Initial flow table data structure

[mvachhar]

This PR adds the initial flow table data structure, but not the corresponding pipeline stages.

The appropriate pipeline stages will be added as part of NAT integration and the interface for the flow table updated for anything needed that was not anticipated here.

We also need a way to run the shuttle tests in CI, but that is beyond the scope of this PR.

Fixes #783

[Copilot]

Pull Request Overview

This PR introduces the initial flow table data structure for the networking stack, providing a foundation for tracking network flows with timeout capabilities. The implementation uses a combination of DashMap for concurrent hash table operations and thread-local priority queues for managing flow expiration.

• Adds FlowTable with concurrent insert/lookup/remove operations and automatic timeout handling
• Implements FlowKey with support for both unidirectional and bidirectional flows
• Provides thread-local priority queues for efficient timeout management using weak references

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkt-meta/src/lib.rs	Adds flow_table module export
pkt-meta/src/flow_table/mod.rs	Module structure and public API exports
pkt-meta/src/flow_table/flow_key.rs	Flow key data structures with bidirectional/unidirectional support
pkt-meta/src/flow_table/flow_info.rs	Flow information storage with atomic expiration times
pkt-meta/src/flow_table/atomic_instant.rs	Wrapper for atomic Instant operations
pkt-meta/src/flow_table/thread_local_pq.rs	Thread-local priority queue implementation for timeout management
pkt-meta/src/flow_table/table.rs	Main FlowTable implementation with concurrent operations
pkt-meta/src/flow_table/README.md	Documentation of design decisions and future optimizations
pkt-meta/Cargo.toml	Adds required dependencies for flow table functionality
net/src/udp/mod.rs	Exports UdpPort type for flow key usage
Cargo.toml	Adds workspace dependencies for flow table implementation

Comments suppressed due to low confidence (1)

pkt-meta/src/flow_table/thread_local_pq.rs:1

• The #[allow(unused_must_use)] attribute is unnecessary here since expires_at() returns Instant which doesn't have #[must_use]. Remove this attribute to clean up the code.

// SPDX-License-Identifier: Apache-2.0

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[daniel-noland]

This all looks good to me. Minor comments made, but nothing blocking.

I really like the effort which went into testing this code (it isn't easy code to test by any means).

I also appreciate the docs.

I'm slightly concerned about the performance we will get given the number of allocations we can expect, but that requires measurement before we change anything.

[qmonnet]

Great work!

Looks good overall, I don't see anything obvious that would be “missing”, although it's always hard to tell as long as we haven't integrated yet with e.g. NAT.

I've got some minor nits and comments.

More importantly, I may have spotted a couple bugs in flow_keys.rs, please double-check.

I've addressed all the requested changes but due to timezone, I'm going to dismiss the review so we can merge now.