lang: funcs: Rename things for consistency

Also fix a few copy-pasta issues in the documentation.

lang/funcs/core/kvlookup_func.go

@@ -0,0 +1,185 @@
+// Mgmt
+// Copyright (C) 2013-2018+ 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 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package core // TODO: should this be in its own individual package?
+
+import (
+	"fmt"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+
+	errwrap "github.com/pkg/errors"
+)
+
+func init() {
+	funcs.Register("kvlookup", func() interfaces.Func { return &KVLookupFunc{} }) // must register the func and name
+}
+
+// KVLookupFunc is special function which returns all the values of a given key
+// in the exposed world. It is similar to exchange, but it does not set a key.
+type KVLookupFunc struct {
+	init *interfaces.Init
+
+	namespace string
+	value     string
+
+	last   types.Value
+	result types.Value // last calculated output
+
+	watchChan chan error
+	closeChan chan struct{}
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal functions that users can use directly.
+func (obj *KVLookupFunc) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *KVLookupFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false, // definitely false
+		Memo: false,
+		// output is map of: hostname => value
+		Sig: types.NewType("func(namespace str) {str: str}"),
+		Err: obj.Validate(),
+	}
+}
+
+// Init runs some startup code for this function.
+func (obj *KVLookupFunc) Init(init *interfaces.Init) error {
+	obj.init = init
+	obj.watchChan = make(chan error) // XXX: sender should close this, but did I implement that part yet???
+	obj.closeChan = make(chan struct{})
+	return nil
+}
+
+// Stream returns the changing values that this func has over time.
+func (obj *KVLookupFunc) Stream() error {
+	defer close(obj.init.Output) // the sender closes
+	for {
+		select {
+		// TODO: should this first chan be run as a priority channel to
+		// avoid some sort of glitch? is that even possible? can our
+		// hostname check with reality (below) fix that?
+		case input, ok := <-obj.init.Input:
+			if !ok {
+				obj.init.Input = nil // don't infinite loop back
+				continue             // no more inputs, but don't return!
+			}
+			//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
+			//	return errwrap.Wrapf(err, "wrong function input")
+			//}
+
+			if obj.last != nil && input.Cmp(obj.last) == nil {
+				continue // value didn't change, skip it
+			}
+			obj.last = input // store for next
+
+			namespace := input.Struct()["namespace"].Str()
+			if namespace == "" {
+				return fmt.Errorf("can't use an empty namespace")
+			}
+			if obj.init.Debug {
+				obj.init.Logf("namespace: %s", namespace)
+			}
+
+			// TODO: support changing the namespace over time...
+			// TODO: possibly removing our stored value there first!
+			if obj.namespace == "" {
+				obj.namespace = namespace                                 // store it
+				obj.watchChan = obj.init.World.StrMapWatch(obj.namespace) // watch for var changes
+
+				result, err := obj.buildMap() // build the map...
+				if err != nil {
+					return err
+				}
+				select {
+				case obj.init.Output <- result: // send one!
+					// pass
+				case <-obj.closeChan:
+					return nil
+				}
+
+			} else if obj.namespace != namespace {
+				return fmt.Errorf("can't change namespace, previously: `%s`", obj.namespace)
+			}
+
+			continue // we get values on the watch chan, not here!
+
+		case err, ok := <-obj.watchChan:
+			if !ok { // closed
+				// XXX: if we close, perhaps the engine is
+				// switching etcd hosts and we should retry?
+				// maybe instead we should get an "etcd
+				// reconnect" signal, and the lang will restart?
+				return nil
+			}
+			if err != nil {
+				return errwrap.Wrapf(err, "channel watch failed on `%s`", obj.namespace)
+			}
+
+			result, err := obj.buildMap() // build the map...
+			if err != nil {
+				return err
+			}
+
+			// if the result is still the same, skip sending an update...
+			if obj.result != nil && result.Cmp(obj.result) == nil {
+				continue // result didn't change
+			}
+			obj.result = result // store new result
+
+		case <-obj.closeChan:
+			return nil
+		}
+
+		select {
+		case obj.init.Output <- obj.result: // send
+			// pass
+		case <-obj.closeChan:
+			return nil
+		}
+	}
+}
+
+// Close runs some shutdown code for this function and turns off the stream.
+func (obj *KVLookupFunc) Close() error {
+	close(obj.closeChan)
+	return nil
+}
+
+// buildMap builds the result map which we'll need. It uses struct variables.
+func (obj *KVLookupFunc) buildMap() (types.Value, error) {
+	keyMap, err := obj.init.World.StrMapGet(obj.namespace)
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "channel read failed on `%s`", obj.namespace)
+	}
+
+	d := types.NewMap(obj.Info().Sig.Out)
+	for k, v := range keyMap {
+		key := &types.StrValue{V: k}
+		val := &types.StrValue{V: v}
+		if err := d.Add(key, val); err != nil {
+			return nil, errwrap.Wrapf(err, "map could not add key `%s`, val: `%s`", k, v)
+		}
+	}
+	return d, nil // put map into interface type
+}