Add startup code to worker

Author: maiqbal11

python/prod/worker.py

@@ -1,4 +1,66 @@
-from azure_functions_worker import main
+import os
+import sys
+import platform
+import subprocess
+from pathlib import Path
+
+# User packages
+PKGS_PATH = "site/wwwroot/.python_packages"
+VENV_PKGS_PATH = "site/wwwroot/worker_venv"
+
+PKGS_36 = "lib/python3.6/site-packages"
+PKGS = "lib/site-packages"
+
+# Azure environment variables
+AZURE_WEBSITE_INSTANCE_ID = "WEBSITE_INSTANCE_ID"
+AZURE_CONTAINER_NAME = "CONTAINER_NAME"
+
+
+def is_azure_environment():
+    return (AZURE_CONTAINER_NAME in os.environ or
+            AZURE_WEBSITE_INSTANCE_ID in os.environ)
+
+
+def determine_user_pkg_paths():
+    minor_version = sys.version_info[1]
+
+    home = Path.home()
+    pkgs_path = os.path.join(home, PKGS_PATH)
+    venv_pkgs_path = os.path.join(home, VENV_PKGS_PATH)
+
+    user_pkg_paths = []
+    if minor_version == 6:
+        user_pkg_paths.append(os.path.join(venv_pkgs_path, PKGS_36))
+        user_pkg_paths.append(os.path.join(pkgs_path, PKGS_36))
+        user_pkg_paths.append(os.path.join(pkgs_path, PKGS))
+    elif minor_version == 7:
+        user_pkg_paths.append(os.path.join(pkgs_path, PKGS))
+    else:
+        raise RuntimeError(f'Unsupported Python version: 3.{minor_version}')
+
+    return user_pkg_paths
+
 
 if __name__ == '__main__':
-    main.main()
+    user_pkg_paths = []
+    if is_azure_environment():
+        user_pkg_paths = determine_user_pkg_paths()
+
+    env = os.environ
+    # worker.py lives in the same directory as azure_functions_worker
+    func_worker_dir = str(Path(__file__).absolute().parent)
+
+    if platform.system() == 'Windows':
+        joined_pkg_paths = ";".join(user_pkg_paths)
+        env['PYTHONPATH'] = f'{joined_pkg_paths};{func_worker_dir}'
+        # execve doesn't work in Windows: https://bugs.python.org/issue19124
+        subprocess.run([sys.executable,
+                       '-m', 'azure_functions_worker'] + sys.argv[1:],
+                       env=env)
+    else:
+        joined_pkg_paths = ":".join(user_pkg_paths)
+        env['PYTHONPATH'] = f'{joined_pkg_paths}:{func_worker_dir}'
+        os.execve(sys.executable,
+                  [sys.executable, '-m', 'azure_functions_worker']
+                  + sys.argv[1:],
+                  env)