Add MEV-Share backrunner example (closes #38)

[koko1123]

What

examples/08_mev_share_backrunner.zig — a teaching MEV-Share backrunner that ties together the new MEV stack: comptime-built Uniswap V2/V3 swap-selector table, the mev_share SSE hint stream, EIP-1559 backrun construction/signing, and mev_sendBundle bundle composition. DRY_RUN=1 default (prints the bundle JSON instead of submitting); env-var config with Sepolia defaults.

It works against the live network

Run against the mainnet stream, it matched hash-only and bundle hints in real time and printed the bundle it would submit. Sample:

[hash-only]   0x1ad30a93...0241 (no selector hint, skipping)
[bundle]      2 txs, skipping

Bug fixes from dog-fooding (first consumer of mev_share)

MevShareClient.on was uncompilable for any consumer: sse_transport.SseParser.feedLine used std.mem.trimRight (renamed trimEnd in Zig 0.16) and built two anonymous structs with mismatched inferred types. Neither surfaced in CI because feedLine is only reached via the network path, not unit tests. Fixed both in src/sse_transport.zig; zig build test still passes. (The refAllDeclsRecursive test added in #63 covers mev_share itself but not sse_transport — I'll file a follow-up to extend that guard.)

Also

README + docs/content/docs/examples.mdx entries; CHANGELOG Added/Fixed bullets.

Verification

examples build, root zig build test, zig fmt --check, and pnpm -C docs build all pass on Zig 0.16.0.

Closes #38

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added MEV-Share backrunner example—a bot that monitors the MEV-Share event stream and constructs backrun bundles for Uniswap trades.

• Bug Fixes

  • Fixed SSE stream parsing to correctly handle line-ending characters.

• Documentation

  • Updated examples with new MEV-Share backrunner entry and usage instructions.

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Project	Deployment	Actions	Updated (UTC)
eth-zig	Ready	Preview, Comment	Jun 10, 2026 3:55pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7e88da1d-705d-47dc-9f31-170468ef3dd0

📥 Commits

Reviewing files that changed from the base of the PR and between 2d74584 and 28f1e79.

📒 Files selected for processing (6)

• CHANGELOG.md
• README.md
• docs/content/docs/examples.mdx
• examples/08_mev_share_backrunner.zig
• examples/build.zig
• src/sse_transport.zig

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📝 Walkthrough

Walkthrough

This PR introduces a complete MEV-Share backrunner example that demonstrates subscribing to the Flashbots MEV-Share pending-transaction stream, matching hints against compile-time Uniswap swap selectors, and submitting backrun bundles. The change includes a critical fix to the SSE parser and comprehensive documentation.

Changes

MEV-Share Backrunner Bot and Tooling

Layer / File(s)	Summary
SSE Transport Parser Fix src/sse_transport.zig	Replaces std.mem.trimRight with std.mem.trimEnd for trailing carriage-return removal and refactors field/value parsing to use an explicit Parsed struct. Fixes a latent semantic break that affected MevShareClient.on consumption of SSE events.
Backrunner Bot Configuration and Utilities examples/08_mev_share_backrunner.zig (lines 1–90)	Defines compile-time WatchedSwap metadata and a table of Uniswap function selectors via eth.keccak.selector, and provides matchSwap to identify incoming 4-byte selectors against the pre-hashed table.
Bot State and Event Subscription examples/08_mev_share_backrunner.zig (lines 91–141)	Declares the Bot state struct (signer, MEV-Share client, optional RPC provider, chain ID, event counters) and implements the onEvent SSE callback wrapper that catches errors, flushes output, increments event count, and exits when MAX_EVENTS is reached.
Event Processing and Bundle Submission examples/08_mev_share_backrunner.zig (lines 142–283)	Implements handleEvent to extract pending transactions from SSE hints, skip bundle-style events, match revealed selectors, and log outcomes; submitBackrun to construct EIP-1559 transactions, sign with the signer key, and submit bundles (or print dry-run JSON-RPC); and parseKey for hex private-key decoding.
Main Entry Point and Lifecycle examples/08_mev_share_backrunner.zig (lines 285–390)	Wires up stdout buffering, reads environment configuration (auth/signer keys, URLs, dry-run mode), initializes the MEV-Share client and optional RPC provider, prints startup banner and watched selectors, installs SSE subscription with error handling, and logs stream termination statistics.
Build and Documentation examples/build.zig, CHANGELOG.md, README.md, docs/content/docs/examples.mdx	Registers the new example executable in the build manifest, records the SSE parser fix and new backrunner example in the changelog, adds the example to the README examples table, and provides detailed documentation describing the compile-time selector computation, SSE subscription flow, bundle construction, and dry-run execution command targeting Sepolia.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related issues

• StrobeLabs/eth.zig#38: This PR implements the exact MEV-Share backrunner example requested and fixes the SSE parser issue that was blocking the feature.
• StrobeLabs/eth.zig#34: The SSE transport parser fix directly addresses the underlying transport behavior that the MEV-Share client depends on.

Possibly related PRs

• StrobeLabs/eth.zig#48: The SSE transport parser fix in this PR directly corrects behavior introduced in the SSE transport implementation.
• StrobeLabs/eth.zig#63: This PR's src/sse_transport.zig fix addresses the latent semantic break in MevShareClient.on that was surfaced while building the backrunner example.
• StrobeLabs/eth.zig#32: The backrunner example wires up MEV-Share bundle submission via flashbots.Relay and mev_sendBundle functionality introduced in that PR.

Poem

🐰 A backrunner hops through the SSE stream,
Matching swaps with selectors, a fast-paced dream,
Bundle-signing with Zig's compiled grace,
The parser trimmed right, now trimEnd takes its place! 🚀

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: adding a MEV-Share backrunner example. It is concise, descriptive, and directly reflects the primary addition in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/backrunner-example

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