swaitsandClaude Opus 4.7
f83d4088e3
Every "Test vectors: \`corpus/...\`" mention in the spec is now a markdown link pointing at the corresponding file or directory on GitHub. Each version build resolves its links to the correct git ref: - /latest/ -> https://github.com/swaits/meshcore-spec/tree/main/corpus/... - /v0.1.0/ -> https://github.com/swaits/meshcore-spec/tree/v0.1.0/corpus/... - future /vX.Y.Z/ -> /tree/vX.Y.Z/corpus/... Two changes: 1. src/*.md (18 files): the inline-code corpus paths in each "Cross-References" section are now markdown links. Directories point at /tree/main/corpus/..., individual .json files point at /blob/main/corpus/.... CHANGELOG and other non-corpus main links are intentionally left pointing at main — the canonical history lives there regardless of which version you're reading. 2. justfile: `cut-version` now also runs a sed over the snapshot's *.md files replacing /tree/main/corpus -> /tree/<VERSION>/corpus and /blob/main/corpus -> /blob/<VERSION>/corpus. So a freshly-cut version is self-consistent. versions/v0.1.0/* regenerated by re-running `just cut-version v0.1.0` after the new src/ links + recipe sed landed. Tagging the release commit (`git tag v0.1.0`) is now REQUIRED — not "optional" — because the rendered /v0.1.0/ pages reference /tree/v0.1.0/corpus/... on GitHub. Without the tag the links 404. cut-version's output now says so. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
68 lines
2.2 KiB
Markdown
68 lines
2.2 KiB
Markdown
# MeshCore Protocol Specification
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## Section 16: Packet Hash
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### Overview
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MeshCore uses SHA-256 hashing for packet deduplication. Each node maintains a
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table of recently seen packet hashes and discards packets it has already
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processed. The hash is computed over the payload type and payload contents, with
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a special case for TRACE packets.
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### Hash Computation
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The packet hash is computed as:
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```
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hash = SHA-256(payload_type_byte || payload_data)[0..MAX_HASH_SIZE-1]
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```
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Where:
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- `payload_type_byte` is a single byte: `(header >> 2) & 0x0F`
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- `payload_data` is the raw payload bytes (payload_len bytes)
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- The SHA-256 output is truncated to MAX_HASH_SIZE (8) bytes
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### TRACE Packet Special Case
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For TRACE packets (payload_type = 0x09), the path_len byte is included in the
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hash to distinguish trace packets that revisit the same node on their return
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path:
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```
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hash = SHA-256(payload_type_byte || path_len_byte || payload_data)[0..MAX_HASH_SIZE-1]
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```
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### Algorithm
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```
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function calculatePacketHash(packet):
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sha = SHA256_init()
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type_byte = getPayloadType(packet.header) // single byte
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SHA256_update(sha, type_byte)
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if type_byte == 0x09: // TRACE
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SHA256_update(sha, packet.path_len) // 1 byte (as uint8)
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SHA256_update(sha, packet.payload, packet.payload_len)
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hash = SHA256_finalize(sha)
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return hash[0..7] // first MAX_HASH_SIZE bytes
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```
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### Properties
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- The hash does NOT include the header byte, path, or transport codes. This
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means the same logical message received via different routes produces the
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same hash.
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- The hash does NOT include the route type or version. Only the payload type
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and payload content determine the hash.
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- For TRACE packets, including path_len ensures that the same trace payload
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at different stages of traversal produces different hashes.
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### Cross-References
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- [Section 10: Trace](10-payload-trace.md) — TRACE packet special handling
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- Test vectors: [`corpus/crypto/sha256/packet-hash.json`](https://github.com/swaits/meshcore-spec/blob/v0.1.0/corpus/crypto/sha256/packet-hash.json)
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### Reference Implementation
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- `Packet::calculatePacketHash()` in `src/Packet.cpp`
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- `MeshTables::hasSeen()` — Deduplication table lookup
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