include/boost/corosio/ipv6_address.hpp

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ipv6_address.hpp

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1		//
2		// Copyright (c) 2026 Vinnie Falco (vinnie.falco@gmail.com)
3		// Copyright (c) 2026 Michael Vandeberg
4		//
5		// Distributed under the Boost Software License, Version 1.0. (See accompanying
6		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7		//
8		// Official repository: https://github.com/cppalliance/corosio
9		//
10
11		#ifndef BOOST_COROSIO_IPV6_ADDRESS_HPP
12		#define BOOST_COROSIO_IPV6_ADDRESS_HPP
13
14		#include <boost/corosio/detail/config.hpp>
15		#include <boost/corosio/ipv4_address.hpp>
16
17		#include <boost/capy/io_result.hpp>
18
19		#include <array>
20		#include <compare>
21		#include <cstdint>
22		#include <functional>
23		#include <iosfwd>
24		#include <string>
25		#include <string_view>
26		#include <system_error>
27
28		namespace boost::corosio {
29
30		/** An IP version 6 style address.
31
32		Objects of this type are used to construct,
33		parse, and manipulate IP version 6 addresses.
34
35		@par BNF
36		@code
37		IPv6address = 6( h16 ":" ) ls32
38		/ "::" 5( h16 ":" ) ls32
39		/ [ h16 ] "::" 4( h16 ":" ) ls32
40		/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
41		/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
42		/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
43		/ [ *4( h16 ":" ) h16 ] "::" ls32
44		/ [ *5( h16 ":" ) h16 ] "::" h16
45		/ [ *6( h16 ":" ) h16 ] "::"
46
47		ls32 = ( h16 ":" h16 ) / IPv4address
48		; least-significant 32 bits of address
49
50		h16 = 1*4HEXDIG
51		; 16 bits of address represented in hexadecimal
52
53		IPv6addrz = IPv6address "%" ZoneID
54		; rfc6874: an address qualified by its zone
55		@endcode
56
57		The zone accepts a strict decimal interface index on every
58		platform; where the platform names interfaces (POSIX), an
59		interface name maps through `if_nametoindex`. An unknown name
60		or malformed index is a parse error, never a silent zone 0.
61		Formatting always emits the numeric form (`%2`).
62
63		@par Specification
64		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291"
65		>IP Version 6 Addressing Architecture (rfc4291)</a>
66		@li <a href="https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.2"
67		>3.2.2. Host (rfc3986)</a>
68
69		@see
70		@ref ipv4_address,
71		@ref make_ipv6_address.
72		*/
73		class BOOST_COROSIO_DECL ipv6_address
74		{
75		std::array<unsigned char, 16> addr_{};
76		std::uint32_t scope_id_ = 0;
77
78		public:
79		/** The number of characters in the longest possible IPv6 string.
80
81		The longest address body is the IPv4-mapped form
82		`ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255` (45
83		characters), and a numeric zone suffix adds up to eleven
84		more (`%4294967295`), for a worst case of 56; the constant
85		carries a little slack.
86		*/
87		static constexpr std::size_t max_str_len = 60;
88
89		/** The type used to represent an address as an array of bytes.
90
91		Octets are stored in network byte order.
92		*/
93		using bytes_type = std::array<unsigned char, 16>;
94
95		/** Default constructor.
96
97		Constructs the unspecified address (::).
98
99		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.2"
100		>2.5.2. The Unspecified Address</a>
101
102		@see
103		@ref is_unspecified
104		*/
105	160374x	ipv6_address() = default;
106
107		/** Copy constructor.
108		*/
109		ipv6_address(ipv6_address const&) = default;
110
111		/** Copy assignment.
112
113		@return A reference to this object.
114		*/
115		ipv6_address& operator=(ipv6_address const&) = default;
116
117		/** Construct from an array of bytes.
118
119		This function constructs an address
120		from the array in `bytes`, which is
121		interpreted in big-endian.
122
123		@param bytes The value to construct from.
124		@param scope_id The zone the address belongs to, as an
125		interface index; 0 means unscoped.
126		*/
127		explicit ipv6_address(
128		bytes_type const& bytes, std::uint32_t scope_id = 0) noexcept;
129
130		/** Return the zone the address belongs to.
131
132		Link-local addresses (`fe80::/10`) are unique only per
133		network link, so the address bits alone do not identify a
134		destination; the zone — an interface index, written with a
135		`%` suffix in text form — disambiguates. For global
136		addresses the zone is 0 and has no meaning.
