MEV-Share client module (mev_share.zig)

[koko1123]

Motivation

MEV-Share is Flashbots' orderflow auction protocol — the primary mechanism for searchers to backrun private transactions on Ethereum today. The TypeScript reference client (mev-share-client-ts) is the only official SDK. A Zig client would be the fastest implementation and give eth.zig a concrete position in the active MEV ecosystem.

What MEV-Share enables

• Private transaction backrunning: Subscribe to a stream of pending tx hints, backrun profitable ones
• Bundle composition: Compose backrun bundles targeting specific pending txs
• MEV profit sharing: A portion of searcher profit flows back to the user who originated the tx

API surface (mirrors mev-share-client-ts)

New file: src/mev_share.zig

pub const MevShareClient = struct {
    /// Subscribe to the MEV-Share event stream (SSE).
    /// Calls callback for each pending transaction or bundle event.
    pub fn on(
        self: *MevShareClient,
        allocator: std.mem.Allocator,
        callback: *const fn (event: PendingEvent) void,
    ) !void

    /// Submit a private transaction with MEV hints.
    /// Maps to eth_sendPrivateTransaction.
    pub fn sendTransaction(
        self: *MevShareClient,
        allocator: std.mem.Allocator,
        signed_tx: []const u8,
        opts: SendTransactionOpts,
    ) ![32]u8  // tx hash

    /// Simulate a MEV-Share bundle (mev_simBundle).
    pub fn simulateBundle(
        self: *MevShareClient,
        allocator: std.mem.Allocator,
        opts: flashbots.MevSendBundleOpts,
        sim_opts: SimBundleOpts,
    ) !SimBundleResult

    /// Fetch historical event stream data.
    pub fn getEventHistory(
        self: *MevShareClient,
        allocator: std.mem.Allocator,
        params: EventHistoryParams,
    ) ![]EventHistoryEntry
};

Key types needed

/// A pending transaction or bundle from the event stream.
pub const PendingEvent = union(enum) {
    transaction: PendingTransaction,
    bundle: PendingBundle,
};

pub const PendingTransaction = struct {
    hash: [32]u8,
    logs: ?[]Log,
    calldata: ?[]u8,
    function_selector: ?[4]u8,
    contract_address: ?[20]u8,
    to: ?[20]u8,
    value: ?u256,
};

pub const PendingBundle = struct {
    hash: [32]u8,
    txs: []PendingTransaction,
};

Implementation notes

• Transport: Depends on sse_transport.zig (see SSE transport for MEV-Share event streaming #33) for event streaming; uses existing http_transport.zig for JSON-RPC calls
• Auth: Reuse flashbots.zig auth header signing (X-Flashbots-Signature)
• Networks: Mainnet endpoint https://mev-share.flashbots.net; Sepolia https://mev-share-goerli.flashbots.net
• mev_sendBundle is already implemented in flashbots.zig — no duplication needed

Relationship to examples

Once this exists, an example backrunner bot (examples/08_mev_share_backrunner.zig) becomes straightforward.