Tanmaya Udupa

This commit **adds comprehensive unit tests** for the `getRouteAndNextHops` function within the **RIB (Routing Information Base)** module. The new templated tests in `RibLpmTests.cpp` cover critical scenarios such as no route found, unresolved routes, resolved drop routes, route deletion, and correctly resolved routes with next-hops. This **testing enhancement** improves the robustness and reliability of the RIB's longest prefix match (LPM) functionality by thoroughly validating its behavior. A minor build system update in `fboss/agent/rib/BUCK` was also included to support these new tests.

This commit introduces a **new capability** by adding the `getRouteAndNextHops` helper function to the **FBOSS agent's Routing Information Base (RIB) subsystem**. This function is designed to **resolve route and next hop IDs** from the ID manager, addressing cases where IDs in the RIB might not yet be updated in the Forwarding Information Base (FIB). Declared in `RoutingInformationBase.h` and implemented in `RoutingInformationBase.cpp`, it provides a critical mechanism for **FBOSS clients** and state observers to obtain accurate and resolved route information directly from the RIB. This enhances the reliability of route lookups for components relying on the RIB's longest prefix match.

This commit **refactors** the **ACL Next-Hop Handling** subsystem by migrating `AclNexthopHandler::resolveActionNexthops` to use `getRouteAndNormalizedNextHopsFromRib`. This change significantly improves the **atomicity and thread safety** of next-hop resolution within the **Routing Information Base (RIB)**. By performing longest-match lookups and `NextHopSetID` resolution under a single `rlock`, the system ensures more consistent and reliable application of ACL rules, centralizing and optimizing the next-hop retrieval logic.

This commit **refactors** the **NextHopResolver** component within the FBOSS agent to modernize its interaction with the Routing Information Base (RIB). Specifically, the `resolveNextHops` function in `fboss/agent/NextHopResolver.cpp` has been updated to utilize the new `getRib()->getRouteAndNextHops` method. This **migration** streamlines how route and next-hop information is retrieved, improving the internal architecture of the agent's next-hop resolution process. The change primarily impacts the **routing subsystem's** data retrieval mechanisms, enhancing maintainability and potentially efficiency.

This commit provides a **bug fix** for the **`HwRibResolutionBenchmark`** within the FBOSS agent's hardware benchmarks. It corrects the invocation of `RoutingInformationBase::fromThrift()` by passing the actual `FibsInfoMap` from the programmed state, instead of `nullptr`. This ensures the benchmark accurately tests the **ID-aware resolution path** and the correct ID manager, which is crucial for validating the ongoing **ECMP NextHop ID migration**. Without this fix, the benchmark would produce misleading results due to an incorrectly initialized ID manager, failing to reflect real-world performance.

This commit provides a **bug fix** for **BCM-native platforms** to correctly handle **TTL decrement disablement** on neighbor entries. Previously, a migration caused the `disableTTLDecrement` flag to be set only on route nexthops, which BCM-native hardware does not consult for neighbor entries, leading to incorrect TTL behavior. The fix introduces a new utility function, `disableTTLDecrementOnNeighbor()`, to explicitly set this flag on the neighbor entry, ensuring **proper TTL decrement logic** for affected platforms. This change, primarily within the **QoS test utilities**, restores expected functionality for **BCM-native hardware** like TH3.

This commit **refactors** the setup for **network agent tests** by migrating how TTL decrement disabling is configured in `LinkTest` and `MacLearningTests`. Instead of post-hoc FIB mutation, `disableTTLDecrement` is now set directly on nexthops during route creation via `programRoutes`. This involves adding a `disableTTLDecrement` parameter to `programDefaultRoute` overloads in `LinkTest.h` and `LinkTest.cpp`, and updating `createL3DataplaneFlood` and `verifyL2EntryValidated` to use it. This **test infrastructure improvement** ensures that **L3 dataplane flood** and **MAC learning validation tests** more accurately reflect route programming, enhancing their reliability and clarity.

This commit **refactors** and **simplifies** the **TTL decrement handling logic** used in agent tests and benchmarks. The utility function `ttlDecrementHandlingForLoopbackTraffic` is streamlined to exclusively manage `PORT_TTL_DECREMENT_DISABLE` cases, as other scenarios are now either no-ops or directly handled by `programRoutes`. Consequently, the function is **renamed** to `disablePortTTLDecrementIfSupported` for improved clarity, and the redundant `getDisableTTLDecrementForRoutes` function is removed. All **agent hardware tests** and **benchmarks** are updated to consistently pass `disableTTLDecrement=true` to `programRoutes` and then unconditionally invoke the new `disablePortTTLDecrementIfSupported` function. This ensures a unified and more maintainable approach to configuring TTL decrement for loopback traffic in **network configuration testing**.

This commit introduces a new `disableTTLDecrement` optional parameter to **route programming utilities** within `EcmpSetupHelper` and `AgentHwTest`. This **feature enhancement** allows the TTL decrement flag to be specified directly when programming routes, avoiding subsequent FIB entry mutations. Concurrently, it **fixes a bug** in `ForwardingInformationBase::setDisableTTLDecrement` to correctly preserve all `RouteNextHopEntry` fields during updates. This ensures more accurate and complete **FIB entry management** and provides finer control over route next-hop configuration, particularly in **testing scenarios**.

This commit **refactors** the **ECMP resource manager Distributed Switch Fabric (DSF) scale tests** to improve test utility consistency. It updates `fboss/agent/test/EcmpResourceMgrDsfScaleTests.cpp` to utilize a **new, shared utility function** for assigning next hop IDs, replacing an internal method. This **test refactoring** ensures that these critical scale tests, along with other unit tests, leverage a unified and reusable mechanism for ID assignment. The change enhances the maintainability and consistency of the test suite by reducing code duplication and promoting common test helpers.

