISSING_ATTRIBUTE,
+        MISSING_SECTION,
+        MISSING_VALUE,
+        SYNTAX_ERROR,
+        UNKNOWN_ATTRIBUTE,
+        UNKNOWN_SECTION
+    }
+
+    public enum Section {
+        CONFIG("Config"),
+        INTERFACE("Interface"),
+        PEER("Peer");
+
+        private final String name;
+
+        Section(final String name) {
+            this.name = name;
+        }
+
+        public String getName() {
+            return name;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Config.java b/tunnel/src/main/java/com/wireguard/config/Config.java
new file mode 100644
index 00000000..62651b08
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Config.java
@@ -0,0 +1,221 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * Represents the contents of a wg-quick configuration file, made up of one or more "Interface"
+ * sections (combined together), and zero or more "Peer" sections (treated individually).
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Config {
+    private final Interface interfaze;
+    private final List<Peer> peers;
+
+    private Config(final Builder builder) {
+        interfaze = Objects.requireNonNull(builder.interfaze, "An [Interface] section is required");
+        // Defensively copy to ensure immutability even if the Builder is reused.
+        peers = Collections.unmodifiableList(new ArrayList<>(builder.peers));
+    }
+
+    /**
+     * Parses an series of "Interface" and "Peer" sections into a {@code Config}. Throws
+     * {@link BadConfigException} if the input is not well-formed or contains data that cannot
+     * be parsed.
+     *
+     * @param stream a stream of UTF-8 text that is interpreted as a WireGuard configuration
+     * @return a {@code Config} instance representing the supplied configuration
+     */
+    public static Config parse(final InputStream stream)
+            throws IOException, BadConfigException {
+        return parse(new BufferedReader(new InputStreamReader(stream)));
+    }
+
+    /**
+     * Parses an series of "Interface" and "Peer" sections into a {@code Config}. Throws
+     * {@link BadConfigException} if the input is not well-formed or contains data that cannot
+     * be parsed.
+     *
+     * @param reader a BufferedReader of UTF-8 text that is interpreted as a WireGuard configuration
+     * @return a {@code Config} instance representing the supplied configuration
+     */
+    public static Config parse(final BufferedReader reader)
+            throws IOException, BadConfigException {
+        final Builder builder = new Builder();
+        final Collection<String> interfaceLines = new ArrayList<>();
+        final Collection<String> peerLines = new ArrayList<>();
+        boolean inInterfaceSection = false;
+        boolean inPeerSection = false;
+        @Nullable String line;
+        while ((line = reader.readLine()) != null) {
+            final int commentIndex = line.indexOf('#');
+            if (commentIndex != -1)
+                line = line.substring(0, commentIndex);
+            line = line.trim();
+            if (line.isEmpty())
+                continue;
+            if (line.startsWith("[")) {
+                // Consume all [Peer] lines read so far.
+                if (inPeerSection) {
+                    builder.parsePeer(peerLines);
+                    peerLines.clear();
+                }
+                if ("[Interface]".equalsIgnoreCase(line)) {
+                    inInterfaceSection = true;
+                    inPeerSection = false;
+                } else if ("[Peer]".equalsIgnoreCase(line)) {
+                    inInterfaceSection = false;
+                    inPeerSection = true;
+                } else {
+                    throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_SECTION, line);
+                }
+            } else if (inInterfaceSection) {
+                interfaceLines.add(line);
+            } else if (inPeerSection) {
+                peerLines.add(line);
+            } else {
+                throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                        Reason.UNKNOWN_SECTION, line);
+            }
+        }
+        if (inPeerSection)
+            builder.parsePeer(peerLines);
+        else if (!inInterfaceSection)
+            throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                    Reason.MISSING_SECTION, null);
+        // Combine all [Interface] sections in the file.
+        builder.parseInterface(interfaceLines);
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Config))
+            return false;
+        final Config other = (Config) obj;
+        return interfaze.equals(other.interfaze) && peers.equals(other.peers);
+    }
+
+    /**
+     * Returns the interface section of the configuration.
+     *
+     * @return the interface configuration
+     */
+    public Interface getInterface() {
+        return interfaze;
+    }
+
+    /**
+     * Returns a list of the configuration's peer sections.
+     *
+     * @return a list of {@link Peer}s
+     */
+    public List<Peer> getPeers() {
+        return peers;
+    }
+
+    @Override
+    public int hashCode() {
+        return 31 * interfaze.hashCode() + peers.hashCode();
+    }
+
+    /**
+     * Converts the {@code Config} into a string suitable for debugging purposes. The {@code Config}
+     * is identified by its interface's public key and the number of peers it has.
