Services: Renamed from Servers

It didn't feel right to have a "DHCPClient" in a "Servers" directory.
Rename this to Services to better reflect the type of programs we'll
be putting in there.

6 files changed, 833 insertions, 0 deletions

diff --git a/Services/DHCPClient/DHCPv4.cpp b/Services/DHCPClient/DHCPv4.cpp
new file mode 100644
index 0000000000..36430f4eec
--- /dev/null
+++ b/Services/DHCPClient/DHCPv4.cpp
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DHCPv4.h"
+
+//#define DHCPV4_DEBUG
+
+ParsedDHCPv4Options DHCPv4Packet::parse_options() const
+{
+    ParsedDHCPv4Options options;
+    for (size_t index = 4; index < DHCPV4_OPTION_FIELD_MAX_LENGTH; ++index) {
+        auto opt_name = *(const DHCPOption*)&m_options[index];
+        switch (opt_name) {
+        case DHCPOption::Pad:
+            continue;
+        case DHCPOption::End:
+            goto escape;
+        default:
+            ++index;
+            auto length = m_options[index];
+            if ((size_t)length > DHCPV4_OPTION_FIELD_MAX_LENGTH - index) {
+                dbg() << "Bogus option length " << length << " assuming forgotten END";
+                break;
+            }
+#ifdef DHCPV4_DEBUG
+            dbg() << "DHCP Option " << (u8)opt_name << " with length " << length;
+#endif
+            ++index;
+            options.options.set(opt_name, { length, &m_options[index] });
+            index += length - 1;
+            break;
+        }
+    }
+escape:;
+    return options;
+}
diff --git a/Services/DHCPClient/DHCPv4.h b/Services/DHCPClient/DHCPv4.h
new file mode 100644
index 0000000000..07c5787f8a
--- /dev/null
+++ b/Services/DHCPClient/DHCPv4.h
@@ -0,0 +1,300 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/ByteBuffer.h>
+#include <AK/HashMap.h>
+#include <AK/IPv4Address.h>
+#include <AK/MACAddress.h>
+#include <AK/NetworkOrdered.h>
+#include <AK/StringBuilder.h>
+#include <AK/StringView.h>
+#include <AK/Traits.h>
+#include <AK/Types.h>
+#include <string.h>
+
+enum class DHCPv4Flags : u16 {
+    Broadcast = 1,
+    /* everything else is reserved and must be zero */
+};
+
+enum class DHCPv4Op : u8 {
+    BootRequest = 1,
+    BootReply = 2
+};
+
+enum class DHCPOption : u8 {
+    // BOOTP
+    Pad = 0,
+    SubnetMask,
+    TimeOffset,
+    Router,
+    TimeServer,
+    NameServer,
+    DomainNameServer,
+    LogServer,
+    CookieServer,
+    LPRServer,
+    ImpressServer,
+    ResourceLocationServer,
+    HostName,
+    BootFileSize,
+    MeritDumpFile,
+    DomainName,
+    SwapServer,
+    RootPath,
+    ExtensionsPath,
+    IPForwardingEnableDisable,
+    NonLocalSourceRoutingEnableDisable,
+    PolicyFilter,
+    MaximumDatagramReassemblySize,
+    DefaultIPTTL,
+    PathMTUAgingTimeout,
+    PathMTUPlateauTable,
+    InterfaceMTU,
+    AllSubnetsAreLocal,
+    BroadcastAddress,
+    PerformMaskDiscovery,
+    MaskSupplier,
+    PerformRouterDiscovery,
+    RouterSolicitationAddress,
+    StaticRoute,
+    TrailerEncapsulation,
+    ARPCacheTimeout,
+    EthernetEncapsulation,
+    TCPDefaultTTL,
+    TCPKeepaliveInterval,
+    TCPKeepaliveGarbage,
+    NetworkInformationServiceDomain,
+    NetworkInformationServers,
+    NetworkTimeProtocolServers,
+    VendorSpecificInformation,
+    NetBIOSOverTCPIPNameServer,
+    NetBIOSOverTCPIPDatagramDistributionServer,
+    NetBIOSOverTCPIPNodeType,
+    NetBIOSOverTCPIPScope,
+    XWindowSystemFontServer, // wow
+    XWindowSystemDisplayManager,
+    // DHCP
+    RequestedIPAddress = 50,
+    IPAddressLeaseTime,
+    OptionOverload,
+    DHCPMessageType,
+    ServerIdentifier,
+    ParameterRequestList,
