Copy sys.argv in prepare_cmd_args to avoid stacking endpoint flags

bin/awslocal

@@ -168,8 +168,9 @@ def prepare_cmd_args():
         print('ERROR: %s' % msg)
         return sys.exit(1)
 
-    # prepare cmd args
-    cmd_args = sys.argv
+    # prepare cmd args (copy: the inserts below must not mutate sys.argv,
+    # otherwise repeated calls keep stacking --endpoint-url flags)
+    cmd_args = list(sys.argv)
     if endpoint:
         cmd_args.insert(1, '--endpoint-url=%s' % endpoint)
         if 'https' in endpoint:

tests/test_awslocal_prepare_cmd_args.py

@@ -0,0 +1,54 @@
+"""Tests for prepare_cmd_args in bin/awslocal.
+
+bin/awslocal has no .py extension, so it is loaded with SourceFileLoader.
+localstack_client is stubbed: endpoint resolution is the only behavior
+needed here, and the real package is an unrelated optional dependency.
+"""
+
+import sys
+import types
+from importlib.machinery import SourceFileLoader
+from pathlib import Path
+
+import pytest
+
+BIN = Path(__file__).resolve().parent.parent / "bin" / "awslocal"
+
+
+def _load_awslocal(monkeypatch):
+    fake = types.ModuleType("localstack_client")
+
+    class FakeConfig:
+        @staticmethod
+        def get_service_endpoints(localstack_host=None):
+            return {"sts": "http://localhost:4566", "s3": "http://localhost:4566"}
+
+    fake.config = FakeConfig()
+    monkeypatch.setitem(sys.modules, "localstack_client", fake)
+    return SourceFileLoader("awslocal_under_test", str(BIN)).load_module()
+
+
+def test_prepare_cmd_args_inserts_endpoint_once(monkeypatch):
+    awslocal = _load_awslocal(monkeypatch)
+    monkeypatch.setattr(sys, "argv", ["awslocal", "s3", "ls"])
+    cmd_args = awslocal.prepare_cmd_args()
+    assert cmd_args.count("--endpoint-url=http://localhost:4566") == 1
+
+
+def test_prepare_cmd_args_is_repeatable(monkeypatch):
+    """Calling prepare_cmd_args twice must not duplicate flags.
+
+    Regression test: cmd_args aliased sys.argv, so every call inserted
+    another --endpoint-url into the live argv list.
+    """
+    awslocal = _load_awslocal(monkeypatch)
+    monkeypatch.setattr(sys, "argv", ["awslocal", "s3", "ls"])
+    first = awslocal.prepare_cmd_args()
+    second = awslocal.prepare_cmd_args()
+    assert first.count("--endpoint-url=http://localhost:4566") == 1
+    assert second.count("--endpoint-url=http://localhost:4566") == 1
+    assert sys.argv.count("--endpoint-url=http://localhost:4566") <= 1
+
+
+if __name__ == "__main__":
+    pytest.main([__file__])