Implement TR-10-9 Section 15 DNS-SD browse strategy by simonbaren · Pull Request #484 · sony/nmos-cpp

simonbaren · 2026-03-17T09:20:44Z

Summary

Implements the DNS-SD browse strategy required by TR-10-9 Section 15 for IPMX device service discovery.

Changes

New dns_sd_browse_mode setting ("both" / "unicast" / "mdns") to control DNS-SD browse method
- "both" (default): try unicast DNS first with half the timeout budget; fall back to mDNS if no services found
- "unicast": unicast DNS only
- "mdns": mDNS only
Domain class filtering in browse results to prevent mDNS results leaking into unicast DNS queries and vice versa
Refactored resolve_service to delegate to resolve_service_ with the dual-discovery logic

Motivation

TR-10-9 Section 15 requires IPMX devices to support both mDNS and unicast DNS for DNS-SD browse operations, defaulting to using both methods. When using both, unicast DNS must be attempted first, with mDNS as a fallback only if unicast is unsuccessful.

Files changed

Development/nmos/settings.h — new dns_sd_browse_mode field
Development/nmos/mdns.cpp — dual-browse logic and domain class filtering

https://static.vsf.tv/download/technical_recommendations/VSF_TR-10-9_v2_2025-05-13.pdf

TR-10-9 Section 15 requires IPMX devices to: - Support both mDNS and unicast DNS for DNS-SD browse operations - Default to using both methods - Provide user mechanisms to limit browsing to unicast or mDNS only - When using both: try unicast DNS first, fall back to mDNS only if unicast is unsuccessful (no service discovered) - When multiple results are returned: select by best priority, failing over to next-best if unresponsive - Once a service is selected and responsive: perform no further browse operations for that service type - If the selected service becomes unresponsive: perform a new DNS-SD browse and restart selection Add dns_sd_browse_mode setting ("both"/"unicast"/"mdns") to implement the required dual-discovery strategy. In "both" mode (default), unicast DNS is tried first with half the timeout budget; if no records are found, mDNS fallback gets the remaining half. "unicast" and "mdns" modes restrict to a single method. Also filters browse results by domain class to prevent mDNS results leaking into unicast DNS queries and vice versa. Signed-off-by: Semyon Barenboym <simonbaren@gmail.com>

lo-simon · 2026-03-26T11:52:53Z

Thank you, @simonbaren, for your PR, we will look into it shortly.

simonbaren · 2026-04-15T10:41:46Z

Hi @lo-simon, kindly reminder.

lo-simon · 2026-04-28T18:05:29Z

Hi @simonbaren

So sorry for the late reply.

I am happy with your PR. There are a few points I would like to address and offer suggestions on.

For dns_sd_browse_mode, it would be better to use an enum rather than a string, following the style of href_mode.
Add dns_sd_browse_mode to the example nmos-cpp-node/config.json.
Mark the unused resolve_service function (line 711 in mdns.cpp) as deprecated in both the cpp and header files by adding a comment.
Update the resolve_service and resolve_service_ comments in the header and in the cpp.
I think it would be better to keep the same discovery timeout for both primary and fallback resolves, rather than halving it. What do you think, @jonathan-r-thorpe and @garethsb?
Shall we add the following table to settings.h and config.json as a reminder?

dns_sd_browse_mode	domain	expected-resolve-behaviour
both	example.com	unicast->mdns
both	local.	mdns
unicast	example.com	unicast
unicast	local.	mdns
mdns	example.com	mdns
mdns	local.	mdns

- Use string_enum for dns_sd_browse_mode (nmos::dns_sd_browse_modes::{both,unicast,mdns}) - Add dns_sd_browse_mode example + behaviour table to nmos-cpp-node config.json - Add expected-behaviour table to settings.h - Mark unused URI-returning resolve_service overload as deprecated (comment) - Refresh resolve_service / resolve_service_ doc comments in mdns.h/.cpp Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

simonbaren · 2026-04-29T12:52:41Z

Hi @lo-simon, thanks for the review. Pushed a commit addressing items 1–4 and 6:

