Difference between revisions of "RESTXQ"

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This page is part of the [[Developer Section]]. It describes how to use the RESTXQ API of BaseX.
+
This page presents one of the [[Web Application]] services. It describes how to use the RESTXQ API of BaseX.
  
RESTXQ, introduced by [http://www.adamretter.org.uk/ Adam Retter], is a new API that facilitates the use of XQuery
+
RESTXQ, introduced by [http://www.adamretter.org.uk/ Adam Retter], is an API that facilitates the use of XQuery as a server-side processing language for the Web. It has been inspired by the Java [https://en.wikipedia.org/wiki/Java_API_for_RESTful_Web_Services JAX-RS API]: It provides a pre-defined set of XQuery 3.0 annotations for mapping HTTP requests to XQuery functions, which in turn generate and return HTTP responses.
as a Server Side processing language for the Web. RESTXQ has been inspired by Java’s
 
[http://en.wikipedia.org/wiki/Java_API_for_RESTful_Web_Services JAX-RS API]: it defines a pre-defined set of
 
XQuery 3.0 annotations for mapping HTTP requests to XQuery functions, which in turn generate and return
 
HTTP responses.
 
  
As of {{Version|7.2}}, RESTXQ is supported by BaseX. Note that various details of the specification may be subject to change due to the early state of the API.
+
Please note that BaseX provides various extensions to the original draft of the specification:
  
=Getting started=
+
* Multipart types are supported, including {{Code|multipart/form-data}}
 +
* A {{Code|%rest:error}} annotation can be used to catch XQuery errors
 +
* Servlet errors can be redirected to other RESTXQ pages
 +
* A [[RESTXQ Module]] provides some helper functions
 +
* Parameters are implicitly cast to the type of the function argument
 +
* The [[#Paths|Path Annotation]] can contain regular expressions
 +
* <code>%input</code> annotations, support for input-specific content-type parameters
 +
* <code>%rest:single</code> annotation to cancel running RESTXQ functions
 +
* Quality factors in the [[#Content Negotiation|Accept header]] will be evaluated
 +
* Support for server-side quality factors in the [[#Content Negotiation|<code>%rest:produces</code>]] annotation
 +
* Better support for the OPTIONS and HEAD methods
 +
<br />
  
First of all, launch the BaseX as [[Web Application]]. By default, [http://jetty.codehaus.org/jetty/ Jetty] is used as web server. All HTTP services will be available on port <code>8984</code>, and the RESTXQ service is accessible at {{Mono|http://localhost:8984/restxq/}}. If the server is started as servlet, all [[Options#Main Options|Main Options]] (such as the path to the database) can be configured in the {{Mono|web.xml}} file. If run as a standalone application, the settings are stored in the file {{Mono|.basex}}.
+
=Introduction=
  
=Module Declarations=
+
==Preliminaries==
  
A RESTXQ module needs to contain a declaration to the namespace {{Mono|http://exquery.org/ns/restxq}}. A ''Resource Function'' is an XQuery function that has been marked up with RESTXQ annotations (annotations will be introduced with the upcoming [[XQuery 3.0]] standard). When an HTTP request comes in, a resource function will be invoked that matches the constraints indicated by its annotations.
+
The RESTXQ service is accessible via {{Code|http://localhost:8984/}}.
  
All files with extension {{Mono|*.xqm}}, placed inside the directory specified by {{Mono|HTTPPATH}} (refer to [[Web Application#Configuring Database Access|HTTP Server Configuration]]) will be treated as RESTXQ modules. These will be parsed for RESTXQ annotations and cached. If a module is modified, it will be parsed again at runtime.
+
All RESTXQ [[XQuery 3.0#Annotations|annotations]] are assigned to the <code><nowiki>http://exquery.org/ns/restxq</nowiki></code> namespace, which is statically bound to the {{Code|rest}} prefix. A ''Resource Function'' is an XQuery function that has been marked up with RESTXQ annotations. When an HTTP request comes in, a resource function will be invoked that matches the constraints indicated by its annotations.
  
A simple RESTXQ module is shown below, it is part of a clean installation and available at http://localhost:8984/restxq/ .
+
If a RESTXQ URL is requested, the {{Option|RESTXQPATH}} module directory and its sub-directories will be traversed, and all [[XQuery Extensions#Suffixes|XQuery files]] will be parsed for functions with RESTXQ annotations. Sub-directories that include an {{Code|.ignore}} file will be skipped.
  
<pre class="brush:xquery">(:~ simplified module as in http/restxq.xqm :)
+
To speed up processing, the functions of the existing XQuery modules are automatically cached in main memory:
module namespace page = 'http://basex.org/modules/web-page';
+
* Functions will be invalidated and parsed again if the timestamp of their module changes.
declare namespace rest = 'http://exquery.org/ns/restxq';
+
* File monitoring can be adjusted via the {{Option|PARSERESTXQ}} option. In productive environments with a high load, it may be recommendable to change the timeout, or completely disable monitoring.
 +
* If files are replaced while the web server is running, the RESTXQ module cache should be explicitly invalidated by calling the static root path {{Code|/.init}} or by calling the [[RESTXQ Module#rest:init|rest:init]] function.
  
declare %rest:path("hello/{$world}")
+
==Examples==
        %rest:GET
+
 
        %rest:header-param("User-Agent", "{$agent}")
+
A first RESTXQ function is shown below:
        function page:hello($world as xs:string, $agent as xs:string*) {
+
 
 +
<syntaxhighlight lang="xquery">
 +
module namespace page = 'http://basex.org/examples/web-page';
 +
 
 +
declare %rest:path("hello/{$who}") %rest:GET function page:hello($who) {
 
   <response>
 
   <response>
     <title>Hello { $world }!</title>
+
     <title>Hello { $who }!</title>
    <info>You requested this page with { $agent }.</info>
 
 
   </response>
 
   </response>
};</pre>
+
};
 +
</syntaxhighlight>
  
If the URI http://localhost:8984/restxq/hello/world is accessed, the result will be kind of
+
If the URI http://localhost:8984/hello/World is accessed, the result will be:
  
<pre class="brush:xml">
+
<syntaxhighlight lang="xml">
&lt;response>
+
<response>
&lt;title>Hello world!&lt;/title>
+
  <title>Hello World!</title>
&lt;info>You requested this page with Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.2.149.27 Safari/525.13.&lt;/info>
+
</response>
&lt;/response>
+
</syntaxhighlight>
</pre>
 
