Add ReadFrom,WriteTo helpers for server config (#8580)

cmd/admin-handlers-config-kv.go

@@ -17,14 +17,12 @@
 package cmd
 
 import (
-	"bufio"
 	"bytes"
 	"context"
 	"encoding/json"
 	"io"
 	"net/http"
 	"strconv"
-	"strings"
 
 	"github.com/gorilla/mux"
 	"github.com/minio/minio/cmd/config"
@@ -79,24 +77,14 @@ func (a adminAPIHandlers) DelConfigKVHandler(w http.ResponseWriter, r *http.Requ
 		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAdminConfigBadJSON), r.URL)
 		return
 	}
+
 	cfg, err := readServerConfig(ctx, objectAPI)
 	if err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
 
-	scanner := bufio.NewScanner(bytes.NewReader(kvBytes))
-	for scanner.Scan() {
-		// Skip any empty lines
-		if scanner.Text() == "" {
-			continue
-		}
-		if err = cfg.DelKVS(scanner.Text()); err != nil {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-	}
-	if err = scanner.Err(); err != nil {
+	if err = cfg.DelFrom(bytes.NewReader(kvBytes)); err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
@@ -135,31 +123,9 @@ func (a adminAPIHandlers) SetConfigKVHandler(w http.ResponseWriter, r *http.Requ
 		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAdminConfigBadJSON), r.URL)
 		return
 	}
+
 	cfg, err := readServerConfig(ctx, objectAPI)
 	if err != nil {
-		// Config not found for some reason, allow things to continue
-		// by initializing a new fresh config in safe mode.
-		if err == errConfigNotFound && globalSafeMode {
-			cfg = newServerConfig()
-			err = nil
-		} else {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-	}
-
-	scanner := bufio.NewScanner(bytes.NewReader(kvBytes))
-	for scanner.Scan() {
-		// Skip any empty lines, or comment like characters
-		if scanner.Text() == "" || strings.HasPrefix(scanner.Text(), config.KvComment) {
-			continue
-		}
-		if err = cfg.SetKVS(scanner.Text(), defaultKVS()); err != nil {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-	}
-	if err = scanner.Err(); err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
@@ -210,23 +176,10 @@ func (a adminAPIHandlers) GetConfigKVHandler(w http.ResponseWriter, r *http.Requ
 
 	vars := mux.Vars(r)
 	var buf = &bytes.Buffer{}
-	key := vars["key"]
-	if key != "" {
-		kvs, err := cfg.GetKVS(key, defaultKVS())
-		if err != nil {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-		for k, kv := range kvs {
-			buf.WriteString(k)
-			buf.WriteString(config.KvSpaceSeparator)
-			buf.WriteString(kv.String())
-			if len(kvs) > 1 {
-				buf.WriteString(config.KvNewline)
-			}
-		}
-	} else {
-		buf.WriteString(cfg.String())
+	cw := config.NewConfigWriteTo(cfg, vars["key"])
+	if _, err := cw.WriteTo(buf); err != nil {
+		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
+		return
 	}
 
 	password := globalActiveCred.SecretKey
@@ -297,30 +250,11 @@ func (a adminAPIHandlers) RestoreConfigHistoryKVHandler(w http.ResponseWriter, r
 
 	cfg, err := readServerConfig(ctx, objectAPI)
 	if err != nil {
-		// Config not found for some reason, allow things to continue
-		// by initializing a new fresh config in safe mode.
-		if err == errConfigNotFound && globalSafeMode {
-			cfg = newServerConfig()
-			err = nil
-		} else {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
+		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
+		return
 	}
 
-	scanner := bufio.NewScanner(bytes.NewReader(kvBytes))
-	for scanner.Scan() {
-		// Skip any empty lines, or comment like characters
-		if scanner.Text() == "" || strings.HasPrefix(scanner.Text(), config.KvComment) {
-			continue
-		}
-
-		if err = cfg.SetKVS(scanner.Text(), defaultKVS()); err != nil {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-	}
-	if err = scanner.Err(); err != nil {
+	if _, err = cfg.ReadFrom(bytes.NewReader(kvBytes)); err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
@@ -432,19 +366,7 @@ func (a adminAPIHandlers) SetConfigHandler(w http.ResponseWriter, r *http.Reques
 	}
 
 	cfg := newServerConfig()
-	scanner := bufio.NewScanner(bytes.NewReader(kvBytes))
-	for scanner.Scan() {
-		// Skip any empty lines, or comment like characters
-		if scanner.Text() == "" || strings.HasPrefix(scanner.Text(), config.KvComment) {
-			continue
-		}
-		if err = cfg.SetKVS(scanner.Text(), defaultKVS()); err != nil {
-			writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
-			return
-		}
-	}
-
-	if err = scanner.Err(); err != nil {
+	if _, err = cfg.ReadFrom(bytes.NewReader(kvBytes)); err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
@@ -484,14 +406,18 @@ func (a adminAPIHandlers) GetConfigHandler(w http.ResponseWriter, r *http.Reques
 		return
 	}
 
