/usr/share/gocode/src/github.com/google/cups-connector/cups/ppdcache.go is in google-cloud-print-connector 0.0~git20151105.24.1902938-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Copyright 2015 Google Inc. All rights reserved.
Use of this source code is governed by a BSD-style
license that can be found in the LICENSE file or at
https://developers.google.com/open-source/licenses/bsd
*/
package cups
/*
#include "cups.h"
*/
import "C"
import (
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"os"
"sync"
"unsafe"
"github.com/google/cups-connector/cdd"
)
// This isn't really a cache, but an interface to CUPS' quirky PPD interface.
// The connector needs to know when a PPD changes, but the CUPS API can only:
// (1) fetch a PPD to a file
// (2) indicate whether a PPD file is up-to-date.
// So, this "cache":
// (1) maintains temporary file copies of PPDs for each printer
// (2) updates those PPD files as necessary
type ppdCache struct {
cc *cupsCore
cache map[string]*ppdCacheEntry
cacheMutex sync.RWMutex
}
func newPPDCache(cc *cupsCore) *ppdCache {
cache := make(map[string]*ppdCacheEntry)
pc := ppdCache{
cc: cc,
cache: cache,
}
return &pc
}
func (pc *ppdCache) quit() {
pc.cacheMutex.Lock()
defer pc.cacheMutex.Unlock()
for printername, pce := range pc.cache {
pce.free()
delete(pc.cache, printername)
}
}
// removePPD removes a cache entry from the cache.
func (pc *ppdCache) removePPD(printername string) {
pc.cacheMutex.Lock()
defer pc.cacheMutex.Unlock()
if pce, exists := pc.cache[printername]; exists {
pce.free()
delete(pc.cache, printername)
}
}
func (pc *ppdCache) getPPDCacheEntry(printername string) (*cdd.PrinterDescriptionSection, string, string, error) {
pc.cacheMutex.RLock()
pce, exists := pc.cache[printername]
pc.cacheMutex.RUnlock()
if !exists {
pce, err := createPPDCacheEntry(printername)
if err != nil {
return nil, "", "", err
}
if err = pce.refresh(pc.cc); err != nil {
pce.free()
return nil, "", "", err
}
pc.cacheMutex.Lock()
defer pc.cacheMutex.Unlock()
if firstPCE, exists := pc.cache[printername]; exists {
// Two entries were created at the same time. Remove the older one.
delete(pc.cache, printername)
go firstPCE.free()
}
pc.cache[printername] = pce
description, manufacturer, model := pce.getFields()
return &description, manufacturer, model, nil
} else {
if err := pce.refresh(pc.cc); err != nil {
delete(pc.cache, printername)
pce.free()
return nil, "", "", err
}
description, manufacturer, model := pce.getFields()
return &description, manufacturer, model, nil
}
}
// Holds persistent data needed for calling C.cupsGetPPD3.
type ppdCacheEntry struct {
printername *C.char
modtime C.time_t
filename string
description cdd.PrinterDescriptionSection
manufacturer string
model string
mutex sync.Mutex
}
// createPPDCacheEntry creates an instance of ppdCache with the name field set,
// all else empty. The caller must free the name and buffer fields with
// ppdCacheEntry.free()
func createPPDCacheEntry(name string) (*ppdCacheEntry, error) {
file, err := ioutil.TempFile("", "cups-connector-ppd-")
if err != nil {
return nil, fmt.Errorf("Failed to create PPD cache entry file: %s", err)
}
defer file.Close()
filename := file.Name()
pce := &ppdCacheEntry{
printername: C.CString(name),
modtime: C.time_t(0),
filename: filename,
}
return pce, nil
}
// getFields gets externally-interesting fields from this ppdCacheEntry under
// a lock. The description is passed as a value (copy), to protect the cached copy.
func (pce *ppdCacheEntry) getFields() (cdd.PrinterDescriptionSection, string, string) {
pce.mutex.Lock()
defer pce.mutex.Unlock()
return pce.description, pce.manufacturer, pce.model
}
// free frees the memory that stores the name and buffer fields, and deletes
// the file named by the buffer field. If the file doesn't exist, no error is
// returned.
func (pce *ppdCacheEntry) free() {
pce.mutex.Lock()
defer pce.mutex.Unlock()
C.free(unsafe.Pointer(pce.printername))
os.Remove(pce.filename)
}
// refresh calls cupsGetPPD3() to refresh this PPD information, in
// case CUPS has a new PPD for the printer.
func (pce *ppdCacheEntry) refresh(cc *cupsCore) error {
pce.mutex.Lock()
defer pce.mutex.Unlock()
ppdFilename, err := cc.getPPD(pce.printername, &pce.modtime)
if err != nil {
return err
}
if ppdFilename == nil {
// Cache hit.
return nil
}
// (else) Cache miss.
defer C.free(unsafe.Pointer(ppdFilename))
defer os.Remove(C.GoString(ppdFilename))
// Read from CUPS temporary file.
r, err := os.Open(C.GoString(ppdFilename))
if err != nil {
return err
}
defer r.Close()
// Write to this PPD cache file.
file, err := os.OpenFile(pce.filename, os.O_WRONLY|os.O_TRUNC, 0200)
if err != nil {
return fmt.Errorf("Failed to open already-created PPD cache file: %s", err)
}
defer file.Close()
// Also write to a buffer for translation.
var content bytes.Buffer
// Write to these simultaneously.
w := io.MultiWriter(&content, file)
if _, err := io.Copy(w, r); err != nil {
return err
}
description, manufacturer, model := translatePPD(content.String())
if description == nil || manufacturer == "" || model == "" {
return errors.New("Failed to parse PPD")
}
pce.description = *description
pce.manufacturer = manufacturer
pce.model = model
return nil
}
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