  
We added another method within that module:
+
The next function demonstrates a POST request:
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
declare %rest:path("form/")
+
declare
        %rest:POST
+
  %rest:path("/form")
        %rest:form-param("content","{$message}", "'no message delivered'")
+
  %rest:POST
        function page:hello-postman($message as xs:string) {
+
  %rest:form-param("message","{$message}", "(no message)")
   &lt;response>
+
  %rest:header-param("User-Agent", "{$agent}")
     &lt;title>Hello!&lt;/title>
+
function page:hello-postman(
     &lt;info>It seems you posted a message: { $message }&lt;/info>
+
  $message as xs:string,
   &lt;/response>
+
  $agent  as xs:string*
 +
) as element(response) {
 +
   <response type='form'>
 +
     <message>{ $message }</message>
 +
     <user-agent>{ $agent }</user-agent>
 +
   </response>
 
};
 
};
</pre>
+
</syntaxhighlight>
 +
 
 +
If you post something (e.g. using curl or the embedded form at http://localhost:8984/)...
 +
 
 +
<syntaxhighlight lang="shell">
 +
curl -i -X POST --data "message='CONTENT'" http://localhost:8984/form
 +
</syntaxhighlight>
 +
 
 +
...you will receive something similar to the following result:
 +
 
 +
<syntaxhighlight lang="shell">
 +
HTTP/1.1 200 OK
 +
Content-Type: application/xml; charset=UTF-8
 +
Content-Length: 107
 +
Server: Jetty(8.1.11.v20130520)
 +
</syntaxhighlight>
  
If you posted something (e.g. using curl or the embedded form at http://localhost:8984/restxq/ )
+
<syntaxhighlight lang="xml">
<pre class="brush:shell">
+
<response type="form">
curl -i -X POST --data "content='Here comes the post'" http://admin:admin@localhost:8984/restxq/form
+
   <message>'CONTENT'</message>
</pre>
+
   <user-agent>curl/7.31.0</user-agent>
You would recieve
+
</response>
<pre class="brush:xml">
+
</syntaxhighlight>
&lt;response>
 
   &lt;title>Hello!&lt;/title>
 
   &lt;info>It seems you posted a message: 'Here comes the post'&lt;/info>
 
&lt;/response>
 
</pre>
 
  
=Annotations=
+
=Request=
  
This section lists all annotations provided by RESTXQ. <code>rest</code> is used as namespace prefix.
+
This section shows how annotations are used to handle and process HTTP requests.
  
 
==Constraints==
 
==Constraints==
Line 80: Line 106:
 
===Paths===
 
===Paths===
  
A resource function must have a single ''Path Annotation''. It will be called if a URL matches the path segments and templates specified as argument. ''Path templates'' contain variables in curly brackets, and map the values of the actual request path to the function arguments.
+
A resource function must have a single ''Path Annotation'' with a single string as argument. The function will be called if a URL matches the path segments and templates of the argument. ''Path templates'' contain variables in curly brackets, and map the corresponding segments of the request path to the arguments of the resource function. The first slash in the path is optional.
  
 
The following example contains a path annotation with three segments and two templates. One of the function arguments is further specified with a data type, which means that the value for <code>$variable</code> will be cast to an <code>xs:integer</code> before being bound:
 
The following example contains a path annotation with three segments and two templates. One of the function arguments is further specified with a data type, which means that the value for <code>$variable</code> will be cast to an <code>xs:integer</code> before being bound:
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
 
declare %rest:path("/a/path/{$with}/some/{$variable}")
 
declare %rest:path("/a/path/{$with}/some/{$variable}")
   function($with, $variable as xs:integer) { ... };
+
   function page:test($with, $variable as xs:integer) { ... };
 +
</syntaxhighlight>
 +
<!-- TODO how matching works -->
 +
 
 +
Variables can be enhanced by regular expressions:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
(: Matches all paths with "app" as first, a number as second, and "order" as third segment :)
 +
declare %rest:path("app/{$code=[0-9]+}/order")
 +
  function page:order($code) { ... };
 +
 
 +
(: Matches all other all paths starting with "app/" :)
 +
declare %rest:path("app/{$path=.+}")
 +
  function page:others($path) { ... };
 +
</syntaxhighlight>
 +
<!-- TODO how matching works -->
 +
 
 +
If multiple path candidates are found for the request, the one with more segments will be preferred.
 +
 
 +
===Content Negotiation===
 +
 
 +
Functions can be restricted to specific Media Types. The default type is {{Code|*/*}}. Multiple types can either be specified by a single or by multiple annotations.
 +
 
 +
====Consuming Data====
 +
 
 +
A function will only be taken into consideration if the HTTP {{Code|Content-Type}} header of the request matches one of the given types:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:POST("{$body}")
 +
  %rest:path("/xml")
 +
  %rest:consumes("application/xml")
 +
  %rest:consumes("text/xml")
 +
function page:xml($body) { $body };
 +
</syntaxhighlight>
 +
 
 +
====Producing Data====
 +
 
 +
A function will only be chosen if the HTTP {{Code|Accept}} header of the request matches one of the given types:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/xml")
 +
  %rest:produces("application/xml", "text/xml")
 +
function page:xml() { <xml/> };
 +
</syntaxhighlight>
 +
 
 +
Note that the annotations will ''not'' affect the type of the actual response: You will need to supply an additional <code>[[#Output|%output:media-type]]</code> annotation or (if a single function may produce results of different types) generate an apt [[#Custom_Response|Custom Response]].
 +
 
 +
====Quality Factors====
 +
 
 +
A client can supply quality factors to influence the server-side function selection process. If a client sends the following HTTP header with quality factors…
 +
 
 +
<pre>
 +
Accept: */*;q=0.5,text/html;q=1.0
 
</pre>
 
</pre>
<!-- TODO how matching works -->
+
 
 +
…and if two RESTXQ functions exist for the addressed path with two different annotations for producing data…
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare function %rest:produces("text/html") ...
 +
...
 +
declare function %rest:produces("*/*") ...
 +
</syntaxhighlight>
 +
 
 +
…the first of these function will be chosen, as the quality factor for <code>text/html</code> documents is highest.
 +
 
 +
As we cannot ensure that the client may supply quality factors, the selection process can also be controlled server-side. The <code>qs</code> parameter can be attached server-side to the Media Type. If multiple functions are left in the selection process, the one with the highest quality factor will be favored:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare function %rest:produces("application/json;qs=1") ...
 +
...
 +
declare function %rest:produces("*/*;qs=0.5") ...
 +
</syntaxhighlight>
  
 
===HTTP Methods===
 
===HTTP Methods===
The HTTP method annotations relate to some of the [http://en.wikipedia.org/wiki/HTTP#Request_methods HTTP request methods]  (GET, HEAD, DELETE, POST, PUT). Depending on the request method of the request, a function is invoked.
 
