Merge #16563: test: Add unit test for AddTimeData

7cd069d Add test for AddTimeData (Martin Zumsande)

Pull request description:

  `AddTimeData()` has poor test coverage but interesting logic (including a bug turned into a feature). This PR adds a unit test for it.

ACKs for top commit:
  laanwj:
    ACK 7cd069d, thanks for adding a test

Tree-SHA512: 8228f9027e52ed534411d595c7e45cf4edeee9757f26f5141fbcfae3fc6f598a8cea7f734bb8f55238857a37ad2f2d518e859e1fe8c106c0712da976792ac132

Author: laanwj

src/test/timedata_tests.cpp

@@ -2,8 +2,14 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 //
-#include <timedata.h>
+
+#include <netaddress.h>
+#include <noui.h>
 #include <test/setup_common.h>
+#include <timedata.h>
+#include <warnings.h>
+
+#include <string>
 
 #include <boost/test/unit_test.hpp>
 
@@ -34,4 +40,61 @@ BOOST_AUTO_TEST_CASE(util_MedianFilter)
     BOOST_CHECK_EQUAL(filter.median(), 7);
 }
 
+static void MultiAddTimeData(int n, int64_t offset)
+{
+    static int cnt = 0;
+    for (int i = 0; i < n; ++i) {
+        CNetAddr addr;
+        addr.SetInternal(std::to_string(++cnt));
+        AddTimeData(addr, offset);
+    }
+}
+
+
+BOOST_AUTO_TEST_CASE(addtimedata)
+{
+    BOOST_CHECK_EQUAL(GetTimeOffset(), 0);
+
+    //Part 1: Add large offsets to test a warning message that our clock may be wrong.
+    MultiAddTimeData(3, DEFAULT_MAX_TIME_ADJUSTMENT + 1);
+    // Filter size is 1 + 3 = 4: It is always initialized with a single element (offset 0)
+
+    noui_suppress();
+    MultiAddTimeData(1, DEFAULT_MAX_TIME_ADJUSTMENT + 1); //filter size 5
+    noui_reconnect();
+
+    BOOST_CHECK(GetWarnings("gui").find("clock is wrong") != std::string::npos);
+
+    // nTimeOffset is not changed if the median of offsets exceeds DEFAULT_MAX_TIME_ADJUSTMENT
+    BOOST_CHECK_EQUAL(GetTimeOffset(), 0);
+
+    // Part 2: Test positive and negative medians by adding more offsets
+    MultiAddTimeData(4, 100); // filter size 9
+    BOOST_CHECK_EQUAL(GetTimeOffset(), 100);
+    MultiAddTimeData(10, -100); //filter size 19
+    BOOST_CHECK_EQUAL(GetTimeOffset(), -100);
+
+    // Part 3: Test behaviour when filter has reached maximum number of offsets
+    const int MAX_SAMPLES = 200;
+    int nfill = (MAX_SAMPLES - 3 - 19) / 2; //89
+    MultiAddTimeData(nfill, 100);
+    MultiAddTimeData(nfill, -100); //filter size MAX_SAMPLES - 3
+    BOOST_CHECK_EQUAL(GetTimeOffset(), -100);
+
+    MultiAddTimeData(2, 100);
+    //filter size MAX_SAMPLES -1, median is the initial 0 offset
+    //since we added same number of positive/negative offsets
+
+    BOOST_CHECK_EQUAL(GetTimeOffset(), 0);
+
+    // After the number of offsets has reached MAX_SAMPLES -1 (=199), nTimeOffset will never change
+    // because it is only updated when the number of elements in the filter becomes odd. It was decided
+    // not to fix this because it prevents possible attacks. See the comment in AddTimeData() or issue #4521
+    // for a more detailed explanation.
+    MultiAddTimeData(2, 100); // filter median is 100 now, but nTimeOffset will not change
+    BOOST_CHECK_EQUAL(GetTimeOffset(), 0);
+
+    // We want this test to end with nTimeOffset==0, otherwise subsequent tests of the suite will fail.
+}
+
 BOOST_AUTO_TEST_SUITE_END()