-	config, err := readServerConfig(ctx, objectAPI)
+	cfg, err := readServerConfig(ctx, objectAPI)
 	if err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
 	}
 
 	var buf = &bytes.Buffer{}
-	buf.WriteString(config.String())
+	cw := config.NewConfigWriteTo(cfg, "")
+	if _, err = cw.WriteTo(buf); err != nil {
+		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
+		return
+	}
 
 	password := globalActiveCred.SecretKey
 	econfigData, err := madmin.EncryptData(password, buf.Bytes())

cmd/config-current.go

@@ -39,6 +39,154 @@ import (
 	"github.com/minio/minio/pkg/env"
 )
 
+func init() {
+	var kvs = map[string]config.KVS{
+		config.EtcdSubSys:           etcd.DefaultKVS,
+		config.CacheSubSys:          cache.DefaultKVS,
+		config.CompressionSubSys:    compress.DefaultKVS,
+		config.StorageClassSubSys:   storageclass.DefaultKVS,
+		config.IdentityLDAPSubSys:   xldap.DefaultKVS,
+		config.IdentityOpenIDSubSys: openid.DefaultKVS,
+		config.PolicyOPASubSys:      opa.DefaultKVS,
+		config.RegionSubSys:         config.DefaultRegionKVS,
+		config.CredentialsSubSys:    config.DefaultCredentialKVS,
+		config.KmsVaultSubSys:       crypto.DefaultKVS,
+		config.LoggerWebhookSubSys:  logger.DefaultKVS,
+		config.AuditWebhookSubSys:   logger.DefaultAuditKVS,
+	}
+	for k, v := range notify.DefaultNotificationKVS {
+		kvs[k] = v
+	}
+	config.RegisterDefaultKVS(kvs)
+
+	// Captures help for each sub-system
+	var helpSubSys = config.HelpKVS{
+		config.HelpKV{
+			Key:         config.RegionSubSys,
+			Description: "Configure to describe the physical location of the server",
+		},
+		config.HelpKV{
+			Key:         config.StorageClassSubSys,
+			Description: "Configure to control data and parity per object",
+		},
+		config.HelpKV{
+			Key:         config.CacheSubSys,
+			Description: "Configure to enable edge caching",
+		},
+		config.HelpKV{
+			Key:         config.CompressionSubSys,
+			Description: "Configure to enable streaming on disk compression",
+		},
+		config.HelpKV{
+			Key:         config.EtcdSubSys,
+			Description: "Configure to enable 'etcd' configuration",
+		},
+		config.HelpKV{
+			Key:         config.IdentityOpenIDSubSys,
+			Description: "Configure to enable OpenID SSO support",
+		},
+		config.HelpKV{
+			Key:         config.IdentityLDAPSubSys,
+			Description: "Configure to enable LDAP SSO support",
+		},
+		config.HelpKV{
+			Key:         config.PolicyOPASubSys,
+			Description: "Configure to enable external OPA policy support",
+		},
+		config.HelpKV{
+			Key:         config.KmsVaultSubSys,
+			Description: "Configure to enable Vault based external KMS",
+		},
+		config.HelpKV{
+			Key:             config.LoggerWebhookSubSys,
+			Description:     "Configure to enable Webhook based logger",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.AuditWebhookSubSys,
