etcd: Small cleanup of the package

Split things into multiple files, and fix up some doc formatting.

etcd/resources.go

@@ -0,0 +1,182 @@
+// 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"
+	"log"
+	"strings"
+
+	"github.com/purpleidea/mgmt/resources"
+	"github.com/purpleidea/mgmt/util"
+
+	etcd "github.com/coreos/etcd/clientv3"
+)
+
+// WatchResources returns a channel that outputs events when exported resources
+// change.
+// TODO: Filter our watch (on the server side if possible) based on the
+// collection prefixes and filters that we care about...
+func WatchResources(obj *EmbdEtcd) chan error {
+	ch := make(chan error, 1) // buffer it so we can measure it
+	path := fmt.Sprintf("/%s/exported/", NS)
+	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
+		}
+		// we normally need to check if anything changed since the last
+		// event, since a set (export) with no changes still causes the
+		// watcher to trigger and this would cause an infinite loop. we
+		// don't need to do this check anymore because we do the export
+		// transactionally, and only if a change is needed. since it is
+		// atomic, all the changes arrive together which avoids dupes!!
+		if len(ch) == 0 { // send event only if one isn't pending
+			// this check avoids multiple events all queueing up and then
+			// being released continuously long after the changes stopped
+			// do not block!
+			ch <- nil // event
+		}
+		return nil
+	}
+	_, _ = obj.AddWatcher(path, callback, true, false, etcd.WithPrefix()) // no need to check errors
+	return ch
+}
+
+// SetResources exports all of the resources which we pass in to etcd.
+func SetResources(obj *EmbdEtcd, hostname string, resourceList []resources.Res) error {
+	// key structure is /$NS/exported/$hostname/resources/$uid = $data
+
+	var kindFilter []string // empty to get from everyone
+	hostnameFilter := []string{hostname}
+	// this is not a race because we should only be reading keys which we
+	// set, and there should not be any contention with other hosts here!
+	originals, err := GetResources(obj, hostnameFilter, kindFilter)
+	if err != nil {
+		return err
+	}
+
+	if len(originals) == 0 && len(resourceList) == 0 { // special case of no add or del
+		return nil
+	}
+
+	ifs := []etcd.Cmp{} // list matching the desired state
+	ops := []etcd.Op{}  // list of ops in this transaction
+	for _, res := range resourceList {
+		if res.GetKind() == "" {
+			log.Fatalf("Etcd: SetResources: Error: Empty kind: %v", res.GetName())
+		}
+		uid := fmt.Sprintf("%s/%s", res.GetKind(), res.GetName())
+		path := fmt.Sprintf("/%s/exported/%s/resources/%s", NS, hostname, uid)
+		if data, err := resources.ResToB64(res); err == nil {
+			ifs = append(ifs, etcd.Compare(etcd.Value(path), "=", data)) // desired state
+			ops = append(ops, etcd.OpPut(path, data))
+		} else {
+			return fmt.Errorf("can't convert to B64: %v", err)
+		}
+	}
+
+	match := func(res resources.Res, resourceList []resources.Res) bool { // helper lambda
+		for _, x := range resourceList {
+			if res.GetKind() == x.GetKind() && res.GetName() == x.GetName() {
+				return true
+			}
+		}
+		return false
+	}
+
+	hasDeletes := false
+	// delete old, now unused resources here...
+	for _, res := range originals {
+		if res.GetKind() == "" {
+			log.Fatalf("Etcd: SetResources: Error: Empty kind: %v", res.GetName())
+		}
+		uid := fmt.Sprintf("%s/%s", res.GetKind(), res.GetName())
+		path := fmt.Sprintf("/%s/exported/%s/resources/%s", NS, hostname, uid)
+
+		if match(res, resourceList) { // if we match, no need to delete!
+			continue
+		}
+
+		ops = append(ops, etcd.OpDelete(path))
+
+		hasDeletes = true
+	}
+
+	// if everything is already correct, do nothing, otherwise, run the ops!
+	// 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
+	if hasDeletes { // always run, ifs don't matter
+		_, err = obj.Txn(nil, ops, nil) // TODO: does this run? it should!
+	} else {
+		_, err = obj.Txn(ifs, nil, ops) // TODO: do we need to look at response?
+	}
+	return err
+}
+
+// GetResources collects all of the resources which match a filter from etcd.
+// If the kindfilter or hostnameFilter is empty, then it assumes no filtering...
+// TODO: Expand this with a more powerful filter based on what we eventually
+// support in our collect DSL. Ideally a server side filter like WithFilter()
+// We could do this if the pattern was /$NS/exported/$kind/$hostname/$uid = $data.
+func GetResources(obj *EmbdEtcd, hostnameFilter, kindFilter []string) ([]resources.Res, error) {
+	// key structure is /$NS/exported/$hostname/resources/$uid = $data
+	path := fmt.Sprintf("/%s/exported/", NS)
+	resourceList := []resources.Res{}
+	keyMap, err := obj.Get(path, etcd.WithPrefix(), etcd.WithSort(etcd.SortByKey, etcd.SortAscend))
+	if err != nil {
+		return nil, fmt.Errorf("could not get resources: %v", err)
+	}
+	for key, val := range keyMap {
+		if !strings.HasPrefix(key, path) { // sanity check
+			continue
+		}
+
+		str := strings.Split(key[len(path):], "/")
+		if len(str) != 4 {
+			return nil, fmt.Errorf("unexpected chunk count")
+		}
+		hostname, r, kind, name := str[0], str[1], str[2], str[3]
+		if r != "resources" {
+			return nil, fmt.Errorf("unexpected chunk pattern")
+		}
+		if kind == "" {
+			return nil, fmt.Errorf("unexpected kind chunk")
+		}
+
+		// FIXME: ideally this would be a server side filter instead!
+		if len(hostnameFilter) > 0 && !util.StrInList(hostname, hostnameFilter) {
+			continue
+		}
+
+		// FIXME: ideally this would be a server side filter instead!
+		if len(kindFilter) > 0 && !util.StrInList(kind, kindFilter) {
+			continue
+		}
+
+		if obj, err := resources.B64ToRes(val); err == nil {
+			obj.SetKind(kind) // cheap init
+			log.Printf("Etcd: Get: (Hostname, Kind, Name): (%s, %s, %s)", hostname, kind, name)
+			resourceList = append(resourceList, obj)
+		} else {
+			return nil, fmt.Errorf("can't convert from B64: %v", err)
+		}
+	}
+	return resourceList, nil
+}