rea/docs/pcap-analysis.md

Packet capture summaries

REA summarizes already saved pcap/pcapng files through caller-selected Wireshark 4.x tshark and capinfos. Use inspect_packet_capture for selected fields, filters and decode-as rules; use this family for address, DNS, SNI, protocol-stack and URI inventories. It does not acquire traffic or fetch recorded targets.

Supply tools

export REA_TSHARK_COMMAND=/absolute/path/tshark
export REA_CAPINFOS_COMMAND=/absolute/path/capinfos
# Linux only; default /usr/bin/prlimit
export REA_TSHARK_PRLIMIT_COMMAND=/absolute/path/prlimit
rea inspect-pcap-client
rea inspect-pcap-capture /captures/session.pcapng --json

Without explicit tool commands, this family resolves them through PATH and records that selection source. On Linux and macOS it runs the tool found in the first absolute PATH entry holding an executable file, the same selection the packet capture tools make; relative PATH entries are skipped. Windows keeps PATH/PATHEXT resolution in the process launcher. Client inspection reads no capture file; on hosts where PATH/PATHEXT does not expose an absolute candidate, its executable digest and resolved path are reported as unresolved. Otherwise the canonical executable path and SHA-256 are reported. The pcap provider and packet tools share the selected-tool identity check, and changes to a resolved executable during a run fail with artifact-changed Evidence. Capture inspection requires Linux with util-linux prlimit or Windows with owned Job Objects. macOS capture inspection returns a capability gap because the new native memory boundary is unverified; its version probes remain available. binary_session advertises those operations separately: unsupported capture hosts do not disable the client probe or remove either tool from the catalog. A selected tool directory or unreadable tool is a configuration capability refusal naming its selected path, before any capture bytes are opened. Tools and installed libraries/plugins are caller-trusted. An empty private personal Wireshark configuration is used; this is not an OS sandbox.

Inspect only the needed facts

MCP inspect_pcap_capture accepts path and optional detail: "summary". Complete delivery remains the default. Summary commits and retains the same complete Evidence, returning identity, capture metadata, observed counts, retained counts, source coverage and diagnostic lengths without large lists. Then use its normalized_result.parent_evidence_id with inspect_analysis_view source kind retained-evidence:

{"kind":"pcap","facet":"endpoints","offset":0,"limit":20}
{"kind":"pcap","facet":"dns-queries","offset":0,"limit":20}
{"kind":"pcap","facet":"dns-addresses","query":"example.com","offset":0,"limit":20}
{"kind":"pcap","facet":"tls-sni","offset":0,"limit":20}
{"kind":"pcap","facet":"diagnostics","stream":"tshark","offset":0,"limit":4096}

Other row facets are protocols, http-uris and unattributed-addresses. Defaults are offset 0 and limit 64. DNS question pages give address counts; select one exact retained question to page its addresses. Diagnostic windows count UTF-16 code units; other windows count rows. Missing/ambiguous selectors fail. Unknown legacy diagnostics remain unknown, not an observed empty stream. Portable CLI views use the existing inspect-analysis-view workflow with inline complete Evidence. Views never reread the source or launch Wireshark and work after the original file is deleted. Page exhaustion covers the retained facet; it does not establish network completeness or recover missing traffic.

Interpret provenance and coverage

target.sha256 binds observations to an admitted stable capture snapshot. Both tools read that copy, which is hashed again after analysis. Capture metadata and literal field values are producer observations; address/protocol counts and DNS associations are derivations. Capture Evidence has historical-reference authority.

capture_start and capture_end are RFC 3339 UTC instants derived from capinfos -S epoch seconds, retaining all producer fractional digits (up to nanoseconds). Empty captures, malformed timestamps and instants outside years 0000–9999 remain null; host-local timestamps without a zone are not inferred.

snapshot_length is the file-header packet size limit reported by capinfos. Its separate inferred truncation lengths do not replace that limit; an unset file-header limit remains null.

Addresses count once per packet, including loopback and nested IP occurrences. DNS addresses are associated only with one question in the same response packet; additional records may be included, so this does not prove final resolution. Ambiguous addresses remain in a separate inventory. Protocol distribution counts exact nonempty frame.protocols stack strings. Frames for which TShark reports an empty stack, including zero-length packets, still contribute to the packet count without adding a protocol row. An all-empty stack inventory can have complete examined coverage; it does not establish the absence of network traffic. TLS SNI is recorded handshake metadata, not process identity or proof of the destination's authenticity.

All examined inventories are retained within the resource budget; no fixed 200/100/50-item truncation is applied. HTTP transport credentials are excluded without rewriting other URI bytes; ambiguous credential spans cause omission. The URI inventory includes absolute-form HTTP request targets when TShark cannot construct http.request.full_uri because no Host header was reported; relative request targets are not promoted to absolute URIs. The inventory also consumes http2.request.full_uri; a decoded HTTP/2 :path without a corresponding full URI leaves coverage partial. The HTTP URI profile covers HTTP/1 and HTTP/2; HTTP/3 URI semantics are unexamined. All admitted URI fields share the same credential exclusion and source-value retention rules. Counts preserve distinct observed source URIs before omission or coalescing. coverage: "partial" records unresolved DNS attribution or URI item loss; component credential exclusion is also counted explicitly. Diagnostics retain both tool stderr streams. Recorded fields do not establish decrypted payloads, causality, process identity, absence of unrecorded traffic or current deployments.

Resources and lifecycle

One inspection is admitted at a time per provider. Concurrent calls return a capacity error; close drains active work before releasing resources. Captures are streamed into a read-only owned snapshot with a 2 GiB disk budget. Native capture commands enforce Linux address-space ceilings of at most 1 GiB, 300 CPU seconds, 64 MiB per file and no core dumps, preserving stricter inherited limits. Windows uses a 1 GiB committed-memory limit for each owned tool tree. These are not aggregate machine or filesystem quotas.

TShark output is bounded at 8 MiB; its known five-level selected-field shape and 128 MiB graph-expansion estimate are checked before allocation. Retained facts have a separate 16 MiB estimate. Capinfos output is limited to 64 KiB. Command wall deadlines are 300 s for dissection, 60 s for metadata and 20 s for probes. Native ownership preparation has its own bounded lifecycle.

Malformed/oversized output returns no partial success. Unvalidated partial JSON is not returned as facts. Invalid UTF-8 in either capinfos or TShark stdout or stderr is an unreadable-output error; replacement-decoded text is not parsed as producer evidence. A literal U+FFFD character in valid UTF-8 remains text. Cancellation reaches probes, acquisition, commands and projection. Cleanup failure returns a typed error, retains completed Evidence when available, and retains owned resources for retry on close.

Verification scope

Current follow-up verification uses Linux/Node 24.18.0 and Wireshark 4.0.17. Private real recorded corpora are checked against independent raw-frame/IP parsing and Python aggregation, public CLI/stdio MCP parity, SDK schemas, source hashes and retained views. Synthetic native tools separately test malformed output, cancellation, source/snapshot mutation, capacity and cleanup; they do not establish real Wireshark or other-platform behavior.

The original proposal reported Linux 4.6.6, macOS/Windows 4.6.9 verification on its earlier implementation. Those reports do not verify the new final memory boundary. Actual Windows/Bun Wireshark execution is unverified here; macOS capture support needs a separate enforceable-bound decision.

npm run verify:pcap -- --pcap /absolute/saved-capture.pcapng

This verifier exercises built CLI/stdio MCP, schemas, artifact identity and cleanup. Without --pcap, capture inspection is reported as unverified. Private captures, keys and provider runtime files are not committed.