+     *
+     * @return a concise single-line identifier for the {@code Config}
+     */
+    @Override
+    public String toString() {
+        return "(Config " + interfaze + " (" + peers.size() + " peers))";
+    }
+
+    /**
+     * Converts the {@code Config} into a string suitable for use as a {@code wg-quick}
+     * configuration file.
+     *
+     * @return the {@code Config} represented as one [Interface] and zero or more [Peer] sections
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append("[Interface]\n").append(interfaze.toWgQuickString());
+        for (final Peer peer : peers)
+            sb.append("\n[Peer]\n").append(peer.toWgQuickString());
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Config} for use with the WireGuard cross-platform userspace API.
+     *
+     * @return the {@code Config} represented as a series of "key=value" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append(interfaze.toWgUserspaceString());
+        sb.append("replace_peers=true\n");
+        for (final Peer peer : peers)
+            sb.append(peer.toWgUserspaceString());
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // Defaults to an empty set.
+        private final Set<Peer> peers = new LinkedHashSet<>();
+        // No default; must be provided before building.
+        @Nullable private Interface interfaze;
+
+        public Builder addPeer(final Peer peer) {
+            peers.add(peer);
+            return this;
+        }
+
+        public Builder addPeers(final Collection<Peer> peers) {
+            this.peers.addAll(peers);
+            return this;
+        }
+
+        public Config build() {
+            if (interfaze == null)
+                throw new IllegalArgumentException("An [Interface] section is required");
+            return new Config(this);
+        }
+
+        public Builder parseInterface(final Iterable<? extends CharSequence> lines)
+                throws BadConfigException {
+            return setInterface(Interface.parse(lines));
+        }
+
+        public Builder parsePeer(final Iterable<? extends CharSequence> lines)
+                throws BadConfigException {
+            return addPeer(Peer.parse(lines));
+        }
+
+        public Builder setInterface(final Interface interfaze) {
+            this.interfaze = interfaze;
+            return this;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetAddresses.java b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
new file mode 100644
index 00000000..5303e27f
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.lang.reflect.Method;
+import java.net.Inet4Address;
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.regex.Pattern;
+
+import javax.annotation.Nullable;
+
+/**
+ * Utility methods for creating instances of {@link InetAddress}.
+ */
+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]?))$");
+
+    static {
+        Method m = null;
+        try {
+            if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.Q)
+                // noinspection JavaReflectionMemberAccess
+                m = InetAddress.class.getMethod("parseNumericAddress", String.class);
+        } catch (final Exception ignored) {
+        }
+        PARSER_METHOD = m;
+    }
+
+    private InetAddresses() { }
+
+    /**
+     * Parses a numeric IPv4 or IPv6 address without performing any DNS lookups.
+     *
+     * @param address a string representing the IP address
+     * @return an instance of {@link Inet4Address} or {@link Inet6Address}, as appropriate
+     */
+    public static InetAddress parse(final String address) throws ParseException {
+        if (address.isEmpty())
+            throw new ParseException(InetAddress.class, address, "Empty address");
+        try {
+            if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.Q)
+                return android.net.InetAddresses.parseNumericAddress(address);
+            else if (PARSER_METHOD != null)
+                return (InetAddress) PARSER_METHOD.invoke(null, address);
+            else
+                throw new NoSuchMethodException("parseNumericAddress");
+        } catch (final IllegalArgumentException e) {
+            throw new ParseException(InetAddress.class, address, e);
+        } catch (final Exception e) {
+            final Throwable cause = e.getCause();
+            // Re-throw parsing exceptions with the original type, as callers might try to catch
+            // them. On the other hand, callers cannot be expected to handle reflection failures.
+            if (cause instanceof IllegalArgumentException)
+                throw new ParseException(InetAddress.class, address, cause);
+            try {
+                if (WONT_TOUCH_RESOLVER.matcher(address).matches())
+                    return InetAddress.getByName(address);
+                else
+                    throw new ParseException(InetAddress.class, address, "Not an IP address");
+            } catch (final UnknownHostException f) {
+                throw new ParseException(InetAddress.class, address, f);
+            }
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
new file mode 100644
index 00000000..a442258e
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import org.threeten.bp.Duration;
+import org.threeten.bp.Instant;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.UnknownHostException;
+import java.util.regex.Pattern;
+
+import java9.util.Optional;
+
+
+/**
+ * An external endpoint (host and port) used to connect to a WireGuard {@link Peer}.
+ * <p>
+ * Instances of this class are externally immutable.
