rich1.0npub1zw7cc8z78v6s3grujfvcv3ckpvg6kr0w7nz9yzvwyglyg0qu5sjsqhkhpxhttps://nostr.ae/npub1zw7cc8z78v6s3grujfvcv3ckpvg6kr0w7nz9yzvwyglyg0qu5sjsqhkhpxnjumphttps://nostr.ae📅 Original date posted:2016-05-10 📝 Original message:Pieter Wuille via bitcoin-dev <bitcoin-dev at lists.linuxfoundation.org> writes: > On 05/03/2016 12:13 AM, lf-lists at mattcorallo.com (Matt Corallo) wrote: >> Hi all, >> >> The following is a BIP-formatted design spec for compact block relay >> designed to limit on wire bytes during block relay. You can find the >> latest version of this document at >> https://github.com/TheBlueMatt/bips/blob/master/bip-TODO.mediawiki. > > Hi Matt, > > thank you for working on this! Indeed! Sorry for the delayed feedback. >> |shortids||List of uint64_ts||8*shortids_length bytes||Little >> Endian||The short transaction IDs calculated from the transactions which >> were not provided explicitly in prefilledtxn > > I tried to derive what length of short ids is actually necessary (some > write-up is on > https://gist.github.com/sipa/b2eb2e486156b5509ac711edd16153ed but it's > incomplete). I did this for IBLT testing. I used variable-length bit encodings, and used the shortest encoding which is unique to you (including mempool). It's a little more work, but for an average node transmitting a block with 1300 txs and another ~3000 in the mempool, you expect about 12 bits per transaction. IOW, about 1/5 of your current size. Critically, we might be able to fit in two or three TCP packets. The wire encoding of all those bit arrays was: [varint-min-numbits] - Shortest bit array length [varint-array-size] - Number of bit arrays. [varint-num].... - Number of entries in array N (x varint-array-size) [packed-bit-arrays...] Last byte was padded with zeros. See: https://github.com/rustyrussell/bitcoin-iblt/blob/master/wire_encode.cpp#L12 I would also avoid the nonce to save recalculating for each node, and instead define an id as: [<64-bit-short-id>][txid] Since you only ever send as many bits as needed to distinguish, this only makes a difference if there actually are collisions. As Peter R points out, we could later enhance receiver to brute force collisions (you could speed that by sending a XOR of all the txids, but really if there are more than a few collisions, give up). And a prototype could just always send 64-bit ids to start. Cheers, Rusty.