message: OSS backend: fix blob_size method
  Get correct content-length from OSS response header for blob size
diff: @@ -9,6 +9,7 @@ use std::sync::Arc;
  use std::time::SystemTime;
  use hmac::{Hmac, Mac, NewMac};
  +use reqwest::header::CONTENT_LENGTH;
  use reqwest::{Method, StatusCode};
  use sha1::Sha1;
  use url::Url;
  @@ -194,8 +195,16 @@ impl BlobBackend for OSS {
  .request
  .call::<&[u8]>(Method::HEAD, url.as_str(), None, headers, true)?;
  - resp.content_length()
  - .ok_or_else(|| einval!("invalid content length"))
  + let content_length = resp
  + .headers()
  + .get(CONTENT_LENGTH)
  + .ok_or_else(|| einval!("invalid content length"))?;
  +
  + content_length
  + .to_str()
  + .map_err(|err| einval!(format!("invalid content length: {:?}", err)))?
  + .parse::<u64>()
  + .map_err(|err| einval!(format!("invalid content length: {:?}", err)))
  }
  /// read ranged data from oss object
  