Request Redirection and the REST API

Amazon Simple Storage Service: 2006-03-01

Request Redirection and the REST API

Topics

This section describes how to handle HTTP redirects using REST. For general information about Amazon S3 redirects, see Request Redirection and the REST API.

Redirects and HTTP User-Agents

Programs that use the Amazon S3 REST API should handle redirects either at the application layer or the HTTP layer. Many HTTP client libraries and user agents can be configured to correctly handle redirects automatically. However, many others have incorrect or incomplete redirect implementations.

Before relying on a library to fulfill the redirect requirement, test the following cases:

Launch Process

1	Verify all HTTP request headers are correctly included in the redirected request (the second request after receiving a redirect) including HTTP standards such as Authorization and Date.
2	Verify non-GET redirects, such as PUT and DELETE, work correctly.
3	Verify large PUT requests follow redirects correctly.
4	Verify PUT requests follow redirects correctly if the 100-continue response takes a long time to arrive.

HTTP user-agents that strictly conform to RFC2616 might require explicit confirmation before following a redirect when the HTTP request method is not GET or HEAD. It is generally safe to follow redirects generated by Amazon S3 automatically, as the system will only issue redirects to hosts within the amazonaws.com domain and the effect of the redirected request will be the same as the original request.

Redirects and 100-Continue

To simplify redirect handling, improve efficiencies, and avoid the costs associated with sending a redirected request body twice, configure your application to use 100-continues for PUT operations. When your application uses 100-continue, it does not send the request body until it receives an acknowledgement. If the message is rejected based on the headers, the body of the message is not sent. For more information about 100-continue, go to RFC 2616 Section 8.2.3

Note

	Note
According to RFC 2616, when using `Expect: Continue` with an unknown HTTP server, you should not wait an indefinite period before sending the request body. This is because some HTTP servers do not recognize 100-continue. However, Amazon S3 does recognize if your request contains an `Expect: Continue` and will respond with a provisional 100-continue status or a final status code. Additionally, no redirect error will occur after receiving the provisional 100 continue go-ahead. This will help you avoid receiving a redirect response while you are still writing the request body.

According to RFC 2616, when using Expect: Continue with an unknown HTTP server, you should not wait an indefinite period before sending the request body. This is because some HTTP servers do not recognize 100-continue. However, Amazon S3 does recognize if your request contains an Expect: Continue and will respond with a provisional 100-continue status or a final status code. Additionally, no redirect error will occur after receiving the provisional 100 continue go-ahead. This will help you avoid receiving a redirect response while you are still writing the request body.

Redirect Example

This section provides an example of client-server interaction using HTTP redirects and 100-continue.

Following is a sample PUT to the quotes.s3.amazonaws.com bucket.

PUT /nelson.txt HTTP/1.1
Host: quotes.s3.amazonaws.com
Date: Mon, 15 Oct 2007 22:18:46 +0000

Content-Length: 6
Expect: 100-continue

Amazon S3 returns the following:

HTTP/1.1 307 Temporary Redirect
Location: http://quotes.s3-4c25d83b.amazonaws.com/nelson.txt?rk=8d47490b
Content-Type: application/xml
Transfer-Encoding: chunked
Date: Mon, 15 Oct 2007 22:18:46 GMT

Server: AmazonS3

<?xml version="1.0" encoding="UTF-8"?>
<Error>
  <Code>TemporaryRedirect</Code>
  <Message>Please re-send this request to the
  specified temporary endpoint. Continue to use the
  original request endpoint for future requests.
  </Message>
  <Endpoint>quotes.s3-4c25d83b.amazonaws.com</Endpoint>
  <Bucket>quotes</Bucket>
</Error>

The client follows the redirect response and issues a new request to the quotes.s3-4c25d83b.amazonaws.com temporary endpoint.

PUT /nelson.txt?rk=8d47490b HTTP/1.1
Host: quotes.s3-4c25d83b.amazonaws.com
Date: Mon, 15 Oct 2007 22:18:46 +0000

Content-Length: 6
Expect: 100-continue

Amazon S3 returns a 100-continue indicating the client should proceed with sending the request body.

HTTP/1.1 100 Continue

The client sends the request body.

ha ha\n

Amazon S3 returns the final response.

HTTP/1.1 200 OK
Date: Mon, 15 Oct 2007 22:18:48 GMT

ETag: "a2c8d6b872054293afd41061e93bc289"
Content-Length: 0
Server: AmazonS3

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