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minio/cmd/disk-cache-backend.go

810 lines
22 KiB

/*
* MinIO Cloud Storage, (C) 2019 MinIO, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cmd
import (
"bytes"
"context"
"crypto/rand"
"encoding/hex"
"fmt"
"io"
"io/ioutil"
"log"
"net/http"
"os"
"reflect"
"sync"
"time"
"github.com/djherbis/atime"
"github.com/minio/minio/cmd/crypto"
xhttp "github.com/minio/minio/cmd/http"
"github.com/minio/minio/cmd/logger"
"github.com/minio/minio/pkg/disk"
"github.com/minio/sio"
"github.com/ncw/directio"
)
const (
// cache.json object metadata for cached objects.
cacheMetaJSONFile = "cache.json"
cacheDataFile = "part.1"
cacheMetaVersion = "1.0.0"
// SSECacheEncrypted is the metadata key indicating that the object
// is a cache entry encrypted with cache KMS master key in globalCacheKMS.
SSECacheEncrypted = "X-Minio-Internal-Encrypted-Cache"
)
// CacheChecksumInfoV1 - carries checksums of individual blocks on disk.
type CacheChecksumInfoV1 struct {
Algorithm string `json:"algorithm"`
Blocksize int64 `json:"blocksize"`
}
// Represents the cache metadata struct
type cacheMeta struct {
Version string `json:"version"`
Stat statInfo `json:"stat"` // Stat of the current object `cache.json`.
// checksums of blocks on disk.
Checksum CacheChecksumInfoV1 `json:"checksum,omitempty"`
// Metadata map for current object.
Meta map[string]string `json:"meta,omitempty"`
// Ranges maps cached range to associated filename.
Ranges map[string]string `json:"ranges,omitempty"`
}
// RangeInfo has the range, file and range length information for a cached range.
type RangeInfo struct {
Range string
File string
Size int64
}
// Empty returns true if this is an empty struct
func (r *RangeInfo) Empty() bool {
return r.Range == "" && r.File == "" && r.Size == 0
}
func (m *cacheMeta) ToObjectInfo(bucket, object string) (o ObjectInfo) {
if len(m.Meta) == 0 {
m.Meta = make(map[string]string)
m.Stat.ModTime = timeSentinel
}
o = ObjectInfo{
Bucket: bucket,
Name: object,
}
// We set file info only if its valid.
o.ModTime = m.Stat.ModTime
o.Size = m.Stat.Size
o.ETag = extractETag(m.Meta)
o.ContentType = m.Meta["content-type"]
o.ContentEncoding = m.Meta["content-encoding"]
if storageClass, ok := m.Meta[xhttp.AmzStorageClass]; ok {
o.StorageClass = storageClass
} else {
o.StorageClass = globalMinioDefaultStorageClass
}
var (
t time.Time
e error
)
if exp, ok := m.Meta["expires"]; ok {
if t, e = time.Parse(http.TimeFormat, exp); e == nil {
o.Expires = t.UTC()
}
}
// etag/md5Sum has already been extracted. We need to
// remove to avoid it from appearing as part of user-defined metadata
o.UserDefined = cleanMetadata(m.Meta)
return o
}
// represents disk cache struct
type diskCache struct {
dir string // caching directory
quotaPct int // max usage in %
expiry int // cache expiry in days
// mark false if drive is offline
online bool
// mutex to protect updates to online variable
onlineMutex *sync.RWMutex
// purge() listens on this channel to start the cache-purge process
purgeChan chan struct{}
pool sync.Pool
}
// Inits the disk cache dir if it is not initialized already.
func newDiskCache(dir string, expiry int, quotaPct int) (*diskCache, error) {
if err := os.MkdirAll(dir, 0777); err != nil {
return nil, fmt.Errorf("Unable to initialize '%s' dir, %w", dir, err)
}
cache := diskCache{
dir: dir,
expiry: expiry,
quotaPct: quotaPct,
purgeChan: make(chan struct{}),
online: true,
onlineMutex: &sync.RWMutex{},
pool: sync.Pool{
New: func() interface{} {
b := directio.AlignedBlock(int(cacheBlkSize))
return &b
},
},
}
return &cache, nil
}
// Returns if the disk usage is low.