+ */
+public final class InetEndpoint {
+    private static final Pattern BARE_IPV6 = Pattern.compile("^[^\\[\\]]*:[^\\[\\]]*");
+    private static final Pattern FORBIDDEN_CHARACTERS = Pattern.compile("[/?#]");
+
+    private final String host;
+    private final boolean isResolved;
+    private final Object lock = new Object();
+    private final int port;
+    private Instant lastResolution = Instant.EPOCH;
+    @Nullable private InetEndpoint resolved;
+
+    private InetEndpoint(final String host, final boolean isResolved, final int port) {
+        this.host = host;
+        this.isResolved = isResolved;
+        this.port = port;
+    }
+
+    public static InetEndpoint parse(final String endpoint) throws ParseException {
+        if (FORBIDDEN_CHARACTERS.matcher(endpoint).find())
+            throw new ParseException(InetEndpoint.class, endpoint, "Forbidden characters");
+        final URI uri;
+        try {
+            uri = new URI("wg://" + endpoint);
+        } catch (final URISyntaxException e) {
+            throw new IllegalArgumentException(e);
+        }
+        if (uri.getPort() < 0 || uri.getPort() > 65535)
+            throw new ParseException(InetEndpoint.class, endpoint, "Missing/invalid port number");
+        try {
+            InetAddresses.parse(uri.getHost());
+            // Parsing ths host as a numeric address worked, so we don't need to do DNS lookups.
+            return new InetEndpoint(uri.getHost(), true, uri.getPort());
+        } catch (final ParseException ignored) {
+            // Failed to parse the host as a numeric address, so it must be a DNS hostname/FQDN.
+            return new InetEndpoint(uri.getHost(), false, uri.getPort());
+        }
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof InetEndpoint))
+            return false;
+        final InetEndpoint other = (InetEndpoint) obj;
+        return host.equals(other.host) && port == other.port;
+    }
+
+    public String getHost() {
+        return host;
+    }
+
+    public int getPort() {
+        return port;
+    }
+
+    /**
+     * Generate an {@code InetEndpoint} instance with the same port and the host resolved using DNS
+     * to a numeric address. If the host is already numeric, the existing instance may be returned.
+     * Because this function may perform network I/O, it must not be called from the main thread.
+     *
+     * @return the resolved endpoint, or {@link Optional#empty()}
+     */
+    public Optional<InetEndpoint> getResolved() {
+        if (isResolved)
+            return Optional.of(this);
+        synchronized (lock) {
+            //TODO(zx2c4): Implement a real timeout mechanism using DNS TTL
+            if (Duration.between(lastResolution, Instant.now()).toMinutes() > 1) {
+                try {
+                    // Prefer v4 endpoints over v6 to work around DNS64 and IPv6 NAT issues.
+                    final InetAddress[] candidates = InetAddress.getAllByName(host);
+                    InetAddress address = candidates[0];
+                    for (final InetAddress candidate : candidates) {
+                        if (candidate instanceof Inet4Address) {
+                            address = candidate;
+                            break;
+                        }
+                    }
+                    resolved = new InetEndpoint(address.getHostAddress(), true, port);
+                    lastResolution = Instant.now();
+                } catch (final UnknownHostException e) {
+                    resolved = null;
+                }
+            }
+            return Optional.ofNullable(resolved);
+        }
+    }
+
+    @Override
+    public int hashCode() {
+        return host.hashCode() ^ port;
+    }
+
+    @Override
+    public String toString() {
+        final boolean isBareIpv6 = isResolved && BARE_IPV6.matcher(host).matches();
+        return (isBareIpv6 ? '[' + host + ']' : host) + ':' + port;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetNetwork.java b/tunnel/src/main/java/com/wireguard/config/InetNetwork.java
new file mode 100644
index 00000000..f89322fd
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetNetwork.java
@@ -0,0 +1,76 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+
+/**
+ * An Internet network, denoted by its address and netmask
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class InetNetwork {
+    private final InetAddress address;
+    private final int mask;
+
+    private InetNetwork(final InetAddress address, final int mask) {
+        this.address = address;
+        this.mask = mask;
+    }
+
+    public static InetNetwork parse(final String network) throws ParseException {
+        final int slash = network.lastIndexOf('/');
+        final String maskString;
+        final int rawMask;
+        final String rawAddress;
+        if (slash >= 0) {
+            maskString = network.substring(slash + 1);
+            try {
+                rawMask = Integer.parseInt(maskString, 10);
+            } catch (final NumberFormatException ignored) {
+                throw new ParseException(Integer.class, maskString);
+            }
+            rawAddress = network.substring(0, slash);
+        } else {
+            maskString = "";