<!-- TODO [AG] does constraints mean: %rest:GET and %rest:HEAD makes no sense? -->
 
  
====Simple Method Annotations====
+
====Default Methods====
All available simple method annotations:
+
 
<pre class="brush:xquery">
+
The HTTP method annotations are equivalent to all [https://en.wikipedia.org/wiki/HTTP#Request_methods HTTP request methods] except TRACE and CONNECT. Zero or more methods may be used on a function; if none is specified, the function will be invoked for each method.
%rest:GET
+
 
%rest:HEAD
+
The following function will be called if GET or POST is used as request method:
%rest:DELETE
+
 
</pre>
+
<syntaxhighlight lang="xquery">
 +
declare %rest:GET %rest:POST %rest:path("/post")
 +
  function page:post() { "This was a GET or POST request" };
 +
</syntaxhighlight>
 +
 
 +
The POST and PUT annotations may optionally take a string literal in order to map the HTTP request body to a [[#Parameters|function argument]]. Once again, the target variable must be embraced by curly brackets:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare %rest:PUT("{$body}") %rest:path("/put")
 +
  function page:put($body) { "Request body: " || $body };
 +
</syntaxhighlight>
 +
 
 +
====Custom Methods====
 +
 
 +
Custom HTTP methods can be specified with the {{Code|%rest:method}} annotation. An optional body variable can be supplied as second argument:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("binary-size")
 +
  %rest:method("SIZE", "{$body}")
 +
function page:patch(
 +
  $body  as xs:base64Binary
 +
) {
 +
  "Request method: " || request:method(),
 +
  "Size of body: " || bin:length($body)
 +
};
 +
</syntaxhighlight>
 +
 
 +
If an OPTIONS request is received, and if no function is defined, an automatic response will be generated, which includes an <code>Allow</code> header with all supported methods.
 +
 
 +
If a HEAD request is received, and if no function is defined, the corresponding GET function will be processed, but the response body will be discarded.
 +
 
 +
==Content Types==
 +
 
 +
The body of a POST or PUT request will be converted to an XQuery item. Conversion can be
 +
controlled by specifying a content type. It can be further influenced
 +
by specifying additional content-type parameters:
 +
 
 +
{| class="wikitable" width="100%"
 +
|- valign="top"
 +
! Content-Type
 +
! Parameters (<code>;name=value</code>)
 +
! Type of resulting XQuery item
 +
|-
 +
| {{Code|text/xml}}, {{Code|application/xml}}
 +
|
 +
| {{Code|document-node()}}
 +
|-
 +
| {{Code|text/*}}
 +
|
 +
| {{Code|xs:string}}
 +
|-
 +
| {{Code|application/json}}
 +
| [[JSON Module#Options|JSON Options]]
 +
| {{Code|document-node()}} or {{Code|map(*)}}
 +
|-
 +
| {{Code|text/html}}
 +
| [[HTML Module#Options|HTML Options]]
 +
| {{Code|document-node()}}
 +
|-
 +
| {{Code|text/comma-separated-values}}
 +
| [[CSV Module#Options|CSV Options]]
 +
| {{Code|document-node()}} or {{Code|map(*)}}
 +
|-
 +
| ''others''
 +
|
 +
| {{Code|xs:base64Binary}}
 +
|-
 +
| {{Code|multipart/*}}
 +
|
 +
| sequence (see next paragraph)
 +
|}
 +
 
 +
For example, if <code>application/json;lax=yes</code> is specified as content type, the input will be transformed to JSON, and the lax QName conversion rules will be applied, as described in the [[JSON Module]].
 +
 
 +
===Input options===
 +
 
 +
Conversion options for {{Option|JSON}}, {{Option|CSV}} and {{Option|HTML}} can also be specified via annotations with the <code>input</code> prefix. The following function interprets the input as text with the CP1252 encoding and treats the first line as header:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/store.csv")
 +
  %rest:POST("{$csv}")
 +
  %input:csv("header=true,encoding=CP1252")
 +
function page:store-csv($csv as document-node()) {
 +
  "Number of rows: " || count($csv/csv/record)
 +
};
 +
</syntaxhighlight>
  
====Content Method Annotations====
+
===Multipart Types===
The variable declaration, for processing the content in a XQuery function, is optional. All available content method annotations:
 
<pre class="brush:xquery">
 
%rest:POST
 
%rest:POST("{$post-body}")
 
%rest:PUT
 
%rest:PUT("{$put-body}")
 
</pre>
 
  
===Content Types===
+
The single parts of a multipart message are represented as a sequence,
 +
and each part is converted to an XQuery item as described in the last paragraph.
  
* '''HTTP Content Types''': One or more media-types may be specified as strings, e.g.:<br/>
+
A function that is capable of handling multipart types is identical to other RESTXQ functions:
<pre class="brush:xquery">%rest:consumes("application/xml", "text/xml")</pre>
 
* '''HTTP Accept''': One or more media-types may be specified as strings, e.g.:<br/>
 
<pre class="brush:xquery">%rest:produces("application/atom+xml")</pre>
 
  
These default to <code>*/*</code> if no media-type annotations are given.
+
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/multipart")
 +
  %rest:POST("{$data}")
 +
  %rest:consumes("multipart/mixed") (: optional :)
 +
function page:multipart($data as item()*) {
 +
  "Number of items: " || count($data)
 +
};
 +
</syntaxhighlight>
  
 
==Parameters==
 
==Parameters==
  
Parameters are optional annotations that can be used to bind additional values to function arguments:
+
The following annotations can be used to bind request values to function arguments. Values will implicitly be cast to the type of the argument.
  
