/*++

Copyright (c) 2013 Minoca Corp. All Rights Reserved

Module Name:

    dhcp.c

Abstract:

    This module implements support for the Dynamic Host Configuration Protocol,
    or DHCP.

Author:

    Evan Green 5-Apr-2013

Environment:

    Kernel

--*/

//
// ------------------------------------------------------------------- Includes
//

//
// Network layer drivers are supposed to be able to stand on their own (ie be
// able to be implemented outside the core net library). For the builtin ones,
// avoid including netcore.h, but still redefine those functions that would
// otherwise generate imports.
//

#define NET_API __DLLEXPORT

#include <minoca/kernel/driver.h>
#include <minoca/net/netdrv.h>
#include <minoca/net/ip4.h>

//
// --------------------------------------------------------------------- Macros
//

//
// These macros get the renewal and binding times as a percentage of the total
// lease time. The renewal time is at 50% of the lease and the rebinding time
// is at 87.5% of the lease time.
//

#define DHCP_GET_DEFAULT_RENEWAL_TIME(_LeaseTime) (_LeaseTime) >> 1
#define DHCP_GET_DEFAULT_REBINDING_TIME(_LeaseTime) \
    ((_LeaseTime) - ((_LeaseTime) >> 3))

//
// ---------------------------------------------------------------- Definitions
//

#define DHCP_ALLOCATION_TAG 0x70636844 // 'pchD'

//
// Define the maximum number of DNS server addresses that will be saved in this
// implementation.
//

#define DHCP_MAX_DNS_SERVERS 4

//
// Define some well-known port numbers.
//

#define DHCP_CLIENT_PORT 68
#define DHCP_SERVER_PORT 67

//
// Define DHCP packet field values.
//

#define DHCP_OPERATION_REQUEST                0x01
#define DHCP_OPERATION_REPLY                  0x02

#define DHCP_HARDWARE_TYPE_ETHERNET           0x01

#define DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH 6
#define DHCP_FLAG_BROADCAST                   0x01

#define DHCP_MAGIC_COOKIE                     0x63825363

#define DHCP_OPTION_HEADER_SIZE               2
#define DHCP_SCRATCH_PACKET_SIZE              4096

//
// Define how many times discovery should be retried.
//

#define DHCP_DISCOVER_RETRY_COUNT 5

//
// Define how long to wait for an offer and acknowledge, in milliseconds.
//

#define DHCP_OFFER_TIMEOUT                 8000
#define DHCP_ACKNOWLEDGE_TIMEOUT           DHCP_OFFER_TIMEOUT

//
// Define DHCP option codes.
//

#define DHCP_OPTION_PAD                    0
#define DHCP_OPTION_SUBNET_MASK            1
#define DHCP_OPTION_TIME_OFFSET            2
#define DHCP_OPTION_ROUTER                 3
#define DHCP_OPTION_DOMAIN_NAME_SERVER     6
#define DHCP_OPTION_HOST_NAME              12
#define DHCP_OPTION_DOMAIN_NAME            15
#define DHCP_OPTION_REQUESTED_IP_ADDRESS   50
#define DHCP_OPTION_IP_ADDRESS_LEASE_TIME  51
#define DHCP_OPTION_OPTION_OVERLOAD        52
#define DHCP_OPTION_DHCP_MESSAGE_TYPE      53
#define DHCP_OPTION_DHCP_SERVER            54
#define DHCP_OPTION_PARAMETER_REQUEST_LIST 55
#define DHCP_OPTION_MESSAGE                56
#define DHCP_OPTION_RENEWAL_TIME           58
#define DHCP_OPTION_REBINDING_TIME         59
#define DHCP_OPTION_TFTP_SERVER_NAME       66
#define DHCP_OPTION_BOOT_FILE_NAME         67
#define DHCP_OPTION_END                    255

//
// Define DHCP message types.
//

#define DHCP_MESSAGE_DISCOVER    1
#define DHCP_MESSAGE_OFFER       2
#define DHCP_MESSAGE_REQUEST     3
#define DHCP_MESSAGE_DECLINE     4
#define DHCP_MESSAGE_ACKNOWLEDGE 5
#define DHCP_MESSAGE_NAK         6
#define DHCP_MESSAGE_RELEASE     7
#define DHCP_MESSAGE_INFORM      8

//
// Define what goes in the discovery request.
//

#define DHCP_OPTION_MESSAGE_TYPE_SIZE 3

#define DHCP_DISCOVER_OPTION_COUNT            2
#define DHCP_DISCOVER_PARAMETER_REQUEST_COUNT 4
#define DHCP_DISCOVER_OPTIONS_SIZE    \
    (DHCP_OPTION_MESSAGE_TYPE_SIZE +  \
     (DHCP_OPTION_HEADER_SIZE +       \
      DHCP_DISCOVER_PARAMETER_REQUEST_COUNT) + 2)

//
// Define the minimum due time delta for the DHCP lease timer, in seconds.
//

#define DHCP_TIMER_DURATION_MINIMUM 60

//
// Define the debug flags for DHCP.
//

#define DHCP_DEBUG_FLAG_EXTEND 0x1
#define DHCP_DEBUG_FLAG_OFFER 0X2

//
// ------------------------------------------------------ Data Type Definitions
//

/*++

Structure Description:

    This structure defines the structure of a DHCP packet request or response.
    After this structure, zero or more options may follow.

Members:

    OperationCode - Stores the operation code, either request or reply.

    HardwareType - Stores the media type, pretty much always the code for
        "ethernet".

    HardwareAddressLength - Stores the length of a hardware address, pretty
        much always 6 for ethernet MAC addresses.

    Hops - Stores 0 usually, can be optionally set by relay agents when booting
        via a relay agent.

    TransactionIdentifier - Stores a unique value used to match requests to
        replies.

    Seconds - Stores the number of seconds since the client began the
        renewal or request process.

    Flags - Stores the broadcast flag.

    ClientIpAddress - Stores the client's current IP address.

    YourIpAddress - Stores the IP address being offered by the DHCP server.

    ServerIpAddress - Stores the IP address of the DHCP server.

    GatewayIpAddress - Stores the IP address to contact for requests outside
        the subnet.

    ClientHardwareAddress - Stores the hardware address associated with this
        offer.

    ServerName - Stores an optional NULL terminated string containing the
        server name, used by the BOOTP protocol

    BootFileName - Stores an optional fully qualified path to the BOOTP boot
        file name.

    MagicCookie - Stores a constant value. Options potentially follow after this
        magic.

--*/

typedef struct _DHCP_PACKET {
    UCHAR OperationCode;
    UCHAR HardwareType;
    UCHAR HardwareAddressLength;
    UCHAR Hops;
    ULONG TransactionIdentifier;
    USHORT Seconds;
    USHORT Flags;
    ULONG ClientIpAddress;
    ULONG YourIpAddress;
    ULONG ServerIpAddress;
    ULONG GatewayIpAddress;
    UCHAR ClientHardwareAddress[16];
    UCHAR ServerName[64];
    UCHAR BootFileName[128];
    ULONG MagicCookie;
} PACKED DHCP_PACKET, *PDHCP_PACKET;

/*++

Structure Description:

    This structure defines the required data parsed from a DHCP response.

Members:

    MessageType - Stores the DHCP option message type of the response. See
        DHCP_MESSAGE_* for values.

    ServerIpAddress - Stores the IP address of the DHCP server.

    OfferedIpAddress - Stores the IP address being offered by the DHCP server.

    RouterIpAddress - Stores the default gateway IP address associated with the
        offered address.Stores the IP address of the

    SubnetMask - Stores the subnet mask of the local network, as given by the
        DHCP server.

    DomainNameServer - Stores an array of DNS addresses associated with the
        offer.

    DomainNameServerCount - Stores the number of valid addresses in the DNS
        address array.

    LeaseTime - Stores the lease time returned in the offer or acknowledge, in
        seconds.

    RenewalTime - Stores the time until the renewal state begins, in seconds.

    RebindingTime - Stores the time until the rebinding state begins, in
        seconds.

--*/

typedef struct _DHCP_REPLY {
    UCHAR MessageType;
    ULONG ServerIpAddress;
    ULONG OfferedIpAddress;
    ULONG RouterIpAddress;
    ULONG SubnetMask;
    ULONG DomainNameServer[DHCP_MAX_DNS_SERVERS];
    ULONG DomainNameServerCount;
    ULONG LeaseTime;
    ULONG RenewalTime;
    ULONG RebindingTime;
} DHCP_REPLY, *PDHCP_REPLY;

typedef enum _DHCP_LEASE_STATE {
    DhcpLeaseStateInvalid,
    DhcpLeaseStateInitialize,
    DhcpLeaseStateBound,
    DhcpLeaseStateRenewing,
    DhcpLeaseStateRebinding
} DHCP_LEASE_STATE, *PDHCP_LEASE_STATE;

/*++

Structure Description:

    This structure defines the DHCP state for a leased network address.

Members:

    ListEntry - Stores pointers to the next and previous leased address handed
        out by DHCP.

    Link - Stores a pointer to the link that owns the link address entry.

    LinkAddress - Stores a pointer to the link address entry to which the lease
        was given.

    Timer - Stores a pointer to the timer that will trigger work to either
        renew or rebind the lease.

    Dpc - Stores a pointer to the DPC that is to run once the lease timer
        expires.

    WorkItem - Stores a pointer to the work item that is to be queued by the
        DPC.

    LeaseTime - Stores the total time of the lease.

    RenewalTime - Stores the time at which the lease enters the renewal phase.

    RebindingTime - Stores the time at which the lease enters the rebinding
        phase.

    State - Stores the state of the lease.

    ReferenceCount - Stores the number of references taken on the lease.

--*/

typedef struct _DHCP_LEASE {
    LIST_ENTRY ListEntry;
    PNET_LINK Link;
    PNET_LINK_ADDRESS_ENTRY LinkAddress;
    PKTIMER Timer;
    PDPC Dpc;
    PWORK_ITEM WorkItem;
    ULONG LeaseTime;
    ULONG RenewalTime;
    ULONG RebindingTime;
    DHCP_LEASE_STATE State;
    volatile ULONG ReferenceCount;
} DHCP_LEASE, *PDHCP_LEASE;

/*++

Structure Description:

    This structure defines DHCP context used throughout the assignment
    sequence.

Members:

    Link - Stores a pointer to the link to work on.

    LinkAddress - Stores a pointer to the link address entry to assign an
        address for.

    Lease - Stores a pointer to any existing lease for the given link and link
        address combination.

    ScratchPacket - Stores a pointer to a scratch packet, used for building
        requests.

    ScratchPacketSize - Stores the total size of the scratch packet, including
        extra length for options.

    ScratchPacketIoBuffer - Stores a pointer to an I/O buffer containing the
        scratch packet buffer.