+    Message,
+    MaximumDHCPMessageSize,
+    RenewalT1Time,
+    RenewalT2Time,
+    ClassIdentifier,
+    ClientIdentifier,
+    End = 255
+};
+
+enum class DHCPMessageType : u8 {
+    DHCPDiscover = 1,
+    DHCPOffer,
+    DHCPRequest,
+    DHCPDecline,
+    DHCPAck,
+    DHCPNak,
+    DHCPRelease,
+};
+
+template <>
+struct AK::Traits<DHCPOption> : public AK::GenericTraits<DHCPOption> {
+    static constexpr bool is_trivial() { return true; }
+    static unsigned hash(DHCPOption u) { return int_hash((u8)u); }
+};
+
+struct ParsedDHCPv4Options {
+    template <typename T>
+    Optional<const T> get(DHCPOption option_name) const
+    {
+        auto option = options.get(option_name);
+        if (!option.has_value()) {
+            return {};
+        }
+        auto& value = option.value();
+        if (value.length != sizeof(T))
+            return {};
+        return *(const T*)value.value;
+    }
+
+    template <typename T>
+    Vector<T> get_many(DHCPOption option_name, size_t max_number) const
+    {
+        Vector<T> values;
+
+        auto option = options.get(option_name);
+        if (!option.has_value()) {
+            return {};
+        }
+        auto& value = option.value();
+        if (value.length < sizeof(T))
+            return {};
+
+        for (size_t i = 0; i < max_number; ++i) {
+            auto offset = i * sizeof(T);
+            if (offset >= value.length)
+                break;
+            values.append(*(T*)((u8*)const_cast<void*>(value.value) + offset));
+        }
+
+        return values;
+    }
+
+    String to_string() const
+    {
+        StringBuilder builder;
+        builder.append("DHCP Options (");
+        builder.appendf("%d", options.size());
+        builder.append(" entries)\n");
+        for (auto& opt : options) {
+            builder.appendf("\toption %d (%d bytes):", (u8)opt.key, (u8)opt.value.length);
+            for (auto i = 0; i < opt.value.length; ++i)
+                builder.appendf(" %u ", ((const u8*)opt.value.value)[i]);
+            builder.append('\n');
+        }
+        return builder.build();
+    }
+
+    struct DHCPOptionValue {
+        u8 length;
+        const void* value;
+    };
+
+    HashMap<DHCPOption, DHCPOptionValue> options;
+};
+
+constexpr auto DHCPV4_OPTION_FIELD_MAX_LENGTH = 312;
+
+class [[gnu::packed]] DHCPv4Packet
+{
+public:
+    u8 op() const { return m_op; }
+    void set_op(DHCPv4Op op) { m_op = (u8)op; }
+
+    u8 htype() const { return m_htype; }
+    void set_htype(u8 htype) { m_htype = htype; }
+
+    u8 hlen() const { return m_hlen; }
+    void set_hlen(u8 hlen) { m_hlen = hlen; }
+
+    u8 hops() const { return m_hops; }
+    void set_hops(u8 hops) { m_hops = hops; }
+
+    u32 xid() const { return m_xid; }
+    void set_xid(u32 xid) { m_xid = xid; }
+
+    u16 secs() const { return m_secs; }
+    void set_secs(u16 secs) { m_secs = secs; }
+
+    u16 flags() const { return m_flags; }
+    void set_flags(DHCPv4Flags flags) { m_flags = (u16)flags; }
+
+    const IPv4Address& ciaddr() const { return m_ciaddr; }
+    const IPv4Address& yiaddr() const { return m_yiaddr; }
+    const IPv4Address& siaddr() const { return m_siaddr; }
+    const IPv4Address& giaddr() const { return m_giaddr; }
+
+    IPv4Address& ciaddr() { return m_ciaddr; }
+    IPv4Address& yiaddr() { return m_yiaddr; }
+    IPv4Address& siaddr() { return m_siaddr; }
+    IPv4Address& giaddr() { return m_giaddr; }
+
+    u8* options() { return m_options; }
+    ParsedDHCPv4Options parse_options() const;
+
+    const MACAddress& chaddr() const { return *(const MACAddress*)&m_chaddr[0]; }