+			Description:     "Configure to enable Webhook based audit logger",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyWebhookSubSys,
+			Description:     "Configure to publish events to Webhook target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyAMQPSubSys,
+			Description:     "Configure to publish events to AMQP target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyKafkaSubSys,
+			Description:     "Configure to publish events to Kafka target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyMQTTSubSys,
+			Description:     "Configure to publish events to MQTT target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyNATSSubSys,
+			Description:     "Configure to publish events to NATS target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyNSQSubSys,
+			Description:     "Configure to publish events to NSQ target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyMySQLSubSys,
+			Description:     "Configure to publish events to MySQL target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyPostgresSubSys,
+			Description:     "Configure to publish events to Postgres target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyRedisSubSys,
+			Description:     "Configure to publish events to Redis target",
+			MultipleTargets: true,
+		},
+		config.HelpKV{
+			Key:             config.NotifyESSubSys,
+			Description:     "Configure to publish events to Elasticsearch target",
+			MultipleTargets: true,
+		},
+	}
+
+	var helpMap = map[string]config.HelpKVS{
+		"":                          helpSubSys, // Help for all sub-systems.
+		config.RegionSubSys:         config.RegionHelp,
+		config.EtcdSubSys:           etcd.Help,
+		config.CacheSubSys:          cache.Help,
+		config.CompressionSubSys:    compress.Help,
+		config.StorageClassSubSys:   storageclass.Help,
+		config.IdentityOpenIDSubSys: openid.Help,
+		config.IdentityLDAPSubSys:   xldap.Help,
+		config.PolicyOPASubSys:      opa.Help,
+		config.KmsVaultSubSys:       crypto.Help,
+		config.LoggerWebhookSubSys:  logger.Help,
+		config.AuditWebhookSubSys:   logger.HelpAudit,
+		config.NotifyAMQPSubSys:     notify.HelpAMQP,
+		config.NotifyKafkaSubSys:    notify.HelpKafka,
+		config.NotifyMQTTSubSys:     notify.HelpMQTT,
+		config.NotifyNATSSubSys:     notify.HelpNATS,
+		config.NotifyNSQSubSys:      notify.HelpNSQ,
+		config.NotifyMySQLSubSys:    notify.HelpMySQL,
+		config.NotifyPostgresSubSys: notify.HelpPostgres,
+		config.NotifyRedisSubSys:    notify.HelpRedis,
+		config.NotifyWebhookSubSys:  notify.HelpWebhook,
+		config.NotifyESSubSys:       notify.HelpES,
+	}
+
+	config.RegisterHelpSubSys(helpMap)
+}
+
 var (
 	// globalServerConfig server config.
 	globalServerConfig   config.Config
@@ -257,152 +405,6 @@ func lookupConfigs(s config.Config) (err error) {
 	return nil
 }
 