dns_sd_browse_mode as enum — used the string_enum pattern (DEFINE_STRING_ENUM) rather than the integer href_mode style. Rationale: The string-based pattern is consistent with most other JSON-string enums in nmos-cpp (interlace_mode, activation_mode, event_type, etc.) and keeps the config human-readable. Happy to switch to int-enum if you'd prefer.
config.json — added a commented-out dns_sd_browse_mode entry next to domain, with the behaviour table inline.
Deprecated marker — added // DEPRECATED: … comments above the unused web::uri-returning resolve_service overload (and its inline template wrapper) in both mdns.h and mdns.cpp.
Refreshed comments — resolve_service and resolve_service_ doc comments in both mdns.h and mdns.cpp now distinguish the web::uri vs resolved_service return shapes and reference the TR-10-9 mode selection.
Timeout halving — left as-is for now, awaiting input from @jonathan-r-thorpe / @garethsb.
Behaviour table — added next to the dns_sd_browse_mode field declaration in settings.h and next to the entry in config.json.

Let me know if anything needs adjusting.

jonathan-r-thorpe · 2026-04-29T13:41:06Z

@lo-simon @simonbaren on 5. I agree with @lo-simon that I would expect the primary service timeout to remain unchanged, even when there is a fallback service. My expectation would therefore be that the timeout applied per service (i.e. don't halve it).

Per maintainer review (jonathan-r-thorpe, lo-simon): the primary service timeout should remain unchanged when a fallback is in play, with the same timeout applied per service rather than halved across them. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

simonbaren · 2026-04-29T13:57:32Z

Thanks @jonathan-r-thorpe. Done in the latest commit - primary and fallback now both use the full discovery_backoff_max timeout (no more halving).

lo-simon

Use an enum rather than a string for the dns_sd_browse_mode to reduce the risk of typos.

lo-simon · 2026-04-29T17:40:42Z

+    //   "both" (default) = unicast DNS first, mDNS fallback if unsuccessful
+    //   "unicast"        = unicast DNS only
+    //   "mdns"           = mDNS only


Suggested change

// "both" (default) = unicast DNS first, mDNS fallback if unsuccessful

// "unicast" = unicast DNS only

// "mdns" = mDNS only

// both(0) (default) = unicast DNS first, mDNS fallback if unsuccessful

// unicast(1) = unicast DNS only

// mdns(2) = mDNS only

lo-simon · 2026-04-29T17:41:17Z

+    //   unicast | local.      | mdns
+    //   mdns    | example.com | mdns
+    //   mdns    | local.      | mdns
+    //"dns_sd_browse_mode": "both",


Suggested change

//"dns_sd_browse_mode": "both",

//"dns_sd_browse_mode": 0,

lo-simon · 2026-04-29T17:42:16Z

+#ifndef NMOS_DNS_SD_BROWSE_MODE_H
+#define NMOS_DNS_SD_BROWSE_MODE_H
+
+#include "nmos/string_enum.h"


Suggested change

#include "nmos/string_enum.h"

lo-simon · 2026-04-29T17:44:40Z

+    DEFINE_STRING_ENUM(dns_sd_browse_mode)
+    namespace dns_sd_browse_modes
+    {
+        const dns_sd_browse_mode both{ U("both") };       // unicast DNS first, mDNS fallback if unsuccessful
+        const dns_sd_browse_mode unicast{ U("unicast") }; // unicast DNS only
+        const dns_sd_browse_mode mdns{ U("mdns") };       // mDNS only
+    }


Suggested change

DEFINE_STRING_ENUM(dns_sd_browse_mode)

namespace dns_sd_browse_modes

{

const dns_sd_browse_mode both{ U("both") }; // unicast DNS first, mDNS fallback if unsuccessful

const dns_sd_browse_mode unicast{ U("unicast") }; // unicast DNS only

const dns_sd_browse_mode mdns{ U("mdns") }; // mDNS only

}

enum dns_sd_browse_mode

{

both = 0, // unicast DNS first, mDNS fallback if unsuccessful

unicast = 1, // unicast DNS only

mdns = 2 // mDNS only

};

lo-simon · 2026-04-29T17:46:41Z

+        //  - "both" (default): unicast DNS first, mDNS fallback if unsuccessful
+        //  - "unicast"       : unicast DNS only
+        //  - "mdns"          : mDNS only


Suggested change

// - "both" (default): unicast DNS first, mDNS fallback if unsuccessful

// - "unicast" : unicast DNS only

// - "mdns" : mDNS only

// - both (default): unicast DNS first, mDNS fallback if unsuccessful

// - unicast : unicast DNS only

// - mdns : mDNS only

lo-simon · 2026-04-29T17:51:44Z

+        //  - "both" (default): unicast DNS first, mDNS fallback if unsuccessful
+        //  - "unicast"       : unicast DNS only
+        //  - "mdns"          : mDNS only


