RFC 2310 (rfc2310) - Page 2 of 5
The Safe Response Header Field
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RFC 2310 The Safe Response Header Field April 1998 It is sometimes necessary for a user agent to repeat a POST request. Examples of such cases are - when retrying a POST request which gave an indeterminate error result in the previous attempt - when the user presses the RELOAD button while a POST result is displayed - when the history function is used to redisplay a POST result which is no longer in the history buffer. If the POST request is unsafe, HTTP requires explicit user confirmation is before the request is repeated. The confirmation dialog often takes the form of a `repost form data?' dialog box. This dialog is confusing to many users, and slows down navigation in any case. If the repeated POST request is safe, the user-unfriendly confirmation dialog can be omitted. However plain HTTP/1.1 [1] has no mechanism by which agents can tell if POST requests are safe, and they must be assumed unsafe by default. This document adds a mechanism to HTTP, the Safe header field, for telling if a POST request is safe. Using the Safe header field, web applications which require the use of a safe POST request, rather than a GET request, for the submission of web forms, can be made more user-friendly. The use of a POST request may be required for a number of reasons, including - the contents of the form are potentially very large - the form is used to upload a file (see [2]) - the application needs some internationalization features (see [3]) which are only available if the form contents are transmitted in a request body the information in the form cannot be encoded in a GET request URL because of security considerations. 4 The Safe response header field The Safe response header field is defined as an addition to the HTTP/1.x protocol suite. The Safe response header field is used by origin servers to indicate whether repeating the received HTTP request is safe in the sense of Section 9.1.1 (Safe Methods) of the HTTP/1.1 specification [1]. For the purpose of this specification, a HTTP request is considered to be a repetition of a previous request if both requests Holtman Experimental
