liquid native asset id for regtest networks is static, must be retrieved from sidechain daemon

[philippem]

The native asset ids (L-BTC equivalent) for Liquid side chains is currently in a static lookup table https://github.com/Blockstream/electrs/blob/new-index/src/elements/asset.rs#L18

lazy_static! {
    pub static ref NATIVE_ASSET_ID: AssetId =
        "6f0279e9ed041c3d710a9f57d0c02928416460c4b722ae3457a11eec381c526d"
            .parse()
            .unwrap();
    pub static ref NATIVE_ASSET_ID_TESTNET: AssetId =
        "144c654344aa716d6f3abcc1ca90e5641e4e2a7f633bc09fe3baf64585819a49"
            .parse()
            .unwrap();
    pub static ref NATIVE_ASSET_ID_REGTEST: AssetId =
        "5ac9f65c0efcc4775e0baec4ec03abdde22473cd3cf33c0419ca290e0751b225"
            .parse()
            .unwrap();
}

This asset id is used to identify the fees in Liquid transactions, which have explicit fee outputs spending the native asset.
See get_tx_fee at https://github.com/Blockstream/electrs/blob/new-index/src/util/fees.rs#L46

#[cfg(feature = "liquid")]
pub fn get_tx_fee(tx: &Transaction, _prevouts: &HashMap<u32, &TxOut>, network: Network) -> u64 {
    tx.fee_in(*network.native_asset())
}

A static asset id works for liquidv1, liquidtestnet, and elementsregtest (liquidregtest) networks, but doesn't work for any other network with non standard chain params, which are used to define the native asset id (see elements https://github.com/ElementsProject/elements/blob/master/src/chainparams.cpp#L928).

A result of this is that in custom test networks, the fee property for a transaction resource will be 0:

  "weight": 5229,
  "fee": 0,
  "status": {
    "confirmed": false
  },
  "discount_vsize": 191,
  "discount_weight": 762
}

For custom test networks, electrs should make a getsidechaininfo RPC call to the sidechain daemon and use the value of pegged_asset.

Example for liquid staging:

{
  "fedpegscript": "745c87635b21022944b3c8d83d743e83e12b8a5654a9a48d741bae19f0498dd390b038502666b021023927b2c7716358d4f46cc1f8ca753f35818f593bd62ab2e19137522c35d671b721024c726615f549b02ea1db0fd2ab1973bfe20c296aa4ef14f8979da609b88caa6121027d8facb30d8648cbcea166f6094d1631053800332469827f90c5338368e48e3d2102a5ffc6da600cf25ebc01c4dfbe8ba220a0d35615db1a2c306ba06a355c34902b2102ab5b0b8e18d0dd7933176bbe0d0883a360ade9f45403accf7bdfa9c5439514f62102b0ffa5f8a78dd356afecc371bd826acb3671d8627561289d89a627a121a9c2272102b3278e89c3d5c19cbe5956d4a70a93a3bb0da4e8598d13c034ec5d50cce06b542102b43e4bd6c19b984ef36db6a622eea478f955676fe26786c3141b001e8f91402c2102e5a7aedc7889cad6f14d4534b546cd55d1fde039b0dd1ccb4c58ceac246327f72102e5fe77826e39e69421a0b478419a984c45d94228702aeac2acd540839fd034742103595fa9737e2720b9f600926f2350b4b1315b2248b76ef27fa287022609caead82103f2bbf79daf114617f35e719c46790c301ade558c247ced15f745a40db256a1e62103f4f161336c18c9095aff80aa38ca0417c345f73c73937298d49859e5bf7066e02103fec9f90addc21da7fa30da1568c8a5432a2372e89e8616468d55196c6ea2a7a25f6702c00fb275522102aef2b8a39966d49183fdddaefdc75af6d81ea6d16f7aba745cc4855e88f830842102141d452c3deeb937efff9f3378cd50bbde0543b77bbc6df6fc0e0addbf5578c52103948d24a9622cb14b198aed0739783d7c03d74c32c05780a86b43429c65679def5368ae",
  "current_fedpeg_programs": [
    "0020051c5aaa9d09c4ff74778124a18647f347b759d513d6e029e87fc134aff90d86",
    "0020051c5aaa9d09c4ff74778124a18647f347b759d513d6e029e87fc134aff90d86"
  ],
  "current_fedpegscripts": [
    "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",
    "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"
  ],
  "pegged_asset": "2532cc1cff7278b0e3b7d09c8153d7386e61a858c07b8924ea519fd08c42c00d",
  "min_peg_diff": "7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
  "parent_blockhash": "0f9188f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e2206",
  "parent_chain_has_pow": true,
  "enforce_pak": true,
  "pegin_confirmation_depth": 8
}