Pull request 1991: AG-25392 confmigrate vol.2

Merge in DNS/adguard-home from AG-25392-confmigrate-vol.2 to master

Squashed commit of the following:

commit 7bcdf443135523022a7e5ed6b2da05fcd784a896
Merge: 4c25331b5 f84ff2bd0
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 20:33:08 2023 +0300

    Merge branch 'master' into AG-25392-confmigrate-vol.2

commit 4c25331b507078670e7f3505384b53179a210292
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 20:14:23 2023 +0300

    confmigrate: fix fmt

commit d7dbfc46a7f825d248cb028d50b60eede941bf67
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 20:07:25 2023 +0300

    confmigrate: imp code

commit cd29729a23d1782a0b5fbd1e9153fe61ff3dbc71
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 18:21:14 2023 +0300

    confmigrate: imp code, split files

commit f075a14c251c68a13152709e14a326ad17c2f889
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 17:19:47 2023 +0300

    confmigrate: imp code

commit 37335597e7870184528c1d868e2d5bd5525a74bb
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 16:54:13 2023 +0300

    confmigrate: imp code, docs

commit 1df0ddcad99e5056b4989d17490ca4b44ae17838
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Sep 4 14:41:52 2023 +0300

    all: add testdata

commit e62690dbe8e458811bbd6b115b4449affa729560
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 31 16:13:14 2023 +0300

    all: imp code

commit 0934d5974b31a58b31b12412c3cd1a50810ffc4f
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:50:52 2023 +0300

    home: don't reread config

commit 7566ab6f330460bd608aae6dc0428a631e2fa4e3
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:43:57 2023 +0300

    all: imp code

commit 6f6aae6290f8d3101f3678ecc705eee7030ad8d5
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:25:46 2023 +0300

    all: introduce confmigrate

internal/confmigrate/migrator.go

@@ -0,0 +1,139 @@
+// Package confmigrate provides a way to upgrade the YAML configuration file.
+package confmigrate
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/AdguardTeam/golibs/log"
+	yaml "gopkg.in/yaml.v3"
+)
+
+// LastSchemaVersion is the most recent schema version.
+const LastSchemaVersion uint = 26
+
+// Config is a the configuration for initializing a [Migrator].
+type Config struct {
+	// WorkingDir is an absolute path to the working directory of AdGuardHome.
+	WorkingDir string
+}
+
+// Migrator performs the YAML configuration file migrations.
+type Migrator struct {
+	// workingDir is an absolute path to the working directory of AdGuardHome.
+	workingDir string
+}
+
+// New creates a new Migrator.
+func New(cfg *Config) (m *Migrator) {
+	return &Migrator{
+		workingDir: cfg.WorkingDir,
+	}
+}
+
+// Migrate preforms necessary upgrade operations to upgrade file to target
+// schema version, if needed.  It returns the body of the upgraded config file,
+// whether the file was upgraded, and an error, if any.  If upgraded is false,
+// the body is the same as the input.
+func (m *Migrator) Migrate(body []byte, target uint) (newBody []byte, upgraded bool, err error) {
+	diskConf := yobj{}
+	err = yaml.Unmarshal(body, &diskConf)
+	if err != nil {
+		return body, false, fmt.Errorf("parsing config file for upgrade: %w", err)
+	}
+
+	currentInt, _, err := fieldVal[int](diskConf, "schema_version")
+	if err != nil {
+		// Don't wrap the error, since it's informative enough as is.
+		return body, false, err
+	}
+
+	current := uint(currentInt)
+	log.Debug("got schema version %v", current)
+
+	if err = validateVersion(current, target); err != nil {
+		// Don't wrap the error, since it's informative enough as is.
+		return body, false, err
+	} else if current == target {
+		return body, false, nil
+	}
+
+	if err = m.upgradeConfigSchema(current, target, diskConf); err != nil {
+		// Don't wrap the error, since it's informative enough as is.
+		return body, false, err
+	}
+
+	buf := bytes.NewBuffer(newBody)
+	enc := yaml.NewEncoder(buf)
+	enc.SetIndent(2)
+
+	if err = enc.Encode(diskConf); err != nil {
+		return body, false, fmt.Errorf("generating new config: %w", err)
+	}
+
+	return buf.Bytes(), true, nil
+}
+
+// validateVersion validates the current and desired schema versions.
+func validateVersion(current, target uint) (err error) {
+	switch {
+	case current > target:
+		return fmt.Errorf("unknown current schema version %d", current)
+	case target > LastSchemaVersion:
+		return fmt.Errorf("unknown target schema version %d", target)
+	case target < current:
+		return fmt.Errorf("target schema version %d lower than current %d", target, current)
+	default:
+		return nil
+	}
+}
+
+// migrateFunc is a function that upgrades a config and returns an error.
+type migrateFunc = func(diskConf yobj) (err error)
+
+// upgradeConfigSchema upgrades the configuration schema in diskConf from
+// current to target version.  current must be less than target, and both must
+// be non-negative and less or equal to [LastSchemaVersion].
+func (m *Migrator) upgradeConfigSchema(current, target uint, diskConf yobj) (err error) {
+	upgrades := [LastSchemaVersion]migrateFunc{
+		0:  m.migrateTo1,
+		1:  m.migrateTo2,
+		2:  migrateTo3,
+		3:  migrateTo4,
+		4:  migrateTo5,
+		5:  migrateTo6,
+		6:  migrateTo7,
+		7:  migrateTo8,
+		8:  migrateTo9,
+		9:  migrateTo10,
+		10: migrateTo11,
+		11: migrateTo12,
+		12: migrateTo13,
+		13: migrateTo14,
+		14: migrateTo15,
+		15: migrateTo16,
+		16: migrateTo17,
+		17: migrateTo18,
+		18: migrateTo19,
+		19: migrateTo20,
+		20: migrateTo21,
+		21: migrateTo22,
+		22: migrateTo23,
+		23: migrateTo24,
+		24: migrateTo25,
+		25: migrateTo26,
+	}
+
+	for i, migrate := range upgrades[current:target] {
+		cur := current + uint(i)
+		next := current + uint(i) + 1
+
+		log.Printf("Upgrade yaml: %d to %d", cur, next)
+
+		if err = migrate(diskConf); err != nil {
+			return fmt.Errorf("migrating schema %d to %d: %w", cur, next, err)
+		}
+	}
+
+	return nil
+}