save header immediately when forking a chain

lib/blockchain.py

@@ -300,9 +300,9 @@ class Blockchain(util.PrintError):
         new_bits = bitsN << 24 | bitsBase
         return new_bits, bitsBase << (8 * (bitsN-3))
 
-    def can_connect(self, header):
+    def can_connect(self, header, check_height=True):
         height = header['block_height']
-        if self.height() != height - 1:
+        if check_height and self.height() != height - 1:
             return False
         if height == 0:
             return hash_header(header) == bitcoin.GENESIS

lib/network.py

@@ -843,23 +843,27 @@ class Network(util.DaemonThread):
                         raise BaseException('error')
                     next_height = None
                 else:
-                    if interface.blockchain.height() > interface.good:
+                    bh = interface.blockchain.height()
+                    next_height = None
+                    if bh > interface.good:
                         if not interface.blockchain.check_header(interface.bad_header):
-                            self.blockchains[interface.bad] = b = interface.blockchain.fork(interface.bad)
-                            interface.blockchain = b
-                            interface.print_error("new chain", b.checkpoint)
+                            if interface.blockchain.can_connect(interface.bad_header, check_height=False):
+                                b = interface.blockchain.fork(interface.bad)
+                                b.save_header(interface.bad_header)
+                                self.blockchains[interface.bad] = b
+                                interface.blockchain = b
+                                interface.print_error("new chain", b.checkpoint)
+                                interface.mode = 'catch_up'
+                                next_height = interface.bad + 1
+                                interface.blockchain.catch_up = interface.server
                     else:
-                        assert interface.blockchain.height() == interface.good
+                        assert bh == interface.good
+                        if interface.blockchain.catch_up is None and bh < interface.tip:
+                            interface.print_error("catching up from %d"% (bh + 1))
+                            interface.mode = 'catch_up'
+                            next_height = bh + 1
+                            interface.blockchain.catch_up = interface.server
 
-                    bh = interface.blockchain.height()
-                    if interface.blockchain.catch_up is None and bh < interface.tip:
-                        interface.print_error("catching up from %d"% (bh + 1))
-                        interface.mode = 'catch_up'
-                        next_height = bh + 1
-                        interface.blockchain.catch_up = interface.server
-                    else:
-                        interface.print_error('already catching up')
-                        next_height = None
                 self.notify('updated')
 
         elif interface.mode == 'catch_up':