Add RFC4039 rapid commit support.

CHANGELOG

+version 2.80
+	Add support for RFC 4039 DHCP rapid commit. Thanks to Ashram Method
+	for the initial patch and motivation.
+
+
 version 2.79
 	Fix parsing of CNAME arguments, which are confused by extra spaces.
 	Thanks to Diego Aguirre for spotting the bug.

dnsmasq.conf.example

@@ -547,6 +547,14 @@
 # http://www.isc.org/files/auth.html
 #dhcp-authoritative
 
+# Set the DHCP server to enable DHCPv4 Rapid Commit Option per RFC 4039.
+# In this mode it will respond to a DHCPDISCOVER message including a Rapid Commit
+# option with a DHCPACK including a Rapid Commit option and fully committed address
+# and configuration information. This must only be enabled if either the server is 
+# the only server for the subnet, or multiple servers are present and they each
+# commit a binding for all clients.
+#dhcp-rapid-commit
+
 # Run an executable when a DHCP lease is created or destroyed.
 # The arguments sent to the script are "add" or "del",
 # then the MAC address, the IP address and finally the hostname

man/dnsmasq.8

@@ -1452,6 +1452,13 @@ allows dnsmasq to rebuild its lease database without each client needing to
 reacquire a lease, if the database is lost. For DHCPv6 it sets the
 priority in replies to 255 (the maximum) instead of 0 (the minimum).
 .TP
+.B --dhcp-rapid-commit
+Enable DHCPv4 Rapid Commit Option specified in RFC 4039. When enabled, dnsmasq
+will respond to a DHCPDISCOVER message including a Rapid Commit
+option with a DHCPACK including a Rapid Commit option and fully committed
+address and configuration information. Should only be enabled if either the
+server is  the only server for the subnet, or multiple servers are present and they each commit a binding for all clients.
+.TP
 .B --dhcp-alternate-port[=<server port>[,<client port>]]
 (IPv4 only) Change the ports used for DHCP from the default. If this option is
 given alone, without arguments, it changes the ports used for DHCP

src/dhcp-common.c

@@ -556,6 +556,7 @@ static const struct opttab_t {
   { "nntp-server", 71, OT_ADDR_LIST }, 
   { "irc-server", 74, OT_ADDR_LIST }, 
   { "user-class", 77, 0 },
+  { "rapid-commit", 80, 0 },
   { "FQDN", 81, OT_INTERNAL },
   { "agent-id", 82, OT_INTERNAL },
   { "client-arch", 93, 2 | OT_DEC },

src/dhcp-protocol.h

@@ -54,6 +54,7 @@
 #define OPTION_SNAME             66
 #define OPTION_FILENAME          67
 #define OPTION_USER_CLASS        77
+#define OPTION_RAPID_COMMIT      80
 #define OPTION_CLIENT_FQDN       81
 #define OPTION_AGENT_ID          82
 #define OPTION_ARCH              93

src/dnsmasq.h

@@ -250,7 +250,8 @@ struct event_desc {
 #define OPT_MAC_B64        54
 #define OPT_MAC_HEX        55
 #define OPT_TFTP_APREF_MAC 56
-#define OPT_LAST           57
+#define OPT_RAPID_COMMIT   57
+#define OPT_LAST           58
 
 /* extra flags for my_syslog, we use a couple of facilities since they are known 
    not to occupy the same bits as priorities, no matter how syslog.h is set up. */

src/option.c

@@ -160,6 +160,7 @@ struct myoption {
 #define LOPT_DHCPTTL       348
 #define LOPT_TFTP_MTU      349
 #define LOPT_REPLY_DELAY   350
+#define LOPT_RAPID_COMMIT  351
  
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -325,6 +326,7 @@ static const struct myoption opts[] =
     { "script-arp", 0, 0, LOPT_SCRIPT_ARP },
     { "dhcp-ttl", 1, 0 , LOPT_DHCPTTL },
     { "dhcp-reply-delay", 1, 0, LOPT_REPLY_DELAY },
+    { "dhcp-rapid-commit", 0, 0, LOPT_RAPID_COMMIT },
     { NULL, 0, 0, 0 }
   };
 