===Query Strings===
+
===Query Parameters===
  
The value of the <em>first parameter</em>, if found in the [http://en.wikipedia.org/wiki/Query_string Query String], will be assigned to the variable specified as <em>second parameter</em>. Optionally, a <em>third parameter</em> may be specified as default:
+
The value of the ''first parameter'', if found in the [[Request_Module#Conventions|query component]], will be assigned to the variable specified as ''second parameter''. If no value is specified in the HTTP request, all additional parameters will be bound to the variable (if no additional parameter is given, an empty sequence will be bound):
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
%rest:query-param("parameter", "{$value}", "default")
+
declare
%rest:query-param("answer", "{$answer}", 42, 43, 44)
+
  %rest:path("/params")
%rest:query-param("search", "{$search-param}")
+
  %rest:query-param("id", "{$id}")
</pre>
+
  %rest:query-param("add", "{$add}", 42, 43, 44)
 +
function page:params($id as xs:string?, $add as xs:integer+) {
 +
  <result id="{ $id }" sum="{ sum($add) }"/>
 +
};
 +
</syntaxhighlight>
  
 
===HTML Form Fields===
 
===HTML Form Fields===
  
Form parameters are specified the same way as [[#Query Strings|query strings]]. Their values are extracted from GET or POST requests.
+
Form parameters are specified the same way as [[#Query Parameters|query parameters]]:
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
%rest:form-param("parameter", "{$value}", "default")
+
%rest:form-param("city", "{$city}", "no-city-specified")
</pre>
+
</syntaxhighlight>
 +
 
 +
The values are the result of HTML forms submitted with the (default) content type <code>application/x-www-form-urlencoded</code>:
 +
 
 +
<syntaxhighlight lang="xml">
 +
<form action="/process" method="POST" enctype="application/x-www-form-urlencoded">
 +
  <input type="text" name="city"/>
 +
  <input type="submit"/>
 +
</form>
 +
</syntaxhighlight>
 +
 
 +
====File Uploads====
 +
 
 +
Files can be uploaded to the server by using the content type {{Code|multipart/form-data}} (the HTML5 {{Code|multiple}} attribute enables the upload of multiple files):
 +
 
 +
<syntaxhighlight lang="xml">
 +
<form action="/upload" method="POST" enctype="multipart/form-data">
 +
  <input type="file" name="files"  multiple="multiple"/>
 +
  <input type="submit"/>
 +
</form>
 +
</syntaxhighlight>
 +
 
 +
The file contents are placed in a [[Map Module|map]], with the filename serving as key. The following example shows how uploaded files can be stored in a temporary directory:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:POST
 +
  %rest:path("/upload")
 +
  %rest:form-param("files", "{$files}")
 +
function page:upload($files) {
 +
  for $name    in map:keys($files)
 +
  let $content := $files($name)
 +
  let $path    := file:temp-dir() || $name
 +
  return (
 +
    file:write-binary($path, $content),
 +
    <file name="{ $name }" size="{ file:size($path) }"/>
 +
  )
 +
};
 +
</syntaxhighlight>
  
 
===HTTP Headers===
 
===HTTP Headers===
  
Header parameters are specified the same way as [[#Query Strings|query strings]]:
+
Header parameters are specified the same way as [[#Query Parameters|query parameters]]:
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
%rest:header-param("User-Agent","{$user-agent}")
+
%rest:header-param("User-Agent", "{$user-agent}")
%rest:header-param("Referer","{$referer}", "none")
+
%rest:header-param("Referer", "{$referer}", "none")
</pre>
+
</syntaxhighlight>
  
 
===Cookies===
 
===Cookies===
  
Cookie parameters are specified the same way as [[#Query Strings|query strings]]:
+
Cookie parameters are specified the same way as [[#Query Parameters|query parameters]]:
  
<pre class="brush:xquery">
+
<syntaxhighlight lang="xquery">
%rest:cookie-param("username","{$user}")
+
%rest:cookie-param("username", "{$user}")
%rest:cookie-param("authentication","{$auth}", "no_auth")
+
%rest:cookie-param("authentication", "{$auth}", "no_auth")
</pre>
+
</syntaxhighlight>
 +
 
 +
==Query Execution==
 +
 
 +
In many web search scenarios, user input from browser forms is processed and search results are returned. Such operations can be made more interactive by sending a new search request to the server with each key click. However, this may lead to many parallel server-side requests, from which only the result of the last request will be relevant for the client.
 +
 
 +
With the <code>%rest:single</code> annotation, it can be enforced that only one instance of a function will run at the same time and for the same client. If the same function will be called for the second time, a currently executed query will be stopped, and the HTTP error code {{Code|460}} will be returned instead:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
(: If fast enough, returns the result. Otherwise, if called again, raises 460 :)
 +
declare
 +
  %rest:path("/search")
 +
  %rest:query-param("term", "{$term}")
 +
  %rest:single
 +
function page:search($term as xs:string) {
 +
  <ul>{
 +
    for $result in db:open('large-db')//*[text() = $term]
 +
    return <li>{ $result }</li>
 +
  }</ul>
 +
};
 +
</syntaxhighlight>
 +
 
 +
By adding a string value to with the annotation, functions can be bundled together, and a running query can be canceled by calling another one that has the same annotation value. This is shown by another example, in which the first function can be interrupted by the second one. If you call both functions in separate browser tabs, you will note that the first tab will return <code>460</code>, and the second one will return <xml>stopped</xml>.
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/compute")
 +
  %rest:single("EXPENSIVE")
 +
function local:compute() {
 +
  (1 to 100000000000000)[. = 0]
 +
};
 +
 
 +
declare
 +
  %rest:path("/stop")
 +
  %rest:single("EXPENSIVE")
 +
function local:stop() {
 +
  <xml>stopped</xml>
 +
};
 +
</syntaxhighlight>
 +
 
 +
The following things should be noted:
 +
 
 +
* If a query will be canceled, there will be no undesirable side effects. For example, it won’t be possible to abort a query if it is currently updating the database or performing any other I/O operations. As a result, the termination of a running query can take some more time as expected.
 +
* The currently executed function is bound to the current session. This way, a client will not be able to cancel requests from other clients. As a result, functions can only be stopped if there was at least one previous successful response, in which initial session data was returned to the client.
 +
 
