allow specifying existing JAR for open api client build

update_openapi_client

@@ -37,6 +37,10 @@ JAVA_COMPILE_CMD = f"java -jar {{jar}} {OPENAPI_GENERATE_COMMAND_COMMON} -i {{sc
 OPENAPI_SCHEMA_URL = "https://{host}/univention/udm/openapi.json"
 
 
+class OpenAPILibGenerationError(Exception):
+    pass
+
+
 def coro(f):
     """asyncio for click (https://github.com/pallets/click/issues/85)"""
 
@@ -109,9 +113,10 @@ def download_jar(target_path: Path):
         print_error_and_exit(str(exc))
 
 
-def run_openapi_generator_local_java(target_dir, quiet):
-    jar_path = Path(target_dir, "openapi-generator.jar")
-    download_jar(jar_path)
+def run_openapi_generator_local_java(target_dir: str, quiet: bool, jar_path: Path = None):
+    if not jar_path:
+        jar_path = Path(target_dir, "openapi-generator.jar")
+        download_jar(jar_path)
     cmd = JAVA_COMPILE_CMD.format(
         jar=jar_path,
         schema=str(Path(target_dir, TARGET_SCHEMA_FILENAME)),
@@ -120,7 +125,9 @@ def run_openapi_generator_local_java(target_dir, quiet):
     click.echo(f"Starting to generate Python code...")
     process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     stdout, stderr = process.communicate()
-    if not quiet:
+    if process.returncode:
+        print_error_and_exit(stdout.decode())
+    elif not quiet:
         click.echo(stdout.decode())
 
 
@@ -161,6 +168,12 @@ def get_openapi_schema(host: str, secure: bool) -> str:
     "or as a JAR file. Requires either a running Docker daemon or a local"
     " Java (>=8) installation.",
 )
+@click.option(
+    "--jar",
+    type=click.Path(exists=True, readable=True),
+    help="OpenAPI Generator JAR file to use with '--generator java'. If not"
+    "given, the JAR file will be downloaded automatically.",
+)
 @click.option(
     "--keep-image/--dont-keep-image",
     default=False,
@@ -179,10 +192,12 @@ def get_openapi_schema(host: str, secure: bool) -> str:
 )
 @coro
 async def update_openapi_client(
-    host: str, generator: str, keep_image: bool, secure: bool, quiet: bool
+    host: str, generator: str, jar: str, keep_image: bool, secure: bool, quiet: bool
 ):
     if not host:
         print_error_and_exit("Address (FQDN or IP address) of UCS host required.")
+    if jar and generator != "java":
+        print_error_and_exit("The --jar option can only be used together with '--generator java'.")
     txt = get_openapi_schema(host, secure)
     with TemporaryDirectory() as temp_dir, open(
         Path(temp_dir, TARGET_SCHEMA_FILENAME), "w"
@@ -197,7 +212,7 @@ async def update_openapi_client(
         if generator == "docker":
             run_openapi_generator_docker_container(temp_dir, quiet, keep_image)
         else:
-            run_openapi_generator_local_java(temp_dir, quiet)
+            run_openapi_generator_local_java(temp_dir, quiet, Path(jar))
         click.echo("Installing package via pip...")
         pip_main.main(
             ["install", "--compile", "--upgrade", str(Path(temp_dir, "python/"))]