Enable -alertnotify for hard fork detection. Test it.

qa/pull-tester/rpc-tests.sh

@@ -37,6 +37,7 @@ testScriptsExt=(
     'getblocktemplate_proposals.py'
     'pruning.py'
     'forknotify.py'
+    'hardforkdetection.py'
     'invalidateblock.py'
     'keypool.py'
     'receivedby.py'

qa/rpc-tests/hardforkdetection.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python2
+
+#
+# Test hard fork detection
+#
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+import os
+import shutil
+
+class HardForkDetectionTest(BitcoinTestFramework):
+
+    alert_filename = None  # Set by setup_network
+
+    def setup_network(self):
+        self.nodes = []
+        self.alert_filename = os.path.join(self.options.tmpdir, "alert.txt")
+        with open(self.alert_filename, 'w') as f:
+            pass  # Just open then close to create zero-length file
+        self.nodes.append(start_node(0, self.options.tmpdir,
+                            ["-blockversion=2", "-alertnotify=echo %s >> \"" + self.alert_filename + "\""]))
+
+    def assert_safemode_off(self):
+        self.nodes[0].getbalance()
+
+    def assert_safemode_on(self, requiredMessage):
+        errorString = ""
+        try:
+            self.nodes[0].getbalance()
+        except JSONRPCException,e:
+            errorString = e.error['message']
+
+        assert_equal("Safe mode:" in errorString, True)
+        assert_equal(requiredMessage in errorString, True)
+
+    def run_test(self):
+        # Generate 10 blocks
+        self.nodes[0].generate(100)
+
+        # Invalidate all of them.
+        for block_height in range(100, 0, -1):
+            block_hash = self.nodes[0].getblockhash(block_height)
+            self.nodes[0].invalidateblock(block_hash)
+
+        # Check that safe mode is on.
+        self.assert_safemode_on("We do not appear to fully agree with our peers!")
+
+        # Check that an -alertnotify was triggered.
+        with open(self.alert_filename, 'r') as f:
+            alert_text = f.read()
+
+        if len(alert_text) == 0:
+            raise AssertionError("-alertnotify did not warn of detected hard fork")
+
+        # If our chain keeps growing, but the hard forking chain remains longer,
+        # safe mode should stay on.
+        self.nodes[0].generate(50)
+        self.assert_safemode_on("We do not appear to fully agree with our peers!")
+
+        # If we're on the longer side of the hard fork, safe mode should get
+        # turned off.
+        self.nodes[0].generate(50)
+        self.assert_safemode_off()
+
+
+if __name__ == '__main__':
+    HardForkDetectionTest().main()

src/main.cpp

@@ -1454,7 +1454,9 @@ void CheckForkWarningConditions()
         }
         else
         {
-            LogPrintf("%s: Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.\n", __func__);
+            std::string warning = std::string("Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.");
+            LogPrintf("%s: %s\n", warning.c_str(), __func__);
+            CAlert::Notify(warning, true);
             fLargeWorkInvalidChainFound = true;
         }
     }