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resolve: Implement continuous mDNS querying as per RFC6762 5.2

Browse Source 
Allow for mDNS service/domain/types browsing.

A client can connect to the backend via varlink and receive updates as the
requested service becomes available.
The interval between the first two queries MUST be at least one second,
the intervals between successive queries MUST increase by at least a factor of two.
When the interval between queries reaches or exceeds 60 minutes, a querier MAY cap
the interval to a maximum of 60 minutes, and perform subsequent queries at a
steady-state rate of one query per hour.
Delete expired cache entries one second after goodbye packet received
as per RFC6762 Section 10.1

Cache maintenance:
The querier should plan to issue a query at 80% of the record lifetime, and
then if no answer is received, at 85%, 90%, and 95%.
If an answer is received, then the remaining TTL is reset to the value given
in the answer, and this process repeats for as long as the Multicast DNS querier
has an ongoing interest in the record.
If no answer is received after four queries, the record is deleted when it
reaches 100% of its lifetime.

TODO:
Improve the DNS transaction logic when multiple clients subscribe to
the same service, ensuring that continuous queries are optimized.

Co-authored-by: Vishwanath Chandapur <vishwanath.chandapur@philips.com>
This commit is contained in:
Vishal Chillara Srinivas
2025-07-15 22:55:31 +05:30
co-authored by Vishwanath Chandapur
parent 6ccc2b24f5
commit 8458b7fb91
14 changed files with 1057 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/shared/varlink-io.systemd.Resolve.c
+41
View File
@@ -102,6 +102,27 @@ static SD_VARLINK_DEFINE_STRUCT_TYPE(
SD_VARLINK_DEFINE_FIELD(ifindex, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
SD_VARLINK_DEFINE_FIELD(name, SD_VARLINK_STRING, 0));
static SD_VARLINK_DEFINE_ENUM_TYPE(
BrowseServiceUpdateFlag,
SD_VARLINK_FIELD_COMMENT("Indicates that the service was added."),
SD_VARLINK_DEFINE_ENUM_VALUE(added),
SD_VARLINK_FIELD_COMMENT("Indicates that the service was removed."),
SD_VARLINK_DEFINE_ENUM_VALUE(removed));
static SD_VARLINK_DEFINE_STRUCT_TYPE(
ServiceData,
SD_VARLINK_DEFINE_FIELD_BY_TYPE(updateFlag, BrowseServiceUpdateFlag, 0),
SD_VARLINK_FIELD_COMMENT("The address family of the service, one of AF_INET or AF_INET6."),
SD_VARLINK_DEFINE_FIELD(family, SD_VARLINK_INT, 0),
SD_VARLINK_FIELD_COMMENT("The name of the service, e.g., 'My Service'. May be null if not specified."),
SD_VARLINK_DEFINE_FIELD(name, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
SD_VARLINK_FIELD_COMMENT("The type of service, e.g., '_http._tcp'."),
SD_VARLINK_DEFINE_FIELD(type, SD_VARLINK_STRING, 0),
SD_VARLINK_FIELD_COMMENT("The domain in which the service resides, e.g., 'local'."),
SD_VARLINK_DEFINE_FIELD(domain, SD_VARLINK_STRING, 0),
SD_VARLINK_FIELD_COMMENT("The Linux interface index for the network interface associated with this service."),
SD_VARLINK_DEFINE_FIELD(ifindex, SD_VARLINK_INT, 0));
static SD_VARLINK_DEFINE_METHOD(
ResolveAddress,
SD_VARLINK_FIELD_COMMENT("The Linux interface index for the network interface to search on. Typically left unspecified, in order to search on all interfaces."),
@@ -159,6 +180,20 @@ static SD_VARLINK_DEFINE_METHOD(
SD_VARLINK_DEFINE_OUTPUT_BY_TYPE(rrs, ResolvedRecord, SD_VARLINK_ARRAY),
SD_VARLINK_DEFINE_OUTPUT(flags, SD_VARLINK_INT, 0));
static SD_VARLINK_DEFINE_METHOD_FULL(
BrowseServices,
SD_VARLINK_SUPPORTS_MORE,
SD_VARLINK_FIELD_COMMENT("The domain to browse for services. If null, the default browsing domain local is used."),
SD_VARLINK_DEFINE_INPUT(domain, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
SD_VARLINK_FIELD_COMMENT("The service type to browse for (e.g., '_http._tcp')."),
SD_VARLINK_DEFINE_INPUT(type, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
SD_VARLINK_FIELD_COMMENT("The Linux interface index for the network interface to search on."),
SD_VARLINK_DEFINE_INPUT(ifindex, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
SD_VARLINK_FIELD_COMMENT("Various browsing flags to modify the operation."),
SD_VARLINK_DEFINE_INPUT(flags, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
SD_VARLINK_FIELD_COMMENT("An array of service data containing information about discovered services."),
SD_VARLINK_DEFINE_OUTPUT_BY_TYPE(browserServiceData, ServiceData, SD_VARLINK_ARRAY));
static SD_VARLINK_DEFINE_ERROR(NoNameServers);
static SD_VARLINK_DEFINE_ERROR(NoSuchResourceRecord);
static SD_VARLINK_DEFINE_ERROR(QueryTimedOut);
@@ -199,6 +234,8 @@ SD_VARLINK_DEFINE_INTERFACE(
&vl_method_ResolveService,
SD_VARLINK_SYMBOL_COMMENT("Resolves a domain name to one or more DNS resource records."),
&vl_method_ResolveRecord,
SD_VARLINK_SYMBOL_COMMENT("Starts browsing for DNS-SD services of specified type."),
&vl_method_BrowseServices,
SD_VARLINK_SYMBOL_COMMENT("Encapsulates a resolved address."),
&vl_type_ResolvedAddress,
SD_VARLINK_SYMBOL_COMMENT("Encapsulates a resolved host name."),
@@ -213,6 +250,10 @@ SD_VARLINK_DEFINE_INTERFACE(
&vl_type_ResourceRecord,
SD_VARLINK_SYMBOL_COMMENT("Encapsulates information about a resolved DNS resource record "),
&vl_type_ResolvedRecord,
SD_VARLINK_SYMBOL_COMMENT("Describes the update flag for browsing services, indicating whether a service was added or removed during browsing."),
&vl_type_BrowseServiceUpdateFlag,
SD_VARLINK_SYMBOL_COMMENT("Encapsulates the service data obtained from browsing."),
&vl_type_ServiceData,
&vl_error_NoNameServers,
&vl_error_NoSuchResourceRecord,
&vl_error_QueryTimedOut,