 +
=Response=
 +
 
 +
By default, a successful request is answered with the HTTP status code {{Code|200}} (OK) and is followed by the given content. An erroneous request leads to an error code and an optional error message (e.g. {{Code|404}} for “resource not found”).
 +
 
 +
With {{Version|9.6}}, the {{Code|Server-Timing}} HTTP header will be attached to the response. It indicates how much time was spent for parsing, compiling, evaluating and serializing the query. The last value will not necessarily reflect the full time for serializing the result, as the header is generated before the result is sent to the client. Server-side serialization can be enforced by annotating a function with the <code>[[#Query Execution|%rest:single]]</code> annotation.
 +
 
 +
==Custom Response==
 +
 
 +
Custom responses can be generated in XQuery by returning an <code>rest:response</code> element, an <code>http:response</code> child node that matches the syntax of the [http://expath.org/spec/http-client EXPath HTTP Client Module] specification, and optional child nodes that will be serialized as usual. A function that yields a response on an unknown resource may look as follows:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare %output:method("text") %rest:path("") function page:error404() {
 +
  <rest:response>
 +
    <http:response status="404">
 +
      <http:header name="Content-Language" value="en"/>
 +
      <http:header name="Content-Type" value="text/plain; charset=utf-8"/>
 +
    </http:response>
 +
  </rest:response>,
 +
  "The requested resource is not available."
 +
};
 +
</syntaxhighlight>
 +
 
 +
==Forwards and Redirects==
 +
 
 +
===Redirects===
 +
 
 +
The server can invite the client (e.g., the web browser) to make a second request to another URL by sending a 302 response:
 +
 
 +
<syntaxhighlight lang="xml">
 +
<rest:response>
 +
  <http:response status="302">
 +
    <http:header name="Location" value="new-location"/>
 +
  </http:response>
 +
</rest:response>
 +
</syntaxhighlight>
 +
 
 +
The convenience function {{Function|Web|web:redirect}} can be called to create such a response.
 +
 
 +
In the XQuery context, redirects are particularly helpful if [[XQuery Update|Updates]] are performed. An updating request may send a redirect to a second function that generates a success message, or evaluates an updated database:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare %updating %rest:path('/app/init') function local:create() {
 +
  db:create('app', <root/>, 'root.xml'),
 +
  db:output(web:redirect('/app/ok'))
 +
};
 +
 
 +
declare %rest:path('/app/ok') function local:ok() {
 +
  'Stored documents: ' || count(db:open('app'))
 +
};
 +
</syntaxhighlight>
 +
 
 +
===Forwards===
 +
 
 +
A server-side redirect is called forwarding. It reduces traffic among client and server, and the forwarding will not change the URL seen from the client’s perspective:
 +
 
 +
<syntaxhighlight lang="xml">
 +
<rest:forward>new-location</rest:forward>
 +
</syntaxhighlight>
 +
 
 +
The fragment can also be created with the convenience function {{Function|Web|web:forward}}.
 +
 
 +
==Output==
 +
 
 +
The content-type of a response can be influenced by the user via [[Serialization|Serialization Parameters]]. The steps are described in the [[REST#Content Type|REST]] chapter. In RESTXQ, serialization parameters can be specified in the query prolog, via annotations, or within the REST response element:
 +
 
 +
===Query Prolog===
 +
 
 +
In main modules, serialization parameters may be specified in the query prolog. These parameters will then apply to all functions in a module. In the following example, the content type of the response is overwritten with the {{Code|media-type}} parameter:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare option output:media-type 'text/plain';
 +
 
 +
declare %rest:path("version1") function page:version1() {
 +
  'Keep it simple, stupid'
 +
};
 +
</syntaxhighlight>
 +
 
 +
===Annotations===
 +
 
 +
Global serialization parameters can be overwritten via <code>%output</code> annotations. The following example serializes XML nodes as JSON, using the [[JSON Module|JsonML]] format:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("cities")
 +
  %output:method("json")
 +
  %output:json("format=jsonml")
 +
function page:cities() {
 +
  element cities {
 +
    db:open('factbook')//city/name
 +
  }
 +
};
 +
</syntaxhighlight>
 +
 
 +
The next function, when called, generates XHTML headers, and {{Code|text/html}} will be set as content type:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("done")
 +
  %output:method("xhtml")
 +
  %output:omit-xml-declaration("no")
 +
  %output:doctype-public("-//W3C//DTD XHTML 1.0 Transitional//EN") 
 +
  %output:doctype-system("http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd")
 +
function page:html() {
 +
  <html xmlns="http://www.w3.org/1999/xhtml">
 +
    <body>done</body>
 +
  </html>
 +
};
 +
</syntaxhighlight>
 +
 
 +
===Response Element===
 +
 
 +
Serialization parameters can also be specified in a REST reponse element in a query. Serialization parameters will be overwritten:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare %rest:path("version3") function page:version3() {
 +
  <rest:response>
 +
    <output:serialization-parameters>
 +
      <output:media-type value='text/plain'/>
 +
    </output:serialization-parameters>
 +
  </rest:response>,
 +
  'Not that simple anymore'
 +
};
 +
</syntaxhighlight>
 +
 
 +
=Error Handling=
 +
 
 +
If an error is raised when RESTXQ code is parsed, compiled or evaluated, an HTTP response with the status code 500 is generated.
 +
 
 +
By default, all server-side errors will be passed on to the client. This is particularly helpful during the development process. In a productive environment, however, it is advisable not to expose errors to the client. This can be realized via the {{Option|RESTXQERRORS}} option. If disabled,
 +
 
 +
* XQuery modules that cannot be parsed will be ignored and
 +
* full error messages and stack traces will be suppressed and not included in the HTTP response.
 +
 
 +
The full error information can still be looked up in the database logs.
 +
 
 +
==Raise Errors==
 +
 
 +
With {{Function|Web|web:error}}, you can abort query evaluation, enforce a premature HTTP response and report errors back to the client:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/teapot")
 +
function page:teapot() {
 +
  web:error(418, "I'm a pretty teapot")
 +
};
 +
</syntaxhighlight>
 +
 
 +
In contrast to the standard <code>fn:error</code> function, a status code can be supplied, and the response body will only contain the specified error message and no stack trace.
 +
 
