Format timestamps using ISO 8601 formatting (e.g. "2018-02-28T12:34:56Z")

* Z is the zone designator for the zero UTC offset.
* T is the delimiter used to separate date and time.

This makes it clear for the end-user that the date/time logged is
specified in UTC and not in the local time zone.

9 files changed, 55 insertions, 21 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 659f97fec6..bc23d0ff83 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1224,7 +1224,7 @@ bool AppInitMain()
     }
 
     if (!fLogTimestamps)
-        LogPrintf("Startup time: %s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()));
+        LogPrintf("Startup time: %s\n", FormatISO8601DateTime(GetTime()));
     LogPrintf("Default data directory %s\n", GetDefaultDataDir().string());
     LogPrintf("Using data directory %s\n", GetDataDir().string());
     LogPrintf("Using config file %s\n", GetConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME)).string());
diff --git a/src/net.cpp b/src/net.cpp
index 33a60ac96e..53a0a9b180 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2795,7 +2795,7 @@ void CNode::AskFor(const CInv& inv)
         nRequestTime = it->second;
     else
         nRequestTime = 0;
-    LogPrint(BCLog::NET, "askfor %s  %d (%s) peer=%d\n", inv.ToString(), nRequestTime, DateTimeStrFormat("%H:%M:%S", nRequestTime/1000000), id);
+    LogPrint(BCLog::NET, "askfor %s  %d (%s) peer=%d\n", inv.ToString(), nRequestTime, FormatISO8601Time(nRequestTime/1000000), id);
 
     // Make sure not to reuse time indexes to keep things in the same order
     int64_t nNow = GetTimeMicros() - 1000000;
diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index 8ad4fa31f1..4b6fdc8d57 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -770,7 +770,7 @@ bool PaymentServer::verifyExpired(const payments::PaymentDetails& requestDetails
 {
     bool fVerified = (requestDetails.has_expires() && (int64_t)requestDetails.expires() < GetTime());
     if (fVerified) {
-        const QString requestExpires = QString::fromStdString(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", (int64_t)requestDetails.expires()));
+        const QString requestExpires = QString::fromStdString(FormatISO8601DateTime((int64_t)requestDetails.expires()));
         qWarning() << QString("PaymentServer::%1: Payment request expired \"%2\".")
             .arg(__func__)
             .arg(requestExpires);
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 58f033cd89..84b61bea86 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -164,10 +164,27 @@ BOOST_AUTO_TEST_CASE(util_DateTimeStrFormat)
     BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 0), "1970-01-01 00:00:00");
     BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 0x7FFFFFFF), "2038-01-19 03:14:07");
     BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M:%S", 1317425777), "2011-09-30 23:36:17");
+    BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%dT%H:%M:%SZ", 1317425777), "2011-09-30T23:36:17Z");
+    BOOST_CHECK_EQUAL(DateTimeStrFormat("%H:%M:%SZ", 1317425777), "23:36:17Z");
     BOOST_CHECK_EQUAL(DateTimeStrFormat("%Y-%m-%d %H:%M", 1317425777), "2011-09-30 23:36");
     BOOST_CHECK_EQUAL(DateTimeStrFormat("%a, %d %b %Y %H:%M:%S +0000", 1317425777), "Fri, 30 Sep 2011 23:36:17 +0000");
 }
 
+BOOST_AUTO_TEST_CASE(util_FormatISO8601DateTime)
+{
+    BOOST_CHECK_EQUAL(FormatISO8601DateTime(1317425777), "2011-09-30T23:36:17Z");
+}
+
+BOOST_AUTO_TEST_CASE(util_FormatISO8601Date)
+{
+    BOOST_CHECK_EQUAL(FormatISO8601Date(1317425777), "2011-09-30");
+}
+
+BOOST_AUTO_TEST_CASE(util_FormatISO8601Time)
+{
+    BOOST_CHECK_EQUAL(FormatISO8601Time(1317425777), "23:36:17Z");
+}
+
 class TestArgsManager : public ArgsManager
 {
 public:
diff --git a/src/util.cpp b/src/util.cpp
index 82c99a3c2f..62cdce3012 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -315,12 +315,14 @@ static std::string LogTimestampStr(const std::string &str, std::atomic_bool *fSt
 