    Socket - Stores a pointer to the UDP socket connection.

    ExpectedTransactionId - Stores the transaction ID that is expected to come
        back in the response. All others get ignored.

    OfferClientAddress - Stores the network address that the DHCP server is
        offering to this machine.

    OfferSubnetMask - Stores the subnet mask of the local network, as given by
        the DHCP server.

    OfferServerAddress - Stores the network address of the server making the
        offer.

    OfferRouter - Stores the default gateway address associated with the offered
        address.

    OfferDnsAddress - Stores an array of DNS addresses associated with the
        offer.

    OfferDnsAddressCount - Stores the number of valid addresses in the DNS
        address array.

    LeaseTime - Stores the lease time returned in the offer or acknowledge, in
        seconds.

    RenewalTime - Stores the time until the renewal state begins, in seconds.

    RebindingTime - Stores the time until the rebinding state begins, in
        seconds.

    LeaseRequestTime - Stores the time at which the lease was requested.

--*/

typedef struct _DHCP_CONTEXT {
    PNET_LINK Link;
    PNET_LINK_ADDRESS_ENTRY LinkAddress;
    PDHCP_LEASE Lease;
    PDHCP_PACKET ScratchPacket;
    ULONG ScratchPacketSize;
    PIO_BUFFER ScratchPacketIoBuffer;
    PIO_HANDLE Socket;
    ULONG ExpectedTransactionId;
    NETWORK_ADDRESS OfferClientAddress;
    NETWORK_ADDRESS OfferSubnetMask;
    NETWORK_ADDRESS OfferServerAddress;
    NETWORK_ADDRESS OfferRouter;
    NETWORK_ADDRESS OfferDnsAddress[DHCP_MAX_DNS_SERVERS];
    ULONG OfferDnsAddressCount;
    ULONG LeaseTime;
    ULONG RenewalTime;
    ULONG RebindingTime;
    SYSTEM_TIME LeaseRequestTime;
} DHCP_CONTEXT, *PDHCP_CONTEXT;

//
// ----------------------------------------------- Internal Function Prototypes
//

VOID
NetpDhcpAssignmentThread (
    PVOID Parameter
    );

KSTATUS
NetpDhcpBeginLeaseExtension (
    PDHCP_LEASE Lease
    );

VOID
NetpDhcpLeaseExtensionThread (
    PVOID Parameter
    );

KSTATUS
NetpDhcpBeginRelease (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    );

VOID
NetpDhcpReleaseThread (
    PVOID Parameter
    );

KSTATUS
NetpDhcpSendDiscover (
    PDHCP_CONTEXT Context
    );

KSTATUS
NetpDhcpReceiveOffer (
    PDHCP_CONTEXT Context
    );

KSTATUS
NetpDhcpSendRequest (
    PDHCP_CONTEXT Context
    );

KSTATUS
NetpDhcpReceiveAcknowledge (
    PDHCP_CONTEXT Context
    );

KSTATUS
NetpDhcpSendRelease (
    PDHCP_CONTEXT Context
    );

KSTATUS
NetpDhcpReceiveReply (
    PDHCP_CONTEXT Context,
    PDHCP_REPLY Reply
    );

PDHCP_CONTEXT
NetpDhcpCreateContext (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress,
    PDHCP_LEASE Lease
    );

VOID
NetpDhcpDestroyContext (
    PDHCP_CONTEXT Context
    );

PDHCP_LEASE
NetpDhcpCreateLease (
    VOID
    );

VOID
NetpDhcpLeaseAddReference (
    PDHCP_LEASE Lease
    );

VOID
NetpDhcpLeaseReleaseReference (
    PDHCP_LEASE Lease
    );

PDHCP_LEASE
NetpDhcpFindLease (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    );

VOID
NetpDhcpDestroyLease (
    PDHCP_LEASE AssignmentContext
    );

VOID
NetpDhcpQueueLeaseExtension (
    PDHCP_LEASE Lease
    );

VOID
NetpDhcpLeaseDpcRoutine (
    PDPC Dpc
    );

VOID
NetpDhcpLeaseWorkRoutine (
    PVOID Parameter
    );

KSTATUS
NetpDhcpCopyReplyToContext (
    PDHCP_CONTEXT Context,
    PDHCP_REPLY Reply
    );

VOID
NetpDhcpPrintContext (
    PDHCP_CONTEXT Context
    );

//
// -------------------------------------------------------------------- Globals
//

LIST_ENTRY NetDhcpLeaseListHead;
KSPIN_LOCK NetDhcpLeaseListLock;

//
// Store a bitfield of enabled DHCP debug flags. See DHCP_DEBUG_* definitions.
//

ULONG NetDhcpDebugFlags = 0x0;

//
// Set this debug value to overried the lease renewal and rebinding times.
//

BOOL NetDhcpDebugOverrideRenewal = FALSE;

//
// Set these values to the desired renewal and rebinding times if force renewal
// is set.
//

ULONG NetDhcpDebugRenewalTime = 0;
ULONG NetDhcpDebugRebindingTime = 0;

//
// Set these debug values to force failures in the renewal and/or rebinding
// phase.
//

BOOL NetDhcpDebugFailRenewal = FALSE;
BOOL NetDhcpDebugFailRebinding = FALSE;

//
// ------------------------------------------------------------------ Functions
//

VOID
NetpDhcpInitialize (
    VOID
    )

/*++

Routine Description:

    This routine initializes support for DHCP.

Arguments:

    None.

Return Value:

    None.

--*/

{

    INITIALIZE_LIST_HEAD(&NetDhcpLeaseListHead);
    KeInitializeSpinLock(&NetDhcpLeaseListLock);
    return;
}

KSTATUS
NetpDhcpBeginAssignment (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    )

/*++

Routine Description:

    This routine kicks off the process of assigning a network address to this
    link address entry by using DHCP.

Arguments:

    Link - Supplies a pointer to the link to send the discovery request out on.

    LinkAddress - Supplies a pointer to the address structure to bind to.

Return Value:

    Status code indicating whether or not the process was successfully
    initiated.

--*/

{

    PDHCP_CONTEXT DhcpContext;
    KSTATUS Status;

    DhcpContext = NetpDhcpCreateContext(Link, LinkAddress, NULL);
    if (DhcpContext == NULL) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    Status = PsCreateKernelThread(NetpDhcpAssignmentThread,
                                  DhcpContext,
                                  "DhcpAssignThread");

    if (!KSUCCESS(Status)) {
        NetpDhcpDestroyContext(DhcpContext);
    }

    return Status;
}

KSTATUS
NetpDhcpCancelLease (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    )

/*++

Routine Description:

    This routine attempts to cancel a DHCP lease.

Arguments:

    Link - Supplies a pointer to the network link to which the lease was
        provided.

    LinkAddress - Supplies a pointer to the network link address that was
        leased.

Return Value:

    Status code.

--*/

{

    PDHCP_LEASE Lease;
    DHCP_LEASE_STATE LeaseState;
    BOOL LinkUp;
    KSTATUS Status;

    Status = STATUS_SUCCESS;
    Lease = NetpDhcpFindLease(Link, LinkAddress);
    if (Lease == NULL) {
        goto DhcpCancelLeaseEnd;
    }

    //
    // Remove the lease from the global list.
    //

    KeAcquireSpinLock(&NetDhcpLeaseListLock);
    LIST_REMOVE(&(Lease->ListEntry));
    Lease->ListEntry.Next = NULL;
    KeReleaseSpinLock(&NetDhcpLeaseListLock);

    //
    // Save the lease state. If the lease is in the initialized state then the
    // lease has expired (or never started).
    //

    LeaseState = Lease->State;

    ASSERT(LeaseState != DhcpLeaseStateInvalid);

    //
    // Release the original reference on the lease and the reference taken by
    // the find routine.
    //

    NetpDhcpLeaseReleaseReference(Lease);
    NetpDhcpLeaseReleaseReference(Lease);

    //
    // Be kind. If the link is still up, attempt to release the leased IP
    // address if it is in the bound, renewing, or rebinding state.
    //

    NetGetLinkState(Link, &LinkUp, NULL);
    if ((LinkUp != FALSE) && (LeaseState != DhcpLeaseStateInitialize)) {
        Status = NetpDhcpBeginRelease(Link, LinkAddress);
        if (!KSUCCESS(Status)) {
            goto DhcpCancelLeaseEnd;
        }
    }

DhcpCancelLeaseEnd:
    return Status;
}

//
// --------------------------------------------------------- Internal Functions
//

VOID
NetpDhcpAssignmentThread (
    PVOID Parameter
    )

/*++

Routine Description:

    This routine attempts to assign an address to a link using DHCP.

Arguments:

    Parameter - Supplies a pointer supplied by the creator of the thread, in
        this case a pointer to the DHCP context structure.

Return Value:

    None.

--*/

{

    BOOL BroadcastEnabled;
    UINTN DataSize;
    PDHCP_CONTEXT DhcpContext;
    NETWORK_DEVICE_INFORMATION Information;
    PDHCP_LEASE Lease;
    BOOL LeaseAcquired;
    SYSTEM_TIME LeaseEndTime;
    IP4_ADDRESS LocalAddress;
    ULONG RetryCount;
    KSTATUS Status;
    PSTR Step;

    DhcpContext = (PDHCP_CONTEXT)Parameter;
    Lease = NULL;
    LeaseAcquired = FALSE;
    Step = "Init";

    ASSERT(DhcpContext->Lease == NULL);

    //
    // Make sure there are no left over leases for this link and link address
    // combination. If the DHCP assignment results in the same IP address then
    // an old lease will not be canceled by the networking core. If it results
    // in a different IP address then it will attempt to destroy the old lease,
    // preventing reuse of any current lease here.
    //

    Status = NetpDhcpCancelLease(DhcpContext->Link, DhcpContext->LinkAddress);
    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    Lease = NetpDhcpCreateLease();
    if (Lease == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpAssignmentThreadEnd;
    }

    //
    // Create the scratch packet space and the socket.
    //

    DhcpContext->ScratchPacket = MmAllocatePagedPool(DHCP_SCRATCH_PACKET_SIZE,
                                                     DHCP_ALLOCATION_TAG);

    if (DhcpContext->ScratchPacket == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpAssignmentThreadEnd;
    }

    DhcpContext->ScratchPacketSize = DHCP_SCRATCH_PACKET_SIZE;
    Status = MmCreateIoBuffer(DhcpContext->ScratchPacket,
                              DhcpContext->ScratchPacketSize,
                              IO_BUFFER_FLAG_KERNEL_MODE_DATA,
                              &(DhcpContext->ScratchPacketIoBuffer));

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    Status = IoSocketCreate(NetDomainIp4,
                            NetSocketDatagram,
                            SOCKET_INTERNET_PROTOCOL_UDP,
                            0,
                            &(DhcpContext->Socket));

