engine: resources: Add a gsettings resource

This adds a way to run the gsettings command for configuring dconf
settings usually used by GNOME applications.

engine/resources/gsettings.go

@@ -0,0 +1,391 @@
+// Mgmt
+// Copyright (C) James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package resources
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"os/user"
+	"reflect"
+	"strconv"
+	"strings"
+
+	"github.com/purpleidea/mgmt/engine"
+	"github.com/purpleidea/mgmt/engine/traits"
+	engineUtil "github.com/purpleidea/mgmt/engine/util"
+	"github.com/purpleidea/mgmt/util/errwrap"
+)
+
+func init() {
+	engine.RegisterResource("gsettings", func() engine.Res { return &GsettingsRes{} })
+}
+
+const (
+	gsettingsTmpl = "gsettings@%s"
+)
+
+// GsettingsRes is a resource for setting dconf values through gsettings. The
+// ideal scenario is that this runs as the same user that wants settings set.
+// This should be done by a local user-specific mgmt daemon. As a special case,
+// we can run as root (or anyone with permission) which launches a subprocess
+// which setuid/setgid's to that user to run the needed operations. To specify
+// the schema and key, set the resource name as "schema key" (separated by a
+// single space character) or use the parameters.
+type GsettingsRes struct {
+	// XXX: add a dbus version of this-- it will require running as the user
+	// directly since in that scenario we can't spawn a process of the right
+	// uid/gid, and if we set either of those we would interfere with all of
+	// the normal mgmt stuff running inside this process.
+
+	traits.Base // add the base methods without re-implementation
+
+	init *engine.Init
+
+	// Schema is the schema to use in. This can be schema:path if the schema
+	// doesn't have a fixed path. See the `gsettings` manual for more info.
+	Schema string `lang:"schema" yaml:"schema"`
+
+	// Key is the key to set.
+	Key string `lang:"key" yaml:"key"`
+
+	// Type is the type value to set. This can be "bool", "str", "int", or
+	// "custom".
+	// XXX: add support for [][]str and so on...
+	Type string `lang:"type" yaml:"type"`
+
+	// Value is the value to set. It is interface{} because it can hold any
+	// value type.
+	// XXX: Add resource unification to this key
+	Value interface{} `lang:"value" yaml:"value"`
+
+	// User is the (optional) user to use to execute the command. It is used
+	// for any command being run.
+	User string `lang:"user" yaml:"user"`
+
+	// Group is the (optional) group to use to execute the command. It is
+	// used for any command being run.
+	Group string `lang:"group" yaml:"group"`
+
+	// XXX: We should have a "once" functionality if this param is set true.
+	// XXX: Basically it would change that field once, and store a "tag"
+	// file to say it was done.
+	// XXX: Maybe that should be a metaparam called Once that works anywhere.
+	// XXX: Maybe there should be a way to reset the "once" tag too...
+	//Once string `lang:"once" yaml:"once"`
+
+	// We're using the exec resource to build the resources because it's all
+	// done through exec.
+	exec *ExecRes
+}
+
+// Default returns some sensible defaults for this resource.
+func (obj *GsettingsRes) Default() engine.Res {
+	return &GsettingsRes{}
+}
+
+// parse is a helper to pull out the correct schema and key to use.
+func (obj *GsettingsRes) parse() (string, string, error) {
+	schema := obj.Schema
+	key := obj.Key
+
+	sp := strings.Split(obj.Name(), " ")
+	if len(sp) == 2 && obj.Schema == "" && obj.Key == "" {
+		schema = sp[0]
+		key = sp[1]
+	}
+