// Disk usage is low if usage is < 80% of cacheMaxDiskUsagePct
// Ex. for a 100GB disk, if maxUsage is configured as 70% then cacheMaxDiskUsagePct is 70G
// hence disk usage is low if the disk usage is less than 56G (because 80% of 70G is 56G)
func (c *diskCache) diskUsageLow() bool {
minUsage := c.quotaPct * 80 / 100
di, err := disk.GetInfo(c.dir)
if err != nil {
reqInfo := (&logger.ReqInfo{}).AppendTags("cachePath", c.dir)
ctx := logger.SetReqInfo(context.Background(), reqInfo)
logger.LogIf(ctx, err)
return false
}
usedPercent := (di.Total - di.Free) * 100 / di.Total
return int(usedPercent) < minUsage
}
// Return if the disk usage is high.
// Disk usage is high if disk used is > cacheMaxDiskUsagePct
func (c *diskCache) diskUsageHigh() bool {
di, err := disk.GetInfo(c.dir)
if err != nil {
reqInfo := (&logger.ReqInfo{}).AppendTags("cachePath", c.dir)
ctx := logger.SetReqInfo(context.Background(), reqInfo)
logger.LogIf(ctx, err)
return true
}
usedPercent := (di.Total - di.Free) * 100 / di.Total
return int(usedPercent) > c.quotaPct
}
// Returns if size space can be allocated without exceeding
// max disk usable for caching
func (c *diskCache) diskAvailable(size int64) bool {
di, err := disk.GetInfo(c.dir)
if err != nil {
reqInfo := (&logger.ReqInfo{}).AppendTags("cachePath", c.dir)
ctx := logger.SetReqInfo(context.Background(), reqInfo)
logger.LogIf(ctx, err)
return false
}
usedPercent := (di.Total - (di.Free - uint64(size))) * 100 / di.Total
return int(usedPercent) < c.quotaPct
}
// Purge cache entries that were not accessed.
func (c *diskCache) purge() {
// this function returns FileInfo for cached range files and cache data file.
fiStatFn := func(ranges map[string]string, dataFile, pathPrefix string) map[string]os.FileInfo {
fm := make(map[string]os.FileInfo)
fname := pathJoin(pathPrefix, cacheDataFile)
if fi, err := os.Stat(fname); err == nil {
fm[fname] = fi
}
for _, rngFile := range ranges {
fname = pathJoin(pathPrefix, rngFile)
if fi, err := os.Stat(fname); err == nil {
fm[fname] = fi
}
}
return fm
}
ctx := context.Background()
for {
olderThan := c.expiry
for !c.diskUsageLow() {
// delete unaccessed objects older than expiry duration
expiry := UTCNow().AddDate(0, 0, -1*olderThan)
olderThan /= 2
if olderThan < 1 {
break
}
deletedCount := 0
objDirs, err := ioutil.ReadDir(c.dir)
if err != nil {
log.Fatal(err)
}
for _, obj := range objDirs {
if obj.Name() == minioMetaBucket {
continue
}
meta, _, err := c.statCachedMeta(pathJoin(c.dir, obj.Name()))
if err != nil {
// delete any partially filled cache entry left behind.
removeAll(pathJoin(c.dir, obj.Name()))
continue
}
// stat all cached file ranges and cacheDataFile.
fis := fiStatFn(meta.Ranges, cacheDataFile, pathJoin(c.dir, obj.Name()))
objInfo := meta.ToObjectInfo("", "")
cc := cacheControlOpts(objInfo)
for fname, fi := range fis {
if atime.Get(fi).Before(expiry) ||
cc.isStale(objInfo.ModTime) {
if err = removeAll(fname); err != nil {
logger.LogIf(ctx, err)
}
deletedCount++
// break early if sufficient disk space reclaimed.