+    void set_chaddr(const MACAddress& mac) { *(MACAddress*)&m_chaddr[0] = mac; }
+
+    StringView sname() const { return { (const char*)&m_sname[0] }; }
+    StringView file() const { return { (const char*)&m_file[0] }; }
+
+private:
+    NetworkOrdered<u8> m_op;
+    NetworkOrdered<u8> m_htype;
+    NetworkOrdered<u8> m_hlen;
+    NetworkOrdered<u8> m_hops;
+    NetworkOrdered<u32> m_xid;
+    NetworkOrdered<u16> m_secs;
+    NetworkOrdered<u16> m_flags;
+    IPv4Address m_ciaddr;
+    IPv4Address m_yiaddr;
+    IPv4Address m_siaddr;
+    IPv4Address m_giaddr;
+    u8 m_chaddr[16]; // 10 bytes of padding at the end
+    u8 m_sname[64] { 0 };
+    u8 m_file[128] { 0 };
+    u8 m_options[DHCPV4_OPTION_FIELD_MAX_LENGTH] { 0 }; // variable, less than 312 bytes
+};
+
+class DHCPv4PacketBuilder {
+public:
+    DHCPv4PacketBuilder()
+        : m_buffer(ByteBuffer::create_zeroed(sizeof(DHCPv4Packet)))
+    {
+        auto* options = peek().options();
+        // set the magic DHCP cookie value
+        options[0] = 99;
+        options[1] = 130;
+        options[2] = 83;
+        options[3] = 99;
+    }
+
+    void add_option(DHCPOption option, u8 length, const void* data)
+    {
+        ASSERT(m_can_add);
+        // we need enough space to fit the option value, its length, and its data
+        ASSERT(next_option_offset + length + 2 < DHCPV4_OPTION_FIELD_MAX_LENGTH);
+
+        auto* options = peek().options();
+        options[next_option_offset++] = (u8)option;
+        memcpy(options + next_option_offset, &length, 1);
+        next_option_offset++;
+        memcpy(options + next_option_offset, data, length);
+        next_option_offset += length;
+    }
+
+    void set_message_type(DHCPMessageType type) { add_option(DHCPOption::DHCPMessageType, 1, &type); }
+
+    DHCPv4Packet& peek() { return *(DHCPv4Packet*)m_buffer.data(); }
+    DHCPv4Packet& build()
+    {
+        add_option(DHCPOption::End, 0, nullptr);
+        m_can_add = false;
+        return *(DHCPv4Packet*)m_buffer.data();
+    }
+    size_t size() const { return m_buffer.size(); }
+
+private:
+    ByteBuffer m_buffer;
+    size_t next_option_offset { 4 };
+    bool m_can_add { true };
+};
diff --git a/Services/DHCPClient/DHCPv4Client.cpp b/Services/DHCPClient/DHCPv4Client.cpp
new file mode 100644
index 0000000000..918a20b93f
--- /dev/null
+++ b/Services/DHCPClient/DHCPv4Client.cpp
@@ -0,0 +1,283 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DHCPv4Client.h"
+#include <AK/ByteBuffer.h>
+#include <AK/Function.h>
+#include <LibCore/SocketAddress.h>
+#include <LibCore/Timer.h>
+#include <stdio.h>
+
+//#define DHCPV4CLIENT_DEBUG
+
+static void send(const InterfaceDescriptor& iface, const DHCPv4Packet& packet, Core::Object*)
+{
+    int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    if (fd < 0) {
+        dbg() << "ERROR: socket :: " << strerror(errno);
+        return;
+    }
+
+    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, iface.m_ifname.characters(), IFNAMSIZ) < 0) {
+        dbg() << "ERROR: setsockopt(SO_BINDTODEVICE) :: " << strerror(errno);
+        return;
+    }
+
+    sockaddr_in dst;
+    memset(&dst, 0, sizeof(dst));
+    dst.sin_family = AF_INET;
+    dst.sin_port = htons(67);
+    dst.sin_addr.s_addr = IPv4Address { 255, 255, 255, 255 }.to_u32();
+    memset(&dst.sin_zero, 0, sizeof(dst.sin_zero));
+
+    auto rc = sendto(fd, &packet, sizeof(packet), 0, (sockaddr*)&dst, sizeof(dst));
+    if (rc < 0) {
+        dbg() << "sendto failed with " << strerror(errno);
+        // FIXME: what do we do here?
