From 8d7f69b59c9b2593e221a9351948d7350df5021c Mon Sep 17 00:00:00 2001
From: nibbles83 <hardke01@yahoo.co.uk>
Date: Thu, 20 Jul 2023 13:48:35 +0100
Subject: [PATCH] Shrink VM Log on startup

---
 src/init.cpp    |  1 +
 src/logging.cpp | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 src/logging.h   |  2 ++
 3 files changed, 49 insertions(+)

diff --git a/src/init.cpp b/src/init.cpp
index 10944001..596f8477 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1346,6 +1346,7 @@ bool AppInitMain(NodeContext& node)
             // Do this first since it both loads a bunch of debug.log into memory,
             // and because this needs to happen before any other debug.log printing
             LogInstance().ShrinkDebugFile();
+            LogInstance().ShrinkVMLogFile();
         }
     }
     if (!LogInstance().StartLogging()) {
diff --git a/src/logging.cpp b/src/logging.cpp
index e9f05bae..09dca5b2 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -134,6 +134,11 @@ bool BCLog::Logger::WillLogCategory(BCLog::LogFlags category) const
     return (m_categories.load(std::memory_order_relaxed) & category) != 0;
 }
 
+bool BCLog::Logger::DefaultShrinkVMLogFile() const
+{
+    return m_categories == BCLog::NONE;
+}
+
 bool BCLog::Logger::DefaultShrinkDebugFile() const
 {
     return m_categories == BCLog::NONE;
@@ -323,6 +328,47 @@ void BCLog::Logger::LogPrintStr(const std::string& str, bool useVMLog)
     }
 }
 
+void BCLog::Logger::ShrinkVMLogFile()
+{
+    // Amount of vm.log to save at end when shrinking (must fit in memory)
+    constexpr size_t RECENT_DEBUG_HISTORY_SIZE = 10 * 1000000;
+
+    assert(!m_file_pathVM.empty());
+
+    // Scroll vm.log if it's getting too big
+    FILE* file = fsbridge::fopen(m_file_pathVM, "r");
+
+    // Special files (e.g. device nodes) may not have a size.
+    size_t log_size = 0;
+    try {
+        log_size = fs::file_size(m_file_pathVM);
+    } catch (const fs::filesystem_error&) {}
+
+    // If vm.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
+    if (file && log_size > 11 * (RECENT_DEBUG_HISTORY_SIZE / 10))
+    {
+        // Restart the file with some of the end
+        std::vector<char> vch(RECENT_DEBUG_HISTORY_SIZE, 0);
+        if (fseek(file, -((long)vch.size()), SEEK_END)) {
+            LogPrintf("Failed to shrink VM log file: fseek(...) failed\n");
+            fclose(file);
+            return;
+        }
+        int nBytes = fread(vch.data(), 1, vch.size(), file);
+        fclose(file);
+
+        file = fsbridge::fopen(m_file_pathVM, "w");
+        if (file)
+        {
+            fwrite(vch.data(), 1, nBytes, file);
+            fclose(file);
+        }
+    }
+    else if (file != nullptr)
+        fclose(file);
+}
+
 void BCLog::Logger::ShrinkDebugFile()
 {
     // Amount of debug.log to save at end when shrinking (must fit in memory)
diff --git a/src/logging.h b/src/logging.h
index f2ff8b5d..83db0d1e 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -123,6 +123,7 @@ namespace BCLog {
         void DisconnectTestLogger();
 
         void ShrinkDebugFile();
+        void ShrinkVMLogFile();
 
         uint32_t GetCategoryMask() const { return m_categories.load(); }
 
@@ -134,6 +135,7 @@ namespace BCLog {
         bool WillLogCategory(LogFlags category) const;
 
         bool DefaultShrinkDebugFile() const;
+        bool DefaultShrinkVMLogFile() const;
     };
 
 } // namespace BCLog