diff options
author | zeripath <art27@cantab.net> | 2021-06-30 21:58:45 +0100 |
---|---|---|
committer | GitHub <noreply@github.com> | 2021-06-30 22:58:45 +0200 |
commit | 99799832835aae6a8641112cb71eb87baef32afa (patch) | |
tree | a9dd27526f1431f8c7e317a32cb9eae19c8dc993 /vendor/github.com | |
parent | 4f26e0ac0ea32968e94403e16cb776e7a4e5e690 (diff) | |
download | gitea-99799832835aae6a8641112cb71eb87baef32afa.tar.gz gitea-99799832835aae6a8641112cb71eb87baef32afa.zip |
Update Go-Git to take advantage of LargeObjectThreshold (#16316)
Following the merging of https://github.com/go-git/go-git/pull/330 we
can now add a setting to avoid go-git reading and caching large objects.
Signed-off-by: Andrew Thornton <art27@cantab.net>
Diffstat (limited to 'vendor/github.com')
8 files changed, 483 insertions, 31 deletions
diff --git a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/fsobject.go b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/fsobject.go index c5edaf52ee..a395d171ce 100644 --- a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/fsobject.go +++ b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/fsobject.go @@ -7,19 +7,21 @@ import ( "github.com/go-git/go-git/v5/plumbing" "github.com/go-git/go-git/v5/plumbing/cache" "github.com/go-git/go-git/v5/plumbing/format/idxfile" + "github.com/go-git/go-git/v5/utils/ioutil" ) // FSObject is an object from the packfile on the filesystem. type FSObject struct { - hash plumbing.Hash - h *ObjectHeader - offset int64 - size int64 - typ plumbing.ObjectType - index idxfile.Index - fs billy.Filesystem - path string - cache cache.Object + hash plumbing.Hash + h *ObjectHeader + offset int64 + size int64 + typ plumbing.ObjectType + index idxfile.Index + fs billy.Filesystem + path string + cache cache.Object + largeObjectThreshold int64 } // NewFSObject creates a new filesystem object. @@ -32,16 +34,18 @@ func NewFSObject( fs billy.Filesystem, path string, cache cache.Object, + largeObjectThreshold int64, ) *FSObject { return &FSObject{ - hash: hash, - offset: offset, - size: contentSize, - typ: finalType, - index: index, - fs: fs, - path: path, - cache: cache, + hash: hash, + offset: offset, + size: contentSize, + typ: finalType, + index: index, + fs: fs, + path: path, + cache: cache, + largeObjectThreshold: largeObjectThreshold, } } @@ -62,7 +66,21 @@ func (o *FSObject) Reader() (io.ReadCloser, error) { return nil, err } - p := NewPackfileWithCache(o.index, nil, f, o.cache) + p := NewPackfileWithCache(o.index, nil, f, o.cache, o.largeObjectThreshold) + if o.largeObjectThreshold > 0 && o.size > o.largeObjectThreshold { + // We have a big object + h, err := p.objectHeaderAtOffset(o.offset) + if err != nil { + return nil, err + } + + r, err := p.getReaderDirect(h) + if err != nil { + _ = f.Close() + return nil, err + } + return ioutil.NewReadCloserWithCloser(r, f.Close), nil + } r, err := p.getObjectContent(o.offset) if err != nil { _ = f.Close() diff --git a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/packfile.go b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/packfile.go index ddd7f62fce..8dd6041d55 100644 --- a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/packfile.go +++ b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/packfile.go @@ -2,6 +2,8 @@ package packfile import ( "bytes" + "compress/zlib" + "fmt" "io" "os" @@ -35,11 +37,12 @@ const smallObjectThreshold = 16 * 1024 // Packfile allows retrieving information from