1 /** @file
2 * @brief DNS Service Discovery
3 */
4
5 /*
6 * Copyright (c) 2020 Friedt Professional Engineering Services, Inc
7 *
8 * SPDX-License-Identifier: Apache-2.0
9 */
10
11 #ifndef ZEPHYR_INCLUDE_NET_DNS_SD_H_
12 #define ZEPHYR_INCLUDE_NET_DNS_SD_H_
13
14 #include <stdint.h>
15 #include <zephyr/sys/byteorder.h>
16 #include <zephyr/sys/iterable_sections.h>
17
18 #ifdef __cplusplus
19 extern "C" {
20 #endif
21
22 /**
23 * @brief DNS Service Discovery
24 *
25 * @details This API enables services to be advertised via DNS. To
26 * advertise a service, system or application code should use
27 * @ref DNS_SD_REGISTER_TCP_SERVICE or
28 * @ref DNS_SD_REGISTER_UDP_SERVICE.
29 *
30 * @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
31 *
32 * @defgroup dns_sd DNS Service Discovery
33 * @since 2.5
34 * @version 0.8.0
35 * @ingroup networking
36 * @{
37 */
38
39 /** RFC 1034 Section 3.1 */
40 #define DNS_SD_INSTANCE_MIN_SIZE 1
41 /** RFC 1034 Section 3.1, RFC 6763 Section 7.2 */
42 #define DNS_SD_INSTANCE_MAX_SIZE 63
43 /** RFC 6763 Section 7.2 - inclusive of underscore */
44 #define DNS_SD_SERVICE_MIN_SIZE 2
45 /** RFC 6763 Section 7.2 - inclusive of underscore */
46 #define DNS_SD_SERVICE_MAX_SIZE 16
47 /** RFC 6763 Section 4.1.2 */
48 #define DNS_SD_SERVICE_PREFIX '_'
49 /** RFC 6763 Section 4.1.2 - either _tcp or _udp (case insensitive) */
50 #define DNS_SD_PROTO_SIZE 4
51 /** ICANN Rules for TLD naming */
52 #define DNS_SD_DOMAIN_MIN_SIZE 2
53 /** RFC 1034 Section 3.1, RFC 6763 Section 7.2 */
54 #define DNS_SD_DOMAIN_MAX_SIZE 63
55
56 /**
57 * Minimum number of segments in a fully-qualified name
58 *
59 * This represents FQN's of the form below
60 * ```
61 * <sn>._tcp.<domain>.
62 * ```
63 * Currently sub-types and service domains are unsupported and only the
64 * "local" domain is supported. Specifically, that excludes the following:
65 * ```
66 * <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
67 * ```
68 * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
69 */
70 #define DNS_SD_MIN_LABELS 3
71 /**
72 * Maximum number of segments in a fully-qualified name
73 *
74 * This represents FQN's of the form below
75 * ```
76 * <instance>.<sn>._tcp.<domain>.
77 * ```
78 *
79 * Currently sub-types and service domains are unsupported and only the
80 * "local" domain is supported. Specifically, that excludes the following:
81 * ```
82 * <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
83 * ```
84 * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
85 */
86 #define DNS_SD_MAX_LABELS 4
87
88 /**
89 * @brief Register a service for DNS Service Discovery
90 *
91 * This macro should be used for advanced use cases. Two simple use cases are
92 * when a custom @p _domain or a custom (non-standard) @p _proto is required.
93 *
94 * Another use case is when the port number is not preassigned. That could
95 * be for a number of reasons, but the most common use case would be for
96 * ephemeral port usage - i.e. when the service is bound using port number 0.
97 * In that case, Zephyr (like other OS's) will simply choose an unused port.
98 * When using ephemeral ports, it can be helpful to assign @p _port to the
99 * @ref sockaddr_in.sin_port field of an IPv4 @ref sockaddr_in, or to the
100 * @ref sockaddr_in6.sin6_port field of an IPv6 @ref sockaddr_in6.
101 *
102 * The service can be referenced using the @p _id variable.
103 *
104 * @param _id variable name for the DNS-SD service record
105 * @param _instance name of the service instance such as "My HTTP Server"
106 * @param _service name of the service, such as "_http"
107 * @param _proto protocol used by the service - either "_tcp" or "_udp"
108 * @param _domain the domain of the service, such as "local"
109 * @param _text information for the DNS TXT record
110 * @param _port a pointer to the port number that this service will use
111 */
112 #define DNS_SD_REGISTER_SERVICE(_id, _instance, _service, _proto, \
113 _domain, _text, _port) \
114 static const STRUCT_SECTION_ITERABLE(dns_sd_rec, _id) = { \
115 .instance = _instance, \
116 .service = _service, \
117 .proto = _proto, \
118 .domain = _domain, \
119 .text = (const char *)_text, \
120 .text_size = sizeof(_text) - 1, \
121 .port = _port, \
122 }
123
124 /**
125 * @brief Register a TCP service for DNS Service Discovery
126 *
127 * This macro can be used for service advertisement using DNS-SD.
128 *
129 * The service can be referenced using the @p id variable.
130 *
131 * Example (with TXT):
132 * @code{.c}
133 * #include <zephyr/net/dns_sd.h>
134 * static const char bar_txt[] = {
135 * "\x06" "path=/"
136 * "\x0f" "this=is the way"
137 * "\x0e" "foo or=foo not"
138 * "\x17" "this=has\0embedded\0nulls"
139 * "\x04" "true"
140 * };
141 * DNS_SD_REGISTER_TCP_SERVICE(bar, CONFIG_NET_HOSTNAME,
142 * "_bar", "local", bar_txt, 4242);
143 * @endcode
144 *
145 * TXT records begin with a single length byte (hex-encoded)
146 * and contain key=value pairs. Thus, the length of the key-value pair
147 * must not exceed 255 bytes. Care must be taken to ensure that the
148 * encoded length value is correct.
