diff --git a/source/client/src/clientEnv.c b/source/client/src/clientEnv.c
index 53be1fccf4..3b755c2921 100644
--- a/source/client/src/clientEnv.c
+++ b/source/client/src/clientEnv.c
@@ -197,7 +197,12 @@ static int32_t generateWriteSlowLog(STscObj *pTscObj, SRequestObj *pRequest, int
     ENV_JSON_FALSE_CHECK(cJSON_AddItemToObject(json, "db", cJSON_CreateString("")));
   }
 
-  char              *value = cJSON_PrintUnformatted(json);
+  char *value = cJSON_PrintUnformatted(json);
+  if (value == NULL) {
+    tscError("failed to print json");
+    code = TSDB_CODE_FAILED;
+    goto _end;
+  }
   MonitorSlowLogData data = {0};
   data.clusterId = pTscObj->pAppInfo->clusterId;
   data.type = SLOW_LOG_WRITE;
diff --git a/source/client/src/clientMonitor.c b/source/client/src/clientMonitor.c
index f424e4d1a2..6667c4c741 100644
--- a/source/client/src/clientMonitor.c
+++ b/source/client/src/clientMonitor.c
@@ -447,20 +447,19 @@ static char* readFile(TdFilePtr pFile, int64_t* offset, int64_t size) {
   char*   pCont = NULL;
   int64_t totalSize = 0;
   if (size - *offset >= SLOW_LOG_SEND_SIZE_MAX) {
-    pCont = taosMemoryCalloc(1, 4 + SLOW_LOG_SEND_SIZE_MAX);  // 4 reserved for []
     totalSize = 4 + SLOW_LOG_SEND_SIZE_MAX;
   } else {
-    pCont = taosMemoryCalloc(1, 4 + (size - *offset));
     totalSize = 4 + (size - *offset);
   }
 
+  pCont = taosMemoryCalloc(1, totalSize);  // 4 reserved for []
   if (pCont == NULL) {
     tscError("failed to allocate memory for slow log, size:%" PRId64, totalSize);
     return NULL;
   }
   char* buf = pCont;
   (void)strcat(buf++, "[");
-  int64_t readSize = taosReadFile(pFile, buf, SLOW_LOG_SEND_SIZE_MAX);
+  int64_t readSize = taosReadFile(pFile, buf, totalSize - 4); // 4 reserved for []
   if (readSize <= 0) {
     if (readSize < 0) {
       tscError("failed to read len from file:%p since %s", pFile, terrstr());
diff --git a/source/os/src/osFile.c b/source/os/src/osFile.c
index 40f48af266..ef8c1eb860 100644
--- a/source/os/src/osFile.c
+++ b/source/os/src/osFile.c
@@ -426,16 +426,19 @@ int64_t taosReadFile(TdFilePtr pFile, void *buf, int64_t count) {
     return terrno;
   }
 
+  int64_t res = 0;
   DWORD bytesRead;
   if (!ReadFile(pFile->hFile, buf, count, &bytesRead, NULL)) {
     DWORD errCode = GetLastError();
     terrno = TAOS_SYSTEM_WINAPI_ERROR(errCode);
-    bytesRead = -1;
+    res = -1;
+  } else {
+    res = bytesRead;
   }
 #if FILE_WITH_LOCK
   (void)taosThreadRwlockUnlock(&(pFile->rwlock));
 #endif
-  return bytesRead;
+  return res;
 }
 
 int64_t taosWriteFile(TdFilePtr pFile, const void *buf, int64_t count) {