inside a packfile. type Packfile struct { idxfile.Index - fs billy.Filesystem - file billy.File - s *Scanner - deltaBaseCache cache.Object - offsetToType map[int64]plumbing.ObjectType + fs billy.Filesystem + file billy.File + s *Scanner + deltaBaseCache cache.Object + offsetToType map[int64]plumbing.ObjectType + largeObjectThreshold int64 } // NewPackfileWithCache creates a new Packfile with the given object cache. @@ -50,6 +53,7 @@ func NewPackfileWithCache( fs billy.Filesystem, file billy.File, cache cache.Object, + largeObjectThreshold int64, ) *Packfile { s := NewScanner(file) return &Packfile{ @@ -59,6 +63,7 @@ func NewPackfileWithCache( s, cache, make(map[int64]plumbing.ObjectType), + largeObjectThreshold, } } @@ -66,8 +71,8 @@ func NewPackfileWithCache( // and packfile idx. // If the filesystem is provided, the packfile will return FSObjects, otherwise // it will return MemoryObjects. -func NewPackfile(index idxfile.Index, fs billy.Filesystem, file billy.File) *Packfile { - return NewPackfileWithCache(index, fs, file, cache.NewObjectLRUDefault()) +func NewPackfile(index idxfile.Index, fs billy.Filesystem, file billy.File, largeObjectThreshold int64) *Packfile { + return NewPackfileWithCache(index, fs, file, cache.NewObjectLRUDefault(), largeObjectThreshold) } // Get retrieves the encoded object in the packfile with the given hash. @@ -263,6 +268,7 @@ func (p *Packfile) getNextObject(h *ObjectHeader, hash plumbing.Hash) (plumbing. p.fs, p.file.Name(), p.deltaBaseCache, + p.largeObjectThreshold, ), nil } @@ -282,6 +288,50 @@ func (p *Packfile) getObjectContent(offset int64) (io.ReadCloser, error) { return obj.Reader() } +func asyncReader(p *Packfile) (io.ReadCloser, error) { + reader := ioutil.NewReaderUsingReaderAt(p.file, p.s.r.offset) + zr := zlibReaderPool.Get().(io.ReadCloser) + + if err := zr.(zlib.Resetter).Reset(reader, nil); err != nil { + return nil, fmt.Errorf("zlib reset error: %s", err) + } + + return ioutil.NewReadCloserWithCloser(zr, func() error { + zlibReaderPool.Put(zr) + return nil + }), nil + +} + +func (p *Packfile) getReaderDirect(h *ObjectHeader) (io.ReadCloser, error) { + switch h.Type { + case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject: + return asyncReader(p) + case plumbing.REFDeltaObject: + deltaRc, err := asyncReader(p) + if err != nil { + return nil, err + } + r, err := p.readREFDeltaObjectContent(h, deltaRc) + if err != nil { + return nil, err + } + return r, nil + case plumbing.OFSDeltaObject: + deltaRc, err := asyncReader(p) + if err != nil { + return nil, err + } + r, err := p.readOFSDeltaObjectContent(h, deltaRc) + if err != nil { + return nil, err + } + return r, nil + default: + return nil, ErrInvalidObject.AddDetails("type %q", h.Type) + } +} + func (p *Packfile) getNextMemoryObject(h *ObjectHeader) (plumbing.EncodedObject, error) { var obj = new(plumbing.MemoryObject) obj.SetSize(h.Length) @@ -334,6 +384,20 @@ func (p *Packfile) fillREFDeltaObjectContent(obj plumbing.EncodedObject, ref plu return p.fillREFDeltaObjectContentWithBuffer(obj, ref, buf) } +func (p *Packfile) readREFDeltaObjectContent(h *ObjectHeader, deltaRC io.Reader) (io.ReadCloser, error) { + var err error + + base, ok := p.cacheGet(h.Reference) + if !ok { + base, err = p.Get(h.Reference) + if err != nil { + return nil, err + } + } + + return ReaderFromDelta(base, deltaRC) +} + func (p *Packfile) fillREFDeltaObjectContentWithBuffer(obj plumbing.EncodedObject, ref plumbing.Hash, buf *bytes.Buffer) error { var err error @@ -364,6 +428,20 @@ func (p *Packfile) fillOFSDeltaObjectContent(obj plumbing.EncodedObject, offset return p.fillOFSDeltaObjectContentWithBuffer(obj, offset, buf) } +func (p *Packfile) readOFSDeltaObjectContent(h *ObjectHeader, deltaRC io.Reader) (io.ReadCloser, error) { + hash, err := p.FindHash(h.OffsetReference) + if err != nil { + return nil, err + } + + base, err := p.objectAtOffset(h.OffsetReference, hash) + if err != nil { + return nil, err + } + + return ReaderFromDelta(base, deltaRC) +} + func (p *Packfile) fillOFSDeltaObjectContentWithBuffer(obj plumbing.EncodedObject, offset int64, buf *bytes.Buffer) error { hash, err := p.FindHash(offset) if err != nil { diff --git a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/patch_delta.go b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/patch_delta.go index 9e90f30a72..17da11e038 100644 --- a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/patch_delta.go +++ b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/patch_delta.go @@ -1,9 +1,11 @@ package packfile import ( + "bufio" "bytes" "errors" "io" + "math" "github.com/go-git/go-git/v5/plumbing" "github.com/go-git/go-git/v5/utils/ioutil" @@ -73,6 +75,131 @@ func PatchDelta(src, delta []byte) ([]byte, error) { return b.Bytes(), nil } +func ReaderFromDelta(base plumbing.EncodedObject, deltaRC io.Reader) (io.ReadCloser, error) { + deltaBuf := bufio.NewReaderSize(deltaRC, 1024) + srcSz, err := decodeLEB128ByteReader(deltaBuf) + if err != nil { + if err == io.EOF { + return nil, ErrInvalidDelta + } + return nil, err + } + if srcSz != uint(base.Size()) { + return nil, ErrInvalidDelta + } + + targetSz, err := decodeLEB128ByteReader(deltaBuf) + if err != nil { + if err == io.EOF { + return nil, ErrInvalidDelta + } + return nil, err + } + remainingTargetSz := targetSz + + dstRd, dstWr := io.Pipe() + + go func() { + baseRd, err := base.Reader() + if err != nil { + _ = dstWr.CloseWithError(ErrInvalidDelta) + return + } + defer baseRd.Close() + + baseBuf := bufio.NewReader(baseRd) + basePos := uint(0) + + for { + cmd, err := deltaBuf.ReadByte() + if err == io.EOF { + _ = dstWr.CloseWithError(ErrInvalidDelta) + return + } + if err != nil { + _ = dstWr.CloseWithError(err) + return + } + + if isCopyFromSrc(cmd) { + offset, err := decodeOffsetByteReader(cmd, deltaBuf) + if err != nil { + _ = dstWr.CloseWithError(err) + return + } + sz, err := decodeSizeByteReader(cmd, deltaBuf) + if err != nil { + _ = dstWr.CloseWithError(err) + return + } + + if invalidSize(sz, targetSz) || + invalidOffsetSize(offset, sz, srcSz) { + _ = dstWr.Close() + return + } + + discard := offset - basePos + if basePos > offset { + _ = baseRd.Close() + baseRd, err = base.Reader() + if err != nil { + _ = dstWr.CloseWithError(ErrInvalidDelta) + return + } + baseBuf.Reset(baseRd) + discard = offset + } + for discard > math.MaxInt32 { + n, err := baseBuf.Discard(math.MaxInt32) + if err != nil { + _ = dstWr.CloseWithError(err) + return + } + basePos += uint(n) + discard -= uint(n) + } + for discard > 0 { + n, err := baseBuf.Discard(int(discard)) + if err != nil { + _ = dstWr.CloseWithError(err) + return + } + basePos += uint(n) + discard -= uint(n) + } + if _, err := io.Copy(dstWr, io.LimitReader(baseBuf, int64(sz))); err != nil { + _ = dstWr.CloseWithError(err) + return + } + remainingTargetSz -= sz + basePos += sz + } else if isCopyFromDelta(cmd) { + sz := uint(cmd) // cmd is the size