Pull request 1984: AG-25392 confmigrate vol.1

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

Squashed commit of the following:

commit 695717573e228a71e387d1b597f0d32f2eb20e67
Merge: 2c4f3e096 27ec6cd59
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 31 16:22:55 2023 +0300

    Merge branch 'master' into AG-25392-confmigrate

commit 2c4f3e096bb14724c0d0fcc20e5ac1462068504e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 31 16:13:14 2023 +0300

    all: imp code

commit 0fc6854598a67fc5ea74a93ff8c99b32886f43f1
Merge: 719f2db95 a2ca8b5b4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 18:30:36 2023 +0300

    Merge branch 'master' into AG-25392-confmigrate

commit 719f2db95a337f343752f5b18ce935bae83127be
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:50:52 2023 +0300

    home: don't reread config

commit 2e25fb738b11675d25574da9e5eebacd72a793ba
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:43:57 2023 +0300

    all: imp code

commit be3021f03097e18228dd9904dacc283f2576472e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 30 15:25:46 2023 +0300

    all: introduce confmigrate

internal/confmigrate/confmigrate.go

@@ -0,0 +1,143 @@
+// 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"
+)
+
+// CurrentSchemaVersion is the current schema version.
+const CurrentSchemaVersion = 26
+
+// These aliases are provided for convenience.
+type (
+	yarr = []any
+	yobj = map[string]any
+)
+
+// 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 does necessary upgrade operations if needed.  It returns the new
+// configuration file body, and a boolean indicating whether the configuration
+// file was actually upgraded.
+func (m *Migrator) Migrate(body []byte) (newBody []byte, upgraded bool, err error) {
+	// read a config file into an interface map, so we can manipulate values without losing any
+	diskConf := yobj{}
+	err = yaml.Unmarshal(body, &diskConf)
+	if err != nil {
+		log.Printf("parsing config file for upgrade: %s", err)
+
+		return nil, false, err
+	}
+
+	schemaVersionVal, ok := diskConf["schema_version"]
+	log.Tracef("got schema version %v", schemaVersionVal)
+	if !ok {
+		// no schema version, set it to 0
+		schemaVersionVal = 0
+	}
+
+	schemaVersion, ok := schemaVersionVal.(int)
+	if !ok {
+		err = fmt.Errorf("configuration file contains non-integer schema_version, abort")
+		log.Println(err)
+
+		return nil, false, err
+	}
+
+	if schemaVersion == CurrentSchemaVersion {
+		// do nothing
+		return body, false, nil
+	}
+
+	err = m.upgradeConfigSchema(schemaVersion, diskConf)
+	if err != nil {
+		log.Printf("upgrading configuration file: %s", err)
+
+		return nil, false, err
+	}
+
+	buf := &bytes.Buffer{}
+	enc := yaml.NewEncoder(buf)
+	enc.SetIndent(2)
+
+	err = enc.Encode(diskConf)
+	if err != nil {
+		return nil, false, fmt.Errorf("generating new config: %w", err)
+	}
+
+	return buf.Bytes(), true, nil
+}
+
+// upgradeFunc is a function that upgrades a config and returns an error.
+type upgradeFunc = func(diskConf yobj) (err error)
+
+// Upgrade from oldVersion to newVersion
+func (m *Migrator) upgradeConfigSchema(oldVersion int, diskConf yobj) (err error) {
+	upgrades := []upgradeFunc{
+		m.upgradeSchema0to1,
+		m.upgradeSchema1to2,
+		upgradeSchema2to3,
+		upgradeSchema3to4,
+		upgradeSchema4to5,
+		upgradeSchema5to6,
+		upgradeSchema6to7,
+		upgradeSchema7to8,
+		upgradeSchema8to9,
+		upgradeSchema9to10,
+		upgradeSchema10to11,
+		upgradeSchema11to12,
+		upgradeSchema12to13,
+		upgradeSchema13to14,
+		upgradeSchema14to15,
+		upgradeSchema15to16,
+		upgradeSchema16to17,
+		upgradeSchema17to18,
+		upgradeSchema18to19,
+		upgradeSchema19to20,
+		upgradeSchema20to21,
+		upgradeSchema21to22,
+		upgradeSchema22to23,
+		upgradeSchema23to24,
+		upgradeSchema24to25,
+		upgradeSchema25to26,
+	}
+
+	n := 0
+	for i, u := range upgrades {
+		if i >= oldVersion {
+			err = u(diskConf)
+			if err != nil {
+				return err
+			}
+
+			n++
+		}
+	}
+
+	if n == 0 {
+		return fmt.Errorf("unknown configuration schema version %d", oldVersion)
+	}
+
+	return nil
+}