From d63c40af3e8e4c2f70859aeae443112489de80eb Mon Sep 17 00:00:00 2001
From: Martin Stein <martin.stein@genode-labs.com>
Date: Thu, 14 Sep 2017 16:32:29 +0200
Subject: [PATCH] dhcp: extend options utilities

Provide utilities for appending new options to an existing DHCP packet
and a utility for finding existing options that returns a typed option
object. Remove old version that return untyped options.

Ref #2490
---
 repos/os/include/net/dhcp.h           | 304 +++++++++++++++++++-------
 repos/os/src/server/nic_bridge/nic.cc |  15 +-
 2 files changed, 234 insertions(+), 85 deletions(-)

diff --git a/repos/os/include/net/dhcp.h b/repos/os/include/net/dhcp.h
index c370561092..ba2cdbef7d 100644
--- a/repos/os/include/net/dhcp.h
+++ b/repos/os/include/net/dhcp.h
@@ -17,6 +17,7 @@
 /* Genode */
 #include <base/exception.h>
 #include <base/stdint.h>
+#include <util/construct_at.h>
 
 #include <util/endian.h>
 #include <net/ethernet.h>
@@ -65,7 +66,8 @@ class Net::Dhcp_packet
 {
 	public:
 
-		class No_dhcp_packet : Genode::Exception {};
+		struct No_dhcp_packet   : Genode::Exception { };
+		struct Option_not_found : Genode::Exception { };
 
 	private:
 
@@ -92,32 +94,6 @@ class Net::Dhcp_packet
 
 		enum class Htype : Genode::uint8_t { ETH = 1 };
 
-		/**
-		 * This class represents the data layout of an DHCP option.
-		 */
-		class Option
-		{
-			private:
-
-				Genode::uint8_t _code;
-				Genode::uint8_t _len;
-				Genode::uint8_t _value[0];
-
-			public:
-
-				Option() {}
-
-				Genode::uint8_t code()   { return _code;  }
-				Genode::size_t  length() { return _len;   }
-				void*           value()  { return _value; }
-
-				/**
-				 * Placement new.
-				 */
-				void * operator new(__SIZE_TYPE__, void* addr) { return addr; }
-		} __attribute__((packed));
-
-
 		enum Opcode {
 			REQUEST = 1,
 			REPLY   = 2,
@@ -129,39 +105,6 @@ class Net::Dhcp_packet
 			BOOTPC = 68
 		};
 
-		enum Option_type {
-			REQ_IP_ADDR    = 50,
-			IP_LEASE_TIME  = 51,
-			OPT_OVERLOAD   = 52,
-			MSG_TYPE       = 53,
-			SRV_ID         = 54,
-			REQ_PARAMETER  = 55,
-			MESSAGE        = 56,
-			MAX_MSG_SZ     = 57,
-			RENEWAL        = 58,
-			REBINDING      = 59,
-			VENDOR         = 60,
-			CLI_ID         = 61,
-			TFTP_SRV_NAME  = 66,
-			BOOT_FILE      = 67,
-			END            = 255
-		};
-
-		enum Message_type {
-			DHCP_DISCOVER  = 1,
-			DHCP_OFFER     = 2,
-			DHCP_REQUEST   = 3,
-			DHCP_DECLINE   = 4,
-			DHCP_ACK       = 5,
-			DHCP_NAK       = 6,
-			DHCP_RELEASE   = 7,
-			DHCP_INFORM    = 8
-		};
-
-
-		/*****************
-		 ** Constructor **
-		 *****************/
 
 		Dhcp_packet(Genode::size_t size) {
 			/* dhcp packet needs to fit in */
@@ -170,6 +113,228 @@ class Net::Dhcp_packet
 		}
 