 +
==Catch XQuery Errors==
 +
 
 +
XQuery runtime errors can be processed via ''error annotations''. Error annotations have one or more arguments, which represent the error codes to be caught. The codes equal the names of the [[XQuery 3.0#Try.2FCatch|try/catch]] construct:
 +
 
 +
{| class="wikitable"
 +
|- valign="top"
 +
! Precedence
 +
! Syntax
 +
! Example
 +
|-
 +
| 1
 +
| <code>prefix:name</code><br/><code>Q{uri}name</code>
 +
| <code>err:FORG0001</code><br/><code><nowiki>Q{http://www.w3.org/2005/xqt-errors}FORG0001</nowiki></code>
 +
|-
 +
| 2
 +
| <code>prefix:*</code><br/><code>Q{uri}*</code>
 +
| <code>err:*</code><br/><code><nowiki>Q{http://www.w3.org/2005/xqt-errors}*</nowiki></code>
 +
|-
 +
| 3
 +
| <code>*:name</code>
 +
| <code>*:FORG0001</code>
 +
|-
 +
| 4
 +
| <code>*</code>
 +
| <code>*</code>
 +
|}
 +
 
 +
All error codes that are specified for a function must have the same precedence.
 +
The following rules apply when catching errors:
 +
 
 +
* Codes with a higher precedence (smaller number) will be given preference.
 +
* A global RESTXQ error will be raised if two functions with conflicting codes are found.
 +
 
 +
Similar to try/catch, the pre-defined variables ({{Code|code}}, {{Code|description}}, {{Code|value}}, {{Code|module}}, {{Code|line-number}}, {{Code|column-number}}, {{Code|additional}}) can be bound to variables via ''error parameter annotations'', which are specified the same way as [[#Query Parameters|query parameters]].
 +
 
 +
Errors may occur unexpectedly. However, they can also be triggered by a query, as demonstrated by the following example:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare
 +
  %rest:path("/check/{$user}")
 +
function page:check($user) {
 +
  if($user = ('jack', 'lisa'))
 +
  then 'User exists'
 +
  else fn:error(xs:QName('err:user'), $user)
 +
};
 +
 
 +
declare
 +
  %rest:error("err:user")
 +
  %rest:error-param("description", "{$user}")
 +
function page:user-error($user) {
 +
  'User "' || $user || '" is unknown'
 +
};
 +
</syntaxhighlight>
 +
 
 +
==Catch HTTP Errors==
 +
 
 +
Errors that occur outside RESTXQ can be caught by adding {{Code|error-page}} elements with an error code and a target location to the {{Code|web.xml}} configuration file (find more details in the [http://www.eclipse.org/jetty/documentation/current/custom-error-pages.html Jetty Documentation]):
 +
 
 +
<syntaxhighlight lang="xml">
 +
<error-page>
 +
  <error-code>404</error-code>
 +
  <location>/error404</location>
 +
</error-page>
 +
</syntaxhighlight>
 +
 
 +
The target location may be another RESTXQ function. The [[Request Module#request:attribute|request:attribute]] function can be used to request details on the caught error:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
declare %rest:path("/error404") function page:error404() {
 +
  "URL: " || request:attribute("javax.servlet.error.request_uri") || ", " ||
 +
  "Error message: " || request:attribute("javax.servlet.error.message")
 +
};
 +
</syntaxhighlight>
 +
 
 +
=User Authentication=
 +
 
 +
If you want to provide restricted access to parts of a web applications, you will need to check permissions before returning a response to the client. The [[Permissions]] layer is a nice abstraction for defining permission checks.
 +
 
 +
=Functions=
 +
 
 +
The [[Request Module]] contains functions for accessing data related to the current HTTP request. Two modules exist for setting and retrieving server-side session data of the current user ([[Session Module]]) and all users known to the HTTP server ([[Sessions Module]]). The [[RESTXQ Module]] provides functions for requesting RESTXQ base URIs and generating a [https://www.w3.org/Submission/wadl/ WADL description] of all services. Please note that the namespaces of all of these modules must be explicitly specified via module imports in the query prolog.
 +
 
 +
The following example returns the current host name:
 +
 
 +
<syntaxhighlight lang="xquery">
 +
import module namespace request = "http://exquery.org/ns/request";
 +
 
 +
declare %rest:path("/host-name") function page:host() {
 +
  'Remote host name: ' || request:remote-hostname()
 +
};
 +
</syntaxhighlight>
  
 
=References=
 
=References=
  
RESTXQ has been proposed by [http://www.adamretter.org.uk/ Adam Retter].
+
Documentation:
More information on all specifics can be found in the following two documents:
 
  
 +
* [http://exquery.org/spec/restxq RESTXQ Specification], First Draft
 
* [http://www.adamretter.org.uk/papers/restful-xquery_january-2012.pdf RESTful XQuery, Standardised XQuery 3.0 Annotations for REST]. Paper, XMLPrague, 2012
 
* [http://www.adamretter.org.uk/papers/restful-xquery_january-2012.pdf RESTful XQuery, Standardised XQuery 3.0 Annotations for REST]. Paper, XMLPrague, 2012
 
* [http://www.adamretter.org.uk/presentations/restxq_mugl_20120308.pdf RESTXQ]. Slides, MarkLogic User Group London, 2012
 
