HTTP SEARCH Method
greenbytes GmbH
Hafenweg 16
Münster48155
Germany
julian.reschke@greenbytes.de
https://greenbytes.de/tech/webdav/
malhotrasahib@gmail.com
jasnell@gmail.com
Applications and Real-Time
http
search
method
This specification updates the definition and semantics of the
HTTP SEARCH request method originally defined by
RFC 5323.
Distribution of this document is unlimited. Although this is not a work
item of the HTTPbis Working Group, comments should be sent to the
Hypertext Transfer Protocol (HTTP) mailing list at ietf-http-wg@w3.org,
which may be joined by sending a message with subject
"subscribe" to ietf-http-wg-request@w3.org.
Discussions of the HTTPbis Working Group are archived at
.
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 |
|