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    //
    // Bind that socket to the known DHCP client port. The any address must be
    // used as the DHCP server will reply with broadcast packets and only an
    // unbound socket will pick those up.
    //

    RtlZeroMemory(&LocalAddress, sizeof(NETWORK_ADDRESS));
    LocalAddress.Domain = NetDomainIp4;
    LocalAddress.Port = DHCP_CLIENT_PORT;
    Status = IoSocketBindToAddress(TRUE,
                                   DhcpContext->Socket,
                                   DhcpContext->Link,
                                   (PNETWORK_ADDRESS)&LocalAddress,
                                   NULL,
                                   0);

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    //
    // Enable broadcast messages on this socket.
    //

    BroadcastEnabled = TRUE;
    DataSize = sizeof(BOOL);
    Status = IoSocketGetSetInformation(DhcpContext->Socket,
                                       SocketInformationBasic,
                                       SocketBasicOptionBroadcastEnabled,
                                       &BroadcastEnabled,
                                       &DataSize,
                                       TRUE);

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    Lease->State = DhcpLeaseStateInitialize;
    NetpDhcpLeaseAddReference(Lease);
    DhcpContext->Lease = Lease;
    RetryCount = 0;
    while (RetryCount < DHCP_DISCOVER_RETRY_COUNT) {
        RetryCount += 1;

        //
        // Kick off the sequence by sending a discovery packet.
        //

        Step = "SendDiscover";
        Status = NetpDhcpSendDiscover(DhcpContext);
        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Get the offer back from the server.
        //

        Step = "ReceiveOffer";
        Status = NetpDhcpReceiveOffer(DhcpContext);
        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Request the address that came back.
        //

        Step = "SendRequest";
        Status = NetpDhcpSendRequest(DhcpContext);
        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Get the acknowledge back to make sure the DHCP heard the request.
        //

        Step = "RecieveAcknowledge";
        Status = NetpDhcpReceiveAcknowledge(DhcpContext);
        if (!KSUCCESS(Status)) {
            continue;
        }

        break;
    }

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    LeaseAcquired = TRUE;

    //
    // Calculate the lease's end based on the DHCP offer.
    //

    RtlCopyMemory(&LeaseEndTime,
                  &(DhcpContext->LeaseRequestTime),
                  sizeof(SYSTEM_TIME));

    LeaseEndTime.Seconds += DhcpContext->LeaseTime;

    //
    // The address reservation is complete. Set the parameters in the link
    // address entry.
    //

    Step = "SetNetworkAddress";
    RtlZeroMemory(&Information, sizeof(NETWORK_DEVICE_INFORMATION));
    Information.Version = NETWORK_DEVICE_INFORMATION_VERSION;
    Information.Flags = NETWORK_DEVICE_FLAG_CONFIGURED;
    Information.Domain = NetDomainIp4;
    Information.ConfigurationMethod = NetworkAddressConfigurationDhcp;
    RtlCopyMemory(&(Information.Address),
                  &(DhcpContext->OfferClientAddress),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.Subnet),
                  &(DhcpContext->OfferSubnetMask),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.Gateway),
                  &(DhcpContext->OfferRouter),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.DnsServers),
                  &(DhcpContext->OfferDnsAddress),
                  sizeof(NETWORK_ADDRESS) * DhcpContext->OfferDnsAddressCount);

    Information.DnsServerCount = DhcpContext->OfferDnsAddressCount;
    RtlCopyMemory(&(Information.LeaseServerAddress),
                  &(DhcpContext->OfferServerAddress),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.LeaseStartTime),
                  &(DhcpContext->LeaseRequestTime),
                  sizeof(SYSTEM_TIME));

    RtlCopyMemory(&(Information.LeaseEndTime),
                  &LeaseEndTime,
                  sizeof(SYSTEM_TIME));

    Status = NetGetSetNetworkDeviceInformation(DhcpContext->Link,
                                               DhcpContext->LinkAddress,
                                               &Information,
                                               TRUE);

    if (!KSUCCESS(Status)) {
        goto DhcpAssignmentThreadEnd;
    }

    //
    // Celebrate the assignment with some debugger prints.
    //

    RtlDebugPrint("DHCP Assignment:\n");
    NetpDhcpPrintContext(DhcpContext);

    //
    // Finish initializing the lease, including adding it to the global list.
    //

    NetLinkAddReference(DhcpContext->Link);
    Lease->Link = DhcpContext->Link;
    Lease->LinkAddress = DhcpContext->LinkAddress;
    Lease->State = DhcpLeaseStateBound;
    Lease->LeaseTime = DhcpContext->LeaseTime;
    Lease->RenewalTime = DhcpContext->RenewalTime;
    Lease->RebindingTime = DhcpContext->RebindingTime;
    KeAcquireSpinLock(&NetDhcpLeaseListLock);
    INSERT_BEFORE(&(Lease->ListEntry), &NetDhcpLeaseListHead);
    KeReleaseSpinLock(&NetDhcpLeaseListLock);

    //
    // The lease is established. Set the lease timer so that a lease renewal is
    // attemtped at the time specified by the server.
    //

    NetpDhcpQueueLeaseExtension(Lease);

DhcpAssignmentThreadEnd:
    if (!KSUCCESS(Status)) {
        RtlDebugPrint("Net: DHCP assignment failed at step '%s': %d.\n",
                      Step,
                      Status);

        //
        // If the routine failed after the lease was acquired, kindly release
        // the IP address back to the server.
        //

        if (LeaseAcquired != FALSE) {
            RtlZeroMemory(&Information, sizeof(NETWORK_DEVICE_INFORMATION));
            Information.Version = NETWORK_DEVICE_INFORMATION_VERSION;
            Information.Domain = NetDomainIp4;
            Information.ConfigurationMethod = NetworkAddressConfigurationNone;
            NetGetSetNetworkDeviceInformation(DhcpContext->Link,
                                              DhcpContext->LinkAddress,
                                              &Information,
                                              TRUE);

            NetpDhcpSendRelease(DhcpContext);
        }

        if (Lease != NULL) {
            NetpDhcpLeaseReleaseReference(Lease);
        }
    }

    NetpDhcpDestroyContext(DhcpContext);
    return;
}

KSTATUS
NetpDhcpBeginLeaseExtension (
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine kicks off the process of extending the given DHCP lease.

Arguments:

    Lease - Supplies a pointer to a DHCP lease that is to be renewed.

Return Value:

    Status code indicating whether or not the process was successfully
    initiated.

--*/

{

    PDHCP_CONTEXT DhcpContext;
    KSTATUS Status;

    ASSERT(Lease->Link != NULL);
    ASSERT(Lease->LinkAddress != NULL);
    ASSERT((Lease->State == DhcpLeaseStateRenewing) ||
           (Lease->State == DhcpLeaseStateRebinding));

    DhcpContext = NetpDhcpCreateContext(Lease->Link, Lease->LinkAddress, Lease);
    if (DhcpContext == NULL) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    Status = PsCreateKernelThread(NetpDhcpLeaseExtensionThread,
                                  DhcpContext,
                                  "DhcpExtendThread");

    if (!KSUCCESS(Status)) {
        NetpDhcpDestroyContext(DhcpContext);
        return Status;
    }

    return STATUS_SUCCESS;
}

VOID
NetpDhcpLeaseExtensionThread (
    PVOID Parameter
    )

/*++

Routine Description:

    This routine attempts to extend the lease on an address for a link using
    DHCP.

Arguments:

    Parameter - Supplies a pointer supplied by the creator of the thread, in
        this case a pointer to the DHCP context structure.

Return Value:

    None.

--*/

{

    PDHCP_CONTEXT DhcpContext;
    NETWORK_DEVICE_INFORMATION Information;
    PDHCP_LEASE Lease;
    SYSTEM_TIME LeaseEndTime;
    IP4_ADDRESS LocalAddress;
    BOOL LockHeld;
    KSTATUS Status;
    PSTR Step;

    ASSERT(KeGetRunLevel() == RunLevelLow);

    DhcpContext = (PDHCP_CONTEXT)Parameter;
    Lease = DhcpContext->Lease;
    LockHeld = FALSE;
    Step = "Init";

    ASSERT(Lease != NULL);
    ASSERT((Lease->State == DhcpLeaseStateRenewing) ||
           (Lease->State == DhcpLeaseStateRebinding));

    //
    // If the debug state is set to fail this phase, then skip to the end.
    //

    if (((NetDhcpDebugFailRenewal != FALSE) &&
         (Lease->State == DhcpLeaseStateRenewing)) ||
        ((NetDhcpDebugFailRebinding != FALSE) &&
         (Lease->State == DhcpLeaseStateRebinding))) {

        Step = "ForceFailure";
        Status = STATUS_TRY_AGAIN;
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Create the scratch packet space and the socket.
    //

    DhcpContext->ScratchPacket = MmAllocatePagedPool(DHCP_SCRATCH_PACKET_SIZE,
                                                     DHCP_ALLOCATION_TAG);

    if (DhcpContext->ScratchPacket == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpLeaseExtensionThreadEnd;
    }

    DhcpContext->ScratchPacketSize = DHCP_SCRATCH_PACKET_SIZE;
    Status = MmCreateIoBuffer(DhcpContext->ScratchPacket,
                              DhcpContext->ScratchPacketSize,
                              IO_BUFFER_FLAG_KERNEL_MODE_DATA,
                              &(DhcpContext->ScratchPacketIoBuffer));

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    Status = IoSocketCreate(NetDomainIp4,
                            NetSocketDatagram,
                            SOCKET_INTERNET_PROTOCOL_UDP,
                            0,
                            &(DhcpContext->Socket));

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Bind that socket to the known DHCP client port. Make sure the link
    // address is still valid before copying it.
    //

    KeAcquireQueuedLock(DhcpContext->Link->QueuedLock);
    LockHeld = TRUE;
    if (DhcpContext->LinkAddress->Configured == FALSE) {
        Status = STATUS_NO_NETWORK_CONNECTION;
        goto DhcpLeaseExtensionThreadEnd;
    }

    RtlCopyMemory(&LocalAddress,
                  &(DhcpContext->LinkAddress->Address),
                  sizeof(NETWORK_ADDRESS));

    KeReleaseQueuedLock(DhcpContext->Link->QueuedLock);
    LockHeld = FALSE;
    LocalAddress.Port = DHCP_CLIENT_PORT;
    Status = IoSocketBindToAddress(TRUE,
                                   DhcpContext->Socket,
                                   DhcpContext->Link,
                                   (PNETWORK_ADDRESS)&LocalAddress,
                                   NULL,
                                   0);

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Request the address that came back.
    //

