package storage import ( "context" "errors" "io" "io/ioutil" "github.com/docker/distribution/registry/storage/driver" ) const ( maxBlobGetSize = 4 << 20 ) func getContent(ctx context.Context, driver driver.StorageDriver, p string) ([]byte, error) { r, err := driver.Reader(ctx, p, 0) if err != nil { return nil, err } return readAllLimited(r, maxBlobGetSize) } func readAllLimited(r io.Reader, limit int64) ([]byte, error) { r = limitReader(r, limit) return ioutil.ReadAll(r) } // limitReader returns a new reader limited to n bytes. Unlike io.LimitReader, // this returns an error when the limit reached. func limitReader(r io.Reader, n int64) io.Reader { return &limitedReader{r: r, n: n} } // limitedReader implements a reader that errors when the limit is reached. // // Partially cribbed from net/http.MaxBytesReader. type limitedReader struct { r io.Reader // underlying reader n int64 // max bytes remaining err error // sticky error } func (l *limitedReader) Read(p []byte) (n int, err error) { if l.err != nil { return 0, l.err } if len(p) == 0 { return 0, nil } // If they asked for a 32KB byte read but only 5 bytes are // remaining, no need to read 32KB. 6 bytes will answer the // question of the whether we hit the limit or go past it. if int64(len(p)) > l.n+1 { p = p[:l.n+1] } n, err = l.r.Read(p) if int64(n) <= l.n { l.n -= int64(n) l.err = err return n, err } n = int(l.n) l.n = 0 l.err = errors.New("storage: read exceeds limit") return n, l.err }