martinzink commented on code in PR #1889:
URL: https://github.com/apache/nifi-minifi-cpp/pull/1889#discussion_r1829017873


##########
extensions/python/pythonlibloader/PythonLibLoader.cpp:
##########
@@ -0,0 +1,96 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#if !defined(WIN32) && !defined(__APPLE__)
+#include <dlfcn.h>
+#include <cstdio>
+#include <iostream>
+#include <string>
+#include <array>
+#include "utils/StringUtils.h"
+#include "core/logging/LoggerConfiguration.h"
+#endif
+#include "core/extension/Extension.h"
+
+namespace minifi = org::apache::nifi::minifi;
+
+#if !defined(WIN32) && !defined(__APPLE__)
+class PythonLibLoader {
+ public:
+  explicit PythonLibLoader(const std::shared_ptr<minifi::Configure>& config) {
+    std::string python_command = "python3";
+    if (auto python_binary = 
config->get(minifi::Configure::nifi_python_env_setup_binary)) {
+      python_command = python_binary.value();
+    }
+    std::string command = python_command +
+      " -c \"import sysconfig, os, glob; 
print(min(glob.glob(os.path.join(sysconfig.get_config_var('LIBDIR'), 
f\\\"libpython{sysconfig.get_config_var('VERSION')}.so*\\\")), key=len, 
default=''))\"";
+    auto lib_python_path = execCommand(command);
+    if (lib_python_path.empty()) {

Review Comment:
   Maybe we could also check the selected python version and fail if its not up 
to our standards (currently older than 3.6), and have some nice error message.
   This could be useful later aswell if we decide to drop eol version support 
for some reason.
   
   (maybe we could use the Py_LIMITED_API compile definition we set in cmake so 
we dont have to hardcode the supported version here aswell)



##########
extensions/python/pythonlibloader/PythonLibLoader.cpp:
##########
@@ -0,0 +1,96 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#if !defined(WIN32) && !defined(__APPLE__)
+#include <dlfcn.h>
+#include <cstdio>
+#include <iostream>
+#include <string>
+#include <array>
+#include "utils/StringUtils.h"
+#include "core/logging/LoggerConfiguration.h"
+#endif
+#include "core/extension/Extension.h"
+
+namespace minifi = org::apache::nifi::minifi;
+
+#if !defined(WIN32) && !defined(__APPLE__)
+class PythonLibLoader {
+ public:
+  explicit PythonLibLoader(const std::shared_ptr<minifi::Configure>& config) {
+    std::string python_command = "python3";
+    if (auto python_binary = 
config->get(minifi::Configure::nifi_python_env_setup_binary)) {
+      python_command = python_binary.value();
+    }
+    std::string command = python_command +
+      " -c \"import sysconfig, os, glob; 
print(min(glob.glob(os.path.join(sysconfig.get_config_var('LIBDIR'), 
f\\\"libpython{sysconfig.get_config_var('VERSION')}.so*\\\")), key=len, 
default=''))\"";
+    auto lib_python_path = execCommand(command);
+    if (lib_python_path.empty()) {
+      logger_->log_error("Failed to find libpython path from specified python 
binary: {}", python_command);
+      throw std::runtime_error("Failed to find libpython path");
+    }
+
+    lib_python_handle_ = dlopen(lib_python_path.c_str(), RTLD_NOW | 
RTLD_GLOBAL);
+    if (!lib_python_handle_) {
+      logger_->log_error("Failed to load libpython from path '{}' with error: 
{}", lib_python_path, dlerror());
+      throw std::runtime_error("Failed to load libpython");
+    }
+    logger_->log_info("Loaded libpython from path '{}'", lib_python_path);
+  }
+
+  PythonLibLoader(PythonLibLoader&&) = delete;
+  PythonLibLoader(const PythonLibLoader&) = delete;
+  PythonLibLoader& operator=(PythonLibLoader&&) = delete;
+  PythonLibLoader& operator=(const PythonLibLoader&) = delete;
+
+  ~PythonLibLoader() {
+    if (lib_python_handle_) {
+      dlclose(lib_python_handle_);
+    }
+  }
+
+ private:
+  static std::string execCommand(const std::string& cmd) {
+    std::array<char, 128> buffer{};
+    std::string result;
+    std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd.c_str(), "r"), 
pclose);
+    if (!pipe) {
+      return "";
+    }
+    while (fgets(buffer.data(), static_cast<int>(buffer.size()), pipe.get()) 
!= nullptr) {
+      result += buffer.data();
+    }
+    return minifi::utils::string::trim(result);
+  }
+
+  void* lib_python_handle_ = nullptr;
+  std::shared_ptr<minifi::core::logging::Logger> logger_ = 
minifi::core::logging::LoggerFactory<PythonLibLoader>::getLogger();
+};
+#endif
+
+static bool init(const std::shared_ptr<minifi::Configure>& config) {
+#if !defined(WIN32) && !defined(__APPLE__)
+  static PythonLibLoader python_lib_loader(config);
+#else
+  (void)config;
+#endif
+  return true;

Review Comment:
   This should work and its a bit easier on the eyes
   ```suggestion
   static bool init([[maybe_unused]] const std::shared_ptr<minifi::Configure>& 
config) {
   #if !defined(WIN32) && !defined(__APPLE__)
     static PythonLibLoader python_lib_loader(config);
   #endif
     return true;
   ```



##########
extensions/python/pythonlibloader/PythonLibLoader.cpp:
##########
@@ -0,0 +1,96 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#if !defined(WIN32) && !defined(__APPLE__)
+#include <dlfcn.h>
+#include <cstdio>
+#include <iostream>
+#include <string>
+#include <array>
+#include "utils/StringUtils.h"
+#include "core/logging/LoggerConfiguration.h"
+#endif
+#include "core/extension/Extension.h"
+
+namespace minifi = org::apache::nifi::minifi;
+
+#if !defined(WIN32) && !defined(__APPLE__)
+class PythonLibLoader {
+ public:
+  explicit PythonLibLoader(const std::shared_ptr<minifi::Configure>& config) {
+    std::string python_command = "python3";
+    if (auto python_binary = 
config->get(minifi::Configure::nifi_python_env_setup_binary)) {
+      python_command = python_binary.value();
+    }

Review Comment:
   Imho if we tried to be smarter than the user it could cause hard to 
understand bugs. (etc. our logic finds an invalid python installation).
   If we simply let the system pickup the default python than the user can 
easily run minifi from a venv (without minifi.properties) and it will be always 
clear why minifi chose a particular version.
   
   I think if the user develops a script and tests it locally (probably using 
default python), he/she would assume that minifi will run the script the same 
way using the same version.



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