    Step = "SendRequest";
    Status = NetpDhcpSendRequest(DhcpContext);
    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Get the acknowledge back to make sure the DHCP heard the request.
    //

    Step = "RecieveAcknowledge";
    Status = NetpDhcpReceiveAcknowledge(DhcpContext);
    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Calculate the lease's end based on the DHCP offer.
    //

    RtlCopyMemory(&LeaseEndTime,
                  &(DhcpContext->LeaseRequestTime),
                  sizeof(SYSTEM_TIME));

    LeaseEndTime.Seconds += DhcpContext->LeaseTime;

    //
    // The lease extension is complete. Set the parameters in the link address
    // entry.
    //

    Step = "SetNetworkAddress";
    RtlZeroMemory(&Information, sizeof(NETWORK_DEVICE_INFORMATION));
    Information.Version = NETWORK_DEVICE_INFORMATION_VERSION;
    Information.Flags = NETWORK_DEVICE_FLAG_CONFIGURED;
    Information.Domain = NetDomainIp4;
    Information.ConfigurationMethod = NetworkAddressConfigurationDhcp;
    RtlCopyMemory(&(Information.Address),
                  &(DhcpContext->OfferClientAddress),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.Subnet),
                  &(DhcpContext->OfferSubnetMask),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.Gateway),
                  &(DhcpContext->OfferRouter),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.DnsServers),
                  &(DhcpContext->OfferDnsAddress),
                  sizeof(NETWORK_ADDRESS) * DhcpContext->OfferDnsAddressCount);

    Information.DnsServerCount = DhcpContext->OfferDnsAddressCount;
    RtlCopyMemory(&(Information.LeaseServerAddress),
                  &(DhcpContext->OfferServerAddress),
                  sizeof(NETWORK_ADDRESS));

    RtlCopyMemory(&(Information.LeaseStartTime),
                  &(DhcpContext->LeaseRequestTime),
                  sizeof(SYSTEM_TIME));

    RtlCopyMemory(&(Information.LeaseEndTime),
                  &LeaseEndTime,
                  sizeof(SYSTEM_TIME));

    Status = NetGetSetNetworkDeviceInformation(DhcpContext->Link,
                                               DhcpContext->LinkAddress,
                                               &Information,
                                               TRUE);

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseExtensionThreadEnd;
    }

    //
    // Celebrate the extnesion with some debugger prints.
    //

    RtlDebugPrint("DHCP Extension:\n");
    NetpDhcpPrintContext(DhcpContext);
    if ((NetDhcpDebugFlags & DHCP_DEBUG_FLAG_EXTEND) != 0) {
        RtlDebugPrint("Net: DHCP extended lease (0x%08x) for link (0x%08x) "
                      "from state %d.\n",
                      Lease,
                      Lease->Link,
                      Lease->State);
    }

    //
    // Mark that the lease is now in the bound state.
    //

    Lease->State = DhcpLeaseStateBound;

    //
    // The lease has been extended. Set the lease timer so that a lease
    // renewal is attemtped at the time specified by the server.
    //

    NetpDhcpQueueLeaseExtension(Lease);

DhcpLeaseExtensionThreadEnd:
    if (LockHeld != FALSE) {
        KeReleaseQueuedLock(DhcpContext->Link->QueuedLock);
    }

    if (!KSUCCESS(Status)) {
        RtlDebugPrint("Net: DHCP lease extension failed at step '%s': %d.\n",
                      Step,
                      Status);

        //
        // No matter when the extension failed, try to queue lease extension
        // again. This is OK even if this routine fails after extending the
        // lease. There is no harm in prematurely asking the DHCP server for
        // an extension.
        //

        NetpDhcpQueueLeaseExtension(Lease);
    }

    NetpDhcpDestroyContext(DhcpContext);
    return;
}

KSTATUS
NetpDhcpBeginRelease (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    )

/*++

Routine Description:

    This routine kicks off the process of releasing the IP address previously
    assigned to the given link and address via DHCP.

Arguments:

    Link - Supplies a pointer to the link to send the discovery request out on.

    LinkAddress - Supplies a pointer to the address structure to bind to.

Return Value:

    Status code indicating whether or not the process was successfully
    initiated.

--*/

{

    PDHCP_CONTEXT DhcpContext;
    KSTATUS Status;

    DhcpContext = NetpDhcpCreateContext(Link, LinkAddress, NULL);
    if (DhcpContext == NULL) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    Status = PsCreateKernelThread(NetpDhcpReleaseThread,
                                  DhcpContext,
                                  "DhcpReleaseThread");

    if (!KSUCCESS(Status)) {
        NetpDhcpDestroyContext(DhcpContext);
        return Status;
    }

    return STATUS_SUCCESS;
}

VOID
NetpDhcpReleaseThread (
    PVOID Parameter
    )

/*++

Routine Description:

    This routine attempts to release the IP address previously assigned via
    DHCP.

Arguments:

    Parameter - Supplies a pointer supplied by the creator of the thread, in
        this case a pointer to the DHCP context structure.

Return Value:

    None.

--*/

{

    PDHCP_CONTEXT DhcpContext;
    IP4_ADDRESS LocalAddress;
    BOOL LockHeld;
    KSTATUS Status;
    PSTR Step;

    ASSERT(KeGetRunLevel() == RunLevelLow);

    DhcpContext = (PDHCP_CONTEXT)Parameter;
    LockHeld = FALSE;
    Step = "Init";

    //
    // Create the scratch packet space and the socket.
    //

    DhcpContext->ScratchPacket = MmAllocatePagedPool(DHCP_SCRATCH_PACKET_SIZE,
                                                     DHCP_ALLOCATION_TAG);

    if (DhcpContext->ScratchPacket == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpLeaseReleaseThreadEnd;
    }

    DhcpContext->ScratchPacketSize = DHCP_SCRATCH_PACKET_SIZE;
    Status = MmCreateIoBuffer(DhcpContext->ScratchPacket,
                              DhcpContext->ScratchPacketSize,
                              IO_BUFFER_FLAG_KERNEL_MODE_DATA,
                              &(DhcpContext->ScratchPacketIoBuffer));

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseReleaseThreadEnd;
    }

    Status = IoSocketCreate(NetDomainIp4,
                            NetSocketDatagram,
                            SOCKET_INTERNET_PROTOCOL_UDP,
                            0,
                            &(DhcpContext->Socket));

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseReleaseThreadEnd;
    }

    //
    // Bind that socket to the known DHCP client port. Make sure the link
    // address is still valid before copying it.
    //

    KeAcquireQueuedLock(DhcpContext->Link->QueuedLock);
    LockHeld = TRUE;
    if (DhcpContext->LinkAddress->Configured == FALSE) {
        Status = STATUS_NO_NETWORK_CONNECTION;
        goto DhcpLeaseReleaseThreadEnd;
    }

    RtlCopyMemory(&LocalAddress,
                  &(DhcpContext->LinkAddress->Address),
                  sizeof(NETWORK_ADDRESS));

    KeReleaseQueuedLock(DhcpContext->Link->QueuedLock);
    LockHeld = FALSE;
    LocalAddress.Port = DHCP_CLIENT_PORT;
    Status = IoSocketBindToAddress(TRUE,
                                   DhcpContext->Socket,
                                   DhcpContext->Link,
                                   (PNETWORK_ADDRESS)&LocalAddress,
                                   NULL,
                                   0);

    if (!KSUCCESS(Status)) {
        goto DhcpLeaseReleaseThreadEnd;
    }

    //
    // Request the address that came back.
    //

    Step = "SendRelease";
    Status = NetpDhcpSendRelease(DhcpContext);
    if (!KSUCCESS(Status)) {
        goto DhcpLeaseReleaseThreadEnd;
    }

DhcpLeaseReleaseThreadEnd:
    if (LockHeld != FALSE) {
        KeReleaseQueuedLock(DhcpContext->Link->QueuedLock);
    }

    if (!KSUCCESS(Status)) {
        RtlDebugPrint("Net: DHCP lease release failed at step '%s': %d.\n",
                      Step,
                      Status);
    }

    NetpDhcpDestroyContext(DhcpContext);
    return;
}

KSTATUS
NetpDhcpSendDiscover (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine sends the DHCP discovery request out onto the subnet.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

Return Value:

    Status code indicating whether or not the discovery request was
    successfully sent.

--*/

{

    PBYTE OptionByte;
    SOCKET_IO_PARAMETERS Parameters;
    IP4_ADDRESS RemoteAddress;
    PDHCP_PACKET Request;
    KSTATUS Status;
    ULONG TotalPacketSize;

    Request = NULL;

    //
    // Initialize the DHCP discover request.
    //

    Request = Context->ScratchPacket;
    RtlZeroMemory(Request, sizeof(DHCP_PACKET));
    Request->OperationCode = DHCP_OPERATION_REQUEST;
    Request->HardwareType = DHCP_HARDWARE_TYPE_ETHERNET;
    Request->HardwareAddressLength = DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH;
    Request->Hops = 0;
    Request->TransactionIdentifier = HlQueryTimeCounter() & MAX_ULONG;
    Context->ExpectedTransactionId = Request->TransactionIdentifier;
    Request->Seconds = 0;
    Request->Flags = 0;
    Request->ClientIpAddress = 0;
    RtlCopyMemory(&(Request->ClientHardwareAddress),
                  &(Context->LinkAddress->PhysicalAddress.Address),
                  DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH);

    Request->MagicCookie = CPU_TO_NETWORK32(DHCP_MAGIC_COOKIE);

    //
    // Initialize the options, which come right after the request. The first
    // option tells the server this is a discovery request. Options are always
    // a tuple of (OptionType, LengthOfValue, Value).
    //

    OptionByte = (PBYTE)(Request + 1);
    *OptionByte = DHCP_OPTION_DHCP_MESSAGE_TYPE;
    OptionByte += 1;
    *OptionByte = 1;
    OptionByte += 1;
    *OptionByte = DHCP_MESSAGE_DISCOVER;
    OptionByte += 1;

    //
    // Add the parameter request list option. Five parameters are being
    // requested with the offer.
    //

    *OptionByte = DHCP_OPTION_PARAMETER_REQUEST_LIST;
    OptionByte += 1;
    *OptionByte = 5;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_SUBNET_MASK;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_ROUTER;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_DOMAIN_NAME;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_DOMAIN_NAME_SERVER;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_IP_ADDRESS_LEASE_TIME;
    OptionByte += 1;

    //
    // Add the end tag.
    //

    *OptionByte = DHCP_OPTION_END;
    OptionByte += 1;
    *OptionByte = 0;
    OptionByte += 1;
    TotalPacketSize = (UINTN)OptionByte - (UINTN)Request;

    ASSERT(TotalPacketSize <= Context->ScratchPacketSize);

    //
    // Send off this request!
    //

    RtlZeroMemory(&RemoteAddress, sizeof(NETWORK_ADDRESS));
    RemoteAddress.Domain = NetDomainIp4;
    RemoteAddress.Address = IP4_BROADCAST_ADDRESS;
    RemoteAddress.Port = DHCP_SERVER_PORT;
    RtlZeroMemory(&Parameters, sizeof(SOCKET_IO_PARAMETERS));
    Parameters.TimeoutInMilliseconds = WAIT_TIME_INDEFINITE;
    Parameters.NetworkAddress = &(RemoteAddress.NetworkAddress);
    Parameters.Size = TotalPacketSize;
    Status = IoSocketSendData(TRUE,
                              Context->Socket,
                              &Parameters,
                              Context->ScratchPacketIoBuffer);

    if (!KSUCCESS(Status)) {
        goto DhcpSendDiscoverEnd;
    }

    if (Parameters.Size != TotalPacketSize) {
        Status = STATUS_DATA_LENGTH_MISMATCH;
        goto DhcpSendDiscoverEnd;
    }

    Status = STATUS_SUCCESS;

DhcpSendDiscoverEnd:
    return Status;
}

KSTATUS
NetpDhcpReceiveOffer (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine receives the DHCP offer response, hopefully.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

Return Value:

    Status code.

