HTTP SEARCH Method

This specification updates the HTTP SEARCH method originally defined in . Many existing HTTP-based applications use the HTTP GET and POST methods in various ways to implement the functionality provided by SEARCH. Using a GET request with some combination of query parameters included within the request URI (as illustrated in the example below) is arguably the most common mechanism for implementing search in web applications. With this approach, implementations are required to parse the request URI into distinct path (everything before the '?') and query elements (everything after the '?'). The path identifies the resource processing the query (in this case 'http://example.org/feed') while the query identifies the specific parameters of the search operation. A typical use of HTTP GET for requesting a search While there are definite advantages to using GET requests in this manner, the disadvantages should not be overlooked. Specifically:

Without specific knowledge of the resource and server to which the GET request is being sent, there is no way for the client to know that a search operation is being requested. Identical requests sent to two different servers can implement entirely different semantics.
Encoding query parameters directly into the request URI effectively casts every possible combination of query inputs as distinct resources. For instance, because mechanisms such as HTTP caching handle request URIs as opaque character sequences, queries such as 'http://example.org/?q=foo' and 'http://example.org/?q=Foo' will be treated as entirely separate resources even if they yield identical results.
While most modern browser and server implementations allow for long request URIs, there is no standardized minimum or maximum length for URIs in general. Many resource constrained devices enforce strict limits on the maximum number of characters that can be included in a URI. Such limits can prove impractical for large or complex query parameters.
Query expressions included within a request URI must either be restricted to relatively simple key value pairs or encoded such that the query can be safely represented in the limited character-set allowed by URL standards. Such encoding can add significant complexity, introduce bugs, or otherwise reduce the overall visibility of the query being requested.

As an alternative to using GET, many implementations make use of the HTTP POST method to perform queries, as illustrated in the example below. In this case, the input parameters to the search operation are passed along within the request payload as opposed to using the request URI. A typical use of HTTP GET for requesting a search This variation, however, suffers from the same basic limitation as GET in that it is not readily apparent -- absent specific knowledge of the resource and server to which the request is being sent -- that a search operation is what is being requested. Web applications use the POST method for a wide variety of uses including the creation or modification of existing resources. Sending the request above to a different server, or even repeatedly sending the request to the same server could have dramatically different effects. The SEARCH method provides a solution that spans the gap between the use of GET and POST. As with POST, the input to the query operation is passed along within the payload of the request rather than as part of the request URI. Unlike POST, however the semantics of the SEARCH method are specifically defined. In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in .

The SEARCH method is used to initiate a server-side search. Unlike the HTTP GET method, which requests that a server return a representation of the resource identified by the effective request URI (as defined by ), the SEARCH method is used to ask the server to perform a query operation (described by the request payload) over some set of data scoped to the effective request URI. The payload returned in response to a SEARCH cannot be assumed to be a representation of the resource identified by the effective request URI. The body payload of the request defines the query. Implementations MAY use a request body of any content type with the SEARCH method; however, for backwards compatibility with existing WebDAV implementations, SEARCH requests that use the text/xml or application/xml content types MUST be processed per the requirements established by . SEARCH requests are both safe and idempotent with regards to the resource identified by the request URI. That is, SEARCH requests do not alter the state of the targeted resource. However, while processing a search request, a server can be expected to allocate computing and memory resources or even create additional HTTP resources through which the response can be retrieved. A successful response to a SEARCH request is expected to provide some indication as to the final disposition of the search operation. For instance, a successful search that yields no results can be represented by a 204 No Content response. If the response includes a body payload, the payload is expected to describe the results of the search operation. In some cases, the server may choose to respond indirectly to the SEARCH request by returning a 3xx Redirection with a Location header specifying an alternate Request URI from which the search results can be retrieved using an HTTP GET request. Various non-normative examples of successful SEARCH responses are illustrated in . The response to a SEARCH request is not cacheable. It ought to be noted, however, that because SEARCH requests are safe and idempotent, responses to a SEARCH MUST NOT invalidate previously cached responses to other requests directed at the same effective request URI. The semantics of the SEARCH method change to a "conditional SEARCH" if the request message includes an If-Modified-Since, If-Unmodified- Since, If-Match, If-None-Match, or If-Range header field (). A conditional SEARCH requests that the query be performed only under the circumstances described by the conditional header field(s). It is important to note, however, that such conditions are evaluated against the state of the target resource itself as opposed to the collected results of the search operation.

The "Accept-Search" response header field MAY be used by a server to directly signal support for the SEARCH method while identifying the specific query format Content-Type's that may be used. The Accept-Search header specifies a comma-separated listing of media types (with optional parameters) as defined by , Section 3.1.1.1. The order of types listed by the Accept-Search header is insignificant.

The non-normative examples in this section make use of a simple, hypothetical plain-text based query syntax based on SQL with results returned as comma-separated values. This is done for illustration purposes only. Implementations are free to use any format they wish on both the request and response.

A simple query with a direct response: Response:

A simple query with an Indirect Response (303 See Other) Response: Fetch Query Response: Response:

The SEARCH method is subject to the same general security considerations as all HTTP methods as described in .

IANA is requested to update the registration of the SEARCH method in the permanent registry at <http://www.iana.org/assignments/http-methods> (see ).

Method Name	Safe	Idempotent	Specification
SEARCH	Yes	Yes