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/** @file
* @brief DNS Service Discovery
*/
/*
* Copyright (c) 2020 Friedt Professional Engineering Services, Inc
*
* SPDX-License-Identifier: Apache-2.0
*/
#ifndef ZEPHYR_INCLUDE_NET_DNS_SD_H_
#define ZEPHYR_INCLUDE_NET_DNS_SD_H_
#include <stdint.h>
#include <sys/byteorder.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief DNS Service Discovery
*
* @details This API enables services to be advertised via DNS. To
* advvertise a service, system or application code should use
* @ref DNS_SD_REGISTER_TCP_SERVICE or
* @ref DNS_SD_REGISTER_UDP_SERVICE.
*
* @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
*
* @defgroup dns_sd DNS Service Discovery
* @ingroup networking
* @{
*/
/** RFC 1034 Section 3.1 */
#define DNS_SD_INSTANCE_MIN_SIZE 1
/** RFC 1034 Section 3.1, RFC 6763 Section 7.2 */
#define DNS_SD_INSTANCE_MAX_SIZE 63
/** RFC 6763 Section 7.2 - inclusive of underscore */
#define DNS_SD_SERVICE_MIN_SIZE 2
/** RFC 6763 Section 7.2 - inclusive of underscore */
#define DNS_SD_SERVICE_MAX_SIZE 16
/** RFC 6763 Section 4.1.2 */
#define DNS_SD_SERVICE_PREFIX '_'
/** RFC 6763 Section 4.1.2 - either _tcp or _udp (case insensitive) */
#define DNS_SD_PROTO_SIZE 4
/** ICANN Rules for TLD naming */
#define DNS_SD_DOMAIN_MIN_SIZE 2
/** RFC 1034 Section 3.1, RFC 6763 Section 7.2 */
#define DNS_SD_DOMAIN_MAX_SIZE 63
/**
* Minimum number of segments in a fully-qualified name
*
* This reqpresents FQN's of the form below
* ```
* <sn>._tcp.<domain>.
* ```
* Currently sub-types and service domains are unsupported and only the
* "local" domain is supported. Specifically, that excludes the following:
* ```
* <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
* ```
* @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
*/
#define DNS_SD_MIN_LABELS 3
/**
* Maximum number of segments in a fully-qualified name
*
* This reqpresents FQN's of the form below
* ```
* <instance>.<sn>._tcp.<domain>.
* ```
*
* Currently sub-types and service domains are unsupported and only the
* "local" domain is supported. Specifically, that excludes the following:
* ```
* <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
* ```
* @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
*/
#define DNS_SD_MAX_LABELS 4
/**
* @brief Register a service for DNS Service Discovery
*
* This macro should be used for advanced use cases. Two simple use cases are
* when a custom @p domain or a custom (non-standard) @p proto is required.
*
* Another use case is when the port number is not preassigned. That could
* be for a number of reasons, but the most common use case would be for
* ephemeral port usage - i.e. when the service is bound using port number 0.
* In that case, Zephyr (like other OS's) will simply choose an unused port.
* When using ephemeral ports, it can be helpful to assign @p port to the
* @ref sockaddr_in.sin_port field of an IPv4 @ref sockaddr_in, or to the
* @ref sockaddr_in6.sin6_port field of an IPv6 @ref sockaddr_in6.
*
* The service can be referenced using the @p id variable.
*
* @param id variable name for the DNS-SD service record
* @param instance name of the service instance such as "My HTTP Server"
* @param service name of the service, such as "_http"
* @param proto protocol used by the service - either "_tcp" or "_udp"
* @param domain the domain of the service, such as "local"
* @param text information for the DNS TXT record
* @param port a pointer to the port number that this service will use
*/
#define DNS_SD_REGISTER_SERVICE(id, instance, service, proto, domain, \
text, port) \
static const STRUCT_SECTION_ITERABLE(dns_sd_rec, id) = { \
instance, \
service, \
proto, \
domain, \
(const char *)text, \
sizeof(text) - 1, \
port \
}
/**
* @brief Register a TCP service for DNS Service Discovery
*
* This macro can be used for service advertisement using DNS-SD.
*
* The service can be referenced using the @p id variable.
*
* Example (with TXT):
* @code{c}
* #include <net/dns_sd.h>
* static const bar_txt[] = {
* "\x06" "path=/"
* "\x0f" "this=is the way"
* "\x0e" "foo or=foo not"
* "\x17" "this=has\0embedded\0nulls"
* "\x04" "true"
* };
* // Possibly use an ephemeral port
* // Possibly only assign bar_port when the service is running
* static uint16_t bar_port;
* DNS_SD_REGISTER_TCP_SERVICE(bar, CONFIG_NET_HOSTNAME,
* "_bar", "local", bar_txt, &bar_port);
* @endcode{c}
*
* TXT records begin with a single length byte (hex-encoded)
* and contain key=value pairs. Thus, the length of the key-value pair
* must not exceed 255 bytes. Care must be taken to ensure that the
* encoded length value is correct.