 
+		/*******************************
+		 ** Utilities for the options **
+		 *******************************/
+
+		/**
+		 * Header of a DHCP option or DHCP option without a payload
+		 */
+		class Option
+		{
+			private:
+
+				Genode::uint8_t _code;
+				Genode::uint8_t _len;
+				Genode::uint8_t _value[0];
+
+			public:
+
+				enum class Code : Genode::uint8_t {
+					INVALID        = 0,
+					SUBNET_MASK    = 1,
+					ROUTER         = 3,
+					DNS_SERVER     = 6,
+					BROADCAST_ADDR = 28,
+					REQ_IP_ADDR    = 50,
+					IP_LEASE_TIME  = 51,
+					OPT_OVERLOAD   = 52,
+					MSG_TYPE       = 53,
+					SERVER         = 54,
+					REQ_PARAMETER  = 55,
+					MESSAGE        = 56,
+					MAX_MSG_SZ     = 57,
+					RENEWAL        = 58,
+					REBINDING      = 59,
+					VENDOR         = 60,
+					CLI_ID         = 61,
+					TFTP_SRV_NAME  = 66,
+					BOOT_FILE      = 67,
+					END            = 255,
+				};
+
+				Option(Code code, Genode::uint8_t len)
+				: _code((Genode::uint8_t)code), _len(len) { }
+
+				Option() { }
+
+				Code             code() const { return (Code)_code; }
+				Genode::uint8_t len()   const { return _len; }
+
+
+				/*********
+				 ** log **
+				 *********/
+
+				void print(Genode::Output &output) const;
+
+		} __attribute__((packed));
+
+
+		/**
+		 * DHCP option that contains a payload of type T
+		 */
+		template <typename T>
+		class Option_tpl : public Option
+		{
+			protected:
+
+				T _value;
+
+			public:
+
+				Option_tpl(Code code, T value)
+				: Option(code, sizeof(T)), _value(value) { }
+
+		} __attribute__((packed));
+
+
+		/**
+		 * DHCP option that specifies the IP packet lease time in seconds
+		 */
+		struct Ip_lease_time : Option_tpl<Genode::uint32_t>
+		{
+			static constexpr Code CODE = Code::IP_LEASE_TIME;
+
+			Ip_lease_time(Genode::uint32_t time)
+			: Option_tpl(CODE, host_to_big_endian(time)) { }
+		};
+
+		enum class Message_type : Genode::uint8_t {
+			DISCOVER  = 1,
+			OFFER     = 2,
+			REQUEST   = 3,
+			DECLINE   = 4,
+			ACK       = 5,
+			NAK       = 6,
+			RELEASE   = 7,
+			INFORM    = 8
+		};
+
+		/**
+		 * DHCP option that specifies the DHCP message type
+		 */
+		struct Message_type_option : Option_tpl<Genode::uint8_t>
+		{
+			static constexpr Code CODE = Code::MSG_TYPE;
+
+			Message_type_option(Message_type value)
+			: Option_tpl(CODE, (Genode::uint8_t)value) { }
+
+			Message_type value() const { return (Message_type)_value; }
+		};
+
+
+		/**
+		 * DHCP options that have only one IPv4 address as payload
+		 */
+		template <Option::Code _CODE>
+		struct Ipv4_option : Option_tpl<Genode::uint32_t>
+		{
+			static constexpr Code CODE = _CODE;
+
+			Ipv4_option(Ipv4_address value)
+			: Option_tpl(CODE, value.to_uint32_big_endian()) { }
+
+			Ipv4_address value() const {
+				return Ipv4_address::from_uint32_big_endian(_value); }
+		};
+
+		using Dns_server_ipv4 = Ipv4_option<Option::Code::DNS_SERVER>;
+		using Subnet_mask     = Ipv4_option<Option::Code::SUBNET_MASK>;
+		using Broadcast_addr  = Ipv4_option<Option::Code::BROADCAST_ADDR>;
+		using Router_ipv4     = Ipv4_option<Option::Code::ROUTER>;
+		using Server_ipv4     = Ipv4_option<Option::Code::SERVER>;
+
+		/**
+		 * DHCP option that marks the end of an options field
+		 */
+		struct Options_end : Option
+		{
+			static constexpr Code CODE = Code::END;
+
+			Options_end() : Option(CODE, 0) { }
+		};
+
+
+		/**
+		 * Utility to append individual options to an existing DHCP packet
+		 *
+		 * \param SIZE_GUARD  guard that may limit the options list size
+		 *
+		 * Overwrites existing options if any!
+		 */
+		template <typename SIZE_GUARD>
+		class Options_aggregator
+		{
+			private:
+
+				Genode::addr_t  _base;
+				SIZE_GUARD     &_size_guard;
+
+			public:
+
+				Options_aggregator(Dhcp_packet &packet,
+				                   SIZE_GUARD  &size_guard)
+				:
+					_base((Genode::addr_t)packet.opts()),
+					_size_guard(size_guard)
+				{ }
+
+				template <typename OPTION, typename... ARGS>
+				void append_option(ARGS &&... args)
+				{
+					_size_guard.add(sizeof(OPTION));
+					Genode::construct_at<OPTION>((void *)_base,
+					                             static_cast<ARGS &&>(args)...);
+					_base += sizeof(OPTION);
+				}
+		};
+
+
+		/*
+		 * Call 'functor' of type 'FUNC' for each option (except END options)
+		 */
+		template <typename FUNC>
+		void for_each_option(FUNC && functor) const
+		{
+			for (unsigned i = 0; ; ) {
+				Option &opt = *(Option*)&_opts[i];
+				if (opt.code() == Option::Code::INVALID ||
+				    opt.code() == Option::Code::END)
+				{
+					return;
+				}
+				functor(opt);
+				i += 2 + opt.len();
+			}
+		}
+
+
+		/*
+		 * Find and return option of given type 'T'
+		 *
+		 * \throw Option_not_found
+		 */
+		template <typename T>
+		T &option()
+		{
+			void *ptr = &_opts;
+			while (true) {
+				Option &opt = *Genode::construct_at<Option>(ptr);
+				if (opt.code() == Option::Code::INVALID ||
+				    opt.code() == Option::Code::END)
+				{
+					throw Option_not_found();
+				}
+				if (opt.code() == T::CODE) {
+					return *reinterpret_cast<T *>(ptr);
+				}
+				ptr = (void *)((Genode::addr_t)ptr + sizeof(opt) + opt.len());
+			}
+		}
+
+
 		/***************
 		 ** Accessors **
 		 ***************/
@@ -208,25 +373,6 @@ class Net::Dhcp_packet
 		void client_mac(Mac_address v) { v.copy(&_chaddr); }
 
