# OPTIONS Bucket

#### Functions

OPTIONS refers to pre-requests that are sent to servers by clients. Generally, the requests are used to check whether clients have permissions to perform operations on servers. Only after a pre-request is returned successfully, clients start to execute the follow-up requests.

The OBS allows buckets to store static web resources. OBS buckets can serve as website resources if the buckets are properly used. In this scenario, buckets in the OBS serve as servers to process OPTIONS pre-requests from clients.

OBS can process OPTIONS pre-requests only after CORS is configured for buckets in OBS. For details about CORS, see Configuring Bucket CORS.

#### Differences Between OPTIONS Bucket and OPTIONS Object

With the OPTIONS Object, you need to specify an object name in the URL, but an object name is not required with the OPTIONS Bucket, which uses the bucket domain name as the URL. The request lines of the two methods are as follows:

    OPTIONS /object HTTP/1.1

    OPTIONS / HTTP/1.1

#### Request Syntax

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    OPTIONS / HTTP/1.1
    Host: bucketname.obs.region.example.com
    Date: date
    Authorization: authorization
    Origin: origin
    Access-Control-Request-Method: method

#### Request Parameters

This request contains no parameter.

#### Request Headers

This request uses the headers described in Table 1.

Table 1 OPTIONS request headers
Header | Description | Mandatory
--- | --- | ---
Origin | Origin of the cross-domain request specified by the pre-request. Generally, it is a domain name set in CORS. Type: string | Yes
Access-Control-Request-Method | An HTTP method that can be used by a request. The request can use multiple method headers. Type: string Possible values are GET, PUT, HEAD, POST, and DELETE. | Yes
Access-Control-Request-Headers | HTTP headers of a request. The request can use multiple HTTP headers. Type: string | No

#### Request Elements

This request involves no elements.

#### Response Syntax

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    HTTP/1.1 status_code
    Content-Type: application/xml
    Access-Control-Allow-Origin: origin
    Access-Control-Allow-Methods: method
    Access-Control-Allow-Header: header
    Access-Control-Max-Age: time
    Access-Control-Expose-Headers: header
    Date: date
    Content-Length: length

#### Response Headers

The response uses the following headers as described in Table 2.

Table 2 CORS response headers
Header | Description
--- | ---
Access-Control-Allow-Origin | If the origin of a request meets server CORS configuration requirements, the response contains the origin. Type: string
Access-Control-Allow-Headers | If the headers of a request meet server CORS configuration requirements, the response contains the headers. Type: string
Access-Control-Max-Age | Value of MaxAgeSeconds in the CORS configuration of a server Type: integer
Access-Control-Allow-Methods | If the Access-Control-Request-Method of a request meets server CORS configuration requirements, the response contains the methods in the rule. Type: string Possible values are GET, PUT, HEAD, POST, and DELETE.
Access-Control-Expose-Headers | Value of ExposeHeader in the CORS configuration of a server Type: string

#### Response Elements

This response involves no elements.

#### Error Responses

Table 3 describes possible special errors in the request.

Table 3 Special error
Error Code | Description | HTTP Status Code
--- | --- | ---
Bad Request | Invalid Access-Control-Request-Method: null When CORS and OPTIONS are configured for a bucket, no method header is added. | 400 BadRequest
Bad Request | Insufficient information. Origin request header needed. When CORS and OPTIONS are configured for a bucket, no origin header is added. | 400 BadRequest
AccessForbidden | CORSResponse: This CORS request is not allowed. This is usually because the evaluation of Origin, request method / Access-Control-Request-Method or Access-Control-Request-Headers are not whitelisted by the resource's CORS specification. When CORS and OPTIONS are configured for a bucket, origin, method, and headers do not match any rule. | 403 Forbidden

For other errors, see Table 2.

#### Sample Request

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    OPTIONS / HTTP/1.1
    User-Agent: curl/7.29.0
    Host: examplebucket.obs.region.example.com
    Accept: */*
    Date: WED, 01 Jul 2015 04:02:15 GMT
    Authorization: OBS H4IPJX0TQTHTHEBQQCEC:7RqP1vjemo6U+Adv9/Y6eGzWrzA=
    Origin: www.example.com
    Access-Control-Request-Method: PUT

#### Sample Response

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    HTTP/1.1 200 OK
    Server: OBS
    x-obs-request-id: BF260000016436314E8FF936946DBC9C
    Access-Control-Allow-Origin: www.example.com
    Access-Control-Allow-Methods: POST,GET,HEAD,PUT,DELETE
    Access-Control-Max-Age: 100
    Access-Control-Expose-Headers: ExposeHeader_1,ExposeHeader_2
    Access-Control-Allow-Credentials: true
    x-obs-id-2: 32AAAQAAEAABAAAQAAEAABAAAQAAEAABCTlYimJvOyJncCLNm5y/iz6MAGLNxTuS
    Date: WED, 01 Jul 2015 04:02:15 GMT
    Content-Length: 0

Parent topic: Static Website Hosting