if !c.diskUsageLow() {
break
}
}
}
}
if deletedCount == 0 {
break
}
}
lastRunTime := time.Now()
for {
<-c.purgeChan
timeElapsed := time.Since(lastRunTime)
if timeElapsed > time.Hour {
break
}
}
}
}
// sets cache drive status
func (c *diskCache) setOnline(status bool) {
c.onlineMutex.Lock()
c.online = status
c.onlineMutex.Unlock()
}
// returns true if cache drive is online
func (c *diskCache) IsOnline() bool {
c.onlineMutex.RLock()
defer c.onlineMutex.RUnlock()
return c.online
}
// Stat returns ObjectInfo from disk cache
func (c *diskCache) Stat(ctx context.Context, bucket, object string) (oi ObjectInfo, err error) {
cacheObjPath := getCacheSHADir(c.dir, bucket, object)
oi, err = c.statCache(cacheObjPath)
if err != nil {
return
}
oi.Bucket = bucket
oi.Name = object
if err = decryptCacheObjectETag(&oi); err != nil {
return oi, err
}
return
}
// statCachedMeta returns metadata from cache - including ranges cached, partial to indicate
// if partial object is cached.
func (c *diskCache) statCachedMeta(cacheObjPath string) (meta *cacheMeta, partial bool, err error) {
// Stat the file to get file size.
metaPath := pathJoin(cacheObjPath, cacheMetaJSONFile)
f, err := os.Open(metaPath)
if err != nil {
return meta, partial, err
}
defer f.Close()
meta = &cacheMeta{Version: cacheMetaVersion}
if err := jsonLoad(f, meta); err != nil {
return meta, partial, err
}
// get metadata of part.1 if full file has been cached.
partial = true
fi, err := os.Stat(pathJoin(cacheObjPath, cacheDataFile))
if err == nil {
meta.Stat.ModTime = atime.Get(fi)
partial = false
}
return meta, partial, nil
}
// statRange returns ObjectInfo and RangeInfo from disk cache
func (c *diskCache) statRange(ctx context.Context, bucket, object string, rs *HTTPRangeSpec) (oi ObjectInfo, rngInfo RangeInfo, err error) {
// Stat the file to get file size.
cacheObjPath := getCacheSHADir(c.dir, bucket, object)
if rs == nil {
oi, err = c.statCache(cacheObjPath)
return oi, rngInfo, err
}
meta, _, err := c.statCachedMeta(cacheObjPath)
if err != nil {
return oi, rngInfo, err
}
actualSize := uint64(meta.Stat.Size)
_, length, err := rs.GetOffsetLength(int64(actualSize))
if err != nil {
return oi, rngInfo, err
}
actualRngSize := uint64(length)
if globalCacheKMS != nil {
actualRngSize, _ = sio.EncryptedSize(uint64(length))
}
rng := rs.String(int64(actualSize))
rngFile, ok := meta.Ranges[rng]
if !ok {
return oi, rngInfo, ObjectNotFound{Bucket: bucket, Object: object}
}
rngInfo = RangeInfo{Range: rng, File: rngFile, Size: int64(actualRngSize)}
oi = meta.ToObjectInfo("", "")
oi.Bucket = bucket
oi.Name = object
if err = decryptCacheObjectETag(&oi); err != nil {
return oi, rngInfo, err
}
return
}
// statCache is a convenience function for purge() to get ObjectInfo for cached object
func (c *diskCache) statCache(cacheObjPath string) (oi ObjectInfo, e error) {
// Stat the file to get file size.
meta, partial, err := c.statCachedMeta(cacheObjPath)
if err != nil {
return oi, err
}
if partial {
return oi, errFileNotFound
}
return meta.ToObjectInfo("", ""), nil
}
// saves object metadata to disk cache
func (c *diskCache) saveMetadata(ctx context.Context, bucket, object string, meta map[string]string, actualSize int64, rs *HTTPRangeSpec, rsFileName string) error {
fileName := getCacheSHADir(c.dir, bucket, object)
metaPath := pathJoin(fileName, cacheMetaJSONFile)
f, err := os.OpenFile(metaPath, os.O_RDWR|os.O_CREATE, 0666)
if err != nil {
return err
}
defer f.Close()
m := &cacheMeta{Version: cacheMetaVersion}
if err := jsonLoad(f, m); err != nil && err != io.EOF {
return err
}
if rs != nil {
if m.Ranges == nil {
m.Ranges = make(map[string]string)
}
m.Ranges[rs.String(actualSize)] = rsFileName
} else {
// this is necessary cleanup of range files if entire object is cached.
