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Avoiding Dynlink and Config Files

One may not want to use a configuration file (because lacking a file-system or so) and/or dynamic linking of plugins (because dynamic-linking can be problematic).

It is possible! This document shows how.

Plugins

Plugins can be compiled to “good old-school” libraries:

tmp_dir=/tmp/with_dummy_plugin
mkdir -p $tmp_dir
cp src/test/dummy-plugin/dummy_plugin.ml $tmp_dir
ocamlfind opt -package ketrew -thread -c  $tmp_dir/dummy_plugin.ml -o $tmp_dir/dummy_plugin.cmx

And can be linked-in directly with src/app/main.ml:

cp src/app/cli_main.ml $tmp_dir
ocamlfind opt -package ketrew -thread -linkpkg -I $tmp_dir $tmp_dir/dummy_plugin.cmx $tmp_dir/cli_main.ml -o $tmp_dir/new_ketrew_app
$tmp_dir/new_ketrew_app --help=plain

We can run the plugin user to add a workflow:

sed 's/Dummy_plugin_test_lib.//' src/test/dummy_plugin_user.ml > $tmp_dir/dummy_plugin_user.ml
ocamlfind opt -package ketrew -thread -linkpkg -I $tmp_dir $tmp_dir/dummy_plugin.cmx $tmp_dir/dummy_plugin_user.ml -o $tmp_dir/my_workflow
$tmp_dir/my_workflow "du -sh $HOME"

We can run the workflow (type 'q' when done):

$tmp_dir/new_ketrew_app run loop

And explore to the target, to call the custom query:

$tmp_dir/new_ketrew_app interact

(choose the target, 's' for “show-status”, '1' for “display date”).

Configuration

The function Ketrew_command_line.run_main can take an ~override_configuration parameter, which can be created with Ketrew.Configuration.{create,create_server} (c.f. Ketrew.Command_line and Ketrew.Configuration).

See the example in src/test/preconfigured_main.ml, here is how to compile it:

tmp_dir=/tmp/with_preconfiguration
mkdir -p $tmp_dir
cp src/test/preconfigured_main.ml $tmp_dir
ocamlfind opt -package ketrew -thread -linkpkg $tmp_dir/preconfigured_main.ml -o $tmp_dir/new_ketrew_app
$tmp_dir/new_ketrew_app print-configuration

We can check that no configuration file is read with

export KETREW_CONFIGURATION=/some/unknown/path/that/really/does/not/exist.json

The “normal” ketrew fails:

ketrew pc

ketrew: internal error, uncaught exception:
        Sys_error("/some/unknown/path/that/really/does/not/exist.json: No such file or directory")

The new one succeeds:

$tmp_dir/new_ketrew_app print-configuration

[ketrew] 
    Mode: Server
    Engine:
        Database: "/tmp/somepath"
        Unix-failure: does not turn into target failure
        Host-timeout-upper-bound:
        Maximum-successive-attempts: 10
    UI:
        Colors: with colors
        Get-key: uses `cbreak`
        Explorer:
            Default request: Targets younger than 1.5 days
            Targets-per-page: 6
            Targets-to-prefectch: 6
    HTTP-server:
        Authorized tokens:
            Path: "/tmp/tokens"
        Command Pipe: None
        Log-path: None
        Return-error-messages: false
        Max-blocking-time: 300.
        Block-step-time: 3.
        Listen:
            Port: 4242
            Certificate: "somecert.pem"
            Key: "somekey.pem"
    Misc:
        Debug-level: 42
        Plugins:
            OCamlfind package: "lwt.react"
            OCamlfind package: "lwt.unix"

Command Line “Sub-commands”

One can also even add their own sub-commands to the command-line parsing: this is also in the example src/test/preconfigured_main.ml.