+	if schema == "" {
+		return "", "", fmt.Errorf("empty schema")
+	}
+	if key == "" {
+		return "", "", fmt.Errorf("empty key")
+	}
+
+	return schema, key, nil
+}
+
+// value is a helper to pull out the value in the correct format to use.
+func (obj *GsettingsRes) value() (string, error) {
+	if obj.Type == "bool" {
+		v, ok := obj.Value.(bool)
+		if !ok {
+			return "", fmt.Errorf("invalid bool")
+		}
+		if v {
+			return "true", nil
+		}
+		return "false", nil
+	}
+
+	if obj.Type == "str" {
+		v, ok := obj.Value.(string)
+		if !ok {
+			return "", fmt.Errorf("invalid str")
+		}
+		return v, nil
+	}
+
+	if obj.Type == "int" {
+		v, ok := obj.Value.(int)
+		if !ok {
+			return "", fmt.Errorf("invalid int")
+		}
+		return strconv.Itoa(v), nil
+	}
+
+	if obj.Type == "custom" {
+		v, ok := obj.Value.(string)
+		if !ok {
+			return "", fmt.Errorf("invalid custom")
+		}
+		return v, nil
+	}
+
+	// XXX: add proper type parsing
+
+	return "", fmt.Errorf("invalid type: %s", obj.Type)
+}
+
+// uid is a helper to get the correct uid.
+func (obj *GsettingsRes) uid() (int, error) {
+	uid := obj.User // something or empty
+	if obj.User == "" {
+		u, err := user.Current()
+		if err != nil {
+			return -1, err
+		}
+
+		uid = u.Uid
+	}
+
+	out, err := engineUtil.GetUID(uid)
+	if err != nil {
+		return -1, errwrap.Wrapf(err, "error looking up uid for %s", uid)
+	}
+	return out, nil
+}
+
+// makeComposite creates a pointer to a ExecRes. The pointer is used to validate
+// and initialize the nested exec.
+func (obj *GsettingsRes) makeComposite() (*ExecRes, error) {
+	cmd, err := exec.LookPath("gsettings")
+	if err != nil {
+		return nil, err
+	}
+
+	schema, key, err := obj.parse()
+	if err != nil {
+		return nil, err
+	}
+	val, err := obj.value()
+	if err != nil {
+		return nil, err
+	}
+	uid, err := obj.uid()
+	if err != nil {
+		return nil, err
+	}
+
+	res, err := engine.NewNamedResource("exec", fmt.Sprintf(gsettingsTmpl, obj.Name()))
+	if err != nil {
+		return nil, err
+	}
+	exec := res.(*ExecRes)
+
+	exec.Cmd = cmd
+	exec.Args = []string{
+		"set",
+		schema,
+		key,
+		val,
+	}
+	exec.Cwd = "/"
+
+	exec.IfCmd = fmt.Sprintf("%s get %s %s", cmd, schema, key)
+	exec.IfCwd = "/"
+	expected := val + "\n" // value comes with a trailing newline
+	exec.IfEquals = &expected
+
+	exec.WatchCmd = fmt.Sprintf("%s monitor %s %s", cmd, schema, key)
+	exec.WatchCwd = "/"
+
+	exec.User = obj.User
+	exec.Group = obj.Group
+
+	exec.Env = map[string]string{
+		// Either of these will work, so we'll include both for fun.
+		"DBUS_SESSION_BUS_ADDRESS": fmt.Sprintf("unix:path=/run/user/%d/bus", uid),
+		"XDG_RUNTIME_DIR":          fmt.Sprintf("/run/user/%d/", uid),
+	}
+	//exec.Timeout = ? // TODO: should we have a timeout to prevent blocking?
+
+	return exec, nil
+}
+
+// Validate reports any problems with the struct definition.
+func (obj *GsettingsRes) Validate() error {
+	if _, _, err := obj.parse(); err != nil {
+		return err
+	}
+	// validation of obj.Type happens in this function.
+	if _, err := obj.value(); err != nil {
+		return err
+	}
+
+	exec, err := obj.makeComposite()
+	if err != nil {
+		return errwrap.Wrapf(err, "makeComposite failed in validate")
+	}
+	if err := exec.Validate(); err != nil { // composite resource
+		return errwrap.Wrapf(err, "validate failed for embedded exec: %s", exec)
+	}
+	return nil
+}
+
+// Init runs some startup code for this resource.
+func (obj *GsettingsRes) Init(init *engine.Init) error {
+	obj.init = init // save for later
+
+	exec, err := obj.makeComposite()