137
138		@return The zone as an interface index; 0 if unscoped.
139
140		@par Specification
141		@li <a href="https://datatracker.ietf.org/doc/html/rfc4007"
142		>IPv6 Scoped Address Architecture (rfc4007)</a>
143		*/
144	177x	std::uint32_t scope_id() const noexcept
145		{
146	177x	return scope_id_;
147		}
148
149		/** Construct from an IPv4 address.
150
151		This function constructs an IPv6 address
152		from the IPv4 address `addr`. The resulting
153		address is an IPv4-Mapped IPv6 Address.
154
155		@param addr The address to construct from.
156
157		@par Specification
158		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2"
159		>2.5.5.2. IPv4-Mapped IPv6 Address (rfc4291)</a>
160		*/
161		explicit ipv6_address(ipv4_address const& addr) noexcept;
162
163		/** Construct from a string.
164
165		This function constructs an address from
166		the string `s`, which must contain a valid
167		IPv6 address string or else an exception
168		is thrown.
169
170		@par Exception Safety
171		Strong guarantee.
172
173		@throws std::system_error `errc::invalid_argument` if the input
174		failed to parse correctly.
175
176		@note For a non-throwing parse function,
177		use @ref make_ipv6_address.
178
179		@param s The string to parse.
180
181		@par Specification
182		@li <a href="https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.2"
183		>3.2.2. Host (rfc3986)</a>
184
185		@see
186		@ref make_ipv6_address.
187		*/
188		explicit ipv6_address(std::string_view s);
189
190		/** Return the address as bytes, in network byte order.
191
192		The 16 bytes cannot carry the zone: for a scoped address
193		the result identifies the value only together with
194		@ref scope_id.
195
196		@return The address as an array of bytes.
197		*/
198	261x	bytes_type to_bytes() const noexcept
199		{
200	261x	return addr_;
201		}
202
203		/** Return the address as a string.
204
205		The returned string does not
206		contain surrounding square brackets.
207
208		@par Example
209		@par !example to_string
210
211		@return The address as a string.
212
213		@par Specification
214		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.2">
215		2.2. Text Representation of Addresses (rfc4291)</a>
216		*/
217		std::string to_string() const;
218
219		/** Write a string representing the address to a buffer.
220
221		The resulting buffer is not null-terminated.
222
223		@throws std::length_error `dest_size < ipv6_address::max_str_len`
224
225		@param dest The buffer in which to write,
226		which must have at least `dest_size` space.
227
228		@param dest_size The size of the output buffer.
229
230		@return The formatted string view.
231		*/
232		std::string_view to_buffer(char* dest, std::size_t dest_size) const;
233
234		/** Return true if the address is unspecified.
235
236		The address 0:0:0:0:0:0:0:0 is called the
237		unspecified address. It indicates the
238		absence of an address.
239
240		@return `true` if the address is unspecified.
241
242		@par Specification
243		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.2">
244		2.5.2. The Unspecified Address (rfc4291)</a>
245		*/
246		bool is_unspecified() const noexcept;
247
248		/** Return true if the address is a loopback address.
249
250		The unicast address 0:0:0:0:0:0:0:1 is called
251		the loopback address. It may be used by a node
252		to send an IPv6 packet to itself.
253
254		@return `true` if the address is a loopback address.
255
256		@par Specification
257		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.3">
258		2.5.3. The Loopback Address (rfc4291)</a>
259		*/
260		bool is_loopback() const noexcept;
261
262		/** Return true if the address is a mapped IPv4 address.
263
264		This address type is used to represent the
265		addresses of IPv4 nodes as IPv6 addresses.
266
267		@return `true` if the address is a mapped IPv4 address.
268
269		@par Specification
270		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2">
271		2.5.5.2. IPv4-Mapped IPv6 Address (rfc4291)</a>
272		*/
273		bool is_v4_mapped() const noexcept;
274
275		/** Convert a v4-mapped address to the IPv4 address it maps.
276
277		This is the inverse of the mapping constructor
278		`ipv6_address(ipv4_address const&)`: it extracts the low
279		32 bits of an IPv4-Mapped IPv6 Address (`::ffff:a.b.c.d`)
280		as an `ipv4_address`.
281
282		@throws std::system_error `errc::address_family_not_supported`
283		if the address is not v4-mapped.
284
285		@return The mapped IPv4 address.
