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readfile_func.go
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readfile_func.go
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// Mgmt
// Copyright (C) 2013-2021+ 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"
"github.com/purpleidea/mgmt/util/errwrap"
)
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.
// Please note that this is different from the readfile function in the deploy
// package.
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{}
}
// ArgGen returns the Nth arg name for this function.
func (obj *ReadFileFunc) ArgGen(index int) (string, error) {
seq := []string{"filename"}
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 *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?
// TODO: add check for empty string
if obj.filename != nil && *obj.filename == 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
}
}()
continue // wait for an actual event or we'd send empty!
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 != nil && *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.closeChan)
obj.wg.Wait() // block so we don't exit by the closure of obj.events
close(obj.events) // clean up for fun
return nil
}