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HTTP server example and DHCP Server rewrite (#38)

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* improvements to dhcpv4 server

* begin adding examples/httpserver

* add better VLAN tagging methods

* pcap: add error printing; fix bug in CRC

* ipv4: ToS and Flags construction and flag manipulation improvements

* add dhcp interception to httptap and improve httpserver example
This commit is contained in:
Pat Whittingslow
2026-02-18 20:48:30 +01:00
committed by GitHub
parent fae4552ddb
commit bf2d07d9f0
12 changed files with 1403 additions and 48 deletions
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dhcpv4/server.go
+145 -35
View File
@@ -11,15 +11,33 @@ import (
)
type Server struct {
connID uint64
nextAddr netip.Addr
prefix netip.Prefix
hosts map[[36]byte]serverEntry
vld lneto.Validator
pending int
port uint16
siaddr [4]byte
gwaddr [4]byte
connID uint64
nextAddr netip.Addr
prefix netip.Prefix
hosts map[[36]byte]serverEntry
vld lneto.Validator
pending int
leaseSeconds uint32
port uint16
siaddr [4]byte
gwaddr [4]byte
dns [4]byte
}
// ServerConfig contains configuration parameters for [Server.Configure].
type ServerConfig struct {
// ServerAddr is the DHCP server's own IPv4 address.
ServerAddr [4]byte
// Gateway advertised to clients as default router. Zero value omits the option.
Gateway [4]byte
// DNS server address advertised to clients. Zero value omits the option.
DNS [4]byte
// Subnet defines the network prefix for address allocation and subnet mask responses.
Subnet netip.Prefix
// LeaseSeconds is the lease duration. Zero defaults to 3600.
LeaseSeconds uint32
// Port is the server listening port. Zero defaults to DefaultServerPort.
Port uint16
}
type serverEntry struct {
@@ -35,30 +53,53 @@ type serverEntry struct {
// - Init: Server received discover, pending Offer sent out.
// - Selecting: Server sent out offer, request not received.
// - Requesting: Request received, pending Ack sent out.
// - Bound: Request sent out, no more pending data to be sent.
// - Bound: Ack sent out, no more pending data to be sent.
state ClientState
}
func (sv *Server) Reset(serverAddr [4]byte, port uint16) {
*sv = Server{
connID: sv.connID + 1,
siaddr: serverAddr,
port: port,
hosts: sv.hosts,
nextAddr: netip.AddrFrom4(serverAddr),
// Configure resets and configures the server with the given configuration.
// The connection ID is incremented on each call to invalidate existing connections.
// The hosts map is reused across calls to avoid reallocation.
func (sv *Server) Configure(cfg ServerConfig) error {
svAddr := netip.AddrFrom4(cfg.ServerAddr)
if !cfg.Subnet.IsValid() {
return errors.New("dhcpv4 server: invalid subnet")
} else if !cfg.Subnet.Contains(svAddr) {
return errors.New("dhcpv4 server: server address outside subnet")
}
if sv.hosts == nil {
sv.hosts = make(map[[36]byte]serverEntry)
port := cfg.Port
if port == 0 {
port = DefaultServerPort
}
lease := cfg.LeaseSeconds
if lease == 0 {
lease = 3600
}
hosts := sv.hosts
if hosts == nil {
hosts = make(map[[36]byte]serverEntry)
} else {
for k := range sv.hosts {
delete(sv.hosts, k)
for k := range hosts {
delete(hosts, k)
}
}
*sv = Server{
connID: sv.connID + 1,
siaddr: cfg.ServerAddr,
gwaddr: cfg.Gateway,
dns: cfg.DNS,
prefix: cfg.Subnet,
port: port,
leaseSeconds: lease,
nextAddr: svAddr,
hosts: hosts,
}
return nil
}
func (sv *Server) ConnectionID() *uint64 { return &sv.connID }
func (sv *Server) Protocol() uint64 { return uint64(lneto.IPProtoUDP) }
func (sv *Server) Port() uint16 { return sv.port }
func (sv *Server) LocalPort() uint16 { return sv.port }
func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
isIPLayer := frameOffset >= 28
@@ -103,6 +144,9 @@ func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
}
return nil
})
if err != nil {
return err
}
var clientIDRaw [36]byte
var client serverEntry
var clientExists bool
@@ -115,16 +159,17 @@ func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
switch msgType {
case MsgDiscover:
if clientExists {
err = errors.New("DHCP Discover on initialized client")