     if (*fStartedNewLine) {
         int64_t nTimeMicros = GetTimeMicros();
-        strStamped = DateTimeStrFormat("%Y-%m-%d %H:%M:%S", nTimeMicros/1000000);
-        if (fLogTimeMicros)
-            strStamped += strprintf(".%06d", nTimeMicros%1000000);
+        strStamped = FormatISO8601DateTime(nTimeMicros/1000000);
+        if (fLogTimeMicros) {
+            strStamped.pop_back();
+            strStamped += strprintf(".%06dZ", nTimeMicros%1000000);
+        }
         int64_t mocktime = GetMockTime();
         if (mocktime) {
-            strStamped += " (mocktime: " + DateTimeStrFormat("%Y-%m-%d %H:%M:%S", mocktime) + ")";
+            strStamped += " (mocktime: " + FormatISO8601DateTime(mocktime) + ")";
         }
         strStamped += ' ' + str;
     } else
diff --git a/src/utiltime.cpp b/src/utiltime.cpp
index e908173135..8a861039b3 100644
--- a/src/utiltime.cpp
+++ b/src/utiltime.cpp
@@ -85,3 +85,15 @@ std::string DateTimeStrFormat(const char* pszFormat, int64_t nTime)
     ss << boost::posix_time::from_time_t(nTime);
     return ss.str();
 }
+
+std::string FormatISO8601DateTime(int64_t nTime) {
+    return DateTimeStrFormat("%Y-%m-%dT%H:%M:%SZ", nTime);
+}
+
+std::string FormatISO8601Date(int64_t nTime) {
+    return DateTimeStrFormat("%Y-%m-%d", nTime);
+}
+
+std::string FormatISO8601Time(int64_t nTime) {
+    return DateTimeStrFormat("%H:%M:%SZ", nTime);
+}
diff --git a/src/utiltime.h b/src/utiltime.h
index 56cc31da67..807c52ffaf 100644
--- a/src/utiltime.h
+++ b/src/utiltime.h
@@ -27,6 +27,14 @@ void SetMockTime(int64_t nMockTimeIn);
 int64_t GetMockTime();
 void MilliSleep(int64_t n);
 
+/**
+ * ISO 8601 formatting is preferred. Use the FormatISO8601{DateTime,Date,Time}
+ * helper functions if possible.
+ */
 std::string DateTimeStrFormat(const char* pszFormat, int64_t nTime);
 
+std::string FormatISO8601DateTime(int64_t nTime);
+std::string FormatISO8601Date(int64_t nTime);
+std::string FormatISO8601Time(int64_t nTime);
+
 #endif // BITCOIN_UTILTIME_H
diff --git a/src/validation.cpp b/src/validation.cpp
index 51e40c17b5..c677f44b3e 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1267,13 +1267,12 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
 
     LogPrintf("%s: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
       pindexNew->GetBlockHash().ToString(), pindexNew->nHeight,
-      log(pindexNew->nChainWork.getdouble())/log(2.0), DateTimeStrFormat("%Y-%m-%d %H:%M:%S",
-      pindexNew->GetBlockTime()));
+      log(pindexNew->nChainWork.getdouble())/log(2.0), FormatISO8601DateTime(pindexNew->GetBlockTime()));
     CBlockIndex *tip = chainActive.Tip();
     assert (tip);
     LogPrintf("%s:  current best=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
       tip->GetBlockHash().ToString(), chainActive.Height(), log(tip->nChainWork.getdouble())/log(2.0),
-      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", tip->GetBlockTime()));
+      FormatISO8601DateTime(tip->GetBlockTime()));
     CheckForkWarningConditions();
 }
 
