From ab3c4ddf16bb2ba401e9583cffde4e117a24f667 Mon Sep 17 00:00:00 2001
From: Sylvain Chapeland <o2.syc@cern.ch>
Date: Mon, 24 Oct 2022 17:03:11 +0200
Subject: [PATCH 1/2] SimpleLog: when rotateMaxFiles=1, clear file on opening
 and discard messages after reaching rotateMaxBytes

---
 include/Common/SimpleLog.h |  2 +-
 src/SimpleLog.cxx          | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/Common/SimpleLog.h b/include/Common/SimpleLog.h
index 0178f1c..401b888 100644
--- a/include/Common/SimpleLog.h
+++ b/include/Common/SimpleLog.h
@@ -36,7 +36,7 @@ class SimpleLog
   // Optionnaly, an automatic log rotation can be defined. Older files are renamed, appending .1, .2, .3, etc.
   // \param logFilePath Path to log file. If NULL, using stdout/stderr. If /dev/null, messages are completely dropped.
   // \param rotateMaxBytes Maximum file size, after which a new file is created. If zero, no limit.
-  // \param rotateMaxFiles Maximum number of files to keep (including the "current" file). If zero, no limit.
+  // \param rotateMaxFiles Maximum number of files to keep (including the "current" file). If zero, no limit. If one, a single file is created and cleared immediately, and messages are discarded after reaching rotateMaxBytes.
   // \param rotateNow If non-zero, the file is immediately rotated (independently of its size), otherwise it is appended.
   int setLogFile(const char* logFilePath = NULL,
                  unsigned long rotateMaxBytes = 0, unsigned int rotateMaxFiles = 0, unsigned int rotateNow = 0);
diff --git a/src/SimpleLog.cxx b/src/SimpleLog.cxx
index 1ed1507..82b0590 100644
--- a/src/SimpleLog.cxx
+++ b/src/SimpleLog.cxx
@@ -144,6 +144,11 @@ int SimpleLog::Impl::logV(SimpleLog::Impl::Severity s, const char* message, va_l
   if (fp != NULL) {
     if ((ix + logFileSize > rotateMaxBytes) && (rotateMaxBytes > 0)) {
       closeLogFile();
+      if (rotateMaxFiles == 1) {
+        // stop after first file
+        disableOutput = 1;
+        return -1;
+      }
       rotate();
       if (openLogFile())
         return -1;
@@ -195,6 +200,9 @@ int SimpleLog::setLogFile(const char* logFilePath, unsigned long rotateMaxBytes,
       pImpl->disableOutput = 1;
       return 0;
     }
+    if (rotateMaxFiles < 0) {
+      rotateMaxFiles = 1;
+    }
     pImpl->rotateMaxBytes = rotateMaxBytes;
     pImpl->rotateMaxFiles = rotateMaxFiles;
     if (rotateNow) {
@@ -269,6 +277,10 @@ int SimpleLog::Impl::openLogFile()
   if (logFilePath.length() == 0) {
     return 0;
   }
+  const char *mode = "a";
+  if (rotateMaxFiles == 1) {
+    mode = "w";
+  }
   fp = fopen(logFilePath.c_str(), "a");
   if (fp == NULL) {
     return -1;
@@ -371,7 +383,7 @@ void SimpleLog::Impl::rotate()
     } else {
       inFile = dirName + fileName + "." + std::to_string(oldIndex);
     }
-    if ((newIndex > rotateMaxFiles) && (rotateMaxFiles != 0)) {
+    if ((newIndex >= rotateMaxFiles) && (rotateMaxFiles != 0)) {
       // this file should be removed
       unlink(inFile.c_str());
     } else {

From ca352b6c1f157165a95a85c63a745fc671b8d4a9 Mon Sep 17 00:00:00 2001
From: Sylvain Chapeland <o2.syc@cern.ch>
Date: Mon, 24 Oct 2022 17:03:37 +0200
Subject: [PATCH 2/2] clang

---
 src/SimpleLog.cxx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/SimpleLog.cxx b/src/SimpleLog.cxx
index 82b0590..95c8111 100644
--- a/src/SimpleLog.cxx
+++ b/src/SimpleLog.cxx
@@ -277,7 +277,7 @@ int SimpleLog::Impl::openLogFile()
   if (logFilePath.length() == 0) {
     return 0;
   }
-  const char *mode = "a";
+  const char* mode = "a";
   if (rotateMaxFiles == 1) {
     mode = "w";
   }