feat: zstd compression — requires tunnel-node + CodeFull.gs update - 30% saving download - Full Tunnel

[yyoyoian-pixel]

Summary

End-to-end zstd compression for the tunnel batch protocol. Requires updating both the tunnel-node and CodeFull.gs Apps Script deployment for compression to activate.

How it works

1. Batch 1: client sends ops + zc:1 flag → tunnel-node responds with compressed zr + zc:1
2. Batch 2+: client sends compressed zops → tunnel-node responds with zr
3. Apps Script passes zc and zops/zr through opaquely

What needs updating

• tunnel-node: redeploy (Cloud Run or VPS) — handles zops decompression + zr compression
• CodeFull.gs: redeploy Apps Script with new version — passes zc flag to tunnel-node and zops opaque forward
• Client: new binary sends zc capability flag

Backward compatible — zero failures

• Old client + new tunnel: no zc sent → normal r response, nothing changes
• New client + old tunnel: sends zc, old tunnel ignores it → normal r, compression never activates
• New client + old Apps Script: zc stripped by old script → tunnel never sees it, normal r
• New client + new tunnel + new script: full compression both ways

Measured results

• Download compression: ~25-30% bandwidth saved
• RTT improvement: 5-7s → 1.5-2s on data-heavy batches
• Upload compression: ~5% on small batches, ~25% on large uploads (base64 entropy gain)
• Compression works by exploiting base64's 6-bit-per-byte entropy (zstd recovers the 33% base64 expansion)

Apps Script quota impact

• Execution time (6-min limit): UrlFetchApp.fetch() transfers 25-30% less data per batch → faster round-trips → more batches fit within the 6-minute execution window
• Daily data quota: 25-30% less data fetched per response → quota stretches further across all deployments
• URL Fetch call count: unchanged (same number of HTTP requests per batch) — this is usually the tighter constraint
• Net effect: same number of requests but each one moves faster and uses less data budget

Test plan

• Handshake negotiation: client sends ops+zc, gets zr+zc, switches to zops
• Response compression working (zr)
• Request compression working (zops)
• Video streaming with compression
• Photo upload with compression
• Old client with new tunnel-node (no compression, no failure)
• Old tunnel-node with new client (no compression, no failure)

🤖 Generated with Claude Code

[therealaleph]

Reviewed and accepted. I added one small maintainer-side safety commit before merge: keep compressed batch logs redacted, and authenticate the tunnel batch request before decoding compressed zops. Local verification passed on the updated branch:

• cargo test --lib
• cargo build --release
• cargo build --bin mhrv-rs-ui --release --features ui
• cargo test (tunnel-node)
• cargo build --release (tunnel-node)
• Android debug build with Android Studio JBR

Docker local image build was attempted but Docker Desktop/daemon is not running on this Mac (/Users/dev/.docker/run/docker.sock missing), so container image verification will be covered by the release workflow.

---

Answered via LLM, Supervised @therealaleph