etcd, resources, world: Add World API for shared keys

It's up to the end user to decide who is writing and/or overwriting
them.

It could also be useful to reimplement (refactor) some of the existing
World API's to be implemented in terms of these primitives.

etcd/str.go

@@ -18,20 +18,22 @@
 package etcd
 
 import (
+	"errors"
 	"fmt"
-	"strings"
-
-	"github.com/purpleidea/mgmt/util"
 
 	etcd "github.com/coreos/etcd/clientv3"
 	errwrap "github.com/pkg/errors"
 )
 
+// ErrNotExist is returned when GetStr can not find the requested key.
+// TODO: https://dave.cheney.net/2016/04/07/constant-errors
+var ErrNotExist = errors.New("errNotExist")
+
 // WatchStr returns a channel which spits out events on key activity.
 // FIXME: It should close the channel when it's done, and spit out errors when
 // something goes wrong.
 func WatchStr(obj *EmbdEtcd, key string) chan error {
-	// new key structure is /$NS/strings/$key/$hostname = $data
+	// new key structure is /$NS/strings/$key = $data
 	path := fmt.Sprintf("/%s/strings/%s", NS, key)
 	ch := make(chan error, 1)
 	// FIXME: fix our API so that we get a close event on shutdown.
@@ -50,50 +52,38 @@ func WatchStr(obj *EmbdEtcd, key string) chan error {
 	return ch
 }
 
-// GetStr collects all of the strings which match a namespace in etcd.
+// GetStr collects the string which matches a gloabl namespace in etcd.
-func GetStr(obj *EmbdEtcd, hostnameFilter []string, key string) (map[string]string, error) {
+func GetStr(obj *EmbdEtcd, key string) (string, error) {
-	// old key structure is /$NS/strings/$hostname/$key = $data
+	// new key structure is /$NS/strings/$key = $data
-	// new key structure is /$NS/strings/$key/$hostname = $data
-	// FIXME: if we have the $key as the last token (old key structure), we
-	// can allow the key to contain the slash char, otherwise we need to
-	// verify that one isn't present in the input string.
 	path := fmt.Sprintf("/%s/strings/%s", NS, key)
-	keyMap, err := obj.Get(path, etcd.WithPrefix(), etcd.WithSort(etcd.SortByKey, etcd.SortAscend))
+	keyMap, err := obj.Get(path, etcd.WithPrefix())
 	if err != nil {
-		return nil, errwrap.Wrapf(err, "could not get strings in: %s", key)
+		return "", errwrap.Wrapf(err, "could not get strings in: %s", key)
 	}
-	result := make(map[string]string)
-	for key, val := range keyMap {
-		if !strings.HasPrefix(key, path) { // sanity check
-			continue
-		}
 
-		str := strings.Split(key[len(path):], "/")
+	if len(keyMap) == 0 {
-		if len(str) != 2 {
+		return "", ErrNotExist
-			return nil, fmt.Errorf("unexpected chunk count of %d", len(str))
-		}
-		_, hostname := str[0], str[1]
-
-		if hostname == "" {
-			return nil, fmt.Errorf("unexpected chunk length of %d", len(hostname))
-		}
-
-		// FIXME: ideally this would be a server side filter instead!
-		if len(hostnameFilter) > 0 && !util.StrInList(hostname, hostnameFilter) {
-			continue
-		}
-		//log.Printf("Etcd: GetStr(%s): (Hostname, Data): (%s, %s)", key, hostname, val)
-		result[hostname] = val
 	}
-	return result, nil
+
+	if count := len(keyMap); count != 1 {
+		return "", fmt.Errorf("returned %d entries", count)
+	}
+
+	val, exists := keyMap[path]
+	if !exists {
+		return "", fmt.Errorf("path `%s` is missing", path)
+	}
+
+	//log.Printf("Etcd: GetStr(%s): %s", key, val)
+	return val, nil
 }
 
-// SetStr sets a key and hostname pair to a certain value. If the value is nil,
+// SetStr sets a key and hostname pair to a certain value. If the value is
-// then it deletes the key. Otherwise the value should point to a string.
+// nil, then it deletes the key. Otherwise the value should point to a string.
 // TODO: TTL or delete disconnect?
-func SetStr(obj *EmbdEtcd, hostname, key string, data *string) error {
+func SetStr(obj *EmbdEtcd, key string, data *string) error {
-	// key structure is /$NS/strings/$key/$hostname = $data
+	// key structure is /$NS/strings/$key = $data
-	path := fmt.Sprintf("/%s/strings/%s/%s", NS, key, hostname)
+	path := fmt.Sprintf("/%s/strings/%s", NS, key)
 	ifs := []etcd.Cmp{} // list matching the desired state
 	ops := []etcd.Op{}  // list of ops in this transaction (then)
 	els := []etcd.Op{}  // list of ops in this transaction (else)

