Fixed a regression introduced in 4.2.1

The issues manifests itself whenever the checkpoint block is after
the asert anchor. This caused the code in blockchain.py to have a bad time.

The asert anchor calculation code needs all headers, but if we have a
checkpoint after the anchor, all headers are not always available. The fix
is to either have checkpoints before the anchor, or to hard-code the anchor.

This is the case for all chains we support now.

We hard-coded the anchor for all chains except for scalenet, which will
reorg back to before the anchor each time so hard-coding the anchor
would break things in the future.

RELEASE-NOTES

@@ -1060,3 +1060,9 @@ and there is no warning message.
 - Added checkpoint after HF block, also added CLI arg --taxcoin for ABC's coin.
   (Calin Culianu)
 - Network Dialog: Added advanced request throttling params (Calin Culianu)
+
+# RELEASE NOTES 4.2.2
+
+- Fixed a regression introduced in 4.2.1 where the checkpoint block being after
+  the asert anchor caused the code in blockchain.py to have a bad time.
+  (Calin Culianu)

electroncash/asert_daa.py

@@ -72,6 +72,7 @@ class ASERTDaa:
 
     MAX_TARGET = bits_to_target(MAX_BITS)
 
+    # If left as none, blockchain.py will calculate this at runtime as we read headers.
     anchor: Optional[Anchor] = None
 
     def __init__(self, is_testnet=False):

electroncash/blockchain.py

@@ -423,19 +423,24 @@ def get_suitable_block_height(self, suitableheight, chunk=None):
 
         return blocks1['block_height']
 
-    _cached_asert_anchor: Optional[asert_daa.Anchor] = None  # cached Anchor, per-Blockchain instance
+    # cached Anchor, per-Blockchain instance, only used if the checkpoint for this network is *behind* the anchor block
+    _cached_asert_anchor: Optional[asert_daa.Anchor] = None
+
     def get_asert_anchor(self, prevheader, mtp, chunk=None):
+        """Returns the asert_anchor either from Networks.net if hardcoded or
+        calculated in realtime if not."""
         if networks.net.asert_daa.anchor is not None:
             # Checkpointed (hard-coded) value exists, just use that
             return networks.net.asert_daa.anchor
+        # Bug note: The below does not work if we don't have all the intervening
+        # headers -- therefore this execution path should only be taken for networks
+        # where the checkpoint block is before the anchor block.  This means that
+        # adding a checkpoint after the anchor block without setting the anchor
+        # block in networks.net.asert_daa.anchor will result in bugs.
         if (self._cached_asert_anchor is not None
                 and self._cached_asert_anchor.height <= prevheader['block_height']):
             return self._cached_asert_anchor
-        # ****
-        # This may be slow -- we really should be leveraging the hard-coded
-        # checkpointed value. TODO: add hard-coded value to networks.py after
-        # Nov. 15th 2020 HF to ASERT DAA
-        # ****
+
         anchor = prevheader
         activation_mtp = networks.net.asert_daa.MTP_ACTIVATION_TIME
         while mtp >= activation_mtp:

electroncash/networks.py

@@ -22,9 +22,10 @@
 # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-import json, pkgutil
+import json
+import pkgutil
 
-from .asert_daa import ASERTDaa
+from .asert_daa import ASERTDaa, Anchor
 
 def _read_json_dict(filename):
     try:
@@ -36,7 +37,6 @@ def _read_json_dict(filename):
 
 class AbstractNet:
     TESTNET = False
-    asert_daa = ASERTDaa()
     LEGACY_POW_TARGET_TIMESPAN = 14 * 24 * 60 * 60   # 2 weeks
     LEGACY_POW_TARGET_INTERVAL = 10 * 60  # 10 minutes
     LEGACY_POW_RETARGET_BLOCKS = LEGACY_POW_TARGET_TIMESPAN // LEGACY_POW_TARGET_INTERVAL  # 2016 blocks
@@ -73,8 +73,13 @@ class MainNet(AbstractNet):
     #    network.synchronous_get(("blockchain.block.header", [height, height]))
     #
     # Consult the ElectrumX documentation for more details.
-    VERIFICATION_BLOCK_MERKLE_ROOT = "45fca167c5d9b7774eab414e1608cefd37737488fb1e11f10c2e42eaf1be370e"
-    VERIFICATION_BLOCK_HEIGHT = 661648
+    VERIFICATION_BLOCK_MERKLE_ROOT = "68077352cf309072547164625deb11e92bd379e759e87f3f9ac6e61d1532c536"
+    VERIFICATION_BLOCK_HEIGHT = 661942
+    asert_daa = ASERTDaa(is_testnet=False)
+    # Note: We *must* specify the anchor if the checkpoint is after the anchor, due to the way
+    # blockchain.py skips headers after the checkpoint.  So all instances that have a checkpoint
+    # after the anchor must specify the anchor as well.
+    asert_daa.anchor = Anchor(height=661647, bits=402971390, prev_time=1605447844)
 