* [http://www.adamretter.org.uk/presentations/restxq_mugl_20120308.pdf RESTXQ]. Slides, MarkLogic User Group London, 2012
 +
* [https://files.basex.org/publications/xmlprague/2013/Develop-RESTXQ-WebApps-with-BaseX.pdf Web Application Development]. Slides from XMLPrague 2013
 +
 +
Examples:
 +
 +
* Sample code combining XQuery and JavaScript: [https://www.balisage.net/Proceedings/vol17/author-pkg/Galtman01/BalisageVol17-Galtman01.html Materials] and [https://www.balisage.net/Proceedings/vol17/html/Galtman01/BalisageVol17-Galtman01.html paper] from Amanda Galtman, Balisage 2016.
 +
* [[DBA]]: The Database Administration interface, bundled with the full distributions of BaseX.
 +
 +
=Changelog=
 +
 +
;Version 9.6
 +
* Updated: [[#Response|Response]]: {{Code|Server-Timing}} HTTP header.
 +
 +
;Version 9.5
 +
* Updated: [[#Raise Errors|Raise Errors]]: Status code {{Code|400}} changed to {{Code|500}}, omit stack trace.
 +
 +
;Version 9.3
 +
* Updated: [[#Custom Methods|Custom Methods]]: Better support for the OPTIONS and HEAD methods.
 +
* Updated: [[#Catch XQuery Errors|XQuery Errors]]: Suppress stack trace and error code in the HTTP response.
 +
* Removed: {{Code|rest:redirect}} element ({{Function|Web|web:redirect}} can be used instead)
 +
 +
;Version 9.2
 +
* Updated: Ignore XQuery modules that cannot be parsed
 +
 +
;Version 9.0
 +
* Added: Support for server-side quality factors in the [[#Content Negotiation|<code>%rest:produces</code>]] annotation
 +
* Updated: Status code {{Code|410}} was replaced with {{Code|460}}
 +
* Removed: {{Code|restxq}} prefix
 +
 +
;Version 8.4
 +
* Added: <code>%rest:single</code> annotation
 +
 +
;Version 8.1
 +
* Added: support for input-specific content-type parameters
 +
* Added: <code>%input</code> annotations
 +
 +
;Version 8.0
 +
* Added: Support for regular expresssions in the [[#Paths|Path Annotation]]
 +
* Added: Evaluation of quality factors that are supplied in the [[#Content Negotiation|Accept header]]
 +
 +
;Version 7.9
 +
* Updated: [[#Catch XQuery Errors|XQuery Errors]], extended error annotations
 +
* Added: {{Code|%rest:method}}
 +
 +
;Version 7.7
 +
* Added: [[#Error Handling|Error Handling]], [[#File Uploads|File Uploads]], [[#Multipart Types|Multipart Types]]
 +
* Updated: RESTXQ function may now also be specified in main modules (suffix: {{Code|*.xq}}).
 +
* Updated: the RESTXQ prefix has been changed from {{Code|restxq}} to {{Code|rest}}.
 +
* Updated: parameters are implicitly cast to the type of the function argument
 +
* Updated: the RESTXQ root url has been changed to {{Code|http://localhost:8984/}}
  
[[Category:HTTP]]
+
;Version 7.5
[[Category:Developer]]
+
* Added: new XML elements {{Code|<rest:redirect/>}} and {{Code|<rest:forward/>}}

Latest revision as of 13:48, 19 August 2021

This page presents one of the Web Application services. It describes how to use the RESTXQ API of BaseX.

RESTXQ, introduced by Adam Retter, is an API that facilitates the use of XQuery as a server-side processing language for the Web. It has been inspired by the Java JAX-RS API: It provides a pre-defined set of XQuery 3.0 annotations for mapping HTTP requests to XQuery functions, which in turn generate and return HTTP responses.

Please note that BaseX provides various extensions to the original draft of the specification:

  • Multipart types are supported, including multipart/form-data
  • A %rest:error annotation can be used to catch XQuery errors
  • Servlet errors can be redirected to other RESTXQ pages
  • A RESTXQ Module provides some helper functions
  • Parameters are implicitly cast to the type of the function argument
  • The Path Annotation can contain regular expressions
  • %input annotations, support for input-specific content-type parameters
  • %rest:single annotation to cancel running RESTXQ functions
  • Quality factors in the Accept header will be evaluated
  • Support for server-side quality factors in the %rest:produces annotation
  • Better support for the OPTIONS and HEAD methods


Introduction[edit]

Preliminaries[edit]

The RESTXQ service is accessible via http://localhost:8984/.

All RESTXQ annotations are assigned to the http://exquery.org/ns/restxq namespace, which is statically bound to the rest prefix. A Resource Function is an XQuery function that has been marked up with RESTXQ annotations. When an HTTP request comes in, a resource function will be invoked that matches the constraints indicated by its annotations.

If a RESTXQ URL is requested, the RESTXQPATH module directory and its sub-directories will be traversed, and all XQuery files will be parsed for functions with RESTXQ annotations. Sub-directories that include an .ignore file will be skipped.

To speed up processing, the functions of the existing XQuery modules are automatically cached in main memory:

  • Functions will be invalidated and parsed again if the timestamp of their module changes.
  • File monitoring can be adjusted via the PARSERESTXQ option. In productive environments with a high load, it may be recommendable to change the timeout, or completely disable monitoring.
  • If files are replaced while the web server is running, the RESTXQ module cache should be explicitly invalidated by calling the static root path /.init or by calling the rest:init function.

Examples[edit]

A first RESTXQ function is shown below:

module namespace page = 'http://basex.org/examples/web-page';

declare %rest:path("hello/{$who}") %rest:GET function page:hello($who) {
  <response>
    <title>Hello { $who }!</title>
  </response>
};

If the URI http://localhost:8984/hello/World is accessed, the result will be:

<response>
  <title>Hello World!</title>
</response>

The next function demonstrates a POST request:

declare
  %rest:path("/form")
  %rest:POST
  %rest:form-param("message","{$message}", "(no message)")
  %rest:header-param("User-Agent", "{$agent}")
function page:hello-postman(
  $message as xs:string,
  $agent   as xs:string*
) as element(response) {
  <response type='form'>
    <message>{ $message }</message>
    <user-agent>{ $agent }</user-agent>
  </response>
};

If you post something (e.g. using curl or the embedded form at http://localhost:8984/)...

curl -i -X POST --data "message='CONTENT'" http://localhost:8984/form

...you will receive something similar to the following result:

HTTP/1.1 200 OK
Content-Type: application/xml; charset=UTF-8
Content-Length: 107
Server: Jetty(8.1.11.v20130520)
<response type="form">
  <message>'CONTENT'</message>
  <user-agent>curl/7.31.0</user-agent>
</response>

Request[edit]

This section shows how annotations are used to handle and process HTTP requests.

Constraints[edit]

Constraints restrict the HTTP requests that a resource function may process.

Paths[edit]

A resource function must have a single Path Annotation with a single string as argument. The function will be called if a URL matches the path segments and templates of the argument. Path templates contain variables in curly brackets, and map the corresponding segments of the request path to the arguments of the resource function. The first slash in the path is optional.

