[DNM] Add statement-latency-bench example

.github/workflows/docker-pr.yml

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+name: docker-pr
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, labeled]
+
+permissions:
+  contents: read
+
+jobs:
+  build-push:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      - id: meta
+        run: |
+          echo "tag=${{ github.event.pull_request.number }}-$(git rev-parse --short=8 HEAD)" >> "$GITHUB_OUTPUT"
+
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+
+      - if: contains(github.event.pull_request.labels.*.name, 'push-debug-image')
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.PARITYPR_DOCKERHUB_USERNAME }}
+          password: ${{ secrets.PARITYPR_DOCKERHUB_PASSWORD }}
+
+      - uses: docker/build-push-action@v6.18.0
+        with:
+          context: .
+          file: ./examples/statement-latency-bench/Dockerfile
+          push: ${{ contains(github.event.pull_request.labels.*.name, 'push-debug-image') }}
+          tags: paritypr/smoldot:${{ steps.meta.outputs.tag }}

examples/statement-latency-bench/.gitignore

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+node_modules/
+package-lock.json
+chain-specs/
+*.log

examples/statement-latency-bench/Dockerfile

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+# Build & run the statement-latency-bench Node.js tool.
+#
+# The bench depends on the local `smoldot` npm package
+# (wasm-node/javascript), whose `prepack` step compiles Rust → wasm.
+# So the builder stage needs rust + the wasm32 target + node.
+
+FROM rust:1 AS builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends curl ca-certificates \
+    && curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
+    && apt-get install -y --no-install-recommends nodejs \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN rustup target add wasm32-unknown-unknown
+
+COPY ./.. /build
+
+# Build the smoldot npm package first: `npm run build` runs
+# prepare.mjs (compiles Rust → wasm) then tsc, producing dist/.
+# A plain `file:` install of the bench would NOT run these scripts.
+WORKDIR /build/wasm-node/javascript
+RUN npm install
+RUN npm run build
+
+# --install-links materializes the `file:../../wasm-node/javascript`
+# dep as a real copy (including the freshly built dist/) in
+# node_modules instead of a symlink, so the runtime stage can be a
+# self-contained copy of just this directory.
+WORKDIR /build/examples/statement-latency-bench
+RUN npm install --omit=dev --install-links
+
+
+FROM alpine:latest
+
+RUN apk add --no-cache nodejs bash
+
+WORKDIR /app
+COPY --from=builder /build/examples/statement-latency-bench /app
+
+ENTRYPOINT ["node", "/app/bench.js"]

examples/statement-latency-bench/README.md

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+# statement-latency-bench
+
+Smoldot-based Node.js port of `polkadot-sdk/substrate/client/statement-store/statement-latency-bench`.
+
+Each virtual client runs an in-process smoldot light client and joins the
+statement-store libp2p network as its own peer. There is no `--rpc-endpoints`:
+smoldot is a peer, not an RPC client of a node.
+
+## Build smoldot first
+
+```bash
+cd ../../wasm-node/javascript
+npm install && npm run build
+cd -
+npm install
+```
+
+## Usage
+
+`--parachain-spec` and `--relay-chain-spec` each accept either a local file
+path or an `http(s)://` URL. Bootnodes are expected to be embedded in the
+spec; the canonical source is the [paritytech/chainspecs](https://github.com/paritytech/chainspecs)
+repo, and smoldot bundles popular ones under `../../demo-chain-specs/`.
+
+```bash
+# bundled spec from the smoldot repo
+node bench.js \
+  --parachain-spec ../../demo-chain-specs/polkadot_asset_hub.json \
+  --relay-chain-spec ../../demo-chain-specs/polkadot.json \
+  --num-clients 4 --num-rounds 2 --messages-pattern "3:128" \
+  --receive-timeout-ms 30000 --interval-ms 5000
+
+# raw URL straight from polkadot-sdk (paritytech/chainspecs is a symlink-only
+# index repo; raw.githubusercontent doesn't follow its symlinks across submodules,
+# so point at the underlying files directly)
+node bench.js \
+  --parachain-spec https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/cumulus/parachains/chain-specs/asset-hub-polkadot.json \
+  --relay-chain-spec https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/polkadot/node/service/chain-specs/polkadot.json \
+  --num-clients 4 --num-rounds 2 --messages-pattern "3:128"
+```
+
+For a local dev network, splice your bootnode into the parachain spec once
+(e.g. with `jq`, like `examples/statement-chat/dev.sh`) and pass the result
+as `--parachain-spec`.
+
+## Flags
+
+| Flag | Default | Notes |
+|---|---|---|
+| `--parachain-spec` | required | Parachain raw chain spec — file path or `http(s)://` URL. |
+| `--relay-chain-spec` | required | Relay chain raw chain spec — file path or `http(s)://` URL. |
+| `--false-positive-rate` | `0.01` | Statement-store affinity bloom filter rate. |
+| `--num-clients` | `100` | Each spawns its own smoldot instance. |
+| `--workers` | `1` | If >1, fork that many child processes; clients distributed evenly. Use to scale past one event loop's capacity (~150 clients). |
+| `--num-rounds` | `1` | |
+| `--messages-pattern` | `5:512` | `count:size,count:size,…` |
+| `--receive-timeout-ms` | `5000` | |
+| `--interval-ms` | `10000` | Wall-clock pacing between rounds. |
+| `--statement-expiry-ms` | `600000` | |
+| `--warmup-ms` | `15000` | Fixed sleep after `addChain` before round 1. |
+| `--fail-fast` | `false` | First failure aborts all clients via AbortController. |
+| `--log-level` | `info` | error/warn/info/debug/trace |
+
+## Differences from `bench.rs`
+
+- **Connection model.** Rust connects to N WS endpoints; smoldot joins the
+  network directly. Chain specs (with embedded bootnodes) replace
+  `--rpc-endpoints` as the wiring point.
+- **One smoldot per client.** Smoldot dedupes within a client, so one peer per
+  client requires one `start()` per client. Each is ~tens of MB resident; for
+  N=100 expect multi-GB RAM. For larger N, use `--workers <K>` to fork K child
+  processes (each gets its own event loop and runs N/K clients), or follow the
+  same K8s-shard pattern as the Rust bench.
+- **No barrier.** Smoldot startup is variable (5–30s) and gossip readiness is
+  not observable from JSON-RPC, so a barrier on a code line gives false
+  confidence. We use a fixed `--warmup-ms` instead and pace rounds by wall clock.
+- **`--seed` removed.** Always derives sr25519 keys via `//StatementClient//${idx}`,
+  matching `sc_statement_store::test_utils::get_keypair`.
+- **Output line prefixes** match `bench.rs` so log parsers keyed on the leading
+  tokens keep working: `Spawning {N} client tasks... {testRunId}`, `Benchmark
+  Results: send_min=…`, `Benchmark Failed: failed_clients=…`, `Benchmark
+  Finished: rounds_with_any_success=…`. The smoldot port also adds a
+  `Starting Statement Store Latency Benchmark:` config line and an `errors=[…]`
+  segment to `Benchmark Failed`, neither of which exists in `bench.rs`.