lang: Unnested the core package from the functions dir

The core package could contain non-functions, so we might as well move
it upwards.

lang/core/world/exchange_func.go

@@ -0,0 +1,200 @@
+// Mgmt
+// Copyright (C) 2013-2024+ 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 coreworld
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/util/errwrap"
+)
+
+const (
+	// ExchangeFuncName is the name this function is registered as.
+	ExchangeFuncName = "exchange"
+
+	// arg names...
+	exchangeArgNameNamespace = "namespace"
+	exchangeArgNameValue     = "value"
+)
+
+func init() {
+	funcs.ModuleRegister(ModuleName, ExchangeFuncName, func() interfaces.Func { return &ExchangeFunc{} })
+}
+
+// ExchangeFunc is special function which returns all the values of a given key
+// in the exposed world, and sets it's own.
+type ExchangeFunc struct {
+	init *interfaces.Init
+
+	namespace string
+
+	last   types.Value
+	result types.Value // last calculated output
+
+	watchChan chan error
+}
+
+// String returns a simple name for this function. This is needed so this struct
+// can satisfy the pgraph.Vertex interface.
+func (obj *ExchangeFunc) String() string {
+	return ExchangeFuncName
+}
+
+// ArgGen returns the Nth arg name for this function.
+func (obj *ExchangeFunc) ArgGen(index int) (string, error) {
+	seq := []string{exchangeArgNameNamespace, exchangeArgNameValue}
+	if l := len(seq); index >= l {
+		return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
+	}
+	return seq[index], nil
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal functions that users can use directly.
+func (obj *ExchangeFunc) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *ExchangeFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false, // definitely false
+		Memo: false,
+		// TODO: do we want to allow this to be statically polymorphic,
+		// and have value be any type we might want?
+		// output is map of: hostname => value
+		Sig: types.NewType(fmt.Sprintf("func(%s str, %s str) map{str: str}", exchangeArgNameNamespace, exchangeArgNameValue)),
+		Err: obj.Validate(),
+	}
+}
+
+// Init runs some startup code for this function.
+func (obj *ExchangeFunc) 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???
+	return nil
+}
+
+// Stream returns the changing values that this func has over time.
+func (obj *ExchangeFunc) Stream(ctx context.Context) error {
+	defer close(obj.init.Output) // the sender closes
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+	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()[exchangeArgNameNamespace].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
+				var err error
+				obj.watchChan, err = obj.init.World.StrMapWatch(ctx, obj.namespace) // watch for var changes
+				if err != nil {
+					return err
+				}
+
+			} else if obj.namespace != namespace {
+				return fmt.Errorf("can't change namespace, previously: `%s`", obj.namespace)
+			}
+
+			value := input.Struct()[exchangeArgNameValue].Str()
+			if obj.init.Debug {
+				obj.init.Logf("value: %+v", value)
+			}
+
+			if err := obj.init.World.StrMapSet(ctx, obj.namespace, value); err != nil {
+				return errwrap.Wrapf(err, "namespace write error of `%s` to `%s`", value, 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)
+			}
+
+			keyMap, err := obj.init.World.StrMapGet(ctx, obj.namespace)
+			if err != nil {
+				return errwrap.Wrapf(err, "channel read failed on `%s`", obj.namespace)
+			}
+
+			var result types.Value
+
+			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 errwrap.Wrapf(err, "map could not add key `%s`, val: `%s`", k, v)
+				}
+			}
+			result = d // put map into interface type
+
+			// 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 <-ctx.Done():
+			return nil
+		}
+
+		select {
+		case obj.init.Output <- obj.result: // send
+			// pass
+		case <-ctx.Done():
+			return nil
+		}
+	}
+}