[src/libraries/sonic-fib]: Add sonic-fib library to build libnexthopgroup deb for RIB/FIB

[GaladrielZhao]

Why I did it

This is the first PR of the RIB/FIB project.

Currently, fpmsyncd receives only partial nexthop information from FRR. To support nexthop object with full information
(called as NextHopGroupFull) passed from FRR (zebra) to fpmsyncd, a shared serialization library is needed so both processes can encode or decode NHG data consistently.

Work item tracking

• Microsoft ADO (number only):

How I did it

Introduce sonic-fib, a C++ library that provides encoding and decoding capabilities for NextHopGroupFull objects:

• FRR uses the encoding function to generate a JSON string embedded in messages sent to fpmsyncd
• fpmsyncd uses the decoding function to reconstruct the NHG object from the incoming JSON string

To minimize human error, the library uses a JSON Schema as the single source of truth and Jinja2 templates to auto-generate the required code.

(1) Key components:

• Data schema: NextHopGroupFull.json drives auto-generation of C++ classes, JSON codecs, and C struct wrappers via render_schema.py + Jinja2.
• C-API: C-callable interface for FRR to encode NHG objects into JSON.
• Logging callback: pluggable FIB_LOG macro with per-process callback registration (fib_frr_register_callback for FRR, registerLogCallback for SWSS).
• Unit tests: covers C++ class behavior, JSON round-trip, C-API conversion, and logging callback using Google Test.

(2) Architecture

(3) Directory Structure

sonic-fib/
├── schema/
│   └── NextHopGroupFull.json      # Single source of truth: data schema （source)
├── scripts/
│   └── render_schema.py           # Code generation engine (source)
├── templates/
│   ├── *.j2                       # Jinja2 templates for code generation (source)
│   │   ├── nexthopgroupfull.h.j2  
│   │   ├── nexthopgroupfull.cpp.j2
│   │   ├── nexthopgroupfull_json.h.j2
│   │   └── c_nexthopgroupfull.h.j2
│   └── references/                # Generated code (reference only, for review)
│       ├── nexthopgroupfull.h         # NextHopGroupFull definitions
│       ├── nexthopgroupfull.cpp       # NextHopGroupFull function implementation
│       ├── nexthopgroupfull_json.h    # NextHopGroupFull to/from_json functions
│       └── c_nexthopgroupfull.h       # C_NextHopGroupFull definitions
├── src/
│   ├── c-api/
│   │   ├── nexthopgroup_capi.h    # C API header
│   │   └── nexthopgroup_capi.cpp  # C→C++ conversion & JSON wrapper
│   ├── nexthopgroup_debug.h       # Logging callback interface
│   └── nexthopgroup_debug.cpp     # Logging implementation
└── tests/
    ├── nexthopgroupfull_ut.cpp         # C++ class unit tests
    ├── nexthopgroupfull_json_ut.cpp    # JSON serialization tests
    ├── nexthopgroup_debug_ut.cpp       # Logging callback tests
    ├── c_api_ut.cpp                    # C-API round-trip tests
    └── main.cpp                        # gtest entry point

Note: The generated files in templates/references are only kept for review and will not be committed later.

How to verify it

There is a UT module in sonic-fib, containing GTests for all functions.

A picture of a cute animal (not mandatory but encouraged)

[yxieca]

/azpw ms_conflict

[yxieca]

/azpw ms_conflict

[selva-nexthop]

/

[GaladrielZhao]

Hi @deepak-singhal0408 , thanks a lot for your review. I've addressed all the comments above.

[deepak-singhal0408]

Thanks for addressing the review comments @GaladrielZhao .. LGTM.

[radha-danda]

@GaladrielZhao, sairedis PR CI checks are failing with below linking errors. Can you please check if it is related to your PR and kindly fix?

2026-05-25T05:56:13.6377525Z /bin/bash ../libtool  --tag=CXX   --mode=link g++  -g -O2 -ffile-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security  -Wl,-z,relro -o fpmsyncd fpmsyncd-fpmsyncd.o fpmsyncd-fpmlink.o fpmsyncd-routesync.o fpmsyncd-warmRestartHelper.o fpmsyncd-orch_zmq_config.o    -lnl-3 -lnl-route-3 -lswsscommon -lnexthopgroup -lnl-nf-3 -lnl-route-3 -lnl-genl-3 -lnl-3 -lhiredis 
2026-05-25T05:56:13.7125550Z libtool: link: g++ -g -O2 -ffile-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z -Wl,relro -o fpmsyncd fpmsyncd-fpmsyncd.o fpmsyncd-fpmlink.o fpmsyncd-routesync.o fpmsyncd-warmRestartHelper.o fpmsyncd-orch_zmq_config.o  -lswsscommon -lnexthopgroup -lnl-nf-3 -lnl-route-3 -lnl-genl-3 -lnl-3 -lhiredis
2026-05-25T05:56:13.7258134Z /usr/bin/ld: cannot find -lnexthopgroup: No such file or directory
2026-05-25T05:56:13.7465330Z collect2: error: ld returned 1 exit status
2026-05-25T05:56:13.7477116Z make[4]: *** [Makefile:419: fpmsyncd] Error 1
2026-05-25T05:56:13.7478869Z make[4]: Leaving directory '/__w/1/s/fpmsyncd'
2026-05-25T05:56:13.7480812Z make[3]: *** [Makefile:420: all-recursive] Error 1

[GaladrielZhao]

@GaladrielZhao, sairedis PR CI checks are failing with below linking errors. Can you please check if it is related to your PR and kindly fix?

2026-05-25T05:56:13.6377525Z /bin/bash ../libtool  --tag=CXX   --mode=link g++  -g -O2 -ffile-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security  -Wl,-z,relro -o fpmsyncd fpmsyncd-fpmsyncd.o fpmsyncd-fpmlink.o fpmsyncd-routesync.o fpmsyncd-warmRestartHelper.o fpmsyncd-orch_zmq_config.o    -lnl-3 -lnl-route-3 -lswsscommon -lnexthopgroup -lnl-nf-3 -lnl-route-3 -lnl-genl-3 -lnl-3 -lhiredis 
2026-05-25T05:56:13.7125550Z libtool: link: g++ -g -O2 -ffile-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z -Wl,relro -o fpmsyncd fpmsyncd-fpmsyncd.o fpmsyncd-fpmlink.o fpmsyncd-routesync.o fpmsyncd-warmRestartHelper.o fpmsyncd-orch_zmq_config.o  -lswsscommon -lnexthopgroup -lnl-nf-3 -lnl-route-3 -lnl-genl-3 -lnl-3 -lhiredis
2026-05-25T05:56:13.7258134Z /usr/bin/ld: cannot find -lnexthopgroup: No such file or directory
2026-05-25T05:56:13.7465330Z collect2: error: ld returned 1 exit status
2026-05-25T05:56:13.7477116Z make[4]: *** [Makefile:419: fpmsyncd] Error 1
2026-05-25T05:56:13.7478869Z make[4]: Leaving directory '/__w/1/s/fpmsyncd'
2026-05-25T05:56:13.7480812Z make[3]: *** [Makefile:420: all-recursive] Error 1

Hi @radha-danda , thanks for your update.
I believe this is caused by sonic-swss PR #4394 which added -lnexthopgroup to fpmsyncd's link dependencies and updated swss's own CI pipeline to download the libnexthopgroup deb, but did not update the sairedis CI pipeline accordingly. So when sairedis CI compiles swss from master, it cannot find the library.

I've opened a PR sonic-net/sonic-sairedis#1908 to fix this. It adds the libnexthopgroup deb download and installation to sairedis CI pipeline files.