+    }
+}
+
+static void set_params(const InterfaceDescriptor& iface, const IPv4Address& ipv4_addr, const IPv4Address& netmask, const IPv4Address& gateway)
+{
+    int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
+    if (fd < 0) {
+        dbg() << "ERROR: socket :: " << strerror(errno);
+        return;
+    }
+
+    struct ifreq ifr;
+    memset(&ifr, 0, sizeof(ifr));
+    strncpy(ifr.ifr_name, iface.m_ifname.characters(), IFNAMSIZ);
+
+    // set the IP address
+    ifr.ifr_addr.sa_family = AF_INET;
+    ((sockaddr_in&)ifr.ifr_addr).sin_addr.s_addr = ipv4_addr.to_in_addr_t();
+
+    if (ioctl(fd, SIOCSIFADDR, &ifr) < 0) {
+        dbg() << "ERROR: ioctl(SIOCSIFADDR) :: " << strerror(errno);
+    }
+
+    // set the network mask
+    ((sockaddr_in&)ifr.ifr_netmask).sin_addr.s_addr = netmask.to_in_addr_t();
+
+    if (ioctl(fd, SIOCSIFNETMASK, &ifr) < 0) {
+        dbg() << "ERROR: ioctl(SIOCSIFNETMASK) :: " << strerror(errno);
+    }
+
+    // set the default gateway
+    struct rtentry rt;
+    memset(&rt, 0, sizeof(rt));
+
+    rt.rt_dev = const_cast<char*>(iface.m_ifname.characters());
+    rt.rt_gateway.sa_family = AF_INET;
+    ((sockaddr_in&)rt.rt_gateway).sin_addr.s_addr = gateway.to_in_addr_t();
+    rt.rt_flags = RTF_UP | RTF_GATEWAY;
+
+    if (ioctl(fd, SIOCADDRT, &rt) < 0) {
+        dbg() << "Error: ioctl(SIOCADDRT) :: " << strerror(errno);
+    }
+}
+
+DHCPv4Client::DHCPv4Client(Vector<InterfaceDescriptor> ifnames)
+    : m_ifnames(ifnames)
+{
+    m_server = Core::UDPServer::construct(this);
+    m_server->on_ready_to_receive = [this] {
+        auto buffer = m_server->receive(sizeof(DHCPv4Packet));
+        dbg() << "Received " << buffer.size() << " bytes";
+        if (buffer.size() != sizeof(DHCPv4Packet)) {
+            dbg() << "we expected " << sizeof(DHCPv4Packet) << " bytes, this is a bad packet";
+            return;
+        }
+        auto& packet = *(DHCPv4Packet*)buffer.data();
+        process_incoming(packet);
+    };
+
+    if (!m_server->bind({}, 68)) {
+        dbg() << "The server we just created somehow came already bound, refusing to continue";
+        ASSERT_NOT_REACHED();
+    }
+
+    for (auto& iface : m_ifnames)
+        dhcp_discover(iface);
+}
+
+DHCPv4Client::~DHCPv4Client()
+{
+}
+
+void DHCPv4Client::handle_offer(const DHCPv4Packet& packet, const ParsedDHCPv4Options& options)
+{
+    dbg() << "We were offered " << packet.yiaddr().to_string() << " for " << options.get<u32>(DHCPOption::IPAddressLeaseTime).value_or(0);
+    auto* transaction = const_cast<DHCPv4Transaction*>(m_ongoing_transactions.get(packet.xid()).value_or(nullptr));
+    if (!transaction) {
+        dbg() << "we're not looking for " << packet.xid();
+        return;
+    }
+    if (transaction->has_ip)
+        return;
+    if (transaction->accepted_offer) {
+        // we've accepted someone's offer, but they haven't given us an ack
+        // TODO: maybe record this offer?