     # Version numbers for BIP32 extended keys
     # standard: xprv, xpub
@@ -89,7 +94,6 @@ class MainNet(AbstractNet):
 
 class TestNet(AbstractNet):
     TESTNET = True
-    asert_daa = ASERTDaa(is_testnet=True)
     WIF_PREFIX = 0xef
     ADDRTYPE_P2PKH = 111
     ADDRTYPE_P2PKH_BITPAY = 111  # Unsure
@@ -113,6 +117,8 @@ class TestNet(AbstractNet):
 
     VERIFICATION_BLOCK_MERKLE_ROOT = "d97d670815829fddcf728fa2d29665de53e83609fd471b0716a49cde383fb888"
     VERIFICATION_BLOCK_HEIGHT = 1421482
+    asert_daa = ASERTDaa(is_testnet=True)
+    asert_daa.anchor = Anchor(height=1421481, bits=486604799, prev_time=1605445400)
 
     # Version numbers for BIP32 extended keys
     # standard: tprv, tpub
@@ -134,38 +140,43 @@ class TestNet4(TestNet):
     DEFAULT_SERVERS = _read_json_dict('servers_testnet4.json')  # DO NOT MODIFY IN CLIENT CODE
     DEFAULT_PORTS = {'t': '62001', 's': '62002'}
 
-    VERIFICATION_BLOCK_MERKLE_ROOT = "9ca8933d4aa7b85093e3ec317e40bdfeda3e2b793fcd7907b38580fa193d9c77"
-    VERIFICATION_BLOCK_HEIGHT = 16845
-
     BITCOIN_CASH_FORK_BLOCK_HEIGHT = 6
     BITCOIN_CASH_FORK_BLOCK_HASH = "00000000d71b9b1f7e13b0c9b218a12df6526c1bcd1b667764b8693ae9a413cb"
 
     # Nov 13. 2017 HF to CW144 DAA height (height of last block mined on old DAA)
     CW144_HEIGHT = 3000
 
+    VERIFICATION_BLOCK_MERKLE_ROOT = "9ca8933d4aa7b85093e3ec317e40bdfeda3e2b793fcd7907b38580fa193d9c77"
+    VERIFICATION_BLOCK_HEIGHT = 16845
+    asert_daa = ASERTDaa(is_testnet=True)  # Redeclare to get instance for this subclass
+    asert_daa.anchor = Anchor(height=16844, bits=486604799, prev_time=1605451779)
+
+
 
 class ScaleNet(TestNet):
     GENESIS = "00000000e6453dc2dfe1ffa19023f86002eb11dbb8e87d0291a4599f0430be52"
     TITLE = 'Electron Cash Scalenet'
     BASE_UNITS = {'sBCH': 8, 'msBCH': 5, 'sbits': 2}
     DEFAULT_UNIT = "tBCH"
 
-    asert_daa = ASERTDaa(is_testnet=False)  # Despite being a "testnet", ScaleNet uses 2d half-life
 
     HEADERS_URL = "http://bitcoincash.com/files/scalenet_headers"  # Unused
 
     DEFAULT_SERVERS = _read_json_dict('servers_scalenet.json')  # DO NOT MODIFY IN CLIENT CODE
     DEFAULT_PORTS = {'t': '63001', 's': '63002'}
 
-    VERIFICATION_BLOCK_MERKLE_ROOT = "41eb32849a353fcb408c8b25e84578c714dbdc5ee774d0fbe25e85755250df6a"
-    VERIFICATION_BLOCK_HEIGHT = 2016
-
     BITCOIN_CASH_FORK_BLOCK_HEIGHT = 6
     BITCOIN_CASH_FORK_BLOCK_HASH = "000000000e16730d293050fc5fe5b0978b858f5d9d91192a5ca2793902493597"
 
     # Nov 13. 2017 HF to CW144 DAA height (height of last block mined on old DAA)
     CW144_HEIGHT = 3000
 
+    VERIFICATION_BLOCK_MERKLE_ROOT = "41eb32849a353fcb408c8b25e84578c714dbdc5ee774d0fbe25e85755250df6a"
+    VERIFICATION_BLOCK_HEIGHT = 2016
+    asert_daa = ASERTDaa(is_testnet=False)  # Despite being a "testnet", ScaleNet uses 2d half-life
+    asert_daa.anchor = None  # Intentionally not specified because it's after checkpoint; blockchain.py will calculate
+
+
 
 class TaxCoinNet(AbstractNet):
     """ This is for supporting ABC tax coin. Use CLI arg --taxcoin to see this network.
@@ -204,6 +215,8 @@ class TaxCoinNet(AbstractNet):
     # Consult the ElectrumX documentation for more details.
     VERIFICATION_BLOCK_MERKLE_ROOT = "d0d925862df595918416020caf5467b7ae67ae8f807daf60626c36755b62f9a2"
     VERIFICATION_BLOCK_HEIGHT = 661648  # ABC fork block
+    asert_daa = ASERTDaa(is_testnet=False)
+    asert_daa.anchor = Anchor(height=661647, bits=402971390, prev_time=1605447844)
 
     # Version numbers for BIP32 extended keys
     # standard: xprv, xpub