FIX: Handling Access token with class level variables and removing static defination (#323)

### Work Item / Issue Reference  
<!-- mssql-python maintainers: ADO Work Item -->
>
[AB#40420](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/40420)



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### Summary   
This pull request refactors the way temporary buffers are managed for
setting connection attributes in the `Connection` class, improving
memory safety and simplifying buffer handling. Instead of using static
vectors to store temporary string and binary data, the code now uses
member variables to hold these buffers directly within each `Connection`
instance.

**Buffer Management Refactor:**

* Removed static vectors (`wstr_buffers`, `buffers`) for storing
temporary wide string and binary buffers, eliminating the need for
manual buffer growth management and cleanup.
[[1]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL211-L212)
[[2]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL221-R219)
[[3]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL269-R262)
* Added member variables `wstrStringBuffer` and `strBytesBuffer` to the
`Connection` class for managing temporary buffers per connection
instance, improving encapsulation and memory safety.
* Updated all relevant buffer usage in `setAttribute` to use these new
member variables, replacing references to static buffers with instance
variables.
[[1]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL248-R237)
[[2]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL221-R219)
[[3]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL269-R262)

**Code Simplification:**

* Removed unnecessary static buffer and related logic, such as buffer
size limits and periodic cleanup, resulting in cleaner and more
maintainable code.
[[1]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL191)
[[2]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL221-R219)
[[3]](diffhunk://#diff-eca696c13d997f510e5f9b16288ed1deb0ad132768c283eda1518f78edf9b6ecL269-R262)

Author: subrata-ms

mssql_python/pybind/connection/connection.cpp

@@ -188,7 +188,6 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
     LOG("Setting SQL attribute");
     // SQLPOINTER ptr = nullptr;
     // SQLINTEGER length = 0;
-    static std::string buffer;  // to hold sensitive data temporarily
 
     if (py::isinstance<py::int_>(value)) {
         // Get the integer value
@@ -208,8 +207,6 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
         return ret;
     } else if (py::isinstance<py::str>(value)) {
         try {
-            // Keep buffers alive
-            static std::vector<std::wstring> wstr_buffers;
             std::string utf8_str = value.cast<std::string>();
 
             // Convert to wide string
@@ -218,24 +215,16 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
                 LOG("Failed to convert string value to wide string");
                 return SQL_ERROR;
             }
-
-            // Limit static buffer growth for memory safety
-            constexpr size_t MAX_BUFFER_COUNT = 100;
-            if (wstr_buffers.size() >= MAX_BUFFER_COUNT) {
-            // Remove oldest 50% of entries when limit reached
-            wstr_buffers.erase(wstr_buffers.begin(),
-                               wstr_buffers.begin() + (MAX_BUFFER_COUNT / 2));
-            }
-
-            wstr_buffers.push_back(wstr);
+            this->wstrStringBuffer.clear();
+            this->wstrStringBuffer = std::move(wstr);
 
             SQLPOINTER ptr;
             SQLINTEGER length;
 
 #if defined(__APPLE__) || defined(__linux__)
             // For macOS/Linux, convert wstring to SQLWCHAR buffer
-            std::vector<SQLWCHAR> sqlwcharBuffer = WStringToSQLWCHAR(wstr);
-            if (sqlwcharBuffer.empty() && !wstr.empty()) {
+            std::vector<SQLWCHAR> sqlwcharBuffer = WStringToSQLWCHAR(this->wstrStringBuffer);
+            if (sqlwcharBuffer.empty() && !this->wstrStringBuffer.empty()) {
                 LOG("Failed to convert wide string to SQLWCHAR buffer");
                 return SQL_ERROR;
             }
@@ -245,9 +234,8 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
                 sqlwcharBuffer.size() * sizeof(SQLWCHAR));
 #else
             // On Windows, wchar_t and SQLWCHAR are the same size
-            ptr = const_cast<SQLWCHAR*>(wstr_buffers.back().c_str());
-            length = static_cast<SQLINTEGER>(
-                wstr.length() * sizeof(SQLWCHAR));
+            ptr = const_cast<SQLWCHAR*>(this->wstrStringBuffer.c_str());
+            length = static_cast<SQLINTEGER>(this->wstrStringBuffer.length() * sizeof(SQLWCHAR));
 #endif
 
             SQLRETURN ret = SQLSetConnectAttr_ptr(_dbcHandle->get(),
@@ -266,21 +254,11 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
     } else if (py::isinstance<py::bytes>(value) ||
                py::isinstance<py::bytearray>(value)) {
         try {
-            static std::vector<std::string> buffers;
             std::string binary_data = value.cast<std::string>();
-
-            // Limit static buffer growth
-            constexpr size_t MAX_BUFFER_COUNT = 100;
-            if (buffers.size() >= MAX_BUFFER_COUNT) {
-            // Remove oldest 50% of entries when limit reached
-            buffers.erase(buffers.begin(),
-                          buffers.begin() + (MAX_BUFFER_COUNT / 2));
-            }
-
-            buffers.emplace_back(std::move(binary_data));
-            SQLPOINTER ptr = const_cast<char*>(buffers.back().c_str());
-            SQLINTEGER length = static_cast<SQLINTEGER>(
-                buffers.back().size());
+            this->strBytesBuffer.clear();
+            this->strBytesBuffer = std::move(binary_data);
+            SQLPOINTER ptr = const_cast<char*>(this->strBytesBuffer.c_str());
+            SQLINTEGER length = static_cast<SQLINTEGER>(this->strBytesBuffer.size());
 
             SQLRETURN ret = SQLSetConnectAttr_ptr(_dbcHandle->get(),
                                                   attribute, ptr, length);

mssql_python/pybind/connection/connection.h

@@ -59,6 +59,8 @@ class Connection {
     bool _autocommit = true;
     SqlHandlePtr _dbcHandle;
     std::chrono::steady_clock::time_point _lastUsed;
+    std::wstring wstrStringBuffer;  // wstr buffer for string attribute setting
+    std::string strBytesBuffer;    // string buffer for byte attributes setting
 };
 
 class ConnectionHandle {