+            rawMask = -1;
+            rawAddress = network;
+        }
+        final InetAddress address = InetAddresses.parse(rawAddress);
+        final int maxMask = (address instanceof Inet4Address) ? 32 : 128;
+        if (rawMask > maxMask)
+            throw new ParseException(InetNetwork.class, maskString, "Invalid network mask");
+        final int mask = rawMask >= 0 && rawMask <= maxMask ? rawMask : maxMask;
+        return new InetNetwork(address, mask);
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof InetNetwork))
+            return false;
+        final InetNetwork other = (InetNetwork) obj;
+        return address.equals(other.address) && mask == other.mask;
+    }
+
+    public InetAddress getAddress() {
+        return address;
+    }
+
+    public int getMask() {
+        return mask;
+    }
+
+    @Override
+    public int hashCode() {
+        return address.hashCode() ^ mask;
+    }
+
+    @Override
+    public String toString() {
+        return address.getHostAddress() + '/' + mask;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Interface.java b/tunnel/src/main/java/com/wireguard/config/Interface.java
new file mode 100644
index 00000000..54944424
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Interface.java
@@ -0,0 +1,355 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+import com.wireguard.crypto.Key;
+import com.wireguard.crypto.KeyFormatException;
+import com.wireguard.crypto.KeyPair;
+
+import java.net.InetAddress;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Locale;
+import java.util.Objects;
+import java.util.Set;
+
+import java9.util.Lists;
+import java9.util.Optional;
+import java9.util.stream.Collectors;
+import java9.util.stream.StreamSupport;
+
+/**
+ * Represents the configuration for a WireGuard interface (an [Interface] block). Interfaces must
+ * have a private key (used to initialize a {@code KeyPair}), and may optionally have several other
+ * attributes.
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Interface {
+    private static final int MAX_UDP_PORT = 65535;
+    private static final int MIN_UDP_PORT = 0;
+
+    private final Set<InetNetwork> addresses;
+    private final Set<InetAddress> dnsServers;
+    private final Set<String> excludedApplications;
+    private final KeyPair keyPair;
+    private final Optional<Integer> listenPort;
+    private final Optional<Integer> mtu;
+
+    private Interface(final Builder builder) {
+        // 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));
+        excludedApplications = Collections.unmodifiableSet(new LinkedHashSet<>(builder.excludedApplications));
+        keyPair = Objects.requireNonNull(builder.keyPair, "Interfaces must have a private key");
+        listenPort = builder.listenPort;
+        mtu = builder.mtu;
+    }
+
+    /**
+     * Parses an series of "KEY = VALUE" lines into an {@code Interface}. Throws
+     * {@link ParseException} if the input is not well-formed or contains unknown attributes.
+     *
+     * @param lines An iterable sequence of lines, containing at least a private key attribute
+     * @return An {@code Interface} with all of the attributes from {@code lines} set
+     */
+    public static Interface parse(final Iterable<? extends CharSequence> lines)
+            throws BadConfigException {
+        final Builder builder = new Builder();
+        for (final CharSequence line : lines) {
+            final Attribute attribute = Attribute.parse(line).orElseThrow(() ->
+                    new BadConfigException(Section.INTERFACE, Location.TOP_LEVEL,
+                            Reason.SYNTAX_ERROR, line));
+            switch (attribute.getKey().toLowerCase(Locale.ENGLISH)) {
+                case "address":
+                    builder.parseAddresses(attribute.getValue());
+                    break;
+                case "dns":
+                    builder.parseDnsServers(attribute.getValue());
+                    break;
+                case "excludedapplications":
+                    builder.parseExcludedApplications(attribute.getValue());
+                    break;
+                case "listenport":
+                    builder.parseListenPort(attribute.getValue());
+                    break;
+                case "mtu":
+                    builder.parseMtu(attribute.getValue());
+                    break;
+                case "privatekey":
+                    builder.parsePrivateKey(attribute.getValue());
+                    break;
+                default:
+                    throw new BadConfigException(Section.INTERFACE, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_ATTRIBUTE, attribute.getKey());
+            }
+        }
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Interface))
+            return false;
+        final Interface other = (Interface) obj;
+        return addresses.equals(other.addresses)
+                && dnsServers.equals(other.dnsServers)
+                && excludedApplications.equals(other.excludedApplications)
+                && keyPair.equals(other.keyPair)
+                && listenPort.equals(other.listenPort)
+                && mtu.equals(other.mtu);
+    }
+
+    /**
+     * Returns the set of IP addresses assigned to the interface.