for _, f := range m.Ranges {
removeAll(pathJoin(fileName, f))
}
m.Ranges = nil
}
m.Stat.Size = actualSize
m.Stat.ModTime = UTCNow()
m.Meta = meta
m.Checksum = CacheChecksumInfoV1{Algorithm: HighwayHash256S.String(), Blocksize: cacheBlkSize}
return jsonSave(f, m)
}
// Backend metadata could have changed through server side copy - reset cache metadata if that is the case
func (c *diskCache) updateMetadataIfChanged(ctx context.Context, bucket, object string, bkObjectInfo, cacheObjInfo ObjectInfo) error {
bkMeta := make(map[string]string)
cacheMeta := make(map[string]string)
for k, v := range bkObjectInfo.UserDefined {
if HasPrefix(k, ReservedMetadataPrefix) {
// Do not need to send any internal metadata
continue
}
bkMeta[http.CanonicalHeaderKey(k)] = v
}
for k, v := range cacheObjInfo.UserDefined {
if HasPrefix(k, ReservedMetadataPrefix) {
// Do not need to send any internal metadata
continue
}
cacheMeta[http.CanonicalHeaderKey(k)] = v
}
if !reflect.DeepEqual(bkMeta, cacheMeta) ||
bkObjectInfo.ETag != cacheObjInfo.ETag ||
bkObjectInfo.ContentType != cacheObjInfo.ContentType ||
bkObjectInfo.Expires != cacheObjInfo.Expires {
return c.saveMetadata(ctx, bucket, object, getMetadata(bkObjectInfo), bkObjectInfo.Size, nil, "")
}
return nil
}
func getCacheSHADir(dir, bucket, object string) string {
return pathJoin(dir, getSHA256Hash([]byte(pathJoin(bucket, object))))
}
// Cache data to disk with bitrot checksum added for each block of 1MB
func (c *diskCache) bitrotWriteToCache(cachePath, fileName string, reader io.Reader, size uint64) (int64, error) {
if err := os.MkdirAll(cachePath, 0777); err != nil {
return 0, err
}
filePath := pathJoin(cachePath, fileName)
if filePath == "" || reader == nil {
return 0, errInvalidArgument
}
if err := checkPathLength(filePath); err != nil {
return 0, err
}
f, err := os.Create(filePath)
if err != nil {
return 0, osErrToFSFileErr(err)
}
defer f.Close()
var bytesWritten int64
h := HighwayHash256S.New()
bufp := c.pool.Get().(*[]byte)
defer c.pool.Put(bufp)
var n, n2 int
for {
n, err = io.ReadFull(reader, *bufp)
if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
return 0, err
}
eof := err == io.EOF || err == io.ErrUnexpectedEOF
if n == 0 && size != 0 {
// Reached EOF, nothing more to be done.
break
}
h.Reset()
if _, err = h.Write((*bufp)[:n]); err != nil {
return 0, err
}
hashBytes := h.Sum(nil)
if _, err = f.Write(hashBytes); err != nil {
return 0, err
}
if n2, err = f.Write((*bufp)[:n]); err != nil {
return 0, err
}
bytesWritten += int64(n2)
if eof {
break
}
}
return bytesWritten, nil
}
func newCacheEncryptReader(content io.Reader, bucket, object string, metadata map[string]string) (r io.Reader, err error) {
objectEncryptionKey, err := newCacheEncryptMetadata(bucket, object, metadata)
if err != nil {
return nil, err
}
reader, err := sio.EncryptReader(content, sio.Config{Key: objectEncryptionKey[:], MinVersion: sio.Version20})
if err != nil {
return nil, crypto.ErrInvalidCustomerKey
}
return reader, nil
}
func newCacheEncryptMetadata(bucket, object string, metadata map[string]string) ([]byte, error) {
var sealedKey crypto.SealedKey
if globalCacheKMS == nil {
return nil, errKMSNotConfigured
}
key, encKey, err := globalCacheKMS.GenerateKey(globalCacheKMS.KeyID(), crypto.Context{bucket: pathJoin(bucket, object)})
if err != nil {
return nil, err
}
objectKey := crypto.GenerateKey(key, rand.Reader)