-func defaultKVS() map[string]config.KVS {
-	var kvs = map[string]config.KVS{
-		config.EtcdSubSys:           etcd.DefaultKVS,
-		config.CacheSubSys:          cache.DefaultKVS,
-		config.CompressionSubSys:    compress.DefaultKVS,
-		config.StorageClassSubSys:   storageclass.DefaultKVS,
-		config.IdentityLDAPSubSys:   xldap.DefaultKVS,
-		config.IdentityOpenIDSubSys: openid.DefaultKVS,
-		config.PolicyOPASubSys:      opa.DefaultKVS,
-		config.RegionSubSys:         config.DefaultRegionKVS,
-		config.CredentialsSubSys:    config.DefaultCredentialKVS,
-		config.KmsVaultSubSys:       crypto.DefaultKVS,
-		config.LoggerWebhookSubSys:  logger.DefaultKVS,
-		config.AuditWebhookSubSys:   logger.DefaultAuditKVS,
-	}
-	for k, v := range notify.DefaultNotificationKVS {
-		kvs[k] = v
-	}
-	return kvs
-}
-
-// Captures help for each sub-system
-var helpSubSys = config.HelpKVS{
-	config.HelpKV{
-		Key:         config.RegionSubSys,
-		Description: "Configure to describe the physical location of the server",
-	},
-	config.HelpKV{
-		Key:         config.StorageClassSubSys,
-		Description: "Configure to control data and parity per object",
-	},
-	config.HelpKV{
-		Key:         config.CacheSubSys,
-		Description: "Configure to enable edge caching",
-	},
-	config.HelpKV{
-		Key:         config.CompressionSubSys,
-		Description: "Configure to enable streaming on disk compression",
-	},
-	config.HelpKV{
-		Key:         config.EtcdSubSys,
-		Description: "Configure to enable 'etcd' configuration",
-	},
-	config.HelpKV{
-		Key:         config.IdentityOpenIDSubSys,
-		Description: "Configure to enable OpenID SSO support",
-	},
-	config.HelpKV{
-		Key:         config.IdentityLDAPSubSys,
-		Description: "Configure to enable LDAP SSO support",
-	},
-	config.HelpKV{
-		Key:         config.PolicyOPASubSys,
-		Description: "Configure to enable external OPA policy support",
-	},
-	config.HelpKV{
-		Key:         config.KmsVaultSubSys,
-		Description: "Configure to enable Vault based external KMS",
-	},
-	config.HelpKV{
-		Key:             config.LoggerWebhookSubSys,
-		Description:     "Configure to enable Webhook based logger",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.AuditWebhookSubSys,
-		Description:     "Configure to enable Webhook based audit logger",
-		MultipleTargets: true,
-	},
-
-	config.HelpKV{
-		Key:             config.NotifyWebhookSubSys,
-		Description:     "Configure to publish events to Webhook target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyAMQPSubSys,
-		Description:     "Configure to publish events to AMQP target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyKafkaSubSys,
-		Description:     "Configure to publish events to Kafka target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyMQTTSubSys,
-		Description:     "Configure to publish events to MQTT target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyNATSSubSys,
-		Description:     "Configure to publish events to NATS target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyNSQSubSys,
-		Description:     "Configure to publish events to NSQ target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyMySQLSubSys,
-		Description:     "Configure to publish events to MySQL target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyPostgresSubSys,
-		Description:     "Configure to publish events to Postgres target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyRedisSubSys,
-		Description:     "Configure to publish events to Redis target",
-		MultipleTargets: true,
-	},
-	config.HelpKV{
-		Key:             config.NotifyESSubSys,
-		Description:     "Configure to publish events to Elasticsearch target",
-		MultipleTargets: true,
-	},
-}
-
-var helpMap = map[string]config.HelpKVS{
-	config.RegionSubSys:         config.RegionHelp,
-	config.EtcdSubSys:           etcd.Help,
-	config.CacheSubSys:          cache.Help,
-	config.CompressionSubSys:    compress.Help,
-	config.StorageClassSubSys:   storageclass.Help,
-	config.IdentityOpenIDSubSys: openid.Help,
-	config.IdentityLDAPSubSys:   xldap.Help,
-	config.PolicyOPASubSys:      opa.Help,
-	config.KmsVaultSubSys:       crypto.Help,
-	config.LoggerWebhookSubSys:  logger.Help,
-	config.AuditWebhookSubSys:   logger.HelpAudit,
-	config.NotifyAMQPSubSys:     notify.HelpAMQP,
-	config.NotifyKafkaSubSys:    notify.HelpKafka,
-	config.NotifyMQTTSubSys:     notify.HelpMQTT,
-	config.NotifyNATSSubSys:     notify.HelpNATS,
-	config.NotifyNSQSubSys:      notify.HelpNSQ,
-	config.NotifyMySQLSubSys:    notify.HelpMySQL,
-	config.NotifyPostgresSubSys: notify.HelpPostgres,
-	config.NotifyRedisSubSys:    notify.HelpRedis,
-	config.NotifyWebhookSubSys:  notify.HelpWebhook,
-	config.NotifyESSubSys:       notify.HelpES,
-}
-
 // Help - return sub-system level help
 type Help struct {
 	SubSys          string         `json:"subSys"`
@@ -414,18 +416,24 @@ type Help struct {
 // GetHelp - returns help for sub-sys, a key for a sub-system or all the help.
 func GetHelp(subSys, key string, envOnly bool) (Help, error) {
 	if len(subSys) == 0 {
-		return Help{KeysHelp: helpSubSys}, nil
+		return Help{KeysHelp: config.HelpSubSysMap[subSys]}, nil
 	}
 	subSystemValue := strings.SplitN(subSys, config.SubSystemSeparator, 2)
 	if len(subSystemValue) == 0 {
 		return Help{}, config.Errorf("invalid number of arguments %s", subSys)
 	}
 