@@ -2229,7 +2228,7 @@ void static UpdateTip(const CBlockIndex *pindexNew, const CChainParams& chainPar
     LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)", __func__,
       pindexNew->GetBlockHash().ToString(), pindexNew->nHeight, pindexNew->nVersion,
       log(pindexNew->nChainWork.getdouble())/log(2.0), (unsigned long)pindexNew->nChainTx,
-      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", pindexNew->GetBlockTime()),
+      FormatISO8601DateTime(pindexNew->GetBlockTime()),
       GuessVerificationProgress(chainParams.TxData(), pindexNew), pcoinsTip->DynamicMemoryUsage() * (1.0 / (1<<20)), pcoinsTip->GetCacheSize());
     if (!warningMessages.empty())
         LogPrintf(" warning='%s'", boost::algorithm::join(warningMessages, ", "));
@@ -3856,7 +3855,7 @@ bool LoadChainTip(const CChainParams& chainparams)
 
     LogPrintf("Loaded best chain: hashBestChain=%s height=%d date=%s progress=%f\n",
         chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(),
-        DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),
+        FormatISO8601DateTime(chainActive.Tip()->GetBlockTime()),
         GuessVerificationProgress(chainparams.TxData(), chainActive.Tip()));
     return true;
 }
@@ -4554,7 +4553,7 @@ void CChainState::CheckBlockIndex(const Consensus::Params& consensusParams)
 
 std::string CBlockFileInfo::ToString() const
 {
-    return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, DateTimeStrFormat("%Y-%m-%d", nTimeFirst), DateTimeStrFormat("%Y-%m-%d", nTimeLast));
+    return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
 }
 
 CBlockFileInfo* GetBlockFileInfo(size_t n)
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
index 0edc8d8d66..c7c54ecb9b 100644
--- a/src/wallet/rpcdump.cpp
+++ b/src/wallet/rpcdump.cpp
@@ -28,10 +28,6 @@
 #include <univalue.h>
 
 
-std::string static EncodeDumpTime(int64_t nTime) {
-    return DateTimeStrFormat("%Y-%m-%dT%H:%M:%SZ", nTime);
-}
-
 int64_t static DecodeDumpTime(const std::string &str) {
     static const boost::posix_time::ptime epoch = boost::posix_time::from_time_t(0);
     static const std::locale loc(std::locale::classic(),
@@ -722,9 +718,9 @@ UniValue dumpwallet(const JSONRPCRequest& request)
 
     // produce output
     file << strprintf("# Wallet dump created by Bitcoin %s\n", CLIENT_BUILD);
-    file << strprintf("# * Created on %s\n", EncodeDumpTime(GetTime()));
+    file << strprintf("# * Created on %s\n", FormatISO8601DateTime(GetTime()));
     file << strprintf("# * Best block at time of backup was %i (%s),\n", chainActive.Height(), chainActive.Tip()->GetBlockHash().ToString());
-    file << strprintf("#   mined on %s\n", EncodeDumpTime(chainActive.Tip()->GetBlockTime()));
+    file << strprintf("#   mined on %s\n", FormatISO8601DateTime(chainActive.Tip()->GetBlockTime()));
     file << "\n";
 
     // add the base58check encoded extended master if the wallet uses HD
@@ -741,7 +737,7 @@ UniValue dumpwallet(const JSONRPCRequest& request)
     }
     for (std::vector<std::pair<int64_t, CKeyID> >::const_iterator it = vKeyBirth.begin(); it != vKeyBirth.end(); it++) {
         const CKeyID &keyid = it->second;
-        std::string strTime = EncodeDumpTime(it->first);
+        std::string strTime = FormatISO8601DateTime(it->first);
         std::string strAddr;
         std::string strLabel;
         CKey key;
@@ -769,7 +765,7 @@ UniValue dumpwallet(const JSONRPCRequest& request)
         // get birth times for scripts with metadata
         auto it = pwallet->m_script_metadata.find(scriptid);
         if (it != pwallet->m_script_metadata.end()) {
-            create_time = EncodeDumpTime(it->second.nCreateTime);
+            create_time = FormatISO8601DateTime(it->second.nCreateTime);
         }
         if(pwallet->GetCScript(scriptid, script)) {
             file << strprintf("%s %s script=1", HexStr(script.begin(), script.end()), create_time);