Functions

Cross-origin resource sharing (CORS) is a standard mechanism proposed by World Wide Web Consortium (W3C) and allows cross-origin requests from clients. For standard web page requests, the scripts and contents at one website cannot interact with those at another website due to the existence of the Same Origin Policy (SOP).

OBS allows buckets to store static web resources. The buckets of OBS can serve as website resources if the buckets are properly used (for details, see Configuring Static Website Hosting for a Bucket). A website in OBS can respond to requests of another websites only after CORS is properly configured.

Typical application scenarios are as follows:

With the support of CORS, you can use JavaScript and HTML5 to construct web applications and directly access the resources in OBS without the need to use proxy servers for transfer.
You can enable the dragging function of HTML 5 to directly upload files to the OBS (with the upload progress displayed) or update the OBS contents using web applications.
Hosts external web pages, style sheets, and HTML 5 applications in different origins. Web fonts or pictures on OBS can be shared by multiple websites.

To perform this operation, you must have the PutBucketCORS permission. By default, only the bucket owner can perform this operation. The bucket owner can grant the permission to other users by configuring the bucket policy or user policy.

Request Syntax

PUT /?cors HTTP/1.1 
Host: bucketname.obs.region.example.com
Content-Length: length
Date: date
Authorization: authorization
Content-MD5: MD5
<?xml version="1.0" encoding="UTF-8"?> 
<CORSConfiguration> 
    <CORSRule> 
        <ID>id</ID> 
        <AllowedMethod>method</AllowedMethod> 
        <AllowedOrigin>origin</AllowedOrigin> 
        <AllowedHeader>header</AllowedHeader> 
        <MaxAgeSeconds>seconds</MaxAgeSeconds> 
        <ExposeHeader>header</ExposeHeader> 
    </CORSRule> 
</CORSConfiguration>

Request Parameters

This request contains no parameters.

Request Headers

This request uses common headers and CORS request headers. For details, see Table 3 and Table 1.

**Table 1** CORS request headers
Header	Type	Mandatory (Yes/No)	Description
Content-MD5	String	Yes	Explanation: Base64-encoded 128-bit MD5 digest of the message according to RFC 1864 Example: n58IG6hfM7vqI4K0vnWpog== Restrictions: None Value range: None Default value: None

Request Elements

In this request body, you must configure the CORS rules for a bucket in XML format. Table 2 describes the specific configuration elements.

**Table 2** CORS configuration elements
Element	Type	Mandatory (Yes/No)	Description
CORSConfiguration	Container	Yes	Explanation: Root node of CORSRules. Parent: none Restrictions: The maximum size is 64 KB. Value range: None Default value: None
CORSRule	Container	Yes	Explanation: CORS rules Parent: CORSConfiguration Restrictions: CORSConfiguration can contain a maximum of 100 rules. Value range: None Default value: None
ID	String	No	Explanation: The ID of a CORS rule. Parent: CORSRule Restrictions: The ID cannot be longer than 255 characters. Value range: A string of 1 to 255 characters. Default value: None
AllowedMethod	String	Yes	Explanation: The allowed HTTP methods (types of operations on buckets and objects) for a cross-origin request. Parent: CORSRule Restrictions: None Value range: The following HTTP methods are supported: GET PUT HEAD POST DELETE Default value: None
AllowedOrigin	String	Yes	Explanation: The origin that is allowed to access the bucket. Parent: CORSRule Restrictions: Only English domain names are supported. Regular expressions are used to match. Each rule allows at most one asterisk (). For example, https://.vbs.example.com. Value range: The value must comply with the CORS protocol and contain 0 to 20480 characters. Default value**: None
AllowedHeader	String	No	Explanation: What headers are allowed in a CORS request. If a CORS request contains the Access-Control-Request-Headers header, the headers listed in this header must match the headers in the AllowedHeader element so that the request can be considered valid. The matching is based on regular expressions. Parent: CORSRule Restrictions: At most one asterisk () is allowed. Spaces, ampersands (&), colons (:), less-than signs (<), and full-width characters are not allowed. Value range: The value must comply with the CORS protocol and contain 0 to 20480 characters. Default value*: None
MaxAgeSeconds	Integer	No	Explanation: How long the response can be cached on a client Parent: CORSRule Restrictions: Each CORS rule can contain at most one MaxAgeSeconds. Value range: An integer greater than or equal to 0, in seconds Default value: 3000
ExposeHeader	String	No	Explanation: Specifies additional headers allowed in the response by a CORS rule, which are used to provide extra information to clients. By default, a browser can access only headers Content-Length and Content-Type. If the browser needs to access other headers, you need to configure them in this parameter. Parent: CORSRule Restrictions: Spaces, asterisks (), ampersands (&), colons (:), less-than signs (<), and full-width characters are not allowed. Value range: The value that complies with the CORS Default value*: None

Response Syntax

HTTP/1.1 status_code

Date: date
Content-Length: length

Response Headers

The response to the request uses common headers. For details, see Table 1.

Response Elements

This response contains no elements.

Error Responses

No special error responses are returned. For details about error responses, see Table 2.

Sample Request

PUT /?cors HTTP/1.1
User-Agent: curl/7.29.0
Host: examplebucket.obs.region.example.com
Accept: */*
Date: WED, 01 Jul 2015 03:51:52 GMT
Authorization: OBS H4IPJX0TQTHTHEBQQCEC:lq7BGoqE9yyhdEwE6KojJ7ysVxU=
Content-MD5: NGLzvw81f/A2C9PiGO0aZQ==
Content-Length: 617

<?xml version="1.0" encoding="utf-8"?>
<CORSConfiguration> 
  <CORSRule> 
    <AllowedMethod>POST</AllowedMethod>  
    <AllowedMethod>GET</AllowedMethod>  
    <AllowedMethod>HEAD</AllowedMethod>  
    <AllowedMethod>PUT</AllowedMethod>  
    <AllowedMethod>DELETE</AllowedMethod>  
    <AllowedOrigin>www.example.com</AllowedOrigin>  
    <AllowedHeader>AllowedHeader_1</AllowedHeader>  
    <AllowedHeader>AllowedHeader_2</AllowedHeader>  
    <MaxAgeSeconds>100</MaxAgeSeconds>  
    <ExposeHeader>ExposeHeader_1</ExposeHeader>  
    <ExposeHeader>ExposeHeader_2</ExposeHeader> 
  </CORSRule>
</CORSConfiguration>

Sample Response

HTTP/1.1 100 Continue
HTTP/1.1 200 OK
Server: OBS
x-obs-request-id: BF26000001643627112BD03512FC94A4
x-obs-id-2: 32AAAQAAEAABSAAgAAEAABAAAQAAEAABCSYi6wLC4bkrvuS9sqnlRjxK2a5Fe3ry
Date: WED, 01 Jul 2015 03:51:52 GMT
Content-Length: 0

Configuring Bucket CORS