+        return;
+    }
+    // TAKE IT...
+    transaction->offered_lease_time = options.get<u32>(DHCPOption::IPAddressLeaseTime).value();
+    dhcp_request(*transaction, packet);
+}
+
+void DHCPv4Client::handle_ack(const DHCPv4Packet& packet, const ParsedDHCPv4Options& options)
+{
+#ifdef DHCPV4CLIENT_DEBUG
+    dbg() << "The DHCP server handed us " << packet.yiaddr().to_string();
+    dbg() << "Here are the options: " << options.to_string();
+#endif
+    auto* transaction = const_cast<DHCPv4Transaction*>(m_ongoing_transactions.get(packet.xid()).value_or(nullptr));
+    if (!transaction) {
+        dbg() << "we're not looking for " << packet.xid();
+        return;
+    }
+    transaction->has_ip = true;
+    auto& interface = transaction->interface;
+    auto new_ip = packet.yiaddr();
+    auto lease_time = convert_between_host_and_network(options.get<u32>(DHCPOption::IPAddressLeaseTime).value_or(transaction->offered_lease_time));
+    // set a timer for the duration of the lease, we shall renew if needed
+    Core::Timer::create_single_shot(
+        lease_time * 1000,
+        [this, transaction, interface = InterfaceDescriptor { interface }, new_ip] {
+            transaction->accepted_offer = false;
+            transaction->has_ip = false;
+            dhcp_discover(interface, new_ip);
+        },
+        this);
+    set_params(transaction->interface, new_ip, options.get<IPv4Address>(DHCPOption::SubnetMask).value(), options.get_many<IPv4Address>(DHCPOption::Router, 1).first());
+}
+
+void DHCPv4Client::handle_nak(const DHCPv4Packet& packet, const ParsedDHCPv4Options& options)
+{
+    dbg() << "The DHCP server told us to go chase our own tail about " << packet.yiaddr().to_string();
+    dbg() << "Here are the options: " << options.to_string();
+    // make another request a bit later :shrug:
+    auto* transaction = const_cast<DHCPv4Transaction*>(m_ongoing_transactions.get(packet.xid()).value_or(nullptr));
+    if (!transaction) {
+        dbg() << "we're not looking for " << packet.xid();
+        return;
+    }
+    transaction->accepted_offer = false;
+    transaction->has_ip = false;
+    auto& iface = transaction->interface;
+    Core::Timer::create_single_shot(
+        10000,
+        [this, iface = InterfaceDescriptor { iface }] {
+            dhcp_discover(iface);
+        },
+        this);
+}
+
+void DHCPv4Client::process_incoming(const DHCPv4Packet& packet)
+{
+    auto options = packet.parse_options();
+#ifdef DHCPV4CLIENT_DEBUG
+    dbg() << "Here are the options: " << options.to_string();
+#endif
+    auto value = options.get<DHCPMessageType>(DHCPOption::DHCPMessageType).value();
+    switch (value) {
+    case DHCPMessageType::DHCPOffer:
+        handle_offer(packet, options);
+        break;
+    case DHCPMessageType::DHCPAck:
+        handle_ack(packet, options);
+        break;
+    case DHCPMessageType::DHCPNak:
+        handle_nak(packet, options);
+        break;
+    case DHCPMessageType::DHCPDiscover:
+    case DHCPMessageType::DHCPRequest:
+    case DHCPMessageType::DHCPRelease:
+        // These are not for us
+        // we're just getting them because there are other people on our subnet
+        // broadcasting stuff
