---
phase: 04-power-user-features
verified: 2026-03-26T00:00:00Z
status: passed
score: 10/10 must-haves verified
re_verification: false
---

# Phase 4: Power User Features Verification Report

**Phase Goal:** Users can scope capture with BPF expressions and sonify historical pcap files
**Verified:** 2026-03-26
**Status:** passed
**Re-verification:** No — initial verification

## Goal Achievement

### Observable Truths

| # | Truth | Status | Evidence |
|---|-------|--------|----------|
| 1 | BPF filter expressions can be validated without a live socket | VERIFIED | `capture/bpf.go` exports `ValidateBPFFilter`; uses `go-pcap/filter` without opening a handle; `TestValidateBPFFilter` and `TestValidateBPFFilterInvalid` both pass |
| 2 | A valid pcap file can be read and packets emitted on a channel | VERIFIED | `capture/pcap_reader.go` exports `ReadPcapFile`; uses `pcapgo.NewReader`; `TestReadPcapFile` verifies 3 packets emitted and channel closed |
| 3 | Invalid/missing pcap files produce clear error messages | VERIFIED | Error strings "cannot open" and "not a valid pcap file" confirmed in source; `TestReadPcapFileNotFound` and `TestReadPcapFileInvalid` pass |
| 4 | Pcap packets are aggregated into time windows using packet timestamps, not wall clock | VERIFIED | `aggregate/window.go` `AggregatePcap` uses `ev.Timestamp.Sub(minTS).Milliseconds()/windowMs`; `TestAggregatePcapBasic`, `TestAggregatePcapMultipleWindows` pass |
| 5 | Gap windows (no packets) produce empty snapshots preserving silence | VERIFIED | `AggregatePcap` initialises all windows with `make(map)` at creation time; `TestAggregatePcapGaps` passes |
| 6 | BPF filter can be applied to live capture handles | VERIFIED | `capture/capture.go` `OpenCapture` and `StartCapture` accept `filter string`; `handle.SetBPFFilter(filter)` called when non-empty |
| 7 | Software BPF filtering works for pcap file packets | VERIFIED | `ReadPcapFile` compiles software BPF VM via `CompileSoftwareBPF` and runs `vm.Run(pkt.Data())`; `TestReadPcapFileWithFilter` (tcp only, 2 of 3 packets) passes |
| 8 | User can run `netsynth -i eth0 --filter "port 53"` and only matching traffic is captured | VERIFIED | `--filter` flag registered; `ValidateBPFFilter` called in `run()` before capture; `bpfFilter` passed to `StartCapture`; `TestInvalidBPFFilter` and `TestFilterFlagRegistered` pass |
| 9 | User can run `netsynth --read capture.pcap -o out.mp3` and receive a valid MP3 | VERIFIED | `--read` flag registered; `runPcapMode` wired to `ReadPcapFile` -> classify -> `AggregatePcap` -> `encode.RunSynthesis`; `TestReadFlagRegistered` pass; full build clean |
| 10 | An invalid BPF filter expression produces a clear error before any capture begins | VERIFIED | `run()` calls `capture.ValidateBPFFilter(bpfFilter)` before branching to `runLiveMode`/`runPcapMode`; `TestInvalidBPFFilter` confirms error contains "invalid" without capture attempt |

**Score:** 10/10 truths verified

---

### Required Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `capture/bpf.go` | BPF validation and software filter compilation | VERIFIED | Exports `ValidateBPFFilter` and `CompileSoftwareBPF`; 41 lines, substantive implementation |
| `capture/pcap_reader.go` | Pcap file reading into packet channel | VERIFIED | Exports `ReadPcapFile`; uses `pcapgo.NewReader`, software BPF VM, goroutine emitting to channel; 58 lines |
| `aggregate/window.go` | Timestamp-based aggregation for pcap mode | VERIFIED | Exports `AggregatePcap`; 71 lines of substantive implementation alongside existing `Aggregate` |
| `classify/types.go` | Timestamp field on ClassifiedPacket | VERIFIED | `Timestamp time.Time` present at line 42 with doc comment |
| `cmd/netsynth/main.go` | CLI wiring for --filter and --read flags | VERIFIED | Both flags registered, `run()` branches, `runPcapMode` and `runLiveMode` fully wired |

---

### Key Link Verification

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| `capture/pcap_reader.go` | `gopacket/pcapgo` | `pcapgo.NewReader` | WIRED | Line 22: `r, err := pcapgo.NewReader(f)` |
| `capture/bpf.go` | `packetcap/go-pcap/filter` | `filter.NewExpression` | WIRED | Line 18: `e := gpcapfilter.NewExpression(expr)` |
| `aggregate/window.go` | `classify/types.go` | `ClassifiedPacket.Timestamp` | WIRED | Lines 29-34, 51: `ev.Timestamp.Before/After/Sub` |
| `cmd/netsynth/main.go` | `capture/bpf.go` | `capture.ValidateBPFFilter` | WIRED | Line 77: `if err := capture.ValidateBPFFilter(bpfFilter); err != nil` |
| `cmd/netsynth/main.go` | `capture/pcap_reader.go` | `capture.ReadPcapFile` | WIRED | Line 169: `packets, err := capture.ReadPcapFile(readPath, bpfFilter)` |
| `cmd/netsynth/main.go` | `aggregate/window.go` | `aggregate.AggregatePcap` | WIRED | Line 196: `collectedSnapshots := aggregate.AggregatePcap(classified, ...)` |
| `cmd/netsynth/main.go` | `capture/capture.go` | `capture.StartCapture` with filter | WIRED | Line 105: `capture.StartCapture(ctx, ifaceName, bpfFilter)` |