etcd/strmap.go

@@ -0,0 +1,115 @@
+// Mgmt
+// Copyright (C) 2013-2017+ 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 Affero 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package etcd
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/purpleidea/mgmt/util"
+
+	etcd "github.com/coreos/etcd/clientv3"
+	errwrap "github.com/pkg/errors"
+)
+
+// WatchStrMap returns a channel which spits out events on key activity.
+// FIXME: It should close the channel when it's done, and spit out errors when
+// something goes wrong.
+func WatchStrMap(obj *EmbdEtcd, key string) chan error {
+	// new key structure is /$NS/strings/$key/$hostname = $data
+	path := fmt.Sprintf("/%s/strings/%s", NS, key)
+	ch := make(chan error, 1)
+	// FIXME: fix our API so that we get a close event on shutdown.
+	callback := func(re *RE) error {
+		// TODO: is this even needed? it used to happen on conn errors
+		//log.Printf("Etcd: Watch: Path: %v", path) // event
+		if re == nil || re.response.Canceled {
+			return fmt.Errorf("watch is empty") // will cause a CtxError+retry
+		}
+		if len(ch) == 0 { // send event only if one isn't pending
+			ch <- nil // event
+		}
+		return nil
+	}
+	_, _ = obj.AddWatcher(path, callback, true, false, etcd.WithPrefix()) // no need to check errors
+	return ch
+}
+
+// GetStrMap collects all of the strings which match a namespace in etcd.
+func GetStrMap(obj *EmbdEtcd, hostnameFilter []string, key string) (map[string]string, error) {
+	// old key structure is /$NS/strings/$hostname/$key = $data
+	// new key structure is /$NS/strings/$key/$hostname = $data
+	// FIXME: if we have the $key as the last token (old key structure), we
+	// can allow the key to contain the slash char, otherwise we need to
+	// verify that one isn't present in the input string.
+	path := fmt.Sprintf("/%s/strings/%s", NS, key)
+	keyMap, err := obj.Get(path, etcd.WithPrefix(), etcd.WithSort(etcd.SortByKey, etcd.SortAscend))
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "could not get strings in: %s", key)
+	}
+	result := make(map[string]string)
+	for key, val := range keyMap {
+		if !strings.HasPrefix(key, path) { // sanity check
+			continue
+		}
+
+		str := strings.Split(key[len(path):], "/")
+		if len(str) != 2 {
+			return nil, fmt.Errorf("unexpected chunk count of %d", len(str))
+		}
+		_, hostname := str[0], str[1]
+
+		if hostname == "" {
+			return nil, fmt.Errorf("unexpected chunk length of %d", len(hostname))
+		}
+
+		// FIXME: ideally this would be a server side filter instead!
+		if len(hostnameFilter) > 0 && !util.StrInList(hostname, hostnameFilter) {
+			continue
+		}
+		//log.Printf("Etcd: GetStr(%s): (Hostname, Data): (%s, %s)", key, hostname, val)
+		result[hostname] = val
+	}
+	return result, nil
+}
+
+// SetStrMap sets a key and hostname pair to a certain value. If the value is
+// nil, then it deletes the key. Otherwise the value should point to a string.
+// TODO: TTL or delete disconnect?
+func SetStrMap(obj *EmbdEtcd, hostname, key string, data *string) error {
+	// key structure is /$NS/strings/$key/$hostname = $data
+	path := fmt.Sprintf("/%s/strings/%s/%s", NS, key, hostname)
+	ifs := []etcd.Cmp{} // list matching the desired state
+	ops := []etcd.Op{}  // list of ops in this transaction (then)
+	els := []etcd.Op{}  // list of ops in this transaction (else)
+	if data == nil {    // perform a delete
+		// TODO: use https://github.com/coreos/etcd/pull/7417 if merged
+		//ifs = append(ifs, etcd.KeyExists(path))
+		ifs = append(ifs, etcd.Compare(etcd.Version(path), ">", 0))
+		ops = append(ops, etcd.OpDelete(path))
+	} else {
+		data := *data                                                // get the real value
+		ifs = append(ifs, etcd.Compare(etcd.Value(path), "=", data)) // desired state
+		els = append(els, etcd.OpPut(path, data))
+	}
+
+	// it's important to do this in one transaction, and atomically, because
+	// this way, we only generate one watch event, and only when it's needed
+	_, err := obj.Txn(ifs, ops, els) // TODO: do we need to look at response?
+	return errwrap.Wrapf(err, "could not set strings in: %s", key)
+}

etcd/world.go

@@ -48,23 +48,48 @@ func (obj *World) ResCollect(hostnameFilter, kindFilter []string) ([]resources.R
 	return GetResources(obj.EmbdEtcd, hostnameFilter, kindFilter)
 }
 