+	if err != nil {
+		return errwrap.Wrapf(err, "makeComposite failed in init")
+	}
+	obj.exec = exec
+
+	newInit := obj.init.Copy()
+	newInit.Send = func(interface{}) error { // override so exec can't send
+		return nil
+	}
+	newInit.Logf = func(format string, v ...interface{}) {
+		//if format == "cmd out empty!" {
+		//	return
+		//}
+		//obj.init.Logf("exec: "+format, v...)
+	}
+
+	return obj.exec.Init(newInit)
+}
+
+// Cleanup is run by the engine to clean up after the resource is done.
+func (obj *GsettingsRes) Cleanup() error {
+	if obj.exec != nil {
+		return obj.exec.Cleanup()
+	}
+	return nil
+}
+
+// Watch is the primary listener for this resource and it outputs events.
+func (obj *GsettingsRes) Watch(ctx context.Context) error {
+	return obj.exec.Watch(ctx)
+}
+
+// CheckApply checks the resource state and applies the resource if the bool
+// input is true. It returns error info and if the state check passed or not.
+func (obj *GsettingsRes) CheckApply(ctx context.Context, apply bool) (bool, error) {
+	obj.init.Logf("%s", obj.exec.IfCmd) // "gsettings get"
+
+	checkOK, err := obj.exec.CheckApply(ctx, apply)
+	if err != nil {
+		return checkOK, err
+	}
+
+	if !checkOK {
+		// "gsettings set"
+		obj.init.Logf("%s %s", obj.exec.Cmd, strings.Join(obj.exec.Args, " "))
+	}
+
+	return checkOK, nil
+}
+
+// Cmp compares two resources and returns an error if they are not equivalent.
+func (obj *GsettingsRes) Cmp(r engine.Res) error {
+	// we can only compare GsettingsRes to others of the same resource kind
+	res, ok := r.(*GsettingsRes)
+	if !ok {
+		return fmt.Errorf("not a %s", obj.Kind())
+	}
+
+	if obj.Schema != res.Schema {
+		return fmt.Errorf("the Schema differs")
+	}
+	if obj.Key != res.Key {
+		return fmt.Errorf("the Key differs")
+	}
+	if obj.Type != res.Type {
+		return fmt.Errorf("the Type differs")
+	}
+
+	//if obj.Value != res.Value {
+	//	return fmt.Errorf("the Value differs")
+	//}
+	if !reflect.DeepEqual(obj.Value, res.Value) {
+		return fmt.Errorf("the Value field differs")
+	}
+
+	if obj.User != res.User {
+		return fmt.Errorf("the User differs")
+	}
+	if obj.Group != res.Group {
+		return fmt.Errorf("the Group differs")
+	}
+
+	// TODO: why is res.exec ever nil?
+	if (obj.exec == nil) != (res.exec == nil) { // xor
+		return fmt.Errorf("the exec differs")
+	}
+	if obj.exec != nil && res.exec != nil {
+		if err := obj.exec.Cmp(res.exec); err != nil {
+			return errwrap.Wrapf(err, "the exec differs")
+		}
+	}
+
+	return nil
+}
+
+// UnmarshalYAML is the custom unmarshal handler for this struct. It is
+// primarily useful for setting the defaults.
+func (obj *GsettingsRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	type rawRes GsettingsRes // indirection to avoid infinite recursion
+
+	def := obj.Default()           // get the default
+	res, ok := def.(*GsettingsRes) // put in the right format
+	if !ok {
+		return fmt.Errorf("could not convert to GsettingsRes")
+	}
+	raw := rawRes(*res) // convert; the defaults go here
+
+	if err := unmarshal(&raw); err != nil {
+		return err
+	}
+
+	*obj = GsettingsRes(raw) // restore from indirection with type conversion!
+	return nil
+}

examples/lang/gsettings.mcl

@@ -0,0 +1,11 @@
+gsettings "org.gnome.desktop.interface clock-show-seconds" {
+	type => "bool",
+	value => true,
+}
+
+gsettings "org.gnome.desktop.input-sources sources" { # happens to match schema/key args
+	schema => "org.gnome.desktop.input-sources",
+	key => "sources",
+	type => "custom",
+	value => "[('xkb', 'ca+eng'), ('xkb', 'ca'), ('xkb', 'us')]",
+}