From 088daa202aa70d5553754500dee2fa1684007d38 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jes=C3=BAs=20Fern=C3=A1ndez?=
 <7312236+fernandezcuesta@users.noreply.github.com>
Date: Fri, 11 Sep 2026 22:58:40 +0200
Subject: [PATCH] feat: add standard CLI options
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Signed-off-by: Jesús Fernández <7312236+fernandezcuesta@users.noreply.github.com>
---
 crossplane/function/cli.py | 125 +++++++++++++++++++++++++++++++++++++
 pyproject.toml             |   1 +
 2 files changed, 126 insertions(+)
 create mode 100644 crossplane/function/cli.py

diff --git a/crossplane/function/cli.py b/crossplane/function/cli.py
new file mode 100644
index 0000000..8e15c27
--- /dev/null
+++ b/crossplane/function/cli.py
@@ -0,0 +1,125 @@
+# Copyright 2026 The Crossplane Authors.
+#
+# Licensed 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.
+
+"""Standard CLI options for Python composition functions.
+
+Provides reusable options and a run helper so that every composition
+function shares a standard set of flags, environment variables, and defaults.
+
+Usage in a function's main.py::
+
+    import click
+    from crossplane.function import cli as sdkcli
+    from function import fn
+
+    @click.command()
+    @sdkcli.standard_options
+    def cli(**kwargs):
+        sdkcli.run(fn.FunctionRunner(), **kwargs)
+
+To add custom options, stack them with the decorator::
+
+    @click.command()
+    @sdkcli.standard_options
+    @click.option("--cache-size", default=100, envvar="CACHE_SIZE")
+    def cli(cache_size, **kwargs):
+        runner = fn.FunctionRunner(cache_size=cache_size)
+        sdkcli.run(runner, **kwargs)
+"""
+
+import functools
+from collections.abc import Callable
+from typing import TypeVar
+
+import click
+
+from crossplane.function import logging, runtime
+from crossplane.function.proto.v1 import run_function_pb2_grpc as grpcv1
+
+F = TypeVar("F", bound=Callable)
+
+DEFAULT_ADDRESS = "0.0.0.0:9443"
+DEFAULT_MAX_RECV_MESSAGE_SIZE = 4  # MB
+
+
+def standard_options(func: F) -> F:
+    """Apply the standard Composition Function CLI options to a Click command."""
+
+    @click.option(
+        "--max-recv-message-size",
+        type=int,
+        default=DEFAULT_MAX_RECV_MESSAGE_SIZE,
+        show_default=True,
+        envvar="MAX_RECV_MESSAGE_SIZE",
+        help="Maximum size of received gRPC messages in MB.",
+    )
+    @click.option(
+        "--insecure",
+        is_flag=True,
+        envvar="INSECURE",
+        help="Run without mTLS credentials. "
+        "If you supply this flag --tls-certs-dir will be ignored.",
+    )
+    @click.option(
+        "--tls-certs-dir",
+        envvar="TLS_SERVER_CERTS_DIR",
+        help="Serve using mTLS certificates.",
+    )
+    @click.option(
+        "--address",
+        default=DEFAULT_ADDRESS,
+        show_default=True,
+        envvar="ADDRESS",
+        help="Address at which to listen for gRPC connections.",
+    )
+    @click.option(
+        "--debug",
+        "-d",
+        is_flag=True,
+        envvar="DEBUG",
+        help="Emit debug logs.",
+    )
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+def run(  # noqa: PLR0913
+    function_runner: grpcv1.FunctionRunnerServiceServicer,
+    *,
+    debug: bool,
+    address: str,
+    tls_certs_dir: str | None,
+    insecure: bool,
+    max_recv_message_size: int,
+) -> None:
+    """Start a composition function gRPC server with standard options."""
+    level = logging.Level.DEBUG if debug else logging.Level.INFO
+    logging.configure(level=level)
+
+    size_bytes = max_recv_message_size * 1024 * 1024
+    options = [
+        ("grpc.max_receive_message_length", size_bytes),
+        ("grpc.max_send_message_length", size_bytes),
+    ]
+
+    runtime.serve(
+        function_runner,
+        address,
+        creds=runtime.load_credentials(tls_certs_dir),
+        insecure=insecure,
+        options=options,
+    )
diff --git a/pyproject.toml b/pyproject.toml
index b07d1bd..bd9cd8a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -18,6 +18,7 @@ classifiers = [
 ]
 
 dependencies = [
+  "click==8.*",
   "grpcio==1.83.1",
   "grpcio-reflection==1.*",
   "protobuf==7.36.1", # Must be compatible with grpcio-tools.