-// SetWatch returns a channel which spits out events on possible string changes.
+// StrWatch returns a channel which spits out events on possible string changes.
 func (obj *World) StrWatch(namespace string) chan error {
 	return WatchStr(obj.EmbdEtcd, namespace)
 }
 
-// StrGet returns a map of hostnames to values in the given namespace.
+// StrIsNotExist returns whether the error from StrGet is a key missing error.
-func (obj *World) StrGet(namespace string) (map[string]string, error) {
+func (obj *World) StrIsNotExist(err error) bool {
-	return GetStr(obj.EmbdEtcd, []string{}, namespace)
+	return err == ErrNotExist
 }
 
-// StrSet sets the namespace value to a particular string under the identity of
+// StrGet returns the value for the the given namespace.
-// its own hostname.
+func (obj *World) StrGet(namespace string) (string, error) {
+	return GetStr(obj.EmbdEtcd, namespace)
+}
+
+// StrSet sets the namespace value to a particular string.
 func (obj *World) StrSet(namespace, value string) error {
-	return SetStr(obj.EmbdEtcd, obj.Hostname, namespace, &value)
+	return SetStr(obj.EmbdEtcd, namespace, &value)
 }
 
 // StrDel deletes the value in a particular namespace.
 func (obj *World) StrDel(namespace string) error {
-	return SetStr(obj.EmbdEtcd, obj.Hostname, namespace, nil)
+	return SetStr(obj.EmbdEtcd, namespace, nil)
+}
+
+// StrMapWatch returns a channel which spits out events on possible string changes.
+func (obj *World) StrMapWatch(namespace string) chan error {
+	return WatchStrMap(obj.EmbdEtcd, namespace)
+}
+
+// StrMapGet returns a map of hostnames to values in the given namespace.
+func (obj *World) StrMapGet(namespace string) (map[string]string, error) {
+	return GetStrMap(obj.EmbdEtcd, []string{}, namespace)
+}
+
+// StrMapSet sets the namespace value to a particular string under the identity
+// of its own hostname.
+func (obj *World) StrMapSet(namespace, value string) error {
+	return SetStrMap(obj.EmbdEtcd, obj.Hostname, namespace, &value)
+}
+
+// StrMapDel deletes the value in a particular namespace.
+func (obj *World) StrMapDel(namespace string) error {
+	return SetStrMap(obj.EmbdEtcd, obj.Hostname, namespace, nil)
 }

resources/kv.go

@@ -101,7 +101,7 @@ func (obj *KVRes) Watch() error {
 		return err // bubble up a NACK...
 	}
 
-	ch := obj.Data().World.StrWatch(obj.Key) // get possible events!
+	ch := obj.Data().World.StrMapWatch(obj.Key) // get possible events!
 
 	var send = false // send event?
 	var exit *error
@@ -185,7 +185,7 @@ func (obj *KVRes) CheckApply(apply bool) (checkOK bool, err error) {
 	}
 
 	hostname := obj.Data().Hostname // me
-	keyMap, err := obj.Data().World.StrGet(obj.Key)
+	keyMap, err := obj.Data().World.StrMapGet(obj.Key)
 	if err != nil {
 		return false, errwrap.Wrapf(err, "check error during StrGet")
 	}
@@ -205,7 +205,7 @@ func (obj *KVRes) CheckApply(apply bool) (checkOK bool, err error) {
 		return true, nil // nothing to delete, we're good!
 
 	} else if ok && obj.Value == nil { // delete
-		err := obj.Data().World.StrDel(obj.Key)
+		err := obj.Data().World.StrMapDel(obj.Key)
 		return false, errwrap.Wrapf(err, "apply error during StrDel")
 	}
 
@@ -213,7 +213,7 @@ func (obj *KVRes) CheckApply(apply bool) (checkOK bool, err error) {
 		return false, nil
 	}
 
-	if err := obj.Data().World.StrSet(obj.Key, *obj.Value); err != nil {
+	if err := obj.Data().World.StrMapSet(obj.Key, *obj.Value); err != nil {
 		return false, errwrap.Wrapf(err, "apply error during StrSet")
 	}
 

resources/resources.go

@@ -81,9 +81,15 @@ type World interface { // TODO: is there a better name for this interface?
 	ResCollect(hostnameFilter, kindFilter []string) ([]Res, error)
 
 	StrWatch(namespace string) chan error
-	StrGet(namespace string) (map[string]string, error)
+	StrIsNotExist(error) bool
+	StrGet(namespace string) (string, error)
 	StrSet(namespace, value string) error
 	StrDel(namespace string) error
+
+	StrMapWatch(namespace string) chan error
+	StrMapGet(namespace string) (map[string]string, error)
+	StrMapSet(namespace, value string) error
+	StrMapDel(namespace string) error
 }
 
 // Data is the set of input values passed into the pgraph for the resources.