engine: resources: Add dhcp:server and dhcp:host resources

This adds a new dhcp server resource, as well as a dhcp host resource
used to specify the static mapping between mac address and ip address.
It also adds a simple, pure-golang example dhcp client which might make
testing easier.

The dhcp resource is not meant to be a full-featured dhcp server
replacement, and it might still be useful to use the venerable dhcpd,
however for integrated, pure-golang bootstrapping environments, this
might prove to be very useful.

It can be combined with the tftp resource to build PXE setups with mgmt.

This resource can be extended further to support a dhcp:range directive,
automatic edges, and more!

examples/dhcp_client/.gitignore

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+dhcp_client

examples/dhcp_client/Makefile

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+# Mgmt
+# Copyright (C) 2013-2020+ James Shubin and the project contributors
+# Written by James Shubin <james@shubin.ca> and the project contributors
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+SHELL = /usr/bin/env bash
+
+.PHONY: clean
+.SILENT: clean
+
+all: dhcp_client
+
+dhcp_client: dhcp_client.go
+	go build -o dhcp_client dhcp_client.go
+
+clean:
+	rm -f dhcp_client

examples/dhcp_client/dhcp_client.go

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+// Mgmt
+// Copyright (C) 2013-2020+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"os"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+	"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
+)
+
+const (
+	iface   = "lo" // loopback for local testing
+	address = "127.0.0.1"
+)
+
+func main() {
+	if len(os.Args) < 2 || len(os.Args) > 3 {
+		log.Printf("Usage: %s [port] <mac address>", os.Args[0])
+		return
+	}
+
+	port := string(nclient4.ServerPort) // the default is 67
+	if len(os.Args) >= 3 {
+		port = os.Args[1]
+	}
+	hwAddr := os.Args[len(os.Args)-1] // argv[1]
+
+	hw, err := net.ParseMAC(hwAddr)
+	if err != nil {
+		log.Printf("Invalid mac address: %v", err)
+		return
+	}
+
+	addr := fmt.Sprintf("%s:%s", address, port)
+	log.Printf("Connecting to: %s", addr)
+
+	opts := []nclient4.ClientOpt{}
+	{
+		opt := nclient4.WithHWAddr(hw)
+		opts = append(opts, opt)
+	}
+	{
+		opt := nclient4.WithSummaryLogger()
+		opts = append(opts, opt)
+	}
+	//{
+	//	opt := nclient4.WithDebugLogger()
+	//	opts = append(opts, opt)
+	//}
+
+	//c, err := nclient4.NewWithConn(conn net.PacketConn, ifaceHWAddr net.HardwareAddr, opts...)
+	c, err := nclient4.New(iface, opts...)
+	if err != nil {
+		log.Printf("Error connecting to server: %v", err)
+		return
+	}
+	defer func() {
+		if err := c.Close(); err != nil {
+			log.Printf("Error closing client: %v", err)
+		}
+	}()
+
+	modifiers := []dhcpv4.Modifier{}
+	//{
+	//	mod := dhcpv4.WithYourIP(net.ParseIP(?))
+	//	modifiers = append(modifiers, mod)
+	//}
+	//{
+	//	mod := dhcpv4.WithClientIP(net.ParseIP(?))
+	//	modifiers = append(modifiers, mod)
+	//}
+	// TODO: add modifiers
+
+	log.Printf("Requesting...")
+	ctx := context.Background()                     // TODO: add to ^C handler
+	offer, ack, err := c.Request(ctx, modifiers...) // (offer, ack *dhcpv4.DHCPv4, err error)
+	if err != nil {
+		log.Printf("Error requesting from server: %v", err)
+		return
+	}
+
+	// Show the results of the D-O-R-A exchange.
+	log.Printf("Offer: %+v", offer)
+	log.Printf("Ack: %+v", ack)
+
+	log.Printf("Done!")
+}

examples/lang/dhcp0.mcl

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+$iface = "lo"	# replace with your desired interface like eth0
+
+net $iface {
+	state => "up",
+	addrs => ["192.168.42.1/24",],
+}
+
+dhcp:server ":67" {
+	interface => $iface,		# required for now
+	leasetime => "60s",		# increase this for normal production
+	dns => ["8.8.8.8", "1.1.1.1",],	# pick your own better ones!
+	routers => ["192.168.42.1",],
+
+	Depend => Net[$iface],	# TODO: add autoedges
+}
+
+dhcp:host "hostname1" {
+	mac => "00:11:22:33:44:55",	# replace with your own!
+	ip => "192.168.42.101/24",	# cidr notation is required
+}
+
+dhcp:host "hostname2" {
+	mac => "ba:98:76:54:32:11",			# replace with your own!
+	ip => "192.168.42.102/24",
+	nbp => "tftp://192.168.42.1/pxelinux.0",	# for bios clients
+}