Merged PR 5318: Use DDBC module path to find ODBC module path

This PR removes reliance on current working directory (CWD) when locating ODBC dll. User can run their apps from any directory. We cannot rely on CWD to find ODBC dll. Additionally, GetCurrentDirectory API is not safe to use from a shared library & in a multithreaded app (acc to it's [documentation](https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-getcurrentdirectory#remarks))

Instead, look for ODBC dll relative to the ddbc_bindings.pyd file path. The pyd will be installed somewhere inside the Python installation directory. The expectation is that we will find msodbcsql18.dll in the following directory - **<ddbc_bindings.pyd directory>\libs\win\msodbcsql18.dll**

Related work items: #33826

Author: Theekshna Kotian

mssql_python/cursor.py

@@ -10,9 +10,6 @@
 import uuid
 import os
 from mssql_python.exceptions import raise_exception
-
-os.chdir(os.path.dirname(__file__))
-
 from mssql_python import ddbc_bindings
 
 # Setting up logging

mssql_python/pybind/ddbc_bindings.cpp

@@ -1,6 +1,9 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
+// INFO|TODO - Note that is file is Windows specific right now. Making it arch agnostic will be
+//             taken up in beta release
+
 #include <pybind11/pybind11.h> // pybind11.h must be the first include - https://pybind11.readthedocs.io/en/latest/basics.html#header-and-namespace-conventions
 
 #include <cstdint>
@@ -237,14 +240,33 @@ void ThrowStdException(const std::string& message) { throw std::runtime_error(me
 // TODO: We don't need to do explicit linking using LoadLibrary. We can just use implicit
 //       linking to load this DLL. It will simplify the code a lot.
 void LoadDriverOrThrowException() {
-    // Get the DLL directory to the current directory
-    wchar_t currentDir[MAX_PATH];
-    GetCurrentDirectoryW(MAX_PATH, currentDir);
-    std::wstring dllDir = std::wstring(currentDir) + L"\\libs\\win\\msodbcsql18.dll";
+    HMODULE hDdbcModule;
+    wchar_t ddbcModulePath[MAX_PATH];
+    // Get the path to DDBC module:
+    // GetModuleHandleExW returns a handle to current shared library (ddbc_bindings.pyd) given a
+    // function from the library (LoadDriverOrThrowException). GetModuleFileNameW takes in the
+    // library handle (hDdbcModule) & returns the full path to this library (ddbcModulePath)
+    if (GetModuleHandleExW(
+            GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+            (LPWSTR)&LoadDriverOrThrowException, &hDdbcModule) &&
+        GetModuleFileNameW(hDdbcModule, ddbcModulePath, MAX_PATH)) {
+        // Look for last occurence of '\' in the path and set it to null
+        wchar_t* lastBackSlash = wcsrchr(ddbcModulePath, L'\\');
+        if (lastBackSlash == nullptr) {
+            DEBUG_LOG("Invalid DDBC module path - %S", ddbcModulePath);
+            ThrowStdException("Failed to load driver");
+        }
+        *lastBackSlash = 0;
+    } else {
+        DEBUG_LOG("Failed to get DDBC module path. Error code - %d", GetLastError());
+        ThrowStdException("Failed to load driver");
+    }
 
-    // Load the DLL from the specified path
+    // Look for msodbcsql18.dll in a path relative to DDBC module
+    std::wstring dllDir = std::wstring(ddbcModulePath) + L"\\libs\\win\\msodbcsql18.dll";
     HMODULE hModule = LoadLibraryW(dllDir.c_str());
     if (!hModule) {
+        DEBUG_LOG("LoadLibraryW failed to load driver from - %S", dllDir.c_str());
         ThrowStdException("Failed to load driver");
     }
     DEBUG_LOG("Driver loaded successfully from - %S", dllDir.c_str());
@@ -294,6 +316,7 @@ void LoadDriverOrThrowException() {
                    SQLFreeHandle_ptr && SQLDisconnect_ptr && SQLFreeStmt_ptr && SQLGetDiagRec_ptr;
 
     if (!success) {
+        DEBUG_LOG("Failed to load required function pointers from driver - %S", dllDir.c_str());
         ThrowStdException("Failed to load required function pointers from driver");
     }
     DEBUG_LOG("Sucessfully loaded function pointers from driver");