-	if !config.SubSystems.Contains(subSystemValue[0]) {
+	subSys = subSystemValue[0]
+
+	subSysHelp, ok := config.HelpSubSysMap[""].Lookup(subSys)
+	if !ok {
 		return Help{}, config.Errorf("unknown sub-system %s", subSys)
 	}
 
-	h := helpMap[subSystemValue[0]]
+	h, ok := config.HelpSubSysMap[subSys]
+	if !ok {
+		return Help{}, config.Errorf("unknown sub-system %s", subSys)
+	}
 	if key != "" {
 		value, ok := h.Lookup(key)
 		if !ok {
@@ -434,8 +442,6 @@ func GetHelp(subSys, key string, envOnly bool) (Help, error) {
 		h = config.HelpKVS{value}
 	}
 
-	subSys = subSystemValue[0]
-
 	envHelp := config.HelpKVS{}
 	if envOnly {
 		for _, hkv := range h {
@@ -452,11 +458,6 @@ func GetHelp(subSys, key string, envOnly bool) (Help, error) {
 		h = envHelp
 	}
 
-	subSysHelp, ok := helpSubSys.Lookup(subSys)
-	if !ok {
-		return Help{}, config.Errorf("unknown sub-system %s", subSys)
-	}
-
 	return Help{
 		SubSys:          subSys,
 		Description:     subSysHelp.Description,

cmd/config.go

@@ -151,6 +151,11 @@ func readServerConfig(ctx context.Context, objAPI ObjectLayer) (config.Config, e
 	configFile := path.Join(minioConfigPrefix, minioConfigFile)
 	configData, err := readConfig(ctx, objAPI, configFile)
 	if err != nil {
+		// Config not found for some reason, allow things to continue
+		// by initializing a new fresh config in safe mode.
+		if err == errConfigNotFound && globalSafeMode {
+			return newServerConfig(), nil
+		}
 		return nil, err
 	}
 

cmd/config/config.go

@@ -18,7 +18,9 @@
 package config
 
 import (
+	"bufio"
 	"fmt"
+	"io"
 	"regexp"
 	"strings"
 
@@ -145,6 +147,35 @@ const (
 	EnvWordDelimiter = `_`
 )
 
+// DefaultKVS - default kvs for all sub-systems
+var DefaultKVS map[string]KVS
+
+// RegisterDefaultKVS - this function saves input kvsMap
+// globally, this should be called only once preferably
+// during `init()`.
+func RegisterDefaultKVS(kvsMap map[string]KVS) {
+	DefaultKVS = map[string]KVS{}
+	for subSys, kvs := range kvsMap {
+		DefaultKVS[subSys] = kvs
+	}
+}
+
+// HelpSubSysMap - help for all individual KVS for each sub-systems
+// also carries a special empty sub-system which dumps
+// help for each sub-system key.
+var HelpSubSysMap map[string]HelpKVS
+
+// RegisterHelpSubSys - this function saves
+// input help KVS for each sub-system globally,
+// this function should be called only once
+// preferably in during `init()`.
+func RegisterHelpSubSys(helpKVSMap map[string]HelpKVS) {
+	HelpSubSysMap = map[string]HelpKVS{}
+	for subSys, hkvs := range helpKVSMap {
+		HelpSubSysMap[subSys] = hkvs
+	}
+}
+
 // KV - is a shorthand of each key value.
 type KV struct {
 	Key   string `json:"key"`
@@ -216,6 +247,81 @@ func (c Config) String() string {
 	return s.String()
 }
 
+// DelFrom - deletes all keys in the input reader.
+func (c Config) DelFrom(r io.Reader) error {
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		// Skip any empty lines, or comment like characters
+		if scanner.Text() == "" || strings.HasPrefix(scanner.Text(), KvComment) {
+			continue
+		}
+		if err := c.DelKVS(scanner.Text()); err != nil {
+			return err
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ReadFrom - implements io.ReaderFrom interface
+func (c Config) ReadFrom(r io.Reader) (int64, error) {
+	var n int
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		// Skip any empty lines, or comment like characters
+		if scanner.Text() == "" || strings.HasPrefix(scanner.Text(), KvComment) {
+			continue
+		}
+		if err := c.SetKVS(scanner.Text(), DefaultKVS); err != nil {
+			return 0, err
+		}
+		n += len(scanner.Text())
+	}
+	if err := scanner.Err(); err != nil {
+		return 0, err
+	}
+	return int64(n), nil
+}
+
+type configWriteTo struct {
+	Config
+	filterByKey string
+}
+
+// NewConfigWriteTo - returns a struct which
+// allows for serializing the config/kv struct
+// to a io.WriterTo
+func NewConfigWriteTo(cfg Config, key string) io.WriterTo {
+	return &configWriteTo{Config: cfg, filterByKey: key}
+}
+
+// WriteTo - implements io.WriterTo interface implementation for config.
+func (c *configWriteTo) WriteTo(w io.Writer) (int64, error) {
+	if c.filterByKey == "" {
+		n, err := w.Write([]byte(c.String()))
+		return int64(n), err
+	}
+	kvs, err := c.GetKVS(c.filterByKey, DefaultKVS)
+	if err != nil {
+		return 0, err
+	}
+	var n int
+	for k, kv := range kvs {
+		m1, _ := w.Write([]byte(k))
+		m2, _ := w.Write([]byte(KvSpaceSeparator))
+		m3, _ := w.Write([]byte(kv.String()))
+		if len(kvs) > 1 {
+			m4, _ := w.Write([]byte(KvNewline))
+			n += m1 + m2 + m3 + m4
+		} else {
+			n += m1 + m2 + m3
+		}
+	}
+	return int64(n), nil
+}
+
 // Default KV configs for worm and region
 var (
 	DefaultCredentialKVS = KVS{