Extract ParseDescriptorRange

So as to be consistently informative when the checks fail, and
to protect against unintentional divergence among the checks.

test/functional/rpc_scantxoutset.py

@@ -4,7 +4,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test the scantxoutset rpc call."""
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal
+from test_framework.util import assert_equal, assert_raises_rpc_error
 
 from decimal import Decimal
 import shutil
@@ -67,6 +67,13 @@ class ScantxoutsetTest(BitcoinTestFramework):
         assert_equal(self.nodes[0].scantxoutset("start", [ "addr(" + addr_P2SH_SEGWIT + ")", "addr(" + addr_LEGACY + ")", "addr(" + addr_BECH32 + ")"])['total_amount'], Decimal("0.007"))
         assert_equal(self.nodes[0].scantxoutset("start", [ "addr(" + addr_P2SH_SEGWIT + ")", "addr(" + addr_LEGACY + ")", "combo(" + pubk3 + ")"])['total_amount'], Decimal("0.007"))
 
+        self.log.info("Test range validation.")
+        assert_raises_rpc_error(-8, "End of range is too high", self.nodes[0].scantxoutset, "start", [ {"desc": "desc", "range": -1}])
+        assert_raises_rpc_error(-8, "Range should be greater or equal than 0", self.nodes[0].scantxoutset, "start", [ {"desc": "desc", "range": [-1, 10]}])
+        assert_raises_rpc_error(-8, "End of range is too high", self.nodes[0].scantxoutset, "start", [ {"desc": "desc", "range": [(2 << 31 + 1) - 1000000, (2 << 31 + 1)]}])
+        assert_raises_rpc_error(-8, "Range specified as [begin,end] must not have begin after end", self.nodes[0].scantxoutset, "start", [ {"desc": "desc", "range": [2, 1]}])
+        assert_raises_rpc_error(-8, "Range is too large", self.nodes[0].scantxoutset, "start", [ {"desc": "desc", "range": [0, 1000001]}])
+
         self.log.info("Test extended key derivation.")
         # Run various scans, and verify that the sum of the amounts of the matches corresponds to the expected subset.
         # Note that all amounts in the UTXO set are powers of 2 multiplied by 0.001 BTC, so each amounts uniquely identifies a subset.