--*/

{

    ULONG Attempts;
    DHCP_REPLY Reply;
    KSTATUS Status;

    Attempts = 5;
    while (Attempts != 0) {
        Attempts -= 1;

        //
        // Atempt to receive a reply from the DHCP server. Quit if the request
        // times out but try again for any other failure.
        //

        Status = NetpDhcpReceiveReply(Context, &Reply);
        if (Status == STATUS_TIMEOUT) {
            break;
        }

        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Try again if an offer message was not received.
        //

        if (Reply.MessageType != DHCP_MESSAGE_OFFER) {
            RtlDebugPrint("Skipping DHCP message as it wasn't an offer (%d), "
                          "instead it had a message type of %d.\n",
                          DHCP_MESSAGE_OFFER,
                          Reply.MessageType);

            continue;
        }

        //
        // Copy the reply to the context. This will make sure that all the
        // required information is present in the reply.
        //

        Status = NetpDhcpCopyReplyToContext(Context, &Reply);
        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Print the offer to the debugger now that the context is filled in,
        // if requested.
        //

        if ((NetDhcpDebugFlags & DHCP_DEBUG_FLAG_OFFER) != 0) {
            RtlDebugPrint("Net: DHCP Offer\n");
            NetpDhcpPrintContext(Context);
        }

        Status = STATUS_SUCCESS;
        break;
    }

    return Status;
}

KSTATUS
NetpDhcpSendRequest (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine sends the DHCP address request out onto the subnet.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

    Renew - Supplies a boolean indicating whether or not this is a request to
        renew a lease.

Return Value:

    Status code indicating whether or not the discovery request was
    successfully sent.

--*/

{

    PIP4_ADDRESS Ip4Address;
    PDHCP_LEASE Lease;
    BOOL LockHeld;
    PBYTE OptionByte;
    SOCKET_IO_PARAMETERS Parameters;
    IP4_ADDRESS RemoteAddress;
    PDHCP_PACKET Request;
    PIP4_ADDRESS RequestedIp4Address;
    PIP4_ADDRESS ServerIp4Address;
    KSTATUS Status;
    ULONG TotalPacketSize;

    ASSERT(KeGetRunLevel() == RunLevelLow);
    ASSERT(Context->Lease != NULL);

    Lease = Context->Lease;
    LockHeld = FALSE;
    Request = NULL;

    //
    // Initialize the DHCP discover request.
    //

    Request = Context->ScratchPacket;
    RtlZeroMemory(Request, sizeof(DHCP_PACKET));
    Request->OperationCode = DHCP_OPERATION_REQUEST;
    Request->HardwareType = DHCP_HARDWARE_TYPE_ETHERNET;
    Request->HardwareAddressLength = DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH;
    Request->Hops = 0;
    Request->TransactionIdentifier = Context->ExpectedTransactionId;
    Request->Seconds = 0;
    Request->Flags = 0;
    Request->ClientIpAddress = 0;

    //
    // To renew or rebind a lease, the client IP address is set in the reqest
    // header.
    //

    if ((Lease->State == DhcpLeaseStateRenewing) ||
        (Lease->State == DhcpLeaseStateRebinding)) {

        //
        // Renew and rebind are trying to extend an already configured link
        // address's IP address. Make sure that the link address is still
        // configured before copying its data.
        //

        KeAcquireQueuedLock(Context->Link->QueuedLock);
        LockHeld = TRUE;
        if (Context->LinkAddress->Configured == FALSE) {
            Status = STATUS_NO_NETWORK_CONNECTION;
            goto DhcpSendRequestEnd;
        }

        Ip4Address = (PIP4_ADDRESS)&(Context->LinkAddress->Address);

        ASSERT(Ip4Address->Domain == NetDomainIp4);
        ASSERT(Ip4Address->Address != 0);

        Request->ClientIpAddress = Ip4Address->Address;
        KeReleaseQueuedLock(Context->Link->QueuedLock);
        LockHeld = FALSE;
    }

    //
    // The physical address of a link address entry does not change. There is
    // no need to acquire the lock here.
    //

    RtlCopyMemory(&(Request->ClientHardwareAddress),
                  &(Context->LinkAddress->PhysicalAddress.Address),
                  DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH);

    Request->MagicCookie = CPU_TO_NETWORK32(DHCP_MAGIC_COOKIE);

    //
    // Initialize the options, which come right after the request. The first
    // option tells the server this is a request (for an address). Options are
    // always a tuple of (OptionType, LengthOfValue, Value).
    //

    OptionByte = (PBYTE)(Request + 1);
    *OptionByte = DHCP_OPTION_DHCP_MESSAGE_TYPE;
    OptionByte += 1;
    *OptionByte = 1;
    OptionByte += 1;
    *OptionByte = DHCP_MESSAGE_REQUEST;
    OptionByte += 1;

    //
    // Add the parameter request list option. Five parameters are being
    // requested. This must match the parameters requested during the
    // discover message (if a discover message was sent before the request).
    //

    *OptionByte = DHCP_OPTION_PARAMETER_REQUEST_LIST;
    OptionByte += 1;
    *OptionByte = 5;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_SUBNET_MASK;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_ROUTER;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_DOMAIN_NAME;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_DOMAIN_NAME_SERVER;
    OptionByte += 1;
    *OptionByte = DHCP_OPTION_IP_ADDRESS_LEASE_TIME;
    OptionByte += 1;

    //
    // The requested IP address and server identifier options must not be sent
    // on a renew or rebind request.
    //

    if ((Lease->State != DhcpLeaseStateRenewing) &&
        (Lease->State != DhcpLeaseStateRebinding)) {

        //
        // Add the requested address.
        //

        ASSERT(sizeof(ULONG) == 4);

        RequestedIp4Address = (PIP4_ADDRESS)(&(Context->OfferClientAddress));
        *OptionByte = DHCP_OPTION_REQUESTED_IP_ADDRESS;
        OptionByte += 1;
        *OptionByte = 4;
        OptionByte += 1;
        *((PULONG)OptionByte) = RequestedIp4Address->Address;
        OptionByte += sizeof(ULONG);

        //
        // Add the server address.
        //

        ServerIp4Address = (PIP4_ADDRESS)(&(Context->OfferServerAddress));
        *OptionByte = DHCP_OPTION_DHCP_SERVER;
        OptionByte += 1;
        *OptionByte = 4;
        OptionByte += 1;
        *((PULONG)OptionByte) = ServerIp4Address->Address;
        OptionByte += sizeof(ULONG);
    }

    //
    // Add the end tag.
    //

    *OptionByte = DHCP_OPTION_END;
    OptionByte += 1;
    *OptionByte = 0;
    OptionByte += 1;
    TotalPacketSize = (UINTN)OptionByte - (UINTN)Request;

    ASSERT(TotalPacketSize <= Context->ScratchPacketSize);

    //
    // Record the time at which the request was sent. This will be considered
    // the lease start time upon success.
    //

    KeGetSystemTime(&(Context->LeaseRequestTime));

    //
    // Send off this request! On renew, it is unicast to the server that
    // initially offered the lease. Otherwise it's broadcast to let all the
    // other DHCP servers that made offers know which one was selected.
    //

    RtlZeroMemory(&RemoteAddress, sizeof(NETWORK_ADDRESS));
    RemoteAddress.Domain = NetDomainIp4;
    if (Lease->State == DhcpLeaseStateRenewing) {

        //
        // Make sure that the link address is still configured before copying
        // its data.
        //

        KeAcquireQueuedLock(Context->Link->QueuedLock);
        LockHeld = TRUE;
        if (Context->LinkAddress->Configured == FALSE) {
            Status = STATUS_NO_NETWORK_CONNECTION;
            goto DhcpSendRequestEnd;
        }

        Ip4Address = (PIP4_ADDRESS)&(Context->LinkAddress->LeaseServerAddress);

        ASSERT(Ip4Address->Domain == NetDomainIp4);
        ASSERT(Ip4Address->Address != 0);

        RemoteAddress.Address = Ip4Address->Address;
        KeReleaseQueuedLock(Context->Link->QueuedLock);
        LockHeld = FALSE;

    } else {
        RemoteAddress.Address = IP4_BROADCAST_ADDRESS;
    }

    RemoteAddress.Port = DHCP_SERVER_PORT;
    RtlZeroMemory(&Parameters, sizeof(SOCKET_IO_PARAMETERS));
    Parameters.TimeoutInMilliseconds = WAIT_TIME_INDEFINITE;
    Parameters.NetworkAddress = &(RemoteAddress.NetworkAddress);
    Parameters.Size = TotalPacketSize;
    Status = IoSocketSendData(TRUE,
                              Context->Socket,
                              &Parameters,
                              Context->ScratchPacketIoBuffer);

    if (!KSUCCESS(Status)) {
        goto DhcpSendRequestEnd;
    }

    if (Parameters.Size != TotalPacketSize) {
        Status = STATUS_DATA_LENGTH_MISMATCH;
        goto DhcpSendRequestEnd;
    }

    Status = STATUS_SUCCESS;

DhcpSendRequestEnd:
    if (LockHeld != FALSE) {
        KeReleaseQueuedLock(Context->Link->QueuedLock);
    }

    return Status;
}

KSTATUS
NetpDhcpReceiveAcknowledge (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine receives the acknowledgement from the DHCP server to the
    request just made.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

Return Value:

    Status code.