+     *
+     * @return a set of {@link InetNetwork}s
+     */
+    public Set<InetNetwork> getAddresses() {
+        // The collection is already immutable.
+        return addresses;
+    }
+
+    /**
+     * Returns the set of DNS servers associated with the interface.
+     *
+     * @return a set of {@link InetAddress}es
+     */
+    public Set<InetAddress> getDnsServers() {
+        // The collection is already immutable.
+        return dnsServers;
+    }
+
+    /**
+     * Returns the set of applications excluded from using the interface.
+     *
+     * @return a set of package names
+     */
+    public Set<String> getExcludedApplications() {
+        // The collection is already immutable.
+        return excludedApplications;
+    }
+
+    /**
+     * Returns the public/private key pair used by the interface.
+     *
+     * @return a key pair
+     */
+    public KeyPair getKeyPair() {
+        return keyPair;
+    }
+
+    /**
+     * Returns the UDP port number that the WireGuard interface will listen on.
+     *
+     * @return a UDP port number, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getListenPort() {
+        return listenPort;
+    }
+
+    /**
+     * Returns the MTU used for the WireGuard interface.
+     *
+     * @return the MTU, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getMtu() {
+        return mtu;
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 1;
+        hash = 31 * hash + addresses.hashCode();
+        hash = 31 * hash + dnsServers.hashCode();
+        hash = 31 * hash + excludedApplications.hashCode();
+        hash = 31 * hash + keyPair.hashCode();
+        hash = 31 * hash + listenPort.hashCode();
+        hash = 31 * hash + mtu.hashCode();
+        return hash;
+    }
+
+    /**
+     * Converts the {@code Interface} into a string suitable for debugging purposes. The {@code
+     * Interface} is identified by its public key and (if set) the port used for its UDP socket.
+     *
+     * @return A concise single-line identifier for the {@code Interface}
+     */
+    @Override
+    public String toString() {
+        final StringBuilder sb = new StringBuilder("(Interface ");
+        sb.append(keyPair.getPublicKey().toBase64());
+        listenPort.ifPresent(lp -> sb.append(" @").append(lp));
+        sb.append(')');
+        return sb.toString();
+    }
+
+    /**
+     * Converts the {@code Interface} into a string suitable for inclusion in a {@code wg-quick}
+     * configuration file.
+     *
+     * @return The {@code Interface} represented as a series of "Key = Value" lines
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        if (!addresses.isEmpty())
+            sb.append("Address = ").append(Attribute.join(addresses)).append('\n');
+        if (!dnsServers.isEmpty()) {
+            final List<String> dnsServerStrings = StreamSupport.stream(dnsServers)
+                    .map(InetAddress::getHostAddress)
+                    .collect(Collectors.toUnmodifiableList());
+            sb.append("DNS = ").append(Attribute.join(dnsServerStrings)).append('\n');
+        }
+        if (!excludedApplications.isEmpty())
+            sb.append("ExcludedApplications = ").append(Attribute.join(excludedApplications)).append('\n');
+        listenPort.ifPresent(lp -> sb.append("ListenPort = ").append(lp).append('\n'));
+        mtu.ifPresent(m -> sb.append("MTU = ").append(m).append('\n'));
+        sb.append("PrivateKey = ").append(keyPair.getPrivateKey().toBase64()).append('\n');
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Interface} for use with the WireGuard cross-platform userspace API.
+     * Note that not all attributes are included in this representation.
+     *
+     * @return the {@code Interface} represented as a series of "KEY=VALUE" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append("private_key=").append(keyPair.getPrivateKey().toHex()).append('\n');
+        listenPort.ifPresent(lp -> sb.append("listen_port=").append(lp).append('\n'));
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // Defaults to an empty set.
+        private final Set<InetNetwork> addresses = new LinkedHashSet<>();
+        // Defaults to an empty set.
+        private final Set<InetAddress> dnsServers = new LinkedHashSet<>();
+        // Defaults to an empty set.
+        private final Set<String> excludedApplications = new LinkedHashSet<>();
+        // No default; must be provided before building.
+        @Nullable private KeyPair keyPair;
+        // Defaults to not present.
+        private Optional<Integer> listenPort = Optional.empty();
+        // Defaults to not present.