---

### Data-Flow Trace (Level 4)

| Artifact | Data Variable | Source | Produces Real Data | Status |
|----------|--------------|--------|--------------------|--------|
| `cmd/netsynth/main.go runPcapMode` | `collectedSnapshots` | `aggregate.AggregatePcap(classified, ...)` where `classified` is fed from `ReadPcapFile` | Yes — channel drained from pcap file packets with timestamps | FLOWING |
| `cmd/netsynth/main.go runLiveMode` | `collectedSnapshots` | `aggregate.Aggregate(ctx.Done(), classified, ...)` where `classified` is fed from `StartCapture` | Yes — live packet channel; filter applied at kernel level | FLOWING |
| `aggregate/window.go AggregatePcap` | `snapshots` | Drains `events` channel, assigns by `ev.Timestamp.Sub(minTS)` | Yes — populated from actual packet data | FLOWING |

---

### Behavioral Spot-Checks

| Behavior | Command | Result | Status |
|----------|---------|--------|--------|
| All tests pass | `go test ./... -count=1` | 6 packages: ok | PASS |
| Binary builds clean | `go build ./...` | No output (clean) | PASS |
| AggregatePcap gap test | `go test ./aggregate/... -run TestAggregatePcapGaps -v` | PASS | PASS |
| BPF invalid filter returns error | `go test ./capture/... -run TestValidateBPFFilterInvalid -v` | PASS | PASS |
| Mutual exclusion error | `go test ./cmd/netsynth/... -run TestFlagMutualExclusion -v` | PASS | PASS |
| deriveOutputPath derivation | `go test ./cmd/netsynth/... -run TestDeriveOutputPath -v` | PASS (5 cases) | PASS |

---

### Requirements Coverage

| Requirement | Source Plan | Description | Status | Evidence |
|-------------|------------|-------------|--------|----------|
| CAPT-05 | 04-01, 04-02 | User can filter captured traffic using BPF syntax via `--filter` flag | SATISFIED | `ValidateBPFFilter` validates before capture; `SetBPFFilter` applied to live handle; software BPF applied to pcap reads; `--filter` flag registered in CLI |
| CAPT-06 | 04-01, 04-02 | User can sonify a pcap file instead of live traffic via `--read` flag | SATISFIED | `ReadPcapFile` reads pcap; `AggregatePcap` does timestamp windowing; `runPcapMode` end-to-end path to `encode.RunSynthesis`; `--read` flag registered in CLI |

No orphaned requirements: REQUIREMENTS.md lists only CAPT-05 and CAPT-06 for Phase 4, and both are claimed by the plans.

---

### Anti-Patterns Found

| File | Line | Pattern | Severity | Impact |
|------|------|---------|----------|--------|
| None | — | — | — | — |

Scan result: No TODO/FIXME/placeholder comments found in phase-modified files. No empty return stubs. No hardcoded empty data flowing to output. `NoCopy = false` correctly set in `pcap_reader.go` (not a stub — it is a deliberate safety measure per Pitfall 3).

---

### Human Verification Required

#### 1. Live BPF filter on a real interface

**Test:** Run `sudo netsynth -i eth0 --filter "port 53"` on a host with DNS traffic (e.g., run `dig google.com` in another terminal).
**Expected:** Only DNS packets are captured; the protocol summary shows DNS counts but no HTTPS/HTTP/other traffic.
**Why human:** Requires root/CAP_NET_RAW privileges and a live network interface; cannot be run in the test harness.

#### 2. End-to-end pcap-to-MP3 round trip

**Test:** Run `netsynth --read <real-capture.pcap> -o out.mp3` against a non-trivial pcap file (e.g., a Wireshark sample). Verify `out.mp3` plays back with audible audio.
**Expected:** MP3 file is created with non-zero audio content; file size is proportional to pcap duration; bookend messages appear on stderr.
**Why human:** Requires a real pcap file and subjective audio verification; the test suite only validates the pipeline compiles and wires correctly.

#### 3. --verbose output in pcap mode

**Test:** Run `netsynth --read capture.pcap --verbose` with a multi-second pcap file.
**Expected:** Per-window protocol activity lines printed to stderr as windows are processed before the final summary.
**Why human:** `onSnapshot` callback path in `runPcapMode` is wired correctly in code but the visual output format needs human inspection.

---

### Gaps Summary

No gaps. All 10 observable truths are verified. All five required artifacts exist with substantive implementations. All seven key links are wired. Both CAPT-05 and CAPT-06 are satisfied. The full test suite (6 packages, 27+ tests) passes. `go build ./...` is clean. The four documented commits (52c6010, d13844f, 09e78bf, 4adb3c4) all exist in git log.

---

_Verified: 2026-03-26_
_Verifier: Claude (gsd-verifier)_