Introduce "drivers" for executable user-defined functions. A driver is a
small adapter program declared in a server config under
`<user_defined_executable_function_drivers_config>` that knows how to take a
user-supplied code snippet and produce a runnable executable user-defined
function configuration.
New CREATE FUNCTION syntax:
CREATE [OR REPLACE] FUNCTION [IF NOT EXISTS] name [ON CLUSTER c]
ARGUMENTS (a UInt8, b String) RETURNS UInt64
ENGINE = DriverName(key1 = 'value1', key2 = 42)
AS '...code body...'
On CREATE FUNCTION, the corresponding `create_command` of the driver is
invoked: arguments are passed via `--name`, `--return`, `--args` and the
declared engine arguments; the body is sent on stdin; the driver writes the
resulting executable UDF configuration (XML or YAML) to stdout, which is
saved into the new `<dynamic_user_defined_executable_functions_path>` and
picked up by the existing executable UDF loader. The corresponding SQL is
persisted as `ATTACH FUNCTION ...` in `<user_defined>` and re-evaluated on
restart: if the dynamic configuration is still present, the driver is not
invoked; otherwise the driver is re-run to materialize it.
On DROP FUNCTION, the `drop_command` (if any) is invoked, then the dynamic
configuration file and per-function working directory are removed.
Includes a proof-of-concept driver `c_function_body`, which compiles a user
C body into a binary (inside Docker by default for build-time isolation) and
runs it inside Docker at query time with strict sandboxing (`--network=none`,
`--read-only`, dropped capabilities, no-new-privileges, unprivileged user,
resource limits) in `executable_pool` mode for batched per-row evaluation.
See https://github.com/ClickHouse/ClickHouse/issues/71172
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