itself + if invalidSize(sz, targetSz) { + _ = dstWr.CloseWithError(ErrInvalidDelta) + return + } + if _, err := io.Copy(dstWr, io.LimitReader(deltaBuf, int64(sz))); err != nil { + _ = dstWr.CloseWithError(err) + return + } + + remainingTargetSz -= sz + } else { + _ = dstWr.CloseWithError(ErrDeltaCmd) + return + } + if remainingTargetSz <= 0 { + _ = dstWr.Close() + return + } + } + }() + + return dstRd, nil +} + func patchDelta(dst *bytes.Buffer, src, delta []byte) error { if len(delta) < deltaSizeMin { return ErrInvalidDelta @@ -161,6 +288,25 @@ func decodeLEB128(input []byte) (uint, []byte) { return num, input[sz:] } +func decodeLEB128ByteReader(input io.ByteReader) (uint, error) { + var num, sz uint + for { + b, err := input.ReadByte() + if err != nil { + return 0, err + } + + num |= (uint(b) & payload) << (sz * 7) // concats 7 bits chunks + sz++ + + if uint(b)&continuation == 0 { + break + } + } + + return num, nil +} + const ( payload = 0x7f // 0111 1111 continuation = 0x80 // 1000 0000 @@ -174,6 +320,40 @@ func isCopyFromDelta(cmd byte) bool { return (cmd&0x80) == 0 && cmd != 0 } +func decodeOffsetByteReader(cmd byte, delta io.ByteReader) (uint, error) { + var offset uint + if (cmd & 0x01) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + offset = uint(next) + } + if (cmd & 0x02) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + offset |= uint(next) << 8 + } + if (cmd & 0x04) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + offset |= uint(next) << 16 + } + if (cmd & 0x08) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + offset |= uint(next) << 24 + } + + return offset, nil +} + func decodeOffset(cmd byte, delta []byte) (uint, []byte, error) { var offset uint if (cmd & 0x01) != 0 { @@ -208,6 +388,36 @@ func decodeOffset(cmd byte, delta []byte) (uint, []byte, error) { return offset, delta, nil } +func decodeSizeByteReader(cmd byte, delta io.ByteReader) (uint, error) { + var sz uint + if (cmd & 0x10) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + sz = uint(next) + } + if (cmd & 0x20) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + sz |= uint(next) << 8 + } + if (cmd & 0x40) != 0 { + next, err := delta.ReadByte() + if err != nil { + return 0, err + } + sz |= uint(next) << 16 + } + if sz == 0 { + sz = 0x10000 + } + + return sz, nil +} + func decodeSize(cmd byte, delta []byte) (uint, []byte, error) { var sz uint if (cmd & 0x10) != 0 { diff --git a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/scanner.go b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/scanner.go index 6e6a687886..5d9e8fb65a 100644 --- a/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/scanner.go +++ b/vendor/github.com/go-git/go-git/v5/plumbing/format/packfile/scanner.go @@ -320,6 +320,21 @@ func (s *Scanner) NextObject(w io.Writer) (written int64, crc32 uint32, err erro return } +// ReadObject returns a reader for the object content and an error +func (s *Scanner) ReadObject() (io.ReadCloser, error) { + s.pendingObject = nil + zr := zlibReaderPool.Get().(io.ReadCloser) + + if err := zr.