sealedKey = objectKey.Seal(key, crypto.GenerateIV(rand.Reader), crypto.S3.String(), bucket, object)
crypto.S3.CreateMetadata(metadata, globalCacheKMS.KeyID(), encKey, sealedKey)
if etag, ok := metadata["etag"]; ok {
metadata["etag"] = hex.EncodeToString(objectKey.SealETag([]byte(etag)))
}
metadata[SSECacheEncrypted] = ""
return objectKey[:], nil
}
// Caches the object to disk
func (c *diskCache) Put(ctx context.Context, bucket, object string, data io.Reader, size int64, rs *HTTPRangeSpec, opts ObjectOptions) error {
if c.diskUsageHigh() {
select {
case c.purgeChan <- struct{}{}:
default:
}
return errDiskFull
}
if rs != nil {
return c.putRange(ctx, bucket, object, data, size, rs, opts)
}
if !c.diskAvailable(size) {
return errDiskFull
}
cachePath := getCacheSHADir(c.dir, bucket, object)
if err := os.MkdirAll(cachePath, 0777); err != nil {
return err
}
var metadata = make(map[string]string)
for k, v := range opts.UserDefined {
metadata[k] = v
}
var reader = data
var actualSize = uint64(size)
var err error
if globalCacheKMS != nil {
reader, err = newCacheEncryptReader(data, bucket, object, metadata)
if err != nil {
return err
}
actualSize, _ = sio.EncryptedSize(uint64(size))
}
n, err := c.bitrotWriteToCache(cachePath, cacheDataFile, reader, actualSize)
if IsErr(err, baseErrs...) {
c.setOnline(false)
}
if err != nil {
removeAll(cachePath)
return err
}
if actualSize != uint64(n) {
removeAll(cachePath)
return IncompleteBody{}
}
return c.saveMetadata(ctx, bucket, object, metadata, n, nil, "")
}
// Caches the range to disk
func (c *diskCache) putRange(ctx context.Context, bucket, object string, data io.Reader, size int64, rs *HTTPRangeSpec, opts ObjectOptions) error {
rlen, err := rs.GetLength(size)
if err != nil {
return err
}
if !c.diskAvailable(rlen) {
return errDiskFull
}
cachePath := getCacheSHADir(c.dir, bucket, object)
if err := os.MkdirAll(cachePath, 0777); err != nil {
return err
}
var metadata = make(map[string]string)
for k, v := range opts.UserDefined {
metadata[k] = v
}
var reader = data
var actualSize = uint64(rlen)
// objSize is the actual size of object (with encryption overhead if any)
var objSize = uint64(size)
if globalCacheKMS != nil {
reader, err = newCacheEncryptReader(data, bucket, object, metadata)
if err != nil {
return err
}
actualSize, _ = sio.EncryptedSize(uint64(rlen))
objSize, _ = sio.EncryptedSize(uint64(size))
}
cacheFile := MustGetUUID()
n, err := c.bitrotWriteToCache(cachePath, cacheFile, reader, actualSize)
if IsErr(err, baseErrs...) {
c.setOnline(false)
}
if err != nil {
removeAll(cachePath)
return err
}
if actualSize != uint64(n) {
removeAll(cachePath)
return IncompleteBody{}
}
return c.saveMetadata(ctx, bucket, object, metadata, int64(objSize), rs, cacheFile)
}
// checks streaming bitrot checksum of cached object before returning data
func (c *diskCache) bitrotReadFromCache(ctx context.Context, filePath string, offset, length int64, writer io.Writer) error {
h := HighwayHash256S.New()
checksumHash := make([]byte, h.Size())
startBlock := offset / cacheBlkSize
endBlock := (offset + length) / cacheBlkSize
// get block start offset
var blockStartOffset int64
if startBlock > 0 {
blockStartOffset = (cacheBlkSize + int64(h.Size())) * startBlock
}
tillLength := (cacheBlkSize + int64(h.Size())) * (endBlock - startBlock + 1)
// Start offset cannot be negative.
if offset < 0 {
logger.LogIf(ctx, errUnexpected)
return errUnexpected
}
// Writer cannot be nil.
