/
registrar.go
133 lines (121 loc) · 4.29 KB
/
registrar.go
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/* Copyright (c) 2016 Chris Smith
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
package unifiedbeat
import (
"encoding/json"
"io/ioutil"
"os"
"path/filepath"
"sync"
"github.com/elastic/beats/libbeat/logp"
)
// Registrar should only have one entry, which
// is the offset into the unified2 file
// currently being tailed (if any)
type Registrar struct {
registryFile string // path to the registry file
State FileState // unified2 file name and offset
sync.Mutex // lock and unlock during writes
}
// remove the ",omitempty"s so something is written
// to the registry file instead of just "{}"
type FileState struct {
Offset int64 `json:"offset"`
Source string `json:"source"`
}
func NewRegistrar(registryFile string) (*Registrar, error) {
r := &Registrar{
registryFile: registryFile,
}
// Ensure we have access to write the registry file
// by creating, closing, and removing a test file.
// Of course, access could still fail in later
// calls to LoadState or WriteRegistry.
// There is no perfect solution as files and
// permissions are just a mess, but we tried.
testfile := r.registryFile + ".access.test"
file, err := os.Create(testfile)
if err != nil {
logp.Info("NewRegistrar: test 'create file' access was denied to path for registry file: '%v'\n", r.registryFile)
return nil, err
}
err = file.Close()
if err != nil {
// really? we lost access after Create, really?
logp.Info("NewRegistrar: test 'close file' access was denied to path for registry file: '%v'\n", r.registryFile)
return nil, err
}
err = os.Remove(testfile)
if err != nil {
// really? we lost access after Create and Close, really?
logp.Info("NewRegistrar: test 'remove file' access was denied to path for registry file: '%v'\n", r.registryFile)
return nil, err
}
// set an absolute path to the registryFile:
absPath, err := filepath.Abs(r.registryFile)
if err != nil {
logp.Info("NewRegistrar: failed to set the absolute path for registry file: '%s'\n", r.registryFile)
return nil, err
}
r.registryFile = absPath
return r, err
}
func (r *Registrar) LoadState() {
if existing, e := os.Open(r.registryFile); e == nil {
defer existing.Close()
decoder := json.NewDecoder(existing)
decoder.Decode(&r.State)
}
}
func (r *Registrar) WriteRegistry() error {
r.Lock()
defer r.Unlock()
// can't truncate a file that does not exist:
_, err := os.Stat(r.registryFile)
if os.IsExist(err) {
err := os.Truncate(r.registryFile, 0)
if err != nil {
logp.Info("WriteRegistry: os.Truncate: err=%v\n", err)
return err
}
}
// if "json.Marshal" or "ioutil.WriteFile" fail then most likely
// unifiedbeat does not have access to the registry file
jsonState, err := json.Marshal(r.State)
if err != nil {
logp.Info("WriteRegistry: json.Marshal: err=%v\n", err)
return err
}
// https://golang.org/pkg/io/ioutil/#WriteFile
// If the file does not exist, WriteFile creates it with
// permissions 0644; otherwise it is truncated.
err = ioutil.WriteFile(r.registryFile, jsonState, 0644)
if err != nil {
logp.Info("WriteRegistry: ioutil.WriteFile: err=%v\n", err)
return err
}
return nil
}