engine: resources: Add a line resource

Simple enough for the common cases. It just needs some tests.

engine/resources/line.go

@@ -0,0 +1,371 @@
+// 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 (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/purpleidea/mgmt/engine"
+	"github.com/purpleidea/mgmt/engine/traits"
+	"github.com/purpleidea/mgmt/util/errwrap"
+	"github.com/purpleidea/mgmt/util/recwatch"
+)
+
+func init() {
+	engine.RegisterResource("line", func() engine.Res { return &LineRes{} })
+}
+
+const (
+	// LineStateExists is the string that represents that the line should be
+	// present.
+	LineStateExists = "exists"
+
+	// LineStateAbsent is the string that represents that the line should
+	// not exist.
+	LineStateAbsent = "absent"
+)
+
+// LineRes is a simple resource that adds or removes a line of text from a file.
+// For more complicated control over the file, use the regular File resource.
+type LineRes struct {
+	traits.Base // add the base methods without re-implementation
+
+	init *engine.Init
+
+	// File is the absolute path to the file that we are managing.
+	// TODO: Allow the Name to be something like ${path}:some-contents ?
+	File string `lang:"file" yaml:"file"`
+
+	// State specifies the desired state of the line. It can be either
+	// `exists` or `absent`. If you do not specify this, we will not be able
+	// to create or remove a line.
+	State string `lang:"state" yaml:"state"`
+
+	// Content specifies the line contents to add or remove. If this is
+	// empty, then it does nothing.
+	Content string `lang:"content" yaml:"content"`
+
+	// TODO: consider adding top or bottom insertion preferences?
+	// TODO: consider adding duplicate removal preferences?
+}
+
+// Default returns some sensible defaults for this resource.
+func (obj *LineRes) Default() engine.Res {
+	return &LineRes{}
+}
+
+// Validate if the params passed in are valid data.
+func (obj *LineRes) Validate() error {
+
+	if !strings.HasPrefix(obj.File, "/") {
+		return fmt.Errorf("the File must be absolute")
+	}
+	if strings.HasSuffix(obj.File, "/") {
+		return fmt.Errorf("the File must not end with a slash")
+	}
+
+	if obj.State != LineStateExists && obj.State != LineStateAbsent {
+		return fmt.Errorf("the State is invalid")
+	}
+
+	return nil
+}
+
+// Init runs some startup code for this resource.
+func (obj *LineRes) Init(init *engine.Init) error {
+	obj.init = init // save for later
+
+	return nil
+}
+
+// Cleanup is run by the engine to clean up after the resource is done.
+func (obj *LineRes) Cleanup() error {
+	return nil
+}
+
+// Watch is the primary listener for this resource and it outputs events.
+func (obj *LineRes) Watch(ctx context.Context) error {
+	recWatcher, err := recwatch.NewRecWatcher(obj.File, false)
+	if err != nil {
+		return err
+	}
+	defer recWatcher.Close()
+
+	obj.init.Running() // when started, notify engine that we're running
+
+	for {
+		if obj.init.Debug {
+			obj.init.Logf("watching: %s", obj.File) // attempting to watch...
+		}
+
+		select {
+		case event, ok := <-recWatcher.Events():
+			if !ok { // channel shutdown
+				return nil
+			}
+			if err := event.Error; err != nil {
+				return errwrap.Wrapf(err, "unknown %s watcher error", obj)
+			}
+			if obj.init.Debug { // don't access event.Body if event.Error isn't nil
+				obj.init.Logf("event(%s): %v", event.Body.Name, event.Body.Op)
+			}
+
+		case <-ctx.Done(): // closed by the engine to signal shutdown
+			return nil
+		}
+
+		obj.init.Event() // notify engine of an event (this can block)
+	}
+}
+
+// CheckApply method for Value resource. Does nothing, returns happy!
+func (obj *LineRes) CheckApply(ctx context.Context, apply bool) (bool, error) {
+	if obj.Content == "" { // special case
+		return true, nil // done early
+	}
+
+	exists, err := obj.check(ctx)
+	if err != nil {
+		return false, err
+	}
+
+	if obj.State == LineStateExists && exists {
+		return true, nil
+	}
+	if obj.State == LineStateAbsent && !exists {
+		return true, nil
+	}
+
+	if !apply {
+		return false, nil
+	}
+
+	if obj.State == LineStateAbsent { // remove
+		obj.init.Logf("removing line")
+		return obj.remove(ctx)
+	}
+
+	//if obj.State == LineStateExists { // add
+	//}
+	obj.init.Logf("adding line")
+	return obj.add(ctx)
+}
+
+// check returns true if it found a match. false otherwise. It errors if
+// something went permanently wrong. If the file doesn't exist, this returns
+// false.
+func (obj *LineRes) check(ctx context.Context) (bool, error) {
+	matchLines := strings.Split(obj.Content, "\n")
+
+	file, err := os.Open(obj.File)
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	defer file.Close()
+
+	// XXX: make a streaming version of this function without this cache
+	var fileLines []string
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		default:
+		}
+
