yoloyolo/.planning/phases/01-capture-and-classification/01-02-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, requirements-completed, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	requirements-completed	duration	completed
01-capture-and-classification	02	capture	go-pcap gopacket packet-capture privilege-handling cgo-free-capture	phase provides 01-capture-and-classification/01-01 classify/types.go with TrafficClass, ClassifiedPacket, WindowSnapshot types	capture package with OpenCapture, ListInterfaces, StartCapture functions Platform-specific privilege error messages (Linux setcap hint, macOS sudo hint) Channel-based packet source with 512-buffer and atomic drop counter	cmd/root.go (will call StartCapture and ListInterfaces) Phase 2 audio synthesis (receives packets from StartCapture channel)	added patterns github.com/packetcap/go-pcap v0.0.0-20251215 (pure-Go live capture) github.com/sirupsen/logrus v1.9.3 (transitive dep of go-pcap) TDD RED/GREEN write failing tests before implementation net.Interfaces() for listing (not pcap.FindAllDevs which go-pcap lacks) Non-blocking channel send with atomic.AddInt64 drop counter Dynamic link type via layers.LinkType(handle.LinkType()) runtime.GOOS switch for platform-specific error messages	created modified capture/capture.go capture/capture_test.go go.mod (added go-pcap) go.sum (added go-pcap + logrus hashes)	Use net.Interfaces() for interface listing — go-pcap has no FindAllDevs equivalent StartCapture uses 512-buffered channel with atomic drop counter to avoid backpressure blocking capture goroutine Dynamic link type detection via handle.LinkType() — not hardcoded LinkTypeEthernet Permission errors wrap platform-specific messages: Linux shows setcap, macOS shows sudo	Privilege detection: check error string for 'permission denied', 'operation not permitted', 'pcap_create' Platform branching: switch runtime.GOOS with linux case explicit, default for darwin/others Packet pipeline: goroutine reads from packetSource, writes to buffered channel with non-blocking select	CAPT-01 CAPT-02 CAPT-04	2min	2026-03-25

Phase 01 Plan 02: Capture Package Summary

Live packet capture via packetcap/go-pcap with ListInterfaces (stdlib-only), OpenCapture with platform-specific CAP_NET_RAW error messages, and non-blocking StartCapture channel pipeline with atomic drop counter

Performance

• Duration: ~2 min
• Started: 2026-03-25T11:15:54Z
• Completed: 2026-03-25T11:17:34Z
• Tasks: 1 (TDD: 2 commits — RED test + GREEN implementation)
• Files modified: 4 (capture.go, capture_test.go, go.mod, go.sum)

Accomplishments

• capture package implements all 3 required exports: OpenCapture, ListInterfaces, StartCapture
• ListInterfaces uses net.Interfaces() — no CGo or pcap dependency for interface enumeration (CAPT-02)
• Permission error detection covers all documented error strings; returns platform-specific sudo/setcap hints (CAPT-04, D-05)
• StartCapture goroutine uses buffered channel (512) + atomic drop counter — backpressure-safe for high-traffic interfaces

Task Commits

Each task was committed atomically:

1. Task 1 RED: failing tests for capture package - 1eb1dd4 (test)
2. Task 1 GREEN: implement capture package + add go-pcap - 9446dd5 (feat)

Note: TDD task has two commits (test RED then implementation GREEN)

Files Created/Modified

• capture/capture.go - ListInterfaces, OpenCapture, StartCapture, isPermissionError, permissionErrorMsg
• capture/capture_test.go - 5 tests: TestListInterfaces, TestListInterfacesFormat, TestIsPermissionError, TestIsPermissionErrorNegative, TestPermissionErrorMsg (94 lines)
• go.mod - Added github.com/packetcap/go-pcap v0.0.0-20251215
• go.sum - Added go-pcap + logrus hashes

Decisions Made

• net.Interfaces() for interface listing: go-pcap has no FindAllDevs, stdlib net package covers this without privileges
• Dynamic link type: capture uses layers.LinkType(handle.LinkType()) rather than hardcoded LinkTypeEthernet — handles lo (null/loopback) and tunnel interfaces
• Non-blocking packet send: select { case packets <- pkt: default: atomic.AddInt64(&droppedPackets, 1) } prevents slow downstream consumer from blocking capture goroutine

Deviations from Plan

None — plan executed exactly as written. go-pcap version v0.0.0-20251215121130-f2cf9f991e7c resolved correctly (RESEARCH.md listed the date prefix v0.0.0-20251215 which matched).

Issues Encountered

None — all tests passed on first GREEN run.

User Setup Required

None — no external service configuration required. Capture at runtime requires root or CAP_NET_RAW, but build is CGo-free for the capture layer.

Next Phase Readiness

• capture package is ready for consumption by cmd/root.go (Plan 03/04)
• StartCapture channel output type is gopacket.Packet — classifier (classify package from Plan 01) accepts these via layer assertions
• Dropped packets counter (*int64) available for capture-end summary statistics

---

Phase: 01-capture-and-classification Completed: 2026-03-25

Self-Check: PASSED

• capture/capture.go: FOUND
• capture/capture_test.go: FOUND
• 01-02-SUMMARY.md: FOUND
• commit 1eb1dd4 (test RED): FOUND
• commit 9446dd5 (feat GREEN): FOUND