if writer == nil {
logger.LogIf(ctx, errUnexpected)
return errUnexpected
}
var blockOffset, blockLength int64
rc, err := readCacheFileStream(filePath, blockStartOffset, tillLength)
if err != nil {
return err
}
bufp := c.pool.Get().(*[]byte)
defer c.pool.Put(bufp)
for block := startBlock; block <= endBlock; block++ {
switch {
case startBlock == endBlock:
blockOffset = offset % cacheBlkSize
blockLength = length
case block == startBlock:
blockOffset = offset % cacheBlkSize
blockLength = cacheBlkSize - blockOffset
case block == endBlock:
blockOffset = 0
blockLength = (offset + length) % cacheBlkSize
default:
blockOffset = 0
blockLength = cacheBlkSize
}
if blockLength == 0 {
break
}
if _, err := io.ReadFull(rc, checksumHash); err != nil {
return err
}
h.Reset()
n, err := io.ReadFull(rc, *bufp)
if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
logger.LogIf(ctx, err)
return err
}
eof := err == io.EOF || err == io.ErrUnexpectedEOF
if n == 0 && length != 0 {
// Reached EOF, nothing more to be done.
break
}
if _, e := h.Write((*bufp)[:n]); e != nil {
return e
}
hashBytes := h.Sum(nil)
if !bytes.Equal(hashBytes, checksumHash) {
err = fmt.Errorf("hashes do not match expected %s, got %s",
hex.EncodeToString(checksumHash), hex.EncodeToString(hashBytes))
logger.LogIf(context.Background(), err)
return err
}
if _, err := io.Copy(writer, bytes.NewReader((*bufp)[blockOffset:blockOffset+blockLength])); err != nil {
if err != io.ErrClosedPipe {
logger.LogIf(ctx, err)
return err
}
eof = true
}
if eof {
break
}
}
return nil
}
// Get returns ObjectInfo and reader for object from disk cache
func (c *diskCache) Get(ctx context.Context, bucket, object string, rs *HTTPRangeSpec, h http.Header, opts ObjectOptions) (gr *GetObjectReader, err error) {
var objInfo ObjectInfo
cacheObjPath := getCacheSHADir(c.dir, bucket, object)
var rngInfo RangeInfo
if objInfo, rngInfo, err = c.statRange(ctx, bucket, object, rs); err != nil {
return nil, toObjectErr(err, bucket, object)
}
cacheFile := cacheDataFile
objSize := objInfo.Size
if !rngInfo.Empty() {
// for cached ranges, need to pass actual range file size to GetObjectReader
// and clear out range spec
cacheFile = rngInfo.File
objInfo.Size = rngInfo.Size
rs = nil
}
var nsUnlocker = func() {}
// For a directory, we need to send an reader that returns no bytes.
if HasSuffix(object, SlashSeparator) {
// The lock taken above is released when
// objReader.Close() is called by the caller.
return NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, opts.CheckCopyPrecondFn, nsUnlocker)
}
fn, off, length, nErr := NewGetObjectReader(rs, objInfo, opts.CheckCopyPrecondFn, nsUnlocker)
if nErr != nil {
return nil, nErr
}
filePath := pathJoin(cacheObjPath, cacheFile)
pr, pw := io.Pipe()
go func() {
err := c.bitrotReadFromCache(ctx, filePath, off, length, pw)
if err != nil {
removeAll(cacheObjPath)
}
pw.CloseWithError(err)
}()
// Cleanup function to cause the go routine above to exit, in
// case of incomplete read.
pipeCloser := func() { pr.Close() }
gr, gerr := fn(pr, h, opts.CheckCopyPrecondFn, pipeCloser)
if gerr != nil {
return gr, gerr
}
if globalCacheKMS != nil {
// clean up internal SSE cache metadata
delete(gr.ObjInfo.UserDefined, crypto.SSEHeader)
}
if !rngInfo.Empty() {
// overlay Size with actual object size and not the range size
gr.ObjInfo.Size = objSize
}
return gr, nil
}
// Deletes the cached object
func (c *diskCache) Delete(ctx context.Context, bucket, object string) (err error) {
cachePath := getCacheSHADir(c.dir, bucket, object)
return removeAll(cachePath)
}
// convenience function to check if object is cached on this diskCache
func (c *diskCache) Exists(ctx context.Context, bucket, object string) bool {
if _, err := os.Stat(getCacheSHADir(c.dir, bucket, object)); err != nil {
return false
}
return true
}