+        private Optional<Integer> mtu = Optional.empty();
+
+        public Builder addAddress(final InetNetwork address) {
+            addresses.add(address);
+            return this;
+        }
+
+        public Builder addAddresses(final Collection<InetNetwork> addresses) {
+            this.addresses.addAll(addresses);
+            return this;
+        }
+
+        public Builder addDnsServer(final InetAddress dnsServer) {
+            dnsServers.add(dnsServer);
+            return this;
+        }
+
+        public Builder addDnsServers(final Collection<? extends InetAddress> dnsServers) {
+            this.dnsServers.addAll(dnsServers);
+            return this;
+        }
+
+        public Interface build() throws BadConfigException {
+            if (keyPair == null)
+                throw new BadConfigException(Section.INTERFACE, Location.PRIVATE_KEY,
+                        Reason.MISSING_ATTRIBUTE, null);
+            return new Interface(this);
+        }
+
+        public Builder excludeApplication(final String application) {
+            excludedApplications.add(application);
+            return this;
+        }
+
+        public Builder excludeApplications(final Collection<String> applications) {
+            excludedApplications.addAll(applications);
+            return this;
+        }
+
+        public Builder parseAddresses(final CharSequence addresses) throws BadConfigException {
+            try {
+                for (final String address : Attribute.split(addresses))
+                    addAddress(InetNetwork.parse(address));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.ADDRESS, e);
+            }
+        }
+
+        public Builder parseDnsServers(final CharSequence dnsServers) throws BadConfigException {
+            try {
+                for (final String dnsServer : Attribute.split(dnsServers))
+                    addDnsServer(InetAddresses.parse(dnsServer));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.DNS, e);
+            }
+        }
+
+        public Builder parseExcludedApplications(final CharSequence apps) {
+            return excludeApplications(Lists.of(Attribute.split(apps)));
+        }
+
+        public Builder parseListenPort(final String listenPort) throws BadConfigException {
+            try {
+                return setListenPort(Integer.parseInt(listenPort));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT, listenPort, e);
+            }
+        }
+
+        public Builder parseMtu(final String mtu) throws BadConfigException {
+            try {
+                return setMtu(Integer.parseInt(mtu));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.MTU, mtu, e);
+            }
+        }
+
+        public Builder parsePrivateKey(final String privateKey) throws BadConfigException {
+            try {
+                return setKeyPair(new KeyPair(Key.fromBase64(privateKey)));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.PRIVATE_KEY, e);
+            }
+        }
+
+        public Builder setKeyPair(final KeyPair keyPair) {
+            this.keyPair = keyPair;
+            return this;
+        }
+
+        public Builder setListenPort(final int listenPort) throws BadConfigException {
+            if (listenPort < MIN_UDP_PORT || listenPort > MAX_UDP_PORT)
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT,
+                        Reason.INVALID_VALUE, String.valueOf(listenPort));
+            this.listenPort = listenPort == 0 ? Optional.empty() : Optional.of(listenPort);
+            return this;
+        }
+
+        public Builder setMtu(final int mtu) throws BadConfigException {
+            if (mtu < 0)
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT,
+                        Reason.INVALID_VALUE, String.valueOf(mtu));
+            this.mtu = mtu == 0 ? Optional.empty() : Optional.of(mtu);
+            return this;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/ParseException.java b/tunnel/src/main/java/com/wireguard/config/ParseException.java
new file mode 100644
index 00000000..c79d1fa1
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/ParseException.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+/**
+ */
+public class ParseException extends Exception {
+    private final Class<?> parsingClass;
+    private final CharSequence text;
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final String message, @Nullable final Throwable cause) {
+        super(message, cause);
+        this.parsingClass = parsingClass;
+        this.text = text;
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final String message) {
+        this(parsingClass, text, message, null);
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final Throwable cause) {
+        this(parsingClass, text, null, cause);
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text) {
+        this(parsingClass, text, null, null);
+    }
+
+    public Class<?> getParsingClass() {
+        return parsingClass;
+    }
+
+    public CharSequence getText() {
+        return text;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Peer.java b/tunnel/src/main/java/com/wireguard/config/Peer.java
new file mode 100644
index 00000000..37fcfa69
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Peer.java
@@ -0,0 +1,306 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+import com.wireguard.crypto.Key;
+import com.wireguard.crypto.KeyFormatException;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.Locale;
+import java.util.Objects;
+import java.util.Set;
+
+import java9.util.Optional;
+
+/**
+ * Represents the configuration for a WireGuard peer (a [Peer] block). Peers must have a public key,
+ * and may optionally have several other attributes.
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Peer {
+    private final Set<InetNetwork> allowedIps;
+    private final Optional<InetEndpoint> endpoint;
+    private final Optional<Integer> persistentKeepalive;
+    private final Optional<Key> preSharedKey;
+    private final Key publicKey;
+
+    private Peer(final Builder builder) {
+        // Defensively copy to ensure immutability even if the Builder is reused.