--*/

{

    ULONG Attempts;
    PIP4_ADDRESS ClientIp4Address;
    DHCP_REPLY Reply;
    PIP4_ADDRESS ServerIp4Address;
    KSTATUS Status;

    Attempts = 5;
    while (Attempts != 0) {
        Attempts -= 1;

        //
        // Atempt to receive a reply from the DHCP server. Quit if the request
        // times out but try again for any other failure.
        //

        Status = NetpDhcpReceiveReply(Context, &Reply);
        if (Status == STATUS_TIMEOUT) {
            break;
        }

        if (!KSUCCESS(Status)) {
            continue;
        }

        //
        // Try again if an acknowledge message was not received.
        //

        if (Reply.MessageType != DHCP_MESSAGE_ACKNOWLEDGE) {
            RtlDebugPrint("Skipping DHCP message as it wasn't an ACK (%d), "
                          "instead it had a message type of %d.\n",
                          DHCP_MESSAGE_ACKNOWLEDGE,
                          Reply.MessageType);

            continue;
        }

        //
        // If the DHCP lease is initializing, then an offer should have already
        // been received and stored in the context. If the client or server
        // addresses were provided in the acknowledgement, ensure they are the
        // same as the original offer.
        //

        if (Context->Lease->State == DhcpLeaseStateInitialize) {
            ServerIp4Address = (PIP4_ADDRESS)(&(Context->OfferServerAddress));
            ClientIp4Address = (PIP4_ADDRESS)(&(Context->OfferClientAddress));
            if (((Reply.ServerIpAddress != 0) &&
                 (Reply.ServerIpAddress != ServerIp4Address->Address)) ||
                ((Reply.OfferedIpAddress != 0) &&
                 (Reply.OfferedIpAddress != ClientIp4Address->Address))) {

                continue;
            }

            //
            // If the lease time does not equal the offer's lease time, then
            // recalculate the renewal and rebinding times if they were not
            // supplied.
            //

            if ((Reply.LeaseTime != 0) &&
                (Reply.LeaseTime != Context->LeaseTime)) {

                if (Reply.RenewalTime == 0) {
                    Reply.RenewalTime = DHCP_GET_DEFAULT_RENEWAL_TIME(
                                                              Reply.LeaseTime);
                }

                if (Reply.RebindingTime == 0) {
                    Reply.RebindingTime = DHCP_GET_DEFAULT_REBINDING_TIME(
                                                              Reply.LeaseTime);
                }

                Context->LeaseTime = Reply.LeaseTime;
                Context->RenewalTime = Reply.RenewalTime;
                Context->RebindingTime = Reply.RebindingTime;
            }

        //
        // For the renewal and rebinding states, the acknowledgement should
        // contain the complete information for the renewal offer. Copy the
        // whole reply to the context. If something is missing, the copy
        // routine will fail.
        //

        } else {

            ASSERT((Context->Lease->State == DhcpLeaseStateRenewing) ||
                   (Context->Lease->State == DhcpLeaseStateRebinding));

            Status = NetpDhcpCopyReplyToContext(Context, &Reply);
            if (!KSUCCESS(Status)) {
                continue;
            }
        }

        Status = STATUS_SUCCESS;
        break;
    }

    return Status;
}

KSTATUS
NetpDhcpSendRelease (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine sends a release message to the DHCP server in order to release
    the IP address that the server leased to it.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

Return Value:

    Status code.

--*/

{

    PIP4_ADDRESS Ip4Address;
    PBYTE OptionByte;
    SOCKET_IO_PARAMETERS Parameters;
    IP4_ADDRESS RemoteAddress;
    PDHCP_PACKET Request;
    PIP4_ADDRESS ServerIp4Address;
    KSTATUS Status;
    ULONG TotalPacketSize;

    Request = NULL;

    //
    // Initialize the DHCP release request.
    //

    Request = Context->ScratchPacket;
    RtlZeroMemory(Request, sizeof(DHCP_PACKET));
    Request->OperationCode = DHCP_OPERATION_REQUEST;
    Request->HardwareType = DHCP_HARDWARE_TYPE_ETHERNET;
    Request->HardwareAddressLength = DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH;
    Request->Hops = 0;
    Request->TransactionIdentifier = HlQueryTimeCounter() & MAX_ULONG;
    Context->ExpectedTransactionId = Request->TransactionIdentifier;
    Request->Seconds = 0;
    Request->Flags = 0;
    Ip4Address = (PIP4_ADDRESS)&(Context->OfferClientAddress);

    ASSERT(Ip4Address->Domain == NetDomainIp4);
    ASSERT(Ip4Address->Address != 0);

    Request->ClientIpAddress = Ip4Address->Address;
    RtlCopyMemory(&(Request->ClientHardwareAddress),
                  &(Context->LinkAddress->PhysicalAddress.Address),
                  DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH);

    Request->MagicCookie = CPU_TO_NETWORK32(DHCP_MAGIC_COOKIE);

    //
    // Initialize the options, which come right after the request. The first
    // option tells the server this is a release request. Options are always
    // a tuple of (OptionType, LengthOfValue, Value).
    //

    OptionByte = (PBYTE)(Request + 1);
    *OptionByte = DHCP_OPTION_DHCP_MESSAGE_TYPE;
    OptionByte += 1;
    *OptionByte = 1;
    OptionByte += 1;
    *OptionByte = DHCP_MESSAGE_RELEASE;
    OptionByte += 1;

    //
    // Add the server address.
    //

    ServerIp4Address = (PIP4_ADDRESS)(&(Context->OfferServerAddress));

    ASSERT(ServerIp4Address->Domain == NetDomainIp4);
    ASSERT(ServerIp4Address->Address != 0);

    *OptionByte = DHCP_OPTION_DHCP_SERVER;
    OptionByte += 1;
    *OptionByte = 4;
    OptionByte += 1;
    *((PULONG)OptionByte) = ServerIp4Address->Address;
    OptionByte += sizeof(ULONG);

    //
    // Add the end tag.
    //

    *OptionByte = DHCP_OPTION_END;
    OptionByte += 1;
    *OptionByte = 0;
    OptionByte += 1;
    TotalPacketSize = (UINTN)OptionByte - (UINTN)Request;

    ASSERT(TotalPacketSize <= Context->ScratchPacketSize);

    //
    // Send off this request!
    //

    RtlZeroMemory(&RemoteAddress, sizeof(NETWORK_ADDRESS));
    RemoteAddress.Domain = NetDomainIp4;
    Ip4Address = (PIP4_ADDRESS)&(Context->OfferServerAddress);

    ASSERT(Ip4Address->Domain == NetDomainIp4);
    ASSERT(Ip4Address->Address != 0);

    RemoteAddress.Address = Ip4Address->Address;
    RemoteAddress.Port = DHCP_SERVER_PORT;
    RtlZeroMemory(&Parameters, sizeof(SOCKET_IO_PARAMETERS));
    Parameters.TimeoutInMilliseconds = WAIT_TIME_INDEFINITE;
    Parameters.NetworkAddress = &(RemoteAddress.NetworkAddress);
    Parameters.Size = TotalPacketSize;
    Status = IoSocketSendData(TRUE,
                              Context->Socket,
                              &Parameters,
                              Context->ScratchPacketIoBuffer);

    if (!KSUCCESS(Status)) {
        goto DhcpSendDiscoverEnd;
    }

    if (Parameters.Size != TotalPacketSize) {
        Status = STATUS_DATA_LENGTH_MISMATCH;
        goto DhcpSendDiscoverEnd;
    }

    Status = STATUS_SUCCESS;

DhcpSendDiscoverEnd:
    return Status;
}

KSTATUS
NetpDhcpReceiveReply (
    PDHCP_CONTEXT Context,
    PDHCP_REPLY Reply
    )

/*++

Routine Description:

    This routine attempts to receive a replay from the DHCP server for either
    an offer or an acknowledge packet.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

    Reply - Supplies a pointer to the DHCP reply context that is to be filled
        in by this routine.

Return Value:

    Status code.

--*/

{

    ULONG AddressOffset;
    ULONG Offset;
    BYTE OptionByte;
    PBYTE OptionBytePointer;
    BYTE OptionLength;
    ULONGLONG PacketSize;
    SOCKET_IO_PARAMETERS Parameters;
    ULONG RebindingTime;
    PDHCP_PACKET Response;
    ULONG RouterIp;
    NETWORK_ADDRESS ServerAddress;
    ULONG ServerIp;
    KSTATUS Status;

    Response = Context->ScratchPacket;
    OptionBytePointer = (PUCHAR)Response;
    RtlZeroMemory(&Parameters, sizeof(SOCKET_IO_PARAMETERS));
    Parameters.TimeoutInMilliseconds = DHCP_ACKNOWLEDGE_TIMEOUT;
    Parameters.NetworkAddress = &ServerAddress;
    Parameters.Size = Context->ScratchPacketSize;
    Status = IoSocketReceiveData(TRUE,
                                 Context->Socket,
                                 &Parameters,
                                 Context->ScratchPacketIoBuffer);

    if (Status == STATUS_TIMEOUT) {
        goto DhcpReceiveReplyEnd;
    }

    if (!KSUCCESS(Status)) {
        RtlDebugPrint("NetpDhcpReceiveReply skipping packet because receive "
                      "status was %d.\n",
                      Status);

        goto DhcpReceiveReplyEnd;
    }

    PacketSize = Parameters.Size;

    //
    // Validate some basic attributes about the packet.
    //

    if (PacketSize < sizeof(DHCP_PACKET)) {
        RtlDebugPrint("DHCP ack packet too small. Was %d bytes, should "
                      "have been at least %d bytes.\n",
                      PacketSize,
                      sizeof(DHCP_PACKET));

        Status = STATUS_DATA_LENGTH_MISMATCH;
        goto DhcpReceiveReplyEnd;
    }

    if (Response->OperationCode != DHCP_OPERATION_REPLY) {
        Status = STATUS_UNSUCCESSFUL;
        goto DhcpReceiveReplyEnd;
    }

    if ((Response->HardwareType != DHCP_HARDWARE_TYPE_ETHERNET) ||
        (Response->HardwareAddressLength !=
         DHCP_ETHERNET_HARDWARE_ADDRESS_LENGTH)) {

        RtlDebugPrint("DHCP packet skipped because hardware type or "
                      "length didn't match standard ethernet.\n");

        Status = STATUS_UNSUCCESSFUL;
        goto DhcpReceiveReplyEnd;
    }

    if (NETWORK_TO_CPU32(Response->MagicCookie) != DHCP_MAGIC_COOKIE) {
        RtlDebugPrint("DHCP packet skipped because the magic cookie was "
                      "wrong.\n");

        Status = STATUS_UNSUCCESSFUL;
        goto DhcpReceiveReplyEnd;
    }

    //
    // Quietly skip packets not directed at this request.
    //

    if (Response->TransactionIdentifier != Context->ExpectedTransactionId) {
        Status = STATUS_UNSUCCESSFUL;
        goto DhcpReceiveReplyEnd;
    }