Suggested change

// - "both" (default): unicast DNS first, mDNS fallback if unsuccessful

// - "unicast" : unicast DNS only

// - "mdns" : mDNS only

// - both (default): unicast DNS first, mDNS fallback if unsuccessful

// - unicast : unicast DNS only

// - mdns : mDNS only

lo-simon · 2026-04-29T17:52:43Z

+        //   "both" (default) = unicast DNS first, mDNS fallback if unsuccessful
+        //   "unicast"        = unicast DNS only
+        //   "mdns"           = mDNS only


Suggested change

// "both" (default) = unicast DNS first, mDNS fallback if unsuccessful

// "unicast" = unicast DNS only

// "mdns" = mDNS only

// both(0) (default) = unicast DNS first, mDNS fallback if unsuccessful

// unicast(1) = unicast DNS only

// mdns(2) = mDNS only

lo-simon · 2026-04-29T17:53:46Z

+        //   unicast | local.      | mdns
+        //   mdns    | example.com | mdns
+        //   mdns    | local.      | mdns
+        const web::json::field_as_string_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), U("both") };


Suggested change

const web::json::field_as_string_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), U("both") };

const web::json::field_as_integer_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), 0 };

Use an enum rather than a string for the dns_sd_browse_mode to reduce the risk of typos.

Per lo-simon's review: use a typed enum (compile-checked) rather than a string to reduce typo risk in user configurations. - enum dns_sd_browse_mode { dns_sd_browse_mode_both = 0, _unicast = 1, _mdns = 2 } defined file-local in mdns.cpp under nmos::experimental, mirroring how href_mode lives in settings.cpp - field becomes field_as_integer_or with default 0 - example config.json now shows //"dns_sd_browse_mode": 0, - doc comments updated; dns_sd_browse_mode.h header removed Used dns_sd_browse_mode_* prefix on the enumerators (rather than the bare both/unicast/mdns suggested in the review) to avoid polluting nmos:: with generic identifiers, matching the href_mode_* convention. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

simonbaren · 2026-04-30T08:41:17Z

Hi @lo-simon, thanks for the detailed review. Switched to a typed integer enum.
Two small deviations from your literal suggestions, both for consistency with the existing href_mode pattern you originally cited — happy to revert either if you'd prefer:

Enumerator naming — used dns_sd_browse_mode_both / _unicast / _mdns (prefixed) rather than bare both / unicast / mdns. Bare names would land directly in the nmos:: namespace, where nmos::both etc. are quite generic. The prefixed form matches href_mode's href_mode_default / href_mode_name / etc.
Header location — moved the enum into mdns.cpp (file-local, under namespace nmos) and deleted Development/nmos/dns_sd_browse_mode.h that was added in previous commit. This mirrors how href_mode lives entirely in settings.cpp rather than in a public header. The setting field stays in settings.h; the integer value descriptions are inlined in the comment there (per your suggestion).

All other inline suggestions applied verbatim:

field_as_integer_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), 0 }
//"dns_sd_browse_mode": 0, in the example config
both(0) / unicast(1) / mdns(2) in the settings.h and config.json comment tables
doc comments in mdns.h/mdns.cpp use bare both/unicast/mdns

simonbaren force-pushed the feature/tr-10-9-dns-sd-browse-strategy branch from fb842e3 to 8a965c6 Compare March 17, 2026 09:22

simonbaren force-pushed the feature/tr-10-9-dns-sd-browse-strategy branch from 8a965c6 to cc1dab4 Compare March 17, 2026 09:23

lo-simon requested changes Apr 29, 2026

View reviewed changes

simonbaren force-pushed the feature/tr-10-9-dns-sd-browse-strategy branch from 28d14db to 09df043 Compare April 30, 2026 08:38

lo-simon merged commit db23439 into sony:master Apr 30, 2026
10 checks passed

	const web::json::field_as_string_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), U("both") };
	const web::json::field_as_integer_or dns_sd_browse_mode{ U("dns_sd_browse_mode"), 0 };

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lo-simon commented Mar 26, 2026

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simonbaren commented Mar 17, 2026 •

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