+        allowedIps = Collections.unmodifiableSet(new LinkedHashSet<>(builder.allowedIps));
+        endpoint = builder.endpoint;
+        persistentKeepalive = builder.persistentKeepalive;
+        preSharedKey = builder.preSharedKey;
+        publicKey = Objects.requireNonNull(builder.publicKey, "Peers must have a public key");
+    }
+
+    /**
+     * Parses an series of "KEY = VALUE" lines into a {@code Peer}. Throws {@link ParseException} if
+     * the input is not well-formed or contains unknown attributes.
+     *
+     * @param lines an iterable sequence of lines, containing at least a public key attribute
+     * @return a {@code Peer} with all of its attributes set from {@code lines}
+     */
+    public static Peer parse(final Iterable<? extends CharSequence> lines)
+            throws BadConfigException {
+        final Builder builder = new Builder();
+        for (final CharSequence line : lines) {
+            final Attribute attribute = Attribute.parse(line).orElseThrow(() ->
+                    new BadConfigException(Section.PEER, Location.TOP_LEVEL,
+                            Reason.SYNTAX_ERROR, line));
+            switch (attribute.getKey().toLowerCase(Locale.ENGLISH)) {
+                case "allowedips":
+                    builder.parseAllowedIPs(attribute.getValue());
+                    break;
+                case "endpoint":
+                    builder.parseEndpoint(attribute.getValue());
+                    break;
+                case "persistentkeepalive":
+                    builder.parsePersistentKeepalive(attribute.getValue());
+                    break;
+                case "presharedkey":
+                    builder.parsePreSharedKey(attribute.getValue());
+                    break;
+                case "publickey":
+                    builder.parsePublicKey(attribute.getValue());
+                    break;
+                default:
+                    throw new BadConfigException(Section.PEER, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_ATTRIBUTE, attribute.getKey());
+            }
+        }
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Peer))
+            return false;
+        final Peer other = (Peer) obj;
+        return allowedIps.equals(other.allowedIps)
+                && endpoint.equals(other.endpoint)
+                && persistentKeepalive.equals(other.persistentKeepalive)
+                && preSharedKey.equals(other.preSharedKey)
+                && publicKey.equals(other.publicKey);
+    }
+
+    /**
+     * Returns the peer's set of allowed IPs.
+     *
+     * @return the set of allowed IPs
+     */
+    public Set<InetNetwork> getAllowedIps() {
+        // The collection is already immutable.
+        return allowedIps;
+    }
+
+    /**
+     * Returns the peer's endpoint.
+     *
+     * @return the endpoint, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<InetEndpoint> getEndpoint() {
+        return endpoint;
+    }
+
+    /**
+     * Returns the peer's persistent keepalive.
+     *
+     * @return the persistent keepalive, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getPersistentKeepalive() {
+        return persistentKeepalive;
+    }
+
+    /**
+     * Returns the peer's pre-shared key.
+     *
+     * @return the pre-shared key, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Key> getPreSharedKey() {
+        return preSharedKey;
+    }
+
+    /**
+     * Returns the peer's public key.
+     *
+     * @return the public key
+     */
+    public Key getPublicKey() {
+        return publicKey;
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 1;
+        hash = 31 * hash + allowedIps.hashCode();
+        hash = 31 * hash + endpoint.hashCode();
+        hash = 31 * hash + persistentKeepalive.hashCode();
+        hash = 31 * hash + preSharedKey.hashCode();
+        hash = 31 * hash + publicKey.hashCode();
+        return hash;
+    }
+
+    /**
+     * Converts the {@code Peer} into a string suitable for debugging purposes. The {@code Peer} is
+     * identified by its public key and (if known) its endpoint.
+     *
+     * @return a concise single-line identifier for the {@code Peer}
+     */
+    @Override
+    public String toString() {
+        final StringBuilder sb = new StringBuilder("(Peer ");
+        sb.append(publicKey.toBase64());
+        endpoint.ifPresent(ep -> sb.append(" @").append(ep));
+        sb.append(')');
+        return sb.toString();
+    }
+
+    /**
+     * Converts the {@code Peer} into a string suitable for inclusion in a {@code wg-quick}
+     * configuration file.
+     *
+     * @return the {@code Peer} represented as a series of "Key = Value" lines
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        if (!allowedIps.isEmpty())
+            sb.append("AllowedIPs = ").append(Attribute.join(allowedIps)).append('\n');
+        endpoint.ifPresent(ep -> sb.append("Endpoint = ").append(ep).append('\n'));
+        persistentKeepalive.ifPresent(pk -> sb.append("PersistentKeepalive = ").append(pk).append('\n'));
+        preSharedKey.ifPresent(psk -> sb.append("PreSharedKey = ").append(psk.toBase64()).append('\n'));
+        sb.append("PublicKey = ").append(publicKey.toBase64()).append('\n');
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Peer} for use with the WireGuard cross-platform userspace API. Note
+     * that not all attributes are included in this representation.