+		fileLines = append(fileLines, scanner.Text())
+	}
+	if err := scanner.Err(); err != nil {
+		return false, err
+	}
+
+	// XXX: add tests to make sure this is correct
+	for i := 0; i <= len(fileLines)-len(matchLines); i++ {
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		default:
+		}
+
+		match := true
+		for j := 0; j < len(matchLines); j++ {
+			if fileLines[i+j] != matchLines[j] {
+				match = false
+				break
+			}
+		}
+		if match {
+			return true, nil // end early, we found a match!
+		}
+	}
+
+	return false, nil
+}
+
+// remove returns true if it did nothing. false if it removed a match. It errors
+// if something went permanently wrong.
+func (obj *LineRes) remove(ctx context.Context) (bool, error) {
+	matchLines := strings.Split(obj.Content, "\n")
+
+	file, err := os.Open(obj.File)
+	if err != nil {
+		return false, err
+	}
+
+	var fileLines []string
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		default:
+		}
+
+		fileLines = append(fileLines, scanner.Text())
+	}
+	if err := scanner.Err(); err != nil {
+		file.Close() // don't leak
+		return false, err
+	}
+	file.Close() // close before we eventually write
+
+	// check if the last line ends with a newline
+	nl := ""
+	if len(fileLines) > 0 && strings.HasSuffix(fileLines[len(fileLines)-1], "\n") {
+		nl = "\n"
+	}
+
+	// XXX: add tests to make sure this is correct
+	var newLines []string
+	i := 0
+	count := 0
+	for i < len(fileLines) {
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		default:
+		}
+
+		match := true
+		if i+len(matchLines) <= len(fileLines) {
+			for j := 0; j < len(matchLines); j++ {
+				if fileLines[i+j] != matchLines[j] {
+					match = false
+					break
+				}
+			}
+		} else {
+			match = false
+		}
+
+		if match {
+			i += len(matchLines)     // skip over the matched block
+			count += len(matchLines) // count the skips
+		} else {
+			newLines = append(newLines, fileLines[i])
+			i++
+		}
+	}
+
+	if count == 0 {
+		return true, nil // nothing removed!
+	}
+
+	// write out the updated file
+	output := strings.Join(newLines, "\n") + nl // preserve newline at EOF
+	return false, os.WriteFile(obj.File, []byte(output), 0600)
+}
+
+// add returns true if it did nothing. false if it add a line. It errors if
+// something went permanently wrong. It's not strictly required for it to avoid
+// adding duplicates, but it's a nice feature, hence why it can return true.
+// TODO: add at beginning or at end of file?
+// XXX: do the duplicate check at the same time?
+func (obj *LineRes) add(ctx context.Context) (bool, error) {
+	file, err := os.OpenFile(obj.File, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		return false, err
+	}
+	defer file.Close()
+
+	if _, err := file.WriteString(obj.Content + "\n"); err != nil {
+		return false, err
+	}
+
+	return false, nil
+}
+
+// Cmp compares two resources and returns an error if they are not equivalent.
+func (obj *LineRes) Cmp(r engine.Res) error {
+	// we can only compare LineRes to others of the same resource kind
+	res, ok := r.(*LineRes)
+	if !ok {
+		return fmt.Errorf("not a %s", obj.Kind())
+	}
+
+	if obj.File != res.File {
+		return fmt.Errorf("the File field differs")
+	}
+	if obj.State != res.State {
+		return fmt.Errorf("the State field differs")
+	}
+	if obj.Content != res.Content {
+		return fmt.Errorf("the Content field differs")
+	}
+
+	return nil
+}
+
+// UnmarshalYAML is the custom unmarshal handler for this struct. It is
+// primarily useful for setting the defaults.
+func (obj *LineRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	type rawRes LineRes // indirection to avoid infinite recursion
+
+	def := obj.Default()      // get the default
+	res, ok := def.(*LineRes) // put in the right format
+	if !ok {
+		return fmt.Errorf("could not convert to LineRes")
+	}
+	raw := rawRes(*res) // convert; the defaults go here
+
+	if err := unmarshal(&raw); err != nil {
+		return err
+	}
+
+	*obj = LineRes(raw) // restore from indirection with type conversion!
+	return nil
+}

examples/lang/line0.mcl

@@ -0,0 +1,43 @@
+line "add" { # name isn't important
+	file => "/tmp/lines1",
+	state => "exists",
+	content => "hello",
+}
+
+line "remove" {
+	file => "/tmp/lines2",
+	state => "absent",
+	content => "hello",
+}
+
+line "multiple" {
+	file => "/tmp/lines3",
+	state => "exists",
+	content => "hello\nworld\n",
+}
+
+exec "nonl" {
+	cmd => "echo -n hello > /tmp/lines4",
+	shell => "/bin/bash",
+	creates => "/tmp/lines4",
+
+	Before => Line["nonl"],
+}
+line "nonl" {
+	file => "/tmp/lines4",
+	state => "exists",
+	content => "hello",
+}
+
+exec "rmnl" {
+	cmd => "echo hello > /tmp/lines5 && echo -n world >> /tmp/lines5",
+	shell => "/bin/bash",
+	creates => "/tmp/lines5",
+
+	Before => Line["rmnl"],
+}
+line "rmnl" {
+	file => "/tmp/lines5",
+	state => "absent",
+	content => "hello",
+}