Module dhcp 

Minimal DHCPv4 server for access-point clients.

Implements the RFC 2131 subset needed to hand out addresses from a fixed pool: DISCOVER → OFFER, REQUEST → ACK/NAK, plus DECLINE, RELEASE and INFORM. Clients are identified by their hardware address (chaddr); every lease slot owns a stable pool address, so a reconnecting device keeps its previous address.

Replies are broadcast while the client has no address of its own (sender 0.0.0.0 or the RFC 2131 broadcast flag) and unicast for renewals. All packet access goes through the bounds-checked Reader and Writer below — client input is never indexed directly.

Structs

Action 🔒

The reply the server decided on for one client message.

ClientMsg 🔒

A validated client message.

Lease 🔒

One lease slot: a pool address bound to a client hardware address.

Reader 🔒

Bounds-checked cursor over an untrusted packet.

Server 🔒

The server’s fixed lease pool.

Writer 🔒

Bounds-checked cursor that appends to a reply buffer.

Constants

BOOTREPLY 🔒

BOOTP op: reply sent by the server (RFC 951).

BOOTREQUEST 🔒

BOOTP op: request sent by a client (RFC 951).

CLIENT_PORT 🔒

DHCP client port — every reply is sent there.

FLAG_BROADCAST 🔒

RFC 2131 flags broadcast bit.

HLEN_ETHERNET 🔒

hlen: six-byte MAC address length.

HTYPE_ETHERNET 🔒

htype: Ethernet hardware type (RFC 826).

LEASE 🔒

Lease duration (the embassy-time spelling of LEASE_SECS).

LEASE_SECS 🔒

Lease time handed out to clients, in seconds.

MAGIC_COOKIE 🔒

Magic cookie 0x63825363 preceding the options area (RFC 2131 §4.2).

MSG_ACK 🔒

Message type 5: server ACK.

MSG_DECLINE 🔒

Message type 4: client DECLINE.

MSG_DISCOVER 🔒

Message type 1: client DISCOVER.

MSG_INFORM 🔒

Message type 8: client INFORM.

MSG_NAK 🔒

Message type 6: server NAK.

MSG_OFFER 🔒

Message type 2: server OFFER.

MSG_RELEASE 🔒

Message type 7: client RELEASE.

MSG_REQUEST 🔒

Message type 3: client REQUEST.

NETMASK 🔒

Subnet mask sent with every lease — /24, matching super::AP_PREFIX; the pool layout above only supports a /24.

OPT_DNS 🔒

Option 6: DNS server.

OPT_END 🔒

Option 255: end of the options list.

OPT_LEASE_TIME 🔒

Option 51: IP address lease time.

OPT_MESSAGE_TYPE 🔒

Option 53: DHCP message type (see the MSG_* constants).

OPT_PAD 🔒

Option 0: padding byte (skip).

OPT_REQUESTED_IP 🔒

Option 50: requested IP address.

OPT_ROUTER 🔒

Option 3: default router.

OPT_SERVER_ID 🔒

Option 54: server identifier.

OPT_SUBNET_MASK 🔒

Option 1: subnet mask.

POOL_SIZE 🔒

Number of lease slots; slot i owns ….<POOL_START + i> (all slots must fit into that /24).

POOL_START 🔒

First pool address: <AP_IP network>.<POOL_START> — assumes the /24 declared by super::AP_PREFIX.

SERVER_PORT 🔒

DHCP server port — clients broadcast their requests here.

Functions

build_reply 🔒

Assemble a reply packet; returns the number of bytes used.

parse_client 🔒

Parse and validate a DHCP request; None for anything that is not a well-formed ethernet BOOTREQUEST from a client.

task

DHCP server task: answers client requests on the access-point interface until reboot. Spawned by super::task after link-up.