// downloadMeta downloads top-level metadata from remote storage and verifies
// it using the given file metadata.
func (c *Client) downloadMeta(name string, m data.FileMeta) ([]byte, error) {
r, size, err := c.download(name, c.remote.GetMeta, m.Hashes)
if err != nil {
if IsNotFound(err) {
return nil, ErrMissingRemoteMetadata{name}
}
return nil, err
}
defer r.Close()
// return ErrWrongSize if the reported size is known and incorrect
if size >= 0 && size != m.Length {
return nil, ErrWrongSize{name, size, m.Length}
}
// wrap the data in a LimitReader so we download at most m.Length bytes
stream := io.LimitReader(r, m.Length)
// read the data, simultaneously writing it to buf and generating metadata
var buf bytes.Buffer
meta, err := util.GenerateFileMeta(io.TeeReader(stream, &buf), m.HashAlgorithms()...)
if err != nil {
return nil, err
}
if err := util.FileMetaEqual(meta, m); err != nil {
return nil, ErrDownloadFailed{name, err}
}
return buf.Bytes(), nil
}
// hasMeta checks whether local metadata has the given file meta
func (c *Client) hasMeta(name string, m data.FileMeta) bool {
b, ok := c.localMeta[name]
if !ok {
return false
}
meta, err := util.GenerateFileMeta(bytes.NewReader(b), m.HashAlgorithms()...)
if err != nil {
return false
}
err = util.FileMetaEqual(meta, m)
return err == nil
}