@@ -497,6 +499,7 @@ static struct {
   { LOPT_IGNORE_ADDR, ARG_DUP, "<ipaddr>", gettext_noop("Ignore DNS responses containing ipaddr."), NULL }, 
   { LOPT_DHCPTTL, ARG_ONE, "<ttl>", gettext_noop("Set TTL in DNS responses with DHCP-derived addresses."), NULL }, 
   { LOPT_REPLY_DELAY, ARG_ONE, "<integer>", gettext_noop("Delay DHCP replies for at least number of seconds."), NULL },
+  { LOPT_RAPID_COMMIT, OPT_RAPID_COMMIT, NULL, gettext_noop("Enables DHCPv4 Rapid Commit option."), NULL },
   { 0, 0, NULL, NULL, NULL }
 }; 
 

src/rfc2131.c

@@ -75,7 +75,7 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
   struct dhcp_vendor *vendor;
   struct dhcp_mac *mac;
   struct dhcp_netid_list *id_list;
-  int clid_len = 0, ignore = 0, do_classes = 0, selecting = 0, pxearch = -1;
+  int clid_len = 0, ignore = 0, do_classes = 0, rapid_commit = 0, selecting = 0, pxearch = -1;
   struct dhcp_packet *mess = (struct dhcp_packet *)daemon->dhcp_packet.iov_base;
   unsigned char *end = (unsigned char *)(mess + 1); 
   unsigned char *real_end = (unsigned char *)(mess + 1); 
@@ -1073,6 +1073,13 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
 
       log_tags(tagif_netid, ntohl(mess->xid));
       apply_delay(mess->xid, recvtime, tagif_netid);
+
+      if (option_bool(OPT_RAPID_COMMIT) && option_find(mess, sz, OPTION_RAPID_COMMIT, 0))
+	{
+	  rapid_commit = 1;
+	  goto rapid_commit;
+	}
+      
       log_packet("DHCPOFFER" , &mess->yiaddr, emac, emac_len, iface_name, NULL, NULL, mess->xid);
       
       time = calc_time(context, config, option_find(mess, sz, OPTION_LEASE_TIME, 4));
@@ -1085,7 +1092,8 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
 		 netid, subnet_addr, fqdn_flags, borken_opt, pxearch, uuid, vendor_class_len, now, time, fuzz);
       
       return dhcp_packet_size(mess, agent_id, real_end);
-      
+	
+
     case DHCPREQUEST:
       if (ignore || have_config(config, CONFIG_DISABLE))
 	return 0;
@@ -1183,9 +1191,10 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
 	  fuzz = rand16();
 	  mess->yiaddr = mess->ciaddr;
 	}
-      
+
       log_packet("DHCPREQUEST", &mess->yiaddr, emac, emac_len, iface_name, NULL, NULL, mess->xid);
- 
+      
+    rapid_commit:
       if (!message)
 	{
 	  struct dhcp_config *addr_config;
@@ -1256,7 +1265,11 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
 
       if (message)
 	{
-	  log_packet("DHCPNAK", &mess->yiaddr, emac, emac_len, iface_name, NULL, message, mess->xid);
+	  log_packet(rapid_commit ? "NOANSWER" : "DHCPNAK", &mess->yiaddr, emac, emac_len, iface_name, NULL, message, mess->xid);
+
+	  /* rapid commit case: lease allocate failed but don't send DHCPNAK */
+	  if (rapid_commit)
+	    return 0;
 	  
 	  mess->yiaddr.s_addr = 0;
 	  clear_packet(mess, end);
@@ -1414,12 +1427,14 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
 	    override = lease->override;
 
 	  log_packet("DHCPACK", &mess->yiaddr, emac, emac_len, iface_name, hostname, NULL, mess->xid);  
-	  
+
 	  clear_packet(mess, end);
 	  option_put(mess, end, OPTION_MESSAGE_TYPE, 1, DHCPACK);
 	  option_put(mess, end, OPTION_SERVER_IDENTIFIER, INADDRSZ, ntohl(server_id(context, override, fallback).s_addr));
 	  option_put(mess, end, OPTION_LEASE_TIME, 4, time);
-	  do_options(context, mess, end, req_options, hostname, get_domain(mess->yiaddr), 
+	  if (rapid_commit)
+	     option_put(mess, end, OPTION_RAPID_COMMIT, 0, 0);
+	   do_options(context, mess, end, req_options, hostname, get_domain(mess->yiaddr), 
 		     netid, subnet_addr, fqdn_flags, borken_opt, pxearch, uuid, vendor_class_len, now, time, fuzz);
 	}