The following example contains a path annotation with three segments and two templates. One of the function arguments is further specified with a data type, which means that the value for $variable will be cast to an xs:integer before being bound:

declare %rest:path("/a/path/{$with}/some/{$variable}")
  function page:test($with, $variable as xs:integer) { ... };

Variables can be enhanced by regular expressions:

(: Matches all paths with "app" as first, a number as second, and "order" as third segment :)
declare %rest:path("app/{$code=[0-9]+}/order")
  function page:order($code) { ... };

(: Matches all other all paths starting with "app/" :)
declare %rest:path("app/{$path=.+}")
  function page:others($path) { ... };

If multiple path candidates are found for the request, the one with more segments will be preferred.

Content Negotiation[edit]

Functions can be restricted to specific Media Types. The default type is */*. Multiple types can either be specified by a single or by multiple annotations.

Consuming Data[edit]

A function will only be taken into consideration if the HTTP Content-Type header of the request matches one of the given types:

declare
  %rest:POST("{$body}")
  %rest:path("/xml")
  %rest:consumes("application/xml")
  %rest:consumes("text/xml")
function page:xml($body) { $body };

Producing Data[edit]

A function will only be chosen if the HTTP Accept header of the request matches one of the given types:

declare
  %rest:path("/xml")
  %rest:produces("application/xml", "text/xml")
function page:xml() { <xml/> };

Note that the annotations will not affect the type of the actual response: You will need to supply an additional %output:media-type annotation or (if a single function may produce results of different types) generate an apt Custom Response.

Quality Factors[edit]

A client can supply quality factors to influence the server-side function selection process. If a client sends the following HTTP header with quality factors…

Accept: */*;q=0.5,text/html;q=1.0

…and if two RESTXQ functions exist for the addressed path with two different annotations for producing data…

declare function %rest:produces("text/html") ...
...
declare function %rest:produces("*/*") ...

…the first of these function will be chosen, as the quality factor for text/html documents is highest.

As we cannot ensure that the client may supply quality factors, the selection process can also be controlled server-side. The qs parameter can be attached server-side to the Media Type. If multiple functions are left in the selection process, the one with the highest quality factor will be favored:

declare function %rest:produces("application/json;qs=1") ...
...
declare function %rest:produces("*/*;qs=0.5") ...

HTTP Methods[edit]

Default Methods[edit]

The HTTP method annotations are equivalent to all HTTP request methods except TRACE and CONNECT. Zero or more methods may be used on a function; if none is specified, the function will be invoked for each method.

The following function will be called if GET or POST is used as request method:

declare %rest:GET %rest:POST %rest:path("/post")
  function page:post() { "This was a GET or POST request" };

The POST and PUT annotations may optionally take a string literal in order to map the HTTP request body to a function argument. Once again, the target variable must be embraced by curly brackets:

declare %rest:PUT("{$body}") %rest:path("/put")
  function page:put($body) { "Request body: " || $body };

Custom Methods[edit]

Custom HTTP methods can be specified with the %rest:method annotation. An optional body variable can be supplied as second argument:

declare
  %rest:path("binary-size")
  %rest:method("SIZE", "{$body}")
function page:patch(
  $body  as xs:base64Binary
) {
  "Request method: " || request:method(),
  "Size of body: " || bin:length($body)
};

If an OPTIONS request is received, and if no function is defined, an automatic response will be generated, which includes an Allow header with all supported methods.

If a HEAD request is received, and if no function is defined, the corresponding GET function will be processed, but the response body will be discarded.

Content Types[edit]

The body of a POST or PUT request will be converted to an XQuery item. Conversion can be controlled by specifying a content type. It can be further influenced by specifying additional content-type parameters:

Content-Type Parameters (;name=value) Type of resulting XQuery item
text/xml, application/xml document-node()
text/* xs:string
application/json JSON Options document-node() or map(*)
text/html HTML Options document-node()
text/comma-separated-values CSV Options document-node() or map(*)
others xs:base64Binary
multipart/* sequence (see next paragraph)

For example, if application/json;lax=yes is specified as content type, the input will be transformed to JSON, and the lax QName conversion rules will be applied, as described in the JSON Module.

Input options[edit]

Conversion options for JSON, CSV and HTML can also be specified via annotations with the input prefix. The following function interprets the input as text with the CP1252 encoding and treats the first line as header:

declare
  %rest:path("/store.csv")
  %rest:POST("{$csv}")
  %input:csv("header=true,encoding=CP1252")
function page:store-csv($csv as document-node()) {
  "Number of rows: " || count($csv/csv/record)
};

Multipart Types[edit]

The single parts of a multipart message are represented as a sequence, and each part is converted to an XQuery item as described in the last paragraph.

A function that is capable of handling multipart types is identical to other RESTXQ functions:

declare
  %rest:path("/multipart")
  %rest:POST("{$data}")
  %rest:consumes("multipart/mixed") (: optional :)
function page:multipart($data as item()*) {
  "Number of items: " || count($data)
};

Parameters[edit]

The following annotations can be used to bind request values to function arguments. Values will implicitly be cast to the type of the argument.

Query Parameters[edit]

The value of the first parameter, if found in the query component, will be assigned to the variable specified as second parameter. If no value is specified in the HTTP request, all additional parameters will be bound to the variable (if no additional parameter is given, an empty sequence will be bound):

declare
  %rest:path("/params")
  %rest:query-param("id", "{$id}")
  %rest:query-param("add", "{$add}", 42, 43, 44)
function page:params($id as xs:string?, $add as xs:integer+) {
  <result id="{ $id }" sum="{ sum($add) }"/>
};

HTML Form Fields[edit]

Form parameters are specified the same way as query parameters:

%rest:form-param("city", "{$city}", "no-city-specified")

The values are the result of HTML forms submitted with the (default) content type application/x-www-form-urlencoded:

<form action="/process" method="POST" enctype="application/x-www-form-urlencoded">
  <input type="text" name="city"/>
  <input type="submit"/>
</form>

File Uploads[edit]

Files can be uploaded to the server by using the content type multipart/form-data (the HTML5 multiple attribute enables the upload of multiple files):

<form action="/upload" method="POST" enctype="multipart/form-data">
  <input type="file" name="files"  multiple="multiple"/>
  <input type="submit"/>
</form>

The file contents are placed in a map, with the filename serving as key. The following example shows how uploaded files can be stored in