litecoin/doc/mweb/mining-changes.md

MWEB - Mining Changes

Starting with Litecoin Core release v0.21.2, changes have been made to getblocktemplate to support mining blocks with MWEB data. getblocktemplate does not yet provide consumers control over which MWEB transactions can be included in a block, and instead builds the MWEB and integrating transactions for you. Though changes do need to be made to pool software, those changes should be very minimal.

Required Pool Software Changes

1. The "mweb" rule must be supplied to the getblocktemplate "rules" array to signal to the node that MWEB is supported.

getblocktemplate '{"rules": ["segwit", "mweb"]}'

2. In the response, there will be an "mweb" field for all blocks after MWEB activation. If that field exists, then before calling submitblock with your solved block, append a byte with value 1 followed by the data from the "mweb" field, to the very end of the serialized block. NOTE: This <0x01> is just an indicator that tells the node that MWEB data follows.

<Block><0x01><MWEB>

3. If your pool software modifies, reorders, or reprioritizes transactions that it receives from getblocktemplate, it must be updated to ensure it never alters the final transaction, known as the HogEx or "Integrating Transaction." The pool also must be careful to not modify or remove any transaction the HogEx depends on (txs with outputs it spends).

The reason for (3) is that the HogEx commits to the MWEB data, and moves the pegged in coins to the HogAddr (address holding all MMEB coins), and sends the pegout coins to the addresses specified by the pegout transactions in the MWEB. Any mismatch in MWEB data and the HogEx transaction would result in the block not passing consensus checks.

---

Example

GBT Request:

getblocktemplate '{"rules": ["mweb", "segwit"]}'

GBT Response:

{
  "capabilities": [
    "proposal"
  ],
  "version": 536870912,
  "rules": [
    "csv",
    "!segwit",
    "taproot",
    "mweb"
  ],
  "vbavailable": {
  },
  "vbrequired": 0,
  "previousblockhash": "67eb60f64118fdc667e03894c57c10d57c42709fdc0438bafaaee9a3b2bebf0a",
  "transactions": [
    {
      "data": "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",
      "txid": "f695435385ef0d7bd8cc3c1d5c10b9f5f0a2e2d6978a7ed5bf011fd3a4817d03",
      "hash": "5c5211aef305551bcdf90e2f4af78fcc834b51041da8512f9fcb14bcff0b07e7",
      "depends": [
      ],
      "fee": 84371,
      "sigops": 21,
      "weight": 1213
    },
    {
      "data": "020000000008013b41f467a3724144d7875b6c4a1a8792b5d6609385f66295edd304bbd1dfe36e0000000000ffffffff0158913ee998020000225820f78bbf399705e3149d58e19de2e43244f9da33bd5c15b57393ee1a6de61700110000000000",
      "txid": "efe1699039d3a8fa35dd3fad367e446937ab33bd19f9f0252c46d09b29fe733f",
      "hash": "efe1699039d3a8fa35dd3fad367e446937ab33bd19f9f0252c46d09b29fe733f",
      "depends": [
      ],
      "fee": 0,
      "sigops": 0,
      "weight": 376
    }
  ],
  "coinbaseaux": {
  },
  "coinbasevalue": 1250084371,
  "longpollid": "67eb60f64118fdc667e03894c57c10d57c42709fdc0438bafaaee9a3b2bebf0a7329",
  "target": "0000000310500000000000000000000000000000000000000000000000000000",
  "mintime": 1648488758,
  "mutable": [
    "time",
    "transactions",
    "prevblock"
  ],
  "noncerange": "00000000ffffffff",
  "sigoplimit": 80000,
  "sizelimit": 4000000,
  "weightlimit": 4000000,
  "curtime": 1648489088,
  "bits": "1d031050",
  "height": 2273263,
  "default_witness_commitment": "6a24aa21a9ed55644a20af179b1ed32e0d2ad936ae8bf97a52cb442212658aed07b000f0d4eb",
  "mweb": "8089de6f4c6806e610517acedc04c9eb1bbbfc1d44bf89cfc65958e7c9ea13801c2e1d2e00000000000000000000000000000000000000000000000000000000000000007b770abb937280dfb1adb111f3e472312fe55ff679c233e8db42abbdf6ebfa61756a15a4d14f7f19abc3a5d4515a2c071c624327b51f12107ecf53cad49ec16700000000000000000000000000000000000000000000000000000000000000008b4e00000000"
}

Then the pool would create work as normal, ignoring the "mweb" field until after a valid block is found. In our example, the pool solves the block, whose traditional serialization is:

