feat: pack oversized BigInt as MessagePack ext 0x42 - #25693
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Values outside int64/uint64 pack as msgpackr useBigIntExtension (two's-complement, type 0x42) with a 256-byte payload cap. In-range values still use integer wire. Unpack of ext 0x42 returns bigint.
godsflaw
approved these changes
Sep 19, 2026
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Summary
Pack
bigintvalues outside the int64/uint64 range as MessagePack ext type0x42(msgpackruseBigIntExtensiontwo's-complement payload) and unpack that type back tobigint. Payload is capped at 256 bytes. Values that still fit 64-bit integer range keep using integer wire.Test plan
node --test test/bigint.test.js(20 tests)npm test(233 tests, 0 fail)Covers uint256, 64-bit boundaries (
2^64,-2^63-1), nested arrays/maps/objects, 256-byte cap, empty/oversize/other-ext unpack, and in-range BigInt still on integer wire (0xcf/0xd3).