+        break;
+    case DHCPMessageType::DHCPDecline:
+    default:
+        dbg() << "I dunno what to do with this " << (u8)value;
+        ASSERT_NOT_REACHED();
+        break;
+    }
+}
+
+void DHCPv4Client::dhcp_discover(const InterfaceDescriptor& iface, IPv4Address previous)
+{
+    auto transaction_id = rand();
+#ifdef DHCPV4CLIENT_DEBUG
+    dbg() << "Trying to lease an IP for " << iface.m_ifname << " with ID " << transaction_id;
+    if (!previous.is_zero())
+        dbg() << "going to request the server to hand us " << previous.to_string();
+#endif
+    DHCPv4PacketBuilder builder;
+
+    DHCPv4Packet& packet = builder.peek();
+    packet.set_op(DHCPv4Op::BootRequest);
+    packet.set_htype(1); // 10mb ethernet
+    packet.set_hlen(sizeof(MACAddress));
+    packet.set_xid(transaction_id);
+    packet.set_flags(DHCPv4Flags::Broadcast);
+    packet.ciaddr() = previous;
+    packet.set_chaddr(iface.m_mac_address);
+    packet.set_secs(65535); // we lie
+
+    // set packet options
+    builder.set_message_type(DHCPMessageType::DHCPDiscover);
+    auto& dhcp_packet = builder.build();
+
+    // broadcast the discover request
+    send(iface, dhcp_packet, this);
+    m_ongoing_transactions.set(transaction_id, make<DHCPv4Transaction>(iface));
+}
+
+void DHCPv4Client::dhcp_request(DHCPv4Transaction& transaction, const DHCPv4Packet& offer)
+{
+    auto& iface = transaction.interface;
+    dbg() << "Leasing the IP " << offer.yiaddr().to_string() << " for adapter " << iface.m_ifname;
+    DHCPv4PacketBuilder builder;
+
+    DHCPv4Packet& packet = builder.peek();
+    packet.set_op(DHCPv4Op::BootRequest);
+    packet.set_htype(1); // 10mb ethernet
+    packet.set_hlen(sizeof(MACAddress));
+    packet.set_xid(offer.xid());
+    packet.set_flags(DHCPv4Flags::Broadcast);
+    packet.set_chaddr(iface.m_mac_address);
+    packet.set_secs(65535); // we lie
+
+    // set packet options
+    builder.set_message_type(DHCPMessageType::DHCPRequest);
+    auto& dhcp_packet = builder.build();
+
+    // broadcast the "request" request
+    send(iface, dhcp_packet, this);
+    transaction.accepted_offer = true;
+}
diff --git a/Services/DHCPClient/DHCPv4Client.h b/Services/DHCPClient/DHCPv4Client.h
new file mode 100644
index 0000000000..c45f08f0d1
--- /dev/null
+++ b/Services/DHCPClient/DHCPv4Client.h
@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "DHCPv4.h"
+#include <AK/FlyString.h>
+#include <AK/HashMap.h>
+#include <AK/OwnPtr.h>
+#include <AK/Vector.h>
+#include <LibCore/UDPServer.h>
+#include <LibCore/UDPSocket.h>
+#include <net/if.h>
+#include <net/route.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+
+struct InterfaceDescriptor {
+    FlyString m_ifname;
+    MACAddress m_mac_address;
+};
+
+struct DHCPv4Transaction {
+    DHCPv4Transaction(InterfaceDescriptor ifname)
+        : interface(ifname)
+    {
+    }
+
+    InterfaceDescriptor interface;
+    bool accepted_offer { false };
+    bool has_ip { false };
+    u32 offered_lease_time { 0 };
+};
+
+class DHCPv4Client final : public Core::Object {
+    C_OBJECT(DHCPv4Client)
+
+public:
+    explicit DHCPv4Client(Vector<InterfaceDescriptor> ifnames);
+    virtual ~DHCPv4Client() override;
+