286
287		@par Specification
288		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2">
289		2.5.5.2. IPv4-Mapped IPv6 Address (rfc4291)</a>
290
291		@see
292		@ref is_v4_mapped.
293		*/
294		ipv4_address to_v4() const;
295
296		/** Return true if the address is a multicast address.
297
298		IPv6 multicast addresses have the prefix ff00::/8.
299
300		@return `true` if the address is a multicast address.
301
302		@par Specification
303		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.7">
304		2.7. Multicast Addresses (rfc4291)</a>
305		*/
306		bool is_multicast() const noexcept;
307
308		/** Return true if two addresses are equal.
309
310		Addresses are equal if they have the same bytes and the
311		same zone: the same link-local bits on different links are
312		different destinations.
313
314		@return `true` if the addresses are equal.
315		*/
316		friend bool
317	50x	operator==(ipv6_address const& a1, ipv6_address const& a2) noexcept
318		{
319	50x	return a1.addr_ == a2.addr_ && a1.scope_id_ == a2.scope_id_;
320		}
321
322		/** Order two addresses.
323
324		Establishes a strict total ordering consistent with
325		`operator==`: addresses are ordered lexicographically by
326		their bytes in network order, then by zone. This makes
327		`ipv6_address` usable as a key in ordered containers such
328		as `std::map` and `std::set`.
329
330		@return The relative order of `a1` and `a2`.
331		*/
332		friend std::strong_ordering
333	17x	operator<=>(ipv6_address const& a1, ipv6_address const& a2) noexcept
334		{
335	17x	if (auto c = a1.addr_ <=> a2.addr_; c != 0)
336	6x	return c;
337	11x	return a1.scope_id_ <=> a2.scope_id_;
338		}
339
340		/** Return an address object that represents the unspecified address.
341
342		The address 0:0:0:0:0:0:0:0 (::) may be used to bind a socket
343		to all available interfaces.
344
345		@return The unspecified address (::).
346		*/
347	19x	static ipv6_address any() noexcept
348		{
349	19x	return ipv6_address();
350		}
351
352		/** Return an address object that represents the loopback address.
353
354		The unicast address 0:0:0:0:0:0:0:1 is called
355		the loopback address. It may be used by a node
356		to send an IPv6 packet to itself.
357
358		@par Specification
359		@li <a href="https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.3">
360		2.5.3. The Loopback Address (rfc4291)</a>
361
362		@return The loopback address (::1).
363		*/
364		static ipv6_address loopback() noexcept;
365
366		/** Format the address to an output stream.
367
368		This function writes the address to an
369		output stream using standard notation.
370
371		@return The output stream, for chaining.
372
373		@param os The output stream to write to.
374
375		@param addr The address to write.
376		*/
377		friend BOOST_COROSIO_DECL std::ostream&
378		operator<<(std::ostream& os, ipv6_address const& addr);
379
380		private:
381		std::size_t print_impl(char* dest) const noexcept;
382		};
383
384		/** Create an IPv6 address from a string.
385
386		This function attempts to parse the string
387		as an IPv6 address and returns an error code
388		if the string does not contain a valid IPv6 address.
389
390		@par Exception Safety
391		Throws nothing.
392
393		@param s The string to parse.
394		@return The error code, empty on success, and the parsed
395		address — default-constructed on failure.
396		*/
397		[[nodiscard]] BOOST_COROSIO_DECL capy::io_result<ipv6_address>
398		make_ipv6_address(std::string_view s) noexcept;
399
400		} // namespace boost::corosio
401
402		namespace std {
403
404		/// Hash support for `boost::corosio::ipv6_address`.
405		template<>
406		struct hash<boost::corosio::ipv6_address>
407		{
408		/// Return the hash of `addr`.
409		std::size_t
410	21x	operator()(boost::corosio::ipv6_address const& addr) const noexcept
411		{
412	21x	auto const bytes = addr.to_bytes();
413	21x	auto const h = hash<std::string_view>()(std::string_view(
414	21x	reinterpret_cast<char const*>(bytes.data()), bytes.size()));
415		// The zone participates in equality, so it must feed the
416		// hash; combine so it cannot cancel the byte entropy
417	21x	auto const z = hash<std::uint32_t>()(addr.scope_id());
418	21x	return h ^ (z + 0x9e3779b9u + (h << 6) + (h >> 2));
419		}
420		};
421
422		} // namespace std
423
424		#endif
425