000000200abfbeb2a3e9aefaba3804dc9f70427cd5107cc59438e067c6fd1841f660eb67920f547825ab14356af63467bda7c44369ef0d99be3b7512ac049fa408a8d0c1abf241625010031d52d3583f03010000000001010000000000000000000000000000000000000000000000000000000000000000ffffffff2a03efaf22194d696e656420627920416e74506f6f6c20fb000100e0e948ee000003266c00000000000000ffffffff0213c6824a000000001976a914ef94ec7962fc91a3d1df1dd1b274fb02a564eb5f88ac0000000000000000266a24aa21a9ed55644a20af179b1ed32e0d2ad936ae8bf97a52cb442212658aed07b000f0d4eb01200000000000000000000000000000000000000000000000000000000000000000000000000200000000010124d9cf4706e8f141b1be6882916c27b5b31a6cf9206604782186729a3870616202000000171600140dbf1844656d0cc2205f5121622711c5ea43e43afeffffff068ca30100000000001976a9143db645a223d02ecc67738b00377a0b92f90562eb88ac168a0100000000001976a9148f535a63d7e45f98b62042ef6c4be3565c3ba3d388ac5e1b16530400000017a9142bb58162483ff309374d93e62da908851b30b55c87ac930100000000001976a91472c1e50b7c762678092f53f8d99fa555b122531c88ac10a00100000000001976a9147d61748d306421a53ebdf9000c3e855254c2d92388ac32a10100000000001976a914aa96a55e1bbbbfe426639e84f7cb5fbe0a95aeab88ac02473044022044a378e3644a7f4531b253d5e17129394b2e3f68bc710186976bc8aafd28d91602202460c94c0c6d0d973584527454786024da7ab63a5ff07416bbdcf6b18729937e0121022eb2a9786cd2830831b063d0c8b31e26c3aad87cf85eedd8391f57cddf9edebb8d882200020000000008013b41f467a3724144d7875b6c4a1a8792b5d6609385f66295edd304bbd1dfe36e0000000000ffffffff0158913ee998020000225820f78bbf399705e3149d58e19de2e43244f9da33bd5c15b57393ee1a6de61700110000000000

The pool then simply appends a 1 and then the value from the "mweb" field when calling submitblock:

submitblock "000000200abfbeb2a3e9aefaba3804dc9f70427cd5107cc59438e067c6fd1841f660eb67920f547825ab14356af63467bda7c44369ef0d99be3b7512ac049fa408a8d0c1abf241625010031d52d3583f03010000000001010000000000000000000000000000000000000000000000000000000000000000ffffffff2a03efaf22194d696e656420627920416e74506f6f6c20fb000100e0e948ee000003266c00000000000000ffffffff0213c6824a000000001976a914ef94ec7962fc91a3d1df1dd1b274fb02a564eb5f88ac0000000000000000266a24aa21a9ed55644a20af179b1ed32e0d2ad936ae8bf97a52cb442212658aed07b000f0d4eb01200000000000000000000000000000000000000000000000000000000000000000000000000200000000010124d9cf4706e8f141b1be6882916c27b5b31a6cf9206604782186729a3870616202000000171600140dbf1844656d0cc2205f5121622711c5ea43e43afeffffff068ca30100000000001976a9143db645a223d02ecc67738b00377a0b92f90562eb88ac168a0100000000001976a9148f535a63d7e45f98b62042ef6c4be3565c3ba3d388ac5e1b16530400000017a9142bb58162483ff309374d93e62da908851b30b55c87ac930100000000001976a91472c1e50b7c762678092f53f8d99fa555b122531c88ac10a00100000000001976a9147d61748d306421a53ebdf9000c3e855254c2d92388ac32a10100000000001976a914aa96a55e1bbbbfe426639e84f7cb5fbe0a95aeab88ac02473044022044a378e3644a7f4531b253d5e17129394b2e3f68bc710186976bc8aafd28d91602202460c94c0c6d0d973584527454786024da7ab63a5ff07416bbdcf6b18729937e0121022eb2a9786cd2830831b063d0c8b31e26c3aad87cf85eedd8391f57cddf9edebb8d882200020000000008013b41f467a3724144d7875b6c4a1a8792b5d6609385f66295edd304bbd1dfe36e0000000000ffffffff0158913ee998020000225820f78bbf399705e3149d58e19de2e43244f9da33bd5c15b57393ee1a6de61700110000000000018089de6f4c6806e610517acedc04c9eb1bbbfc1d44bf89cfc65958e7c9ea13801c2e1d2e00000000000000000000000000000000000000000000000000000000000000007b770abb937280dfb1adb111f3e472312fe55ff679c233e8db42abbdf6ebfa61756a15a4d14f7f19abc3a5d4515a2c071c624327b51f12107ecf53cad49ec16700000000000000000000000000000000000000000000000000000000000000008b4e00000000"