    RtlZeroMemory(Reply, sizeof(DHCP_REPLY));
    Reply->ServerIpAddress = Response->ServerIpAddress;
    Reply->OfferedIpAddress = Response->YourIpAddress;

    //
    // Parse the options.
    //

    Offset = sizeof(DHCP_PACKET);
    while (Offset < PacketSize) {
        OptionByte = OptionBytePointer[Offset];
        Offset += 1;

        //
        // Skip padding.
        //

        if (OptionByte == DHCP_OPTION_PAD) {
            continue;
        }

        //
        // Stop if the end is reached.
        //

        if (OptionByte == DHCP_OPTION_END) {
            break;
        }

        //
        // Get the length of the option.
        //

        if (Offset >= PacketSize) {
            break;
        }

        OptionLength = OptionBytePointer[Offset];
        Offset += 1;

        //
        // Stop if the entire option value cannot be retrieved.
        //

        if (Offset + OptionLength > PacketSize) {
            break;
        }

        //
        // Parse the known options, starting with the message type.
        //

        if (OptionByte == DHCP_OPTION_DHCP_MESSAGE_TYPE) {
            Reply->MessageType = OptionBytePointer[Offset];

        } else if (OptionByte == DHCP_OPTION_DHCP_SERVER) {
            if (OptionLength == 4) {
                ServerIp = *((PULONG)(&(OptionBytePointer[Offset])));
                Reply->ServerIpAddress = ServerIp;
            }

        } else if (OptionByte == DHCP_OPTION_SUBNET_MASK) {
            if (OptionLength == 4) {
                Reply->SubnetMask = *((PULONG)(&(OptionBytePointer[Offset])));
            }

        } else if (OptionByte == DHCP_OPTION_ROUTER) {
            if (OptionLength == 4) {
                RouterIp = *((PULONG)(&(OptionBytePointer[Offset])));
                Reply->RouterIpAddress = RouterIp;
            }

        } else if (OptionByte == DHCP_OPTION_DOMAIN_NAME_SERVER) {
            AddressOffset = Offset;
            while (AddressOffset + 4 <= Offset + OptionLength) {
                Reply->DomainNameServer[Reply->DomainNameServerCount] =
                              *((PULONG)(&(OptionBytePointer[AddressOffset])));

                AddressOffset += 4;
                Reply->DomainNameServerCount += 1;
                if (Reply->DomainNameServerCount == DHCP_MAX_DNS_SERVERS) {
                    break;
                }
            }

        } else if (OptionByte == DHCP_OPTION_IP_ADDRESS_LEASE_TIME) {
            if (OptionLength == 4) {
                Reply->LeaseTime = *((PULONG)(&(OptionBytePointer[Offset])));
                Reply->LeaseTime = NETWORK_TO_CPU32(Reply->LeaseTime);
            }

        } else if (OptionByte == DHCP_OPTION_RENEWAL_TIME) {
            if (OptionLength == 4) {
                Reply->RenewalTime = *((PULONG)(&(OptionBytePointer[Offset])));
                Reply->RenewalTime = NETWORK_TO_CPU32(Reply->RenewalTime);
            }

        } else if (OptionByte == DHCP_OPTION_REBINDING_TIME) {
            if (OptionLength == 4) {
                RebindingTime = *((PULONG)(&(OptionBytePointer[Offset])));
                Reply->RebindingTime = NETWORK_TO_CPU32(RebindingTime);
            }
        }

        //
        // Skip over the option length.
        //

        Offset += OptionLength;
    }

    ASSERT(Status == STATUS_SUCCESS);

    //
    // Set the override renewal and rebinding times if enabled.
    //

    if (NetDhcpDebugOverrideRenewal != FALSE) {
        Reply->RenewalTime = NetDhcpDebugRenewalTime;
        Reply->RebindingTime = NetDhcpDebugRebindingTime;
    }

DhcpReceiveReplyEnd:
    return Status;
}

PDHCP_CONTEXT
NetpDhcpCreateContext (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress,
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine creates a DHCP context.

Arguments:

    Link - Supplies a pointer to the network link for the DHCP context.

    LinkAddress - Supplies a pointer to the network link address for the DHCP
        context.

    Lease - Supplies an optional pointer to a DHCP lease to be associated with
        the context.

Return Value:

    Returns a pointer to the newly allocated DHCP context on success, or NULL
    on failure.

--*/

{

    PDHCP_CONTEXT Context;

    Context = MmAllocatePagedPool(sizeof(DHCP_CONTEXT), DHCP_ALLOCATION_TAG);
    if (Context == NULL) {
        return NULL;
    }

    RtlZeroMemory(Context, sizeof(DHCP_CONTEXT));
    NetLinkAddReference(Link);
    Context->Link = Link;
    Context->LinkAddress = LinkAddress;
    if (Lease != NULL) {
        NetpDhcpLeaseAddReference(Lease);
        Context->Lease = Lease;
    }

    return Context;
}

VOID
NetpDhcpDestroyContext (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine destroys the given DHCP context.

Arguments:

    Context - Supplies a pointer to the DHCP context to destroy.

Return Value:

    None.

--*/

{

    if (Context->Socket != NULL) {
        IoClose(Context->Socket);
    }

    if (Context->ScratchPacketIoBuffer != NULL) {
        MmFreeIoBuffer(Context->ScratchPacketIoBuffer);
    }

    if (Context->ScratchPacket != NULL) {
        MmFreePagedPool(Context->ScratchPacket);
    }

    ASSERT(Context->Link != NULL);

    NetLinkReleaseReference(Context->Link);
    if (Context->Lease != NULL) {
        NetpDhcpLeaseReleaseReference(Context->Lease);
    }

    MmFreePagedPool(Context);
    return;
}

PDHCP_LEASE
NetpDhcpCreateLease (
    VOID
    )

/*++

Routine Description:

    This routine creates an the context for a DHCP lease.

Arguments:

    None.

Return Value:

    Returns a pointer to a DHCP lease context on success, or NULL on failure.

--*/

{

    PDHCP_LEASE NewLease;
    KSTATUS Status;

    NewLease = MmAllocateNonPagedPool(sizeof(DHCP_LEASE), DHCP_ALLOCATION_TAG);
    if (NewLease == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpCreateAssignmentContextEnd;
    }

    RtlZeroMemory(NewLease, sizeof(DHCP_LEASE));
    NewLease->ReferenceCount = 1;
    NewLease->Timer = KeCreateTimer(DHCP_ALLOCATION_TAG);
    if (NewLease->Timer == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpCreateAssignmentContextEnd;
    }

    NewLease->Dpc = KeCreateDpc(NetpDhcpLeaseDpcRoutine, NewLease);
    if (NewLease->Dpc == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpCreateAssignmentContextEnd;
    }

    NewLease->WorkItem = KeCreateWorkItem(NULL,
                                          WorkPriorityNormal,
                                          NetpDhcpLeaseWorkRoutine,
                                          NewLease,
                                          DHCP_ALLOCATION_TAG);

    if (NewLease->WorkItem == NULL) {
        Status = STATUS_INSUFFICIENT_RESOURCES;
        goto DhcpCreateAssignmentContextEnd;
    }

    Status = STATUS_SUCCESS;

DhcpCreateAssignmentContextEnd:
    if (!KSUCCESS(Status)) {
        if (NewLease != NULL) {
            NetpDhcpDestroyLease(NewLease);
            NewLease = NULL;
        }
    }

    return NewLease;
}

VOID
NetpDhcpLeaseAddReference (
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine increases the reference count on a DHCP lease.

Arguments:

    Lease - Supplies a pointer to the DHCP lease whose reference count should
        be incremented.

Return Value:

    None.

--*/

{

    ULONG OldReferenceCount;

    OldReferenceCount = RtlAtomicAdd32(&(Lease->ReferenceCount), 1);

    ASSERT((OldReferenceCount != 0) & (OldReferenceCount < 0x20000000));

    return;
}

VOID
NetpDhcpLeaseReleaseReference (
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine decreases the reference count of a DHCP lease, and destroys
    the lease if the reference count drops to zero.

Arguments:

    Lease - Supplies a pointer to the DHCP lease whose reference count should
        be decremented.

Return Value:

    None.

--*/

{

    ULONG OldReferenceCount;

    OldReferenceCount = RtlAtomicAdd32(&(Lease->ReferenceCount), -1);

    ASSERT(OldReferenceCount != 0);

    if (OldReferenceCount == 1) {
        NetpDhcpDestroyLease(Lease);
    }

    return;
}

PDHCP_LEASE
NetpDhcpFindLease (
    PNET_LINK Link,
    PNET_LINK_ADDRESS_ENTRY LinkAddress
    )

/*++

Routine Description:

    This routine attemps to find an existing lease for the given link and link
    address. If a lease is found, a reference is added to the lease.

Arguments:

    Link - Supplies a pointer to a network link.

    LinkAddress - Supplies a pointer to a network link address.

Return Value:

    Returns a pointer to the DHCP lease that exists for the given link and link
    address, or NULL if no such lease exists.

--*/

{

    PLIST_ENTRY CurrentEntry;
    PDHCP_LEASE CurrentLease;
    PDHCP_LEASE FoundLease;

    FoundLease = NULL;
    KeAcquireSpinLock(&NetDhcpLeaseListLock);
    CurrentEntry = NetDhcpLeaseListHead.Next;
    while (CurrentEntry != &(NetDhcpLeaseListHead)) {
        CurrentLease = LIST_VALUE(CurrentEntry, DHCP_LEASE, ListEntry);
        if ((CurrentLease->Link == Link) &&
            (CurrentLease->LinkAddress == LinkAddress)) {

            NetpDhcpLeaseAddReference(CurrentLease);
            FoundLease = CurrentLease;
            break;
        }

        CurrentEntry = CurrentEntry->Next;
    }

    KeReleaseSpinLock(&NetDhcpLeaseListLock);
    return FoundLease;
}

VOID
NetpDhcpDestroyLease (
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine destroys a DHCP lease context.

Arguments:

    Lease - Supplies a pointer to a DHCP lease.

Return Value:

    None.

--*/

{

    ASSERT(Lease->ListEntry.Next == NULL);

    if (Lease->Link != NULL) {
        NetLinkReleaseReference(Lease->Link);
    }

    if (Lease->Timer != NULL) {
        KeDestroyTimer(Lease->Timer);
    }

    if (Lease->Dpc != NULL) {
        KeDestroyDpc(Lease->Dpc);
    }

    if (Lease->WorkItem != NULL) {
        KeDestroyWorkItem(Lease->WorkItem);
    }

    MmFreeNonPagedPool(Lease);
    return;
}

VOID
NetpDhcpQueueLeaseExtension (
    PDHCP_LEASE Lease
    )

/*++

Routine Description:

    This routine queues the lease timer to attempt a lease extension. It
    determines the correct duration for the timer.

