From e2fec6eb56c40c49f632c28ee539705bdd799dd2 Mon Sep 17 00:00:00 2001
From: Joseph Prince <57415450+josephdprince@users.noreply.github.com>
Date: Tue, 10 Feb 2026 07:27:58 -0800
Subject: [PATCH] SERVER-117564 Properly handle null device for logpath on
 Windows (#47618)

GitOrigin-RevId: 035f5404e0ef01c1b454c3b204a7d254e1ef1568
---
 src/mongo/db/initialize_server_global_state.cpp |  9 ++++++---
 src/mongo/logv2/file_rotate_sink.cpp            | 15 ++++++++++++++-
 src/mongo/logv2/log_util.h                      | 15 +++++++++++++++
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/src/mongo/db/initialize_server_global_state.cpp b/src/mongo/db/initialize_server_global_state.cpp
index 6e12dc6d219..20329032b54 100644
--- a/src/mongo/db/initialize_server_global_state.cpp
+++ b/src/mongo/db/initialize_server_global_state.cpp
@@ -78,6 +78,10 @@
 #include <boost/move/utility_core.hpp>
 #include <boost/optional/optional.hpp>
 
+#ifdef _WIN32
+#include "mongo/logv2/log_util.h"
+#endif
+
 #if defined(MONGO_CONFIG_HAVE_HEADER_UNISTD_H)
 #include <unistd.h>
 #endif
@@ -376,9 +380,8 @@ MONGO_INITIALIZER_GENERAL(ServerLogRedirection,
         fassert(16448, !serverGlobalParams.logWithSyslog);
         auto [absoluteLogpath, exists] = [&] {
 #ifdef _WIN32
-            constexpr auto kWindowsNUL = "NUL"_sd;
-            if (serverGlobalParams.logpath == kWindowsNUL) {
-                return std::make_tuple(std::string(kWindowsNUL), true);
+            if (logv2::isLogPathWindowsNul(serverGlobalParams.logpath)) {
+                return std::make_tuple(std::string(logv2::kWindowsNUL), true);
             }
 #endif  // defined(_WIN32)
             std::string absolutePath =
diff --git a/src/mongo/logv2/file_rotate_sink.cpp b/src/mongo/logv2/file_rotate_sink.cpp
index bc6dddaed90..fe9888808cd 100644
--- a/src/mongo/logv2/file_rotate_sink.cpp
+++ b/src/mongo/logv2/file_rotate_sink.cpp
@@ -69,6 +69,10 @@
 #include "mongo/util/string_map.h"
 #include "mongo/util/time_support.h"
 
+#ifdef _WIN32
+#include "mongo/logv2/log_util.h"
+#endif
+
 namespace mongo::logv2 {
 namespace {
 
@@ -78,12 +82,21 @@ using stream_t = Win32SharedAccessOfstream;
 using stream_t = std::ofstream;
 #endif
 
+bool checkLogFileExists(const std::string& filename) {
+#ifdef _WIN32
+    if (isLogPathWindowsNul(filename)) {
+        return true;
+    }
+#endif
+    return boost::filesystem::exists(filename);
+}
+
 StatusWith<boost::shared_ptr<stream_t>> openFile(const std::string& filename, bool append) {
     std::ios_base::openmode mode = std::ios_base::out;
     bool exists = false;
     if (append) {
         mode |= std::ios_base::app;
-        exists = boost::filesystem::exists(filename);
+        exists = checkLogFileExists(filename);
     } else
         mode |= std::ios_base::trunc;
     auto file = boost::make_shared<stream_t>(filename, mode);
diff --git a/src/mongo/logv2/log_util.h b/src/mongo/logv2/log_util.h
index f6d76aabfe1..c01b09bfff5 100644
--- a/src/mongo/logv2/log_util.h
+++ b/src/mongo/logv2/log_util.h
@@ -31,6 +31,7 @@
 
 #include "mongo/base/status.h"
 #include "mongo/base/string_data.h"
+#include "mongo/util/str.h"
 
 #include <functional>
 
@@ -42,6 +43,10 @@ namespace mongo::logv2 {
 constexpr auto kServerLogTag = "server"_sd;
 constexpr auto kAuditLogTag = "audit"_sd;
 
+#ifdef _WIN32
+constexpr auto kWindowsNUL = "nul"_sd;
+#endif
+
 using LogRotateCallback = std::function<Status(bool, StringData, std::function<void(Status)>)>;
 using ShouldEmitLogServiceFn = std::function<bool()>;
 
@@ -116,4 +121,14 @@ bool shouldEmitLogService();
  */
 void setShouldEmitLogService(ShouldEmitLogServiceFn fn);
 
+#ifdef _WIN32
+/**
+ * Checks for the Windows NUL file. Although it's a valid file, boost::filesystem::exists() throws
+ * an exception when checking it so we use this function as a special case.
+ */
+inline bool isLogPathWindowsNul(const std::string& path) {
+    return str::equalCaseInsensitive(path, kWindowsNUL);
+}
+#endif
+
 }  // namespace mongo::logv2