149 *
150 * For additional rules on TXT encoding, see RFC 6763, Section 6.
151
152 * @param id variable name for the DNS-SD service record
153 * @param instance name of the service instance such as "My HTTP Server"
154 * @param service name of the service, such as "_http"
155 * @param domain the domain of the service, such as "local"
156 * @param text information for the DNS TXT record
157 * @param port the port number that this service will use
158 *
159 * @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
160 */
161 #define DNS_SD_REGISTER_TCP_SERVICE(id, instance, service, domain, text, \
162 port) \
163 static const uint16_t id ## _port = sys_cpu_to_be16(port); \
164 DNS_SD_REGISTER_SERVICE(id, instance, service, "_tcp", domain, \
165 text, &id ## _port)
166
167 /**
168 * @brief Register a UDP service for DNS Service Discovery
169 *
170 * This macro can be used for service advertisement using DNS-SD.
171 *
172 * The service can be referenced using the @p id variable.
173 *
174 * Example (no TXT):
175 * @code{.c}
176 * #include <zephyr/net/dns_sd.h>
177 * DNS_SD_REGISTER_UDP_SERVICE(foo, CONFIG_NET_HOSTNAME,
178 * "_foo", "local", DNS_SD_EMPTY_TXT, 4242);
179 * @endcode
180 *
181 * @param id variable name for the DNS-SD service record
182 * @param instance name of the service instance such as "My TFTP Server"
183 * @param service name of the service, such as "_tftp"
184 * @param domain the domain of the service, such as "local" or "zephyrproject.org"
185 * @param text information for the DNS TXT record
186 * @param port a pointer to the port number that this service will use
187 *
188 * @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
189 */
190 #define DNS_SD_REGISTER_UDP_SERVICE(id, instance, service, domain, text, \
191 port) \
192 static const uint16_t id ## _port = sys_cpu_to_be16(port); \
193 DNS_SD_REGISTER_SERVICE(id, instance, service, "_udp", domain, \
194 text, &id ## _port)
195
196 /** Empty DNS-SD TXT specifier */
197 #define DNS_SD_EMPTY_TXT dns_sd_empty_txt
198
199 /**
200 * @brief DNS Service Discovery record
201 *
202 * This structure used in the implementation of RFC 6763 and should not
203 * need to be accessed directly from application code.
204 *
205 * The @a port pointer must be non-NULL. When the value in @a port
206 * is non-zero, the service is advertised as being on that particular
207 * port. When the value in @a port is zero, then the service is not
208 * advertised.
209 *
210 * Thus, it is possible for multiple services to advertise on a
211 * particular port if they hard-code the port.
212 *
213 * @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
214 */
215 struct dns_sd_rec {
216 /** "<Instance>" - e.g. "My HTTP Server" */
217 const char *instance;
218 /** Top half of the "<Service>" such as "_http" */
219 const char *service;
220 /** Bottom half of the "<Service>" "_tcp" or "_udp" */
221 const char *proto;
222 /** "<Domain>" such as "local" or "zephyrproject.org" */
223 const char *domain;
224 /** DNS TXT record */
225 const char *text;
226 /** Size (in bytes) of the DNS TXT record */
227 size_t text_size;
228 /** A pointer to the port number used by the service */
229 const uint16_t *port;
230 };
231
232 /** @cond INTERNAL_HIDDEN */
233
234 /**
235 * @brief Empty TXT specifier for DNS-SD
236 *
237 * @internal
238 */
239 extern const char dns_sd_empty_txt[1];
240 /**
241 * @brief Wildcard Port specifier for DNS-SD
242 *
243 * @internal
244 */
245 extern const uint16_t dns_sd_port_zero;
246
247 /** @endcond */
248
249 /**
250 * @brief Obtain the size of DNS-SD TXT data
251 *
252 * @param rec the record to in question
253 * @return the size of the text field
254 */
dns_sd_txt_size(const struct dns_sd_rec * rec)255 static inline size_t dns_sd_txt_size(const struct dns_sd_rec *rec)
256 {
257 return rec->text_size;
258 }
259
260 /**
261 * @brief Check if @a rec is a DNS-SD Service Type Enumeration
262 *
263 * DNS-SD Service Type Enumeration is used by network tooling to
264 * acquire a list of all mDNS-advertised services belonging to a
265 * particular host on a particular domain.
266 *
267 * For example, for the domain '.local', the equivalent query
268 * would be '_services._dns-sd._udp.local'.
269 *
270 * Currently, only the '.local' domain is supported.
271 *
272 * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763#section-9">Service Type Enumeration, RFC 6763</a>.
273 *
274 * @param rec the record to in question
275 * @return true if @a rec is a DNS-SD Service Type Enumeration
276 */
277 bool dns_sd_is_service_type_enumeration(const struct dns_sd_rec *rec);
278
279 /**
280 * @brief Create a wildcard filter for DNS-SD records
281 *
282 * @param filter a pointer to the filter to use
283 */
284 void dns_sd_create_wildcard_filter(struct dns_sd_rec *filter);
285
286 /**
287 * @}
288 */
289
290 #ifdef __cplusplus
291 };
292 #endif
293
294 #endif /* ZEPHYR_INCLUDE_NET_DNS_SD_H_ */
295