 
-		/**********************
-		 ** Option utilities **
-		 **********************/
-
-		Option *option(Option_type op)
-		{
-			void *ptr = &_opts;
-			while (true) {
-				Option *ext = new (ptr) Option();
-				if (ext->code() == op)
-					return ext;
-				if (ext->code() == END || ext->code() == 0)
-					break;
-				ptr = ext + ext->length();
-			}
-			return 0;
-		}
-
-
 		/*************************
 		 ** Convenience methods **
 		 *************************/
diff --git a/repos/os/src/server/nic_bridge/nic.cc b/repos/os/src/server/nic_bridge/nic.cc
index 5d99fde5b1..5f74cd705a 100644
--- a/repos/os/src/server/nic_bridge/nic.cc
+++ b/repos/os/src/server/nic_bridge/nic.cc
@@ -82,14 +82,16 @@ bool Net::Nic::handle_ip(Ethernet_frame *eth, Genode::size_t size) {
 
 			/* check for DHCP ACKs containing new client ips */
 			if (dhcp->op() == Dhcp_packet::REPLY) {
-				Dhcp_packet::Option *ext = dhcp->option(Dhcp_packet::MSG_TYPE);
-				if (ext) {
+
+				try {
+					Dhcp_packet::Message_type const msg_type =
+						dhcp->option<Dhcp_packet::Message_type_option>().value();
+
 					/*
-					 * extract the IP address and set it in the
-					 * client's session-component
+					 * Extract the IP address and set it in the client's
+					 * session-component
 					 */
-					Genode::uint8_t *msg_type =	(Genode::uint8_t*) ext->value();
-					if (*msg_type == Dhcp_packet::DHCP_ACK) {
+					if (msg_type == Dhcp_packet::Message_type::ACK) {
 						Mac_address_node *node =
 							vlan().mac_tree.first();
 						if (node)
@@ -98,6 +100,7 @@ bool Net::Nic::handle_ip(Ethernet_frame *eth, Genode::size_t size) {
 							node->component().set_ipv4_address(dhcp->yiaddr());
 					}
 				}
+				catch (Dhcp_packet::Option_not_found) { }
 			}
 		}
 	}