Add `-debuglogfile` option

This patch adds an option to configure the name and/or directory of the
debug log.

The user can specify either a relative path, in which case the path
is relative to the data directory. They can also specify an absolute
path to put the log anywhere else in the file system.

3 files changed, 35 insertions, 14 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 9356862999..871a585267 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -342,6 +342,7 @@ std::string HelpMessage(HelpMessageMode mode)
     if (showDebug)
         strUsage += HelpMessageOpt("-feefilter", strprintf("Tell other nodes to filter invs to us by our mempool min fee (default: %u)", DEFAULT_FEEFILTER));
     strUsage += HelpMessageOpt("-loadblock=<file>", _("Imports blocks from external blk000??.dat file on startup"));
+    strUsage += HelpMessageOpt("-debuglogfile=<file>", strprintf(_("Specify location of debug log file: this can be an absolute path or a path relative to the data directory (default: %s)"), DEFAULT_DEBUGLOGFILE));
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", strprintf(_("Do not keep transactions in the mempool longer than <n> hours (default: %u)"), DEFAULT_MEMPOOL_EXPIRY));
@@ -1209,8 +1210,11 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
         ShrinkDebugFile();
     }
 
-    if (fPrintToDebugLog)
-        OpenDebugLog();
+    if (fPrintToDebugLog) {
+        if (!OpenDebugLog()) {
+            return InitError(strprintf("Could not open debug log file %s", GetDebugLogPath().string()));
+        }
+    }
 
     if (!fLogTimestamps)
         LogPrintf("Startup time: %s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()));
diff --git a/src/util.cpp b/src/util.cpp
index b2023b8322..6631c236f1 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -89,6 +89,7 @@ const int64_t nStartupTime = GetTime();
 
 const char * const BITCOIN_CONF_FILENAME = "bitcoin.conf";
 const char * const BITCOIN_PID_FILENAME = "bitcoind.pid";
+const char * const DEFAULT_DEBUGLOGFILE = "debug.log";
 
 ArgsManager gArgs;
 bool fPrintToConsole = false;
@@ -189,26 +190,40 @@ static void DebugPrintInit()
     vMsgsBeforeOpenLog = new std::list<std::string>;
 }
 
-void OpenDebugLog()
+fs::path GetDebugLogPath()
+{
+    fs::path logfile(gArgs.GetArg("-debuglogfile", DEFAULT_DEBUGLOGFILE));
+    if (logfile.is_absolute()) {
+        return logfile;
+    } else {
+        return GetDataDir() / logfile;
+    }
+}
+
+bool OpenDebugLog()
 {
     boost::call_once(&DebugPrintInit, debugPrintInitFlag);
     boost::mutex::scoped_lock scoped_lock(*mutexDebugLog);
 
     assert(fileout == nullptr);
     assert(vMsgsBeforeOpenLog);
-    fs::path pathDebug = GetDataDir() / "debug.log";
+    fs::path pathDebug = GetDebugLogPath();
+
     fileout = fsbridge::fopen(pathDebug, "a");
-    if (fileout) {
-        setbuf(fileout, nullptr); // unbuffered
-        // dump buffered messages from before we opened the log
-        while (!vMsgsBeforeOpenLog->empty()) {
-            FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);
-            vMsgsBeforeOpenLog->pop_front();
-        }
+    if (!fileout) {
+        return false;
+    }
+
+    setbuf(fileout, nullptr); // unbuffered
+    // dump buffered messages from before we opened the log
+    while (!vMsgsBeforeOpenLog->empty()) {
+        FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);
+        vMsgsBeforeOpenLog->pop_front();
     }
 
     delete vMsgsBeforeOpenLog;
     vMsgsBeforeOpenLog = nullptr;
+    return true;
 }
 
 struct CLogCategoryDesc
@@ -355,7 +370,7 @@ int LogPrintStr(const std::string &str)
             // reopen the log file, if requested
             if (fReopenDebugLog) {
                 fReopenDebugLog = false;
-                fs::path pathDebug = GetDataDir() / "debug.log";
+                fs::path pathDebug = GetDebugLogPath();
                 if (fsbridge::freopen(pathDebug,"a",fileout) != nullptr)
                     setbuf(fileout, nullptr); // unbuffered
             }
@@ -774,7 +789,7 @@ void ShrinkDebugFile()
     // Amount of debug.log to save at end when shrinking (must fit in memory)
     constexpr size_t RECENT_DEBUG_HISTORY_SIZE = 10 * 1000000;
     // Scroll debug.log if it's getting too big
-    fs::path pathLog = GetDataDir() / "debug.log";
+    fs::path pathLog = GetDebugLogPath();
     FILE* file = fsbridge::fopen(pathLog, "r");
     // If debug.log file is more than 10% bigger the RECENT_DEBUG_HISTORY_SIZE
     // trim it down by saving only the last RECENT_DEBUG_HISTORY_SIZE bytes
diff --git a/src/util.h b/src/util.h
index 08de43d29f..6687b865d2 100644
--- a/src/util.h
+++ b/src/util.h
@@ -36,6 +36,7 @@ int64_t GetStartupTime();
 static const bool DEFAULT_LOGTIMEMICROS = false;
 static const bool DEFAULT_LOGIPS        = false;
 static const bool DEFAULT_LOGTIMESTAMPS = true;
+extern const char * const DEFAULT_DEBUGLOGFILE;
 
 /** Signals for translation. */
 class CTranslationInterface
@@ -180,7 +181,8 @@ void CreatePidFile(const fs::path &path, pid_t pid);
 #ifdef WIN32
 fs::path GetSpecialFolderPath(int nFolder, bool fCreate = true);
 #endif
-void OpenDebugLog();
+fs::path GetDebugLogPath();
+bool OpenDebugLog();
 void ShrinkDebugFile();
 void runCommand(const std::string& strCommand);