(zlib.Resetter).Reset(s.r, nil); err != nil { + return nil, fmt.Errorf("zlib reset error: %s", err) + } + + return ioutil.NewReadCloserWithCloser(zr, func() error { + zlibReaderPool.Put(zr) + return nil + }), nil +} + // ReadRegularObject reads and write a non-deltified object // from it zlib stream in an object entry in the packfile. func (s *Scanner) copyObject(w io.Writer) (n int64, err error) { diff --git a/vendor/github.com/go-git/go-git/v5/storage/filesystem/dotgit/reader.go b/vendor/github.com/go-git/go-git/v5/storage/filesystem/dotgit/reader.go new file mode 100644 index 0000000000..a82ac94eb6 --- /dev/null +++ b/vendor/github.com/go-git/go-git/v5/storage/filesystem/dotgit/reader.go @@ -0,0 +1,79 @@ +package dotgit + +import ( + "fmt" + "io" + "os" + + "github.com/go-git/go-git/v5/plumbing" + "github.com/go-git/go-git/v5/plumbing/format/objfile" + "github.com/go-git/go-git/v5/utils/ioutil" +) + +var _ (plumbing.EncodedObject) = &EncodedObject{} + +type EncodedObject struct { + dir *DotGit + h plumbing.Hash + t plumbing.ObjectType + sz int64 +} + +func (e *EncodedObject) Hash() plumbing.Hash { + return e.h +} + +func (e *EncodedObject) Reader() (io.ReadCloser, error) { + f, err := e.dir.Object(e.h) + if err != nil { + if os.IsNotExist(err) { + return nil, plumbing.ErrObjectNotFound + } + + return nil, err + } + r, err := objfile.NewReader(f) + if err != nil { + return nil, err + } + + t, size, err := r.Header() + if err != nil { + _ = r.Close() + return nil, err + } + if t != e.t { + _ = r.Close() + return nil, objfile.ErrHeader + } + if size != e.sz { + _ = r.Close() + return nil, objfile.ErrHeader + } + return ioutil.NewReadCloserWithCloser(r, f.Close), nil +} + +func (e *EncodedObject) SetType(plumbing.ObjectType) {} + +func (e *EncodedObject) Type() plumbing.ObjectType { + return e.t +} + +func (e *EncodedObject) Size() int64 { + return e.sz +} + +func (e *EncodedObject) SetSize(int64) {} + +func (e *EncodedObject) Writer() (io.WriteCloser, error) { + return nil, fmt.Errorf("Not supported") +} + +func NewEncodedObject(dir *DotGit, h plumbing.Hash, t plumbing.ObjectType, size int64) *EncodedObject { + return &EncodedObject{ + dir: dir, + h: h, + t: t, + sz: size, + } +} diff --git a/vendor/github.com/go-git/go-git/v5/storage/filesystem/object.go b/vendor/github.com/go-git/go-git/v5/storage/filesystem/object.go index 0c25dad613..5c91bcd699 100644 --- a/vendor/github.com/go-git/go-git/v5/storage/filesystem/object.go +++ b/vendor/github.com/go-git/go-git/v5/storage/filesystem/object.go @@ -204,9 +204,9 @@ func (s *ObjectStorage) packfile(idx idxfile.Index, pack plumbing.Hash) (*packfi var p *packfile.Packfile if s.objectCache != nil { - p = packfile.NewPackfileWithCache(idx, s.dir.Fs(), f, s.objectCache) + p = packfile.NewPackfileWithCache(idx, s.dir.Fs(), f, s.objectCache, s.options.LargeObjectThreshold) } else { - p = packfile.NewPackfile(idx, s.dir.Fs(), f) + p = packfile.NewPackfile(idx, s.dir.Fs(), f, s.options.LargeObjectThreshold) } return p, s.storePackfileInCache(pack, p) @@ -389,7 +389,6 @@ func (s *ObjectStorage) getFromUnpacked(h plumbing.Hash) (obj plumbing.EncodedOb return cacheObj, nil } - obj = s.NewEncodedObject() r, err := objfile.NewReader(f) if err != nil { return nil, err @@ -402,6 +401,13 @@ func (s *ObjectStorage) getFromUnpacked(h plumbing.Hash) (obj plumbing.EncodedOb return nil, err } + if s.options.LargeObjectThreshold > 0 && size > s.options.LargeObjectThreshold { + obj = dotgit.NewEncodedObject(s.dir, h, t, size) + return obj, nil + } + + obj = s.NewEncodedObject() + obj.SetType(t) obj.SetSize(size) w, err := obj.Writer() @@ -595,6 +601,7 @@ func (s *ObjectStorage) buildPackfileIters( return newPackfileIter( s.dir.Fs(), pack, t, seen, s.index[h], s.objectCache, s.options.KeepDescriptors, + s.options.LargeObjectThreshold, ) }, }, nil @@ -684,6 +691,7 @@ func