+     *
+     * @return the {@code Peer} represented as a series of "key=value" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        // The order here is important: public_key signifies the beginning of a new peer.
+        sb.append("public_key=").append(publicKey.toHex()).append('\n');
+        for (final InetNetwork allowedIp : allowedIps)
+            sb.append("allowed_ip=").append(allowedIp).append('\n');
+        endpoint.flatMap(InetEndpoint::getResolved).ifPresent(ep -> sb.append("endpoint=").append(ep).append('\n'));
+        persistentKeepalive.ifPresent(pk -> sb.append("persistent_keepalive_interval=").append(pk).append('\n'));
+        preSharedKey.ifPresent(psk -> sb.append("preshared_key=").append(psk.toHex()).append('\n'));
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // See wg(8)
+        private static final int MAX_PERSISTENT_KEEPALIVE = 65535;
+
+        // Defaults to an empty set.
+        private final Set<InetNetwork> allowedIps = new LinkedHashSet<>();
+        // Defaults to not present.
+        private Optional<InetEndpoint> endpoint = Optional.empty();
+        // Defaults to not present.
+        private Optional<Integer> persistentKeepalive = Optional.empty();
+        // Defaults to not present.
+        private Optional<Key> preSharedKey = Optional.empty();
+        // No default; must be provided before building.
+        @Nullable private Key publicKey;
+
+        public Builder addAllowedIp(final InetNetwork allowedIp) {
+            allowedIps.add(allowedIp);
+            return this;
+        }
+
+        public Builder addAllowedIps(final Collection<InetNetwork> allowedIps) {
+            this.allowedIps.addAll(allowedIps);
+            return this;
+        }
+
+        public Peer build() throws BadConfigException {
+            if (publicKey == null)
+                throw new BadConfigException(Section.PEER, Location.PUBLIC_KEY,
+                        Reason.MISSING_ATTRIBUTE, null);
+            return new Peer(this);
+        }
+
+        public Builder parseAllowedIPs(final CharSequence allowedIps) throws BadConfigException {
+            try {
+                for (final String allowedIp : Attribute.split(allowedIps))
+                    addAllowedIp(InetNetwork.parse(allowedIp));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.PEER, Location.ALLOWED_IPS, e);
+            }
+        }
+
+        public Builder parseEndpoint(final String endpoint) throws BadConfigException {
+            try {
+                return setEndpoint(InetEndpoint.parse(endpoint));
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.PEER, Location.ENDPOINT, e);
+            }
+        }
+
+        public Builder parsePersistentKeepalive(final String persistentKeepalive)
+                throws BadConfigException {
+            try {
+                return setPersistentKeepalive(Integer.parseInt(persistentKeepalive));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PERSISTENT_KEEPALIVE,
+                        persistentKeepalive, e);
+            }
+        }
+
+        public Builder parsePreSharedKey(final String preSharedKey) throws BadConfigException {
+            try {
+                return setPreSharedKey(Key.fromBase64(preSharedKey));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PRE_SHARED_KEY, e);
+            }
+        }
+
+        public Builder parsePublicKey(final String publicKey) throws BadConfigException {
+            try {
+                return setPublicKey(Key.fromBase64(publicKey));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PUBLIC_KEY, e);
+            }
+        }
+
+        public Builder setEndpoint(final InetEndpoint endpoint) {
+            this.endpoint = Optional.of(endpoint);
+            return this;
+        }
+
+        public Builder setPersistentKeepalive(final int persistentKeepalive)
+                throws BadConfigException {
+            if (persistentKeepalive < 0 || persistentKeepalive > MAX_PERSISTENT_KEEPALIVE)
+                throw new BadConfigException(Section.PEER, Location.PERSISTENT_KEEPALIVE,
+                        Reason.INVALID_VALUE, String.valueOf(persistentKeepalive));
+            this.persistentKeepalive = persistentKeepalive == 0 ?
+                    Optional.empty() : Optional.of(persistentKeepalive);
+            return this;
+        }
+
+        public Builder setPreSharedKey(final Key preSharedKey) {
+            this.preSharedKey = Optional.of(preSharedKey);
+            return this;
+        }
+
+        public Builder setPublicKey(final Key publicKey) {
+            this.publicKey = publicKey;
+            return this;
+        }
+    }
+}