lang: funcs: core: Drop unnecessary core prefix from imports

This unbreaks the mcl bindata code. Of course we could change the parser
to allow this prefix, but this is cleaner. The packages still have a
core prefix, which it seems we could also remove, but this isn't
particularly important for anything.

lang/funcs/core/os/readfile_func.go

@@ -0,0 +1,211 @@
+// 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 coreos
+
+import (
+	"fmt"
+	"io/ioutil"
+	"sync"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/recwatch"
+
+	errwrap "github.com/pkg/errors"
+)
+
+func init() {
+	funcs.ModuleRegister(moduleName, "readfile", func() interfaces.Func { return &ReadFileFunc{} }) // must register the func and name
+}
+
+// ReadFileFunc is a function that reads the full contents from a local file. If
+// the file contents change or the file path changes, a new string will be sent.
+type ReadFileFunc struct {
+	init *interfaces.Init
+	last types.Value // last value received to use for diff
+
+	filename   string // the active filename
+	recWatcher *recwatch.RecWatcher
+	events     chan error // internal events
+	wg         *sync.WaitGroup
+
+	result string // last calculated output
+
+	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 *ReadFileFunc) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *ReadFileFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false, // maybe false because the file contents can change
+		Memo: false,
+		Sig:  types.NewType("func(filename str) str"),
+	}
+}
+
+// Init runs some startup code for this function.
+func (obj *ReadFileFunc) Init(init *interfaces.Init) error {
+	obj.init = init
+	obj.events = make(chan error)
+	obj.wg = &sync.WaitGroup{}
+	obj.closeChan = make(chan struct{})
+	return nil
+}
+
+// Stream returns the changing values that this func has over time.
+func (obj *ReadFileFunc) Stream() error {
+	defer close(obj.init.Output) // the sender closes
+	defer obj.wg.Wait()
+	defer func() {
+		if obj.recWatcher != nil {
+			obj.recWatcher.Close() // close previous watcher
+			obj.wg.Wait()
+		}
+	}()
+	for {
+		select {
+		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
+
+			filename := input.Struct()["filename"].Str()
+			// TODO: add validation for absolute path?
+			if filename == obj.filename {
+				continue // nothing changed
+			}
+			obj.filename = filename
+
+			if obj.recWatcher != nil {
+				obj.recWatcher.Close() // close previous watcher
+				obj.wg.Wait()
+			}
+			// create new watcher
+			obj.recWatcher = &recwatch.RecWatcher{
+				Path:    obj.filename,
+				Recurse: false,
+				Flags: recwatch.Flags{
+					// TODO: add Logf
+					Debug: obj.init.Debug,
+				},
+			}
+			if err := obj.recWatcher.Init(); err != nil {
+				obj.recWatcher = nil
+				// TODO: should we ignore the error and send ""?
+				return errwrap.Wrapf(err, "could not watch file")
+			}
+
+			// FIXME: instead of sending one event here, the recwatch
+			// library should send one initial event at startup...
+			startup := make(chan struct{})
+			close(startup)
+
+			// watch recwatch events in a proxy goroutine, since
+			// changing the recwatch object would panic the main
+			// select when it's nil...
+			obj.wg.Add(1)
+			go func() {
+				defer obj.wg.Done()
+				for {
+					var err error
+					select {
+					case <-startup:
+						startup = nil
+						// send an initial event
+
+					case event, ok := <-obj.recWatcher.Events():
+						if !ok {
+							return // file watcher shut down
+						}
+						if err = event.Error; err != nil {
+							err = errwrap.Wrapf(err, "error event received")
+						}
+					}
+
+					select {
+					case obj.events <- err:
+						// send event...
+
+					case <-obj.closeChan:
+						// don't block here on shutdown
+						return
+					}
+					//err = nil // reset
+				}
+			}()
+
+		case err, ok := <-obj.events:
+			if !ok {
+				return fmt.Errorf("no more events")
+			}
+			if err != nil {
+				return errwrap.Wrapf(err, "error event received")
+			}
+
+			if obj.last == nil {
+				continue // still waiting for input values
+			}
+
+			// read file...
+			content, err := ioutil.ReadFile(obj.filename)
+			if err != nil {
+				return errwrap.Wrapf(err, "error reading file")
+			}
+			result := string(content) // convert to string
+
+			if obj.result == result {
+				continue // result didn't change
+			}
+			obj.result = result // store new result
+
+		case <-obj.closeChan:
+			return nil
+		}
+
+		select {
+		case obj.init.Output <- &types.StrValue{
+			V: obj.result,
+		}:
+		case <-obj.closeChan:
+			return nil
+		}
+	}
+}
+
+// Close runs some shutdown code for this function and turns off the stream.
+func (obj *ReadFileFunc) Close() error {
+	close(obj.events) // clean up for fun
+	close(obj.closeChan)
+	return nil
+}