Object metadata describes the attributes of objects uploaded to OSS. These attributes include standard HTTP attributes (HTTP headers) and user metadata.

HTTP headers

Header Description
Content-Type The content type of the object. The browser determines the format and encoding type used to read the object based on the content type of the object. If this attribute is not specified, the value is generated based on the extension of the object. If the object does not have an extension, the default value application/octet-stream is used as the content type of the object.
Content-Encoding The encoding method of the object. Default value: identity.
  • identity: The object is not compressed.
  • gzip: The Lempel-Ziv coding (LZ77) compression algorithm and 32-bit CRC are used to encode the object.
Content-Language The language of the object.
Content-Disposition The method based on which the object is accessed.

Valid values:

  • inline: The object is previewed when you access the object.
  • attachment: The object is downloaded to the local computer when you access the object. For example, if this header is set to attachment; filename="example.jpg", the object is downloaded to a file named example.jpg when you access the object.
Notice When you access an object in OSS by using a browser, the object is downloaded even if the Content-Disposition header is set to inline in the following scenarios:
  • The object is a web page object and is not accessed by using the custom domain name bound to the bucket.
  • The object is an image and the bucket in which the object is stored is created after September 23, 2019. In addition, the object is not accessed by using the custom domain name bound to the bucket.
  • The object cannot be previewed by using the browser.
Cache-Control The caching behavior for the object.
  • no-cache: The cache cannot be used before it is verified by the server. If the object is updated, the cache expires. The object must be downloaded again from the server. If the object is not updated, the cache does not expire, and the local cache is used.
  • no-store: All content of the object is not cached.
  • public: All content of the object is cached.
  • private: All content of the object is cached only on the client.
  • max-age=<seconds>: the validity period of the cache. Unit: seconds. This option is available only in HTTP/1.1.
Expires The expiration time of the cache in GMT. Example: 2022-10-12T00:00:00.000Z. If max-age=<seconds> is set for Cache-Control, max-age=<seconds> takes precedence over Expires.
Last-Modified The time when the object is last modified.
Content-Length The size of the object.

User metadata

OSS considers parameters prefixed with x-oss-meta- to be user metadata. Example: x-oss-meta-last-modified:20200909, which indicates that a file is last modified on September 9, 2020.

  • An object may have multiple similar parameters. However, the total size of the user metadata of an object cannot exceed 8 KB.
  • When you call the GetObject or HeadObject operation, the user metadata of the object is returned as response headers.

Implementation methods

The following table describes the methods that you can use to configure, query, and modify the metadata of objects.

Implementation method Description
Console A user-friendly and intuitive web application
ossbrowser An easy-to-use graphical tool
ossutil A high-performance command-line tool
Java SDK SDK demos for various programming languages
Python SDK
Node.js SDK
Android SDK