Minimum range when importing descriptors?

Question

When importing descriptors with a range less than 1000, it seems to be ignored. Is this deliberate? I could‘t find anything about this in the docs.

To reproduce, first, create an empty wallet:

bitcoin-cli -regtest -named createwallet wallet_name=test disable_private_keys=true blank=true descriptors=true

Import a descriptor with range 10:

bitcoin-cli -regtest -named importdescriptors requests='[{ "desc": "'"wpkh([9a6a2580/84'/1'/179']tpubDCMRAYcH71Gib1rASZpnMPpJbj7S1Nzmao1nPv5Jrb8pwSUimsH5TmK842UhnGPJbiNThzxhK4BpRUCsjSckpNYkH9kjKGWLd94yhZFN94J/0/*)#rljv8npg"'", "timestamp":"now", "active": true, "range":10}]'

Check the range with listdescriptors:

{
  "wallet_name": "test",
  "descriptors": [
    {
      "desc": "wpkh([9a6a2580/84'/1'/179']tpubDCMRAYcH71Gib1rASZpnMPpJbj7S1Nzmao1nPv5Jrb8pwSUimsH5TmK842UhnGPJbiNThzxhK4BpRUCsjSckpNYkH9kjKGWLd94yhZFN94J/0/*)#rljv8npg",
      "timestamp": 1666876980,
      "active": true,
      "internal": false,
      "range": [
        0,
        999
      ],
      "next": 0
    }
  ]
}

In contrast, if I import a descriptor with a range larger than 1000, it seems to be respected:

bitcoin-cli -regtest -named importdescriptors requests='[{ "desc": "'"wpkh([9a6a2580/84'/1'/180']tpubDCMRAYcH71GibuLuWcDkwmmY1gXkXhf162QuEHxkMpZPSi7xck2eGQ6MRGKxNTeY8P1FiFTPCLA5x7qZpFx84fnnrNQFpSnUCwd1nPG8Mk9/0/*)#u49n3vuy"'", "timestamp":"now", "active": true, "range":2000}]'

Check the range again with listdescriptors:

(…)
{
      "desc": "wpkh([9a6a2580/84'/1'/180']tpubDCMRAYcH71GibuLuWcDkwmmY1gXkXhf162QuEHxkMpZPSi7xck2eGQ6MRGKxNTeY8P1FiFTPCLA5x7qZpFx84fnnrNQFpSnUCwd1nPG8Mk9/0/*)#u49n3vuy",
      "timestamp": 1666876980,
      "active": true,
      "internal": false,
      "range": [
        0,
        2000
      ],
      "next": 0
    }

Answer 1

Every time we call the DescriptorScriptPubKeyMan::TopUp method (which happens quite a lot internally, including whenever we add a new descriptor) it automatically adjusts the range-end to be at least as big as (next index + keypool size).

If you launch bitcoind with specifying a keypool smaller than the range you want to use (e.g. bitcoind -regtest -keypool=5), you will observe the behaviour you expected.

(Thank you for providing the steps to reproduce.)