NewPackfileIter( idxFile billy.File, t plumbing.ObjectType, keepPack bool, + largeObjectThreshold int64, ) (storer.EncodedObjectIter, error) { idx := idxfile.NewMemoryIndex() if err := idxfile.NewDecoder(idxFile).Decode(idx); err != nil { @@ -695,7 +703,7 @@ func NewPackfileIter( } seen := make(map[plumbing.Hash]struct{}) - return newPackfileIter(fs, f, t, seen, idx, nil, keepPack) + return newPackfileIter(fs, f, t, seen, idx, nil, keepPack, largeObjectThreshold) } func newPackfileIter( @@ -706,12 +714,13 @@ func newPackfileIter( index idxfile.Index, cache cache.Object, keepPack bool, + largeObjectThreshold int64, ) (storer.EncodedObjectIter, error) { var p *packfile.Packfile if cache != nil { - p = packfile.NewPackfileWithCache(index, fs, f, cache) + p = packfile.NewPackfileWithCache(index, fs, f, cache, largeObjectThreshold) } else { - p = packfile.NewPackfile(index, fs, f) + p = packfile.NewPackfile(index, fs, f, largeObjectThreshold) } iter, err := p.GetByType(t) diff --git a/vendor/github.com/go-git/go-git/v5/storage/filesystem/storage.go b/vendor/github.com/go-git/go-git/v5/storage/filesystem/storage.go index 8b69b27b00..7e7a2c50f6 100644 --- a/vendor/github.com/go-git/go-git/v5/storage/filesystem/storage.go +++ b/vendor/github.com/go-git/go-git/v5/storage/filesystem/storage.go @@ -34,6 +34,9 @@ type Options struct { // MaxOpenDescriptors is the max number of file descriptors to keep // open. If KeepDescriptors is true, all file descriptors will remain open. MaxOpenDescriptors int + // LargeObjectThreshold maximum object size (in bytes) that will be read in to memory. + // If left unset or set to 0 there is no limit + LargeObjectThreshold int64 } // NewStorage returns a new Storage backed by a given `fs.Filesystem` and cache. diff --git a/vendor/github.com/go-git/go-git/v5/utils/ioutil/common.go b/vendor/github.com/go-git/go-git/v5/utils/ioutil/common.go index b52e85a380..b0ace4e628 100644 --- a/vendor/github.com/go-git/go-git/v5/utils/ioutil/common.go +++ b/vendor/github.com/go-git/go-git/v5/utils/ioutil/common.go @@ -55,6 +55,28 @@ func NewReadCloser(r io.Reader, c io.Closer) io.ReadCloser { return &readCloser{Reader: r, closer: c} } +type readCloserCloser struct { + io.ReadCloser + closer func() error +} + +func (r *readCloserCloser) Close() (err error) { + defer func() { + if err == nil { + err = r.closer() + return + } + _ = r.closer() + }() + return r.ReadCloser.Close() +} + +// NewReadCloserWithCloser creates an `io.ReadCloser` with the given `io.ReaderCloser` and +// `io.Closer` that ensures that the closer is closed on close +func NewReadCloserWithCloser(r io.ReadCloser, c func() error) io.ReadCloser { + return &readCloserCloser{ReadCloser: r, closer: c} +} + type writeCloser struct { io.Writer closer io.Closer @@ -82,6 +104,24 @@ func WriteNopCloser(w io.Writer) io.WriteCloser { return writeNopCloser{w} } +type readerAtAsReader struct { + io.ReaderAt + offset int64 +} + +func (r *readerAtAsReader) Read(bs []byte) (int, error) { + n, err := r.ReaderAt.ReadAt(bs, r.offset) + r.offset += int64(n) + return n, err +} + +func NewReaderUsingReaderAt(r io.ReaderAt, offset int64) io.Reader { + return &readerAtAsReader{ + ReaderAt: r, + offset: offset, + } +} + // CheckClose calls Close on the given io.Closer. If the given *error points to // nil, it will be assigned the error returned by Close. Otherwise, any error // returned by Close will be ignored. CheckClose is usually called with defer. |