This commit **refactors** the **`ShelManager`** to improve its **route handling logic** by migrating it to use `GetNormalizedNextHops()`. The core change in `fboss/agent/ShelManager.cpp` involves adopting this normalized function for next hop processing and passing `oldState` to `routeDeleted` calls, which enhances state management during route removal. As part of this **maintenance effort**, the `ShelManagerTest.cpp` is updated to integrate `NextHopIDManager` for next hop ID allocation in test scenarios, ensuring comprehensive testing of the new logic. This ensures more consistent and robust management of network routes and their associated next hops within the agent.

This commit performs a **refactoring** within the **ThriftHandler** module, specifically updating the `getRouteTable` method in `ThriftHandler.cpp`. The change migrates the logic to use the new `getNormalizedNextHops()` helper function for populating `overrideNextHops`. This streamlines and standardizes how next-hop information is retrieved and presented for Thrift-based route table queries, improving code consistency and maintainability.

This commit **refactors** the **routing information base** by modifying the `toRouteDetails` method in `fboss/agent/state/Route` to explicitly accept the `RouteNextHopSet` as an argument, rather than calculating it internally. This change improves the clarity and dependency management of the function's inputs. Callers within the **agent's routing subsystem**, specifically in `fboss/agent/ThriftHandler.cpp` and `fboss/agent/rib/RoutingInformationBase.cpp`, are updated to provide the next-hop set when retrieving **route details** for various route tables. This ensures that next-hop information is consistently and explicitly passed during route serialization and retrieval, streamlining the overall process.

This commit **refactors the `RouteManagerTest` suite** and its `ManagerTestBase` to properly handle NextHop IDs. It involves initializing `NextHopIDManager` within the test base, allocating NextHop IDs for routes, and adjusting test setup and state comparison logic in `RouteManagerTest.cpp` to account for these IDs. This **test update** ensures that the **SAI switch agent's route management tests** are compatible with and correctly validate the use of NextHop IDs, thereby improving the **accuracy and reliability of route configuration testing**.

This commit introduces new **test utility functions** in `fboss/agent/test/utils/NextHopIdTestUtils.{h,cpp}` to streamline nexthop ID allocation and `FibInfo` map population for **unit tests**. It provides functions like `allocateRouteNextHopIds` to assign IDs to individual route nexthop entries, `populateFibInfoIdMaps` to update `FibInfo` from a `NextHopIDManager`, and `assignNextHopIdsToAllRoutes` for bulk ID assignment across a `SwitchState`. This **test infrastructure improvement** simplifies the setup of complex routing scenarios, making future **unit tests** more efficient and reliable for the **FBOSS agent's routing subsystem**. These helpers will be used by unit tests to assign IDs to routes, ensuring consistent and accurate testing of nexthop resolution and FIB programming logic.

This commit introduces a **new capability** by adding the `getNormalizedNextHops()` function to the **FIB helper utilities** within `fboss/agent`. This function centralizes the logic for resolving route next hops, ensuring that all such calls now pass through this new entry point. It specifically enhances the **next hop resolution process** by incorporating logic to check for inline override next hops when the ID manager is enabled, falling back to standard ID resolution for non-overrides. This change improves the flexibility and robustness of the **FIB's next hop determination**, particularly in scenarios involving ID management and route overrides.

This commit **adds unit tests** for the `getNormalizedNextHops()` function, specifically targeting the **FIB helper utilities** within the `fboss/agent` component. The new tests cover various scenarios, including cases with and without overrides, to ensure the function's correctness and robustness. This **testing enhancement** improves the overall reliability and stability of the FIB resolution logic by thoroughly validating its behavior under different conditions.

This commit **refactors** the **SAI hardware agent's route programming logic** to enable ID-based next-hop resolution. Specifically, `SaiRouteManager` functions like `addRoute` and `changeRoute` now accept a `SwitchState` parameter, allowing them to use `FibHelpers::getNextHops()` to resolve next-hops by looking up `resolvedNextHopSetID` from the state's `FibInfo` maps. This `SwitchState` is propagated through key `SaiSwitch` methods, such as `processChangedAndAddedRoutesDelta`, ensuring the correct state is available for route programming. This **enhancement** provides a more flexible and robust mechanism for next-hop resolution within the **SAI FIB programming subsystem**.

This commit introduces a **new helper function**, `getNewStateWithOldFibInfo`, within the **`fboss/agent/FibHelpers`** module. This utility **refactors** existing logic by extracting the process of constructing a `SwitchState` that selectively combines information from two different states. Specifically, it creates a new `SwitchState` that retains non-FIB related data (like ports and interfaces) from a "new" state, while preserving the **FIB (Forwarding Information Base)** and ID map information from an "old" state. This function is designed to support **ERM (Egress Replication Manager)** by providing a robust way to manage `SwitchState` updates where FIB consistency is critical during state transitions.

This commit introduces **new unit tests** for the `populateIdMapsForRoute` helper function within the **FBOSS agent's FIB utilities**. These tests specifically verify the function's behavior in various scenarios, including correctly **copying IDs**, handling cases where IDs already exist, and properly processing routes designated for `DROP`. This **testing enhancement** improves the robustness and correctness validation of the FIB programming logic, ensuring reliable route ID management. The added tests in `fboss/agent/test/FibHelperTests.cpp` provide comprehensive coverage for this critical helper.