Arguments:

    Lease - Supplies a pointer to the lease that needs its timer queued.

Return Value:

    None.

--*/

{

    SYSTEM_TIME CurrentSystemTime;
    ULONGLONG DueTime;
    LONGLONG ElapsedLeaseTime;
    ULONGLONG StateChangeTime;
    KSTATUS Status;
    ULONGLONG TimerDuration;
    ULONGLONG TimeToStateChange;

    if (Lease->State == DhcpLeaseStateBound) {

        ASSERT(Lease->RenewalTime != 0);

        TimerDuration = Lease->RenewalTime;

    } else {
        KeGetSystemTime(&CurrentSystemTime);
        ElapsedLeaseTime = CurrentSystemTime.Seconds -
                           Lease->LinkAddress->LeaseStartTime.Seconds;

        ASSERT(ElapsedLeaseTime >= 0);

        //
        // Determine the time of the next state change.
        //

        if (Lease->State == DhcpLeaseStateRenewing) {
            StateChangeTime = Lease->RebindingTime;

        } else {

            ASSERT(Lease->State == DhcpLeaseStateRebinding);

            StateChangeTime = Lease->LeaseTime;
        }

        //
        // Set the time for half the time until the next state change. If
        // that results in a timer duration that is less than the minimum,
        // just schedule the timer for the next state change time.
        //

        TimerDuration = 0;
        if (StateChangeTime > ElapsedLeaseTime) {
            TimeToStateChange = StateChangeTime - ElapsedLeaseTime;
            TimerDuration = TimeToStateChange >> 1;
            if (TimerDuration < DHCP_TIMER_DURATION_MINIMUM) {
                TimerDuration = TimeToStateChange;
            }
        }
    }

    TimerDuration *= MICROSECONDS_PER_SECOND;
    TimerDuration = KeConvertMicrosecondsToTimeTicks(TimerDuration);
    DueTime = HlQueryTimeCounter() + TimerDuration;
    Status = KeQueueTimer(Lease->Timer,
                          TimerQueueSoft,
                          DueTime,
                          0,
                          0,
                          Lease->Dpc);

    ASSERT(KSUCCESS(Status));

    return;
}

VOID
NetpDhcpLeaseDpcRoutine (
    PDPC Dpc
    )

/*++

Routine Description:

    This routine implements the DPC routine that fires when a lease timer
    expires. It queues the work item.

Arguments:

    Dpc - Supplies a pointer to the DPC that is running.

Return Value:

    None.

--*/

{

    PDHCP_LEASE Lease;

    Lease = (PDHCP_LEASE)Dpc->UserData;
    KeQueueWorkItem(Lease->WorkItem);
    return;
}

VOID
NetpDhcpLeaseWorkRoutine (
    PVOID Parameter
    )

/*++

Routine Description:

    This routine implements the lease timer expiration work routine.

Arguments:

    Parameter - Supplies a pointer to a lease context.

Return Value:

    None.

--*/

{

    SYSTEM_TIME CurrentSystemTime;
    LONGLONG ElapsedLeaseTime;
    PDHCP_LEASE Lease;
    BOOL LinkUp;
    KSTATUS Status;

    Lease = (PDHCP_LEASE)Parameter;

    ASSERT(Lease->ReferenceCount >= 1);

    //
    // If the link is down then do not continue.
    //

    NetGetLinkState(Lease->Link, &LinkUp, NULL);
    if (LinkUp == FALSE) {
        return;
    }

    //
    // Determine the current state based on the time.
    //

    KeGetSystemTime(&CurrentSystemTime);
    ElapsedLeaseTime = CurrentSystemTime.Seconds -
                       Lease->LinkAddress->LeaseStartTime.Seconds;

    //
    // If the elapsed time is greater than the lease time, then move back to
    // the initialize phase.
    //

    if (ElapsedLeaseTime >= Lease->LeaseTime) {
        Lease->State = DhcpLeaseStateInitialize;

    //
    // If the elapsed time is greater than or equal to the rebinding time,
    // then the lease is in the rebinding state.
    //

    } else if (ElapsedLeaseTime >= Lease->RebindingTime) {
        Lease->State = DhcpLeaseStateRebinding;

    //
    // Otherwise, even if the elapsed time is less than the renewal time, move
    // the lease to the renewal state.
    //

    } else {
        Lease->State = DhcpLeaseStateRenewing;
    }

    //
    // If the lease is back in the initialization state, then the lease
    // expired. Try to re-initialize the address. Note that the lease cannot be
    // destroyed in its own work-item. The re-assignment process will handle
    // destroying the lease.
    //

    if (Lease->State == DhcpLeaseStateInitialize) {
        Status = NetpDhcpBeginAssignment(Lease->Link, Lease->LinkAddress);
        if (!KSUCCESS(Status)) {

            //
            // TODO: Handle failed DHCP.
            //

            ASSERT(FALSE);
        }

    //
    // Otherwise schedule work to try to renew (or rebind) the lease. If this
    // fails, try again later.
    //

    } else {
        Status = NetpDhcpBeginLeaseExtension(Lease);
        if (!KSUCCESS(Status)) {
            NetpDhcpQueueLeaseExtension(Lease);
        }
    }

    return;
}

KSTATUS
NetpDhcpCopyReplyToContext (
    PDHCP_CONTEXT Context,
    PDHCP_REPLY Reply
    )

/*++

Routine Description:

    This routine copies the state from the given reply into the context. It
    makes sure that all the necessary state is present in the reply.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

    Reply - Supplies a pointer to the DHCP reply context that will be copied to
        the DHCP context.

Return Value:

    Status code.

--*/

{

    ULONG AddressIndex;
    PIP4_ADDRESS Ip4Address;
    KSTATUS Status;

    if ((Reply->ServerIpAddress == 0) ||
        (Reply->OfferedIpAddress == 0) ||
        (Reply->RouterIpAddress == 0) ||
        (Reply->SubnetMask == 0) ||
        (Reply->DomainNameServerCount == 0) ||
        (Reply->LeaseTime == 0)) {

        RtlDebugPrint("DHCP: A required parameter was missing from the "
                      "reply:\n ServerIp: 0x%x\n OfferedIpAddress: 0x%x,\n "
                      "Router: 0x%x\n SubnetMask: 0x%x\n "
                      "DomainNameServerCount: 0x%x\n LeaseTime: 0x%x\n",
                      Reply->ServerIpAddress,
                      Reply->OfferedIpAddress,
                      Reply->RouterIpAddress,
                      Reply->SubnetMask,
                      Reply->DomainNameServerCount,
                      Reply->LeaseTime);

        Status = STATUS_INVALID_PARAMETER;
        goto DhcpCopyReplyToContextEnd;
    }

    //
    // Fill out the network address structures.
    //

    Ip4Address = (PIP4_ADDRESS)(&(Context->OfferClientAddress));
    Ip4Address->Domain = NetDomainIp4;
    Ip4Address->Address = Reply->OfferedIpAddress;
    Ip4Address = (PIP4_ADDRESS)(&(Context->OfferSubnetMask));
    Ip4Address->Domain = NetDomainIp4;
    Ip4Address->Address = Reply->SubnetMask;
    Ip4Address = (PIP4_ADDRESS)(&(Context->OfferServerAddress));
    Ip4Address->Domain = NetDomainIp4;
    Ip4Address->Address = Reply->ServerIpAddress;
    Ip4Address = (PIP4_ADDRESS)(&(Context->OfferRouter));
    Ip4Address->Domain = NetDomainIp4;
    Ip4Address->Address = Reply->RouterIpAddress;
    Context->OfferDnsAddressCount = Reply->DomainNameServerCount;
    for (AddressIndex = 0;
         AddressIndex < Reply->DomainNameServerCount;
         AddressIndex += 1) {

        Ip4Address =
                 (PIP4_ADDRESS)(&(Context->OfferDnsAddress[AddressIndex]));

        Ip4Address->Domain = NetDomainIp4;
        Ip4Address->Address = Reply->DomainNameServer[AddressIndex];
    }

    //
    // Copy the lease time information.
    //

    Context->LeaseTime = Reply->LeaseTime;
    if (Reply->RenewalTime == 0) {
        Reply->RenewalTime = DHCP_GET_DEFAULT_RENEWAL_TIME(Reply->LeaseTime);
    }

    Context->RenewalTime = Reply->RenewalTime;
    if (Reply->RebindingTime == 0) {
        Reply->RebindingTime = DHCP_GET_DEFAULT_REBINDING_TIME(
                                                             Reply->LeaseTime);
    }

    Context->RebindingTime = Reply->RebindingTime;
    Status = STATUS_SUCCESS;

DhcpCopyReplyToContextEnd:
    return Status;
}

VOID
NetpDhcpPrintContext (
    PDHCP_CONTEXT Context
    )

/*++

Routine Description:

    This routine prints out the IP address and lease time information for a
    DHCP context.

Arguments:

    Context - Supplies a pointer to the DHCP context information.

Return Value:

    None.

--*/

{

    RtlDebugPrint("%20s: %d.%d.%d.%d\n"
                  "%20s: %d.%d.%d.%d\n"
                  "%20s: %d.%d.%d.%d\n"
                  "%20s: %d.%d.%d.%d\n"
                  "%20s: %d hours.\n",
                  "Server IP",
                  (UCHAR)Context->OfferServerAddress.Address[0],
                  (UCHAR)(Context->OfferServerAddress.Address[0] >> 8),
                  (UCHAR)(Context->OfferServerAddress.Address[0] >> 16),
                  (UCHAR)(Context->OfferServerAddress.Address[0] >> 24),
                  "Offered IP",
                  (UCHAR)Context->OfferClientAddress.Address[0],
                  (UCHAR)(Context->OfferClientAddress.Address[0] >> 8),
                  (UCHAR)(Context->OfferClientAddress.Address[0] >> 16),
                  (UCHAR)(Context->OfferClientAddress.Address[0] >> 24),
                  "Router IP",
                  (UCHAR)Context->OfferRouter.Address[0],
                  (UCHAR)(Context->OfferRouter.Address[0] >> 8),
                  (UCHAR)(Context->OfferRouter.Address[0] >> 16),
                  (UCHAR)(Context->OfferRouter.Address[0] >> 24),
                  "DNS Server IP",
                  (UCHAR)Context->OfferDnsAddress[0].Address[0],
                  (UCHAR)(Context->OfferDnsAddress[0].Address[0] >> 8),
                  (UCHAR)(Context->OfferDnsAddress[0].Address[0] >> 16),
                  (UCHAR)(Context->OfferDnsAddress[0].Address[0] >> 24),
                  "Lease Time",
                  Context->LeaseTime / 3600);

    return;
}