break
if clientExists && (client.state == StateInit || client.state == StateRequesting) {
sv.pending-- // Cancel unfulfilled pending response.
}
if len(reqAddr) == 4 {
println("requested", reqAddr[0], reqAddr[1], reqAddr[2], reqAddr[3])
if !clientExists {
addr, ok := sv.allocAddr(reqAddr)
if !ok {
return errors.New("dhcpv4 server: address pool exhausted")
}
client.addr = addr
}
sv.nextAddr = sv.nextAddr.Next()
copy(client.requestlist[:], reqlist)
client.addr = sv.nextAddr.As4()
client.state = StateInit
client.hostname = string(hostname)
client.xid = dfrm.XID()
@@ -137,7 +182,7 @@ func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
case MsgRequest:
if !clientExists {
err = errors.New("request for non existing client?")
err = errors.New("request for non existing client")
} else if dfrm.XID() != client.xid {
err = errors.New("unexpected XID for client")
} else if client.state != StateSelecting && client.state != StateRequesting {
@@ -146,11 +191,22 @@ func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
if err != nil {
break
}
client.state = StateRequesting
sv.pending++
if client.state == StateSelecting {
client.state = StateRequesting
sv.pending++
}
case MsgRelease:
if clientExists {
if client.state == StateInit || client.state == StateRequesting {
sv.pending--
}
delete(sv.hosts, clientIDRaw)
return nil
}
default:
err = errors.New("unhandled message type")
err = fmt.Errorf("unhandled message type %s", msgType.String())
}
if err != nil {
return fmt.Errorf("msgtype=%s client=%+v: %w", msgType.String(), client, err)
@@ -169,7 +225,7 @@ func (sv *Server) Encapsulate(carrierData []byte, offsetToIP, offsetToFrame int)
return 0, errOptionNotFit
}
if sv.pending == 0 {
return 0, nil // No pending outgoing frames.a
return 0, nil // No pending outgoing frames.
}
var client serverEntry
@@ -205,6 +261,26 @@ func (sv *Server) Encapsulate(carrierData []byte, offsetToIP, offsetToFrame int)
n, _ = EncodeOption(optBuf[nopt:], OptRouter, sv.gwaddr[:]...)
nopt += n
}
if sv.prefix.IsValid() {
bits := uint(sv.prefix.Bits())
mask := ^uint32(0) << (32 - bits)
var maskBuf [4]byte
binary.BigEndian.PutUint32(maskBuf[:], mask)
n, _ = EncodeOption(optBuf[nopt:], OptSubnetMask, maskBuf[:]...)
nopt += n
}
if sv.dns != [4]byte{} {
n, _ = EncodeOption(optBuf[nopt:], OptDNSServers, sv.dns[:]...)
nopt += n
}
if sv.leaseSeconds > 0 {
n, _ = EncodeOption32(optBuf[nopt:], OptIPAddressLeaseTime, sv.leaseSeconds)
nopt += n
n, _ = EncodeOption32(optBuf[nopt:], OptRenewTimeValue, sv.leaseSeconds/2)
nopt += n
n, _ = EncodeOption32(optBuf[nopt:], OptRebindingTimeValue, sv.leaseSeconds*7/8)
nopt += n
}
optBuf[nopt] = byte(OptEnd)
nopt++
@@ -234,6 +310,40 @@ func (sv *Server) Encapsulate(carrierData []byte, offsetToIP, offsetToFrame int)
return OptionsOffset + nopt, nil
}
// allocAddr allocates the next available address from the pool.
// If reqAddr is a valid 4-byte address within the subnet and not already assigned,
// it is preferred. Returns false if the pool is exhausted.
func (sv *Server) allocAddr(reqAddr []byte) ([4]byte, bool) {
if len(reqAddr) == 4 {
candidate := netip.AddrFrom4([4]byte(reqAddr))
if sv.prefix.Contains(candidate) && candidate.As4() != sv.siaddr && !sv.isAddrAssigned(candidate) {
return candidate.As4(), true
}
}
sv.nextAddr = sv.nextAddr.Next()
if !sv.prefix.Contains(sv.nextAddr) {
return [4]byte{}, false
}
// Reject broadcast address (all host bits set).
a := sv.nextAddr.As4()
hostBits := uint(32 - sv.prefix.Bits())
hostMask := ^uint32(0) >> (32 - hostBits)
if binary.BigEndian.Uint32(a[:])&hostMask == hostMask {
return [4]byte{}, false
}
return a, true
}
func (sv *Server) isAddrAssigned(addr netip.Addr) bool {
a4 := addr.As4()
for _, v := range sv.hosts {
if v.addr == a4 {
return true
}
}
return false
}
func (sv *Server) getClient(clientID [36]byte) (serverEntry, bool) {
entry, ok := sv.hosts[clientID]
return entry, ok
@@ -257,4 +367,4 @@ func getSrcIPPort(ipCarrier []byte) (srcaddr []byte, port uint16, err error) {
}
port = binary.BigEndian.Uint16(ipCarrier[off:]) // TCP and UDP share same port offsets.
return srcaddr, port, nil
}
}