+    void dhcp_discover(const InterfaceDescriptor& ifname, IPv4Address previous = IPv4Address { 0, 0, 0, 0 });
+    void dhcp_request(DHCPv4Transaction& transaction, const DHCPv4Packet& packet);
+
+    void process_incoming(const DHCPv4Packet& packet);
+
+    bool id_is_registered(u32 id) { return m_ongoing_transactions.contains(id); }
+
+private:
+    HashMap<u32, OwnPtr<DHCPv4Transaction>> m_ongoing_transactions;
+    Vector<InterfaceDescriptor> m_ifnames;
+    RefPtr<Core::UDPServer> m_server;
+
+    void handle_offer(const DHCPv4Packet&, const ParsedDHCPv4Options&);
+    void handle_ack(const DHCPv4Packet&, const ParsedDHCPv4Options&);
+    void handle_nak(const DHCPv4Packet&, const ParsedDHCPv4Options&);
+};
diff --git a/Services/DHCPClient/Makefile b/Services/DHCPClient/Makefile
new file mode 100644
index 0000000000..ce7c27b86d
--- /dev/null
+++ b/Services/DHCPClient/Makefile
@@ -0,0 +1,10 @@
+OBJS = \
+    DHCPv4.o \
+    DHCPv4Client.o \
+    main.o
+
+PROGRAM = DHCPClient
+
+LIB_DEPS = Core
+
+include ../../Makefile.common
diff --git a/Services/DHCPClient/main.cpp b/Services/DHCPClient/main.cpp
new file mode 100644
index 0000000000..b65b63eb46
--- /dev/null
+++ b/Services/DHCPClient/main.cpp
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DHCPv4Client.h"
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/String.h>
+#include <AK/Types.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibCore/LocalServer.h>
+#include <stdio.h>
+#include <string.h>
+
+static u8 mac_part(const Vector<String>& parts, size_t index)
+{
+    auto chars = parts.at(index).characters();
+    return (chars[0] - '0') * 16 + (chars[1] - '0');
+}
+
+static MACAddress mac_from_string(const String& str)
+{
+    auto chunks = str.split(':');
+    ASSERT(chunks.size() == 6); // should we...worry about this?
+    return {
+        mac_part(chunks, 0), mac_part(chunks, 1), mac_part(chunks, 2),
+        mac_part(chunks, 3), mac_part(chunks, 4), mac_part(chunks, 5)
+    };
+}
+
+int main(int argc, char** argv)
+{
+    (void)argc;
+    (void)argv;
+
+    if (pledge("stdio unix inet cpath rpath fattr", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    Core::EventLoop event_loop;
+
+    if (unveil("/proc/net/", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    unveil(nullptr, nullptr);
+
+    auto file = Core::File::construct("/proc/net/adapters");
+    if (!file->open(Core::IODevice::ReadOnly)) {
+        fprintf(stderr, "Error: %s\n", file->error_string());
+        return 1;
+    }
+
+    auto file_contents = file->read_all();
+    auto json = JsonValue::from_string(file_contents).as_array();
+    Vector<InterfaceDescriptor> ifnames;
+    json.for_each([&ifnames](auto& value) {
+        auto if_object = value.as_object();
+
+        if (if_object.get("class_name").to_string() == "LoopbackAdapter")
+            return;
+
+        auto name = if_object.get("name").to_string();
+        auto mac = if_object.get("mac_address").to_string();
+        ifnames.append({ name, mac_from_string(mac) });
+    });
+
+    auto client = DHCPv4Client::construct(move(ifnames));
+
+    if (pledge("stdio inet", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    return event_loop.exec();
+}