*
* For additional rules on TXT encoding, see RFC 6763, Section 6.
* @param id variable name for the DNS-SD service record
* @param instance name of the service instance such as "My HTTP Server"
* @param service name of the service, such as "_http"
* @param domain the domain of the service, such as "local"
* @param text information for the DNS TXT record
* @param port the port number that this service will use
*
* @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
*/
#define DNS_SD_REGISTER_TCP_SERVICE(id, instance, service, domain, text, \
port) \
static const uint16_t id ## _port = sys_cpu_to_be16(port); \
DNS_SD_REGISTER_SERVICE(id, instance, service, "_tcp", domain, \
text, &id ## _port)
/**
* @brief Register a UDP service for DNS Service Discovery
*
* This macro can be used for service advertisement using DNS-SD.
*
* The service can be referenced using the @p id variable.
*
* Example (no TXT):
* @code{c}
* #include <net/dns_sd.h>
* #include <sys/byteorder.h>
* static const foo_port = sys_cpu_to_be16(4242);
* DNS_SD_REGISTER_UDP_SERVICE(foo, CONFIG_NET_HOSTNAME,
* "_foo", DNS_SD_EMPTY_TXT, &foo_port);
* @endcode{c}
*
* @param id variable name for the DNS-SD service record
* @param instance name of the service instance such as "My TFTP Server"
* @param service name of the service, such as "_tftp"
* @param domain the domain of the service, such as "local" or "zephyrproject.org"
* @param text information for the DNS TXT record
* @param port a pointer to the port number that this service will use
*
* @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
*/
#define DNS_SD_REGISTER_UDP_SERVICE(id, instance, service, domain, text, \
port) \
static const uint16_t id ## _port = sys_cpu_to_be16(port); \
DNS_SD_REGISTER_SERVICE(id, instance, service, "_udp", domain, \
text, &id ## _port)
/** Empty DNS-SD TXT specifier */
#define DNS_SD_EMPTY_TXT dns_sd_empty_txt
/** @cond INTERNAL_HIDDEN */
/**
* @brief DNS Service Discovery record
*
* This structure used in the implementation of RFC 6763 and should not
* need to be accessed directly from application code.
*
* The @a port pointer must be non-NULL. When the value in @a port
* is non-zero, the service is advertized as being on that particular
* port. When the value in @a port is zero, then the service is not
* advertised.
*
* Thus, it is possible for multiple services to advertise on a
* particular port if they hard-code the port.
*
* @internal
*
* @see <a href="https://tools.ietf.org/html/rfc6763">RFC 6763</a>
*/
struct dns_sd_rec {
/** <Instance> - e.g. "My HTTP Server" */
const char *instance;
/** Top half of the <Service> such as "_http" */
const char *service;
/** Bottom half of the <Service> "_tcp" or "_udp" */
const char *proto;
/** <Domain> such as "local" or "zephyrproject.org" */
const char *domain;
/** DNS TXT record */
const char *text;
/** Size (in bytes) of the DNS TXT record */
size_t text_size;
/** A pointer to the port number used by the service */
const uint16_t *port;
};
/**
* @brief Empty TXT specifier for DNS-SD
*
* @internal
*/
extern const char dns_sd_empty_txt[1];
/**
* @brief Wildcard Port specifier for DNS-SD
*
* @internal
*/
extern const uint16_t dns_sd_port_zero;
/** @endcond */
/**
* @brief Obtain the size of DNS-SD TXT data
*
* @param rec the record to in question
* @return the size of the text field
*/
static inline size_t dns_sd_txt_size(const struct dns_sd_rec *rec)
{
return rec->text_size;
}
/**
* @brief Check if @a rec is a DNS-SD Service Type Enumeration
*
* DNS-SD Service Type Enumeration is used by network tooling to
* acquire a list of all mDNS-advertised services belonging to a
* particular host on a particular domain.
*
* For example, for the domain '.local', the equivalent query
* would be '_services._dns-sd._udp.local'.
*
* Currently, only the '.local' domain is supported.
*
* @see <a href="https://datatracker.ietf.org/doc/html/rfc6763#section-9">Service Type Enumeration, RFC 6763</a>.
*
* @param rec the record to in question
* @return true if @a rec is a DNS-SD Service Type Enumeration
*/
bool dns_sd_is_service_type_enumeration(const struct dns_sd_rec *rec);
/**
* @brief Create a wildcard filter for DNS-SD records
*
* @param filter a pointer to the filter to use
*/
void dns_sd_create_wildcard_filter(struct dns_sd_rec *filter);
/**
* @}
*/
#ifdef __cplusplus
};
#endif
#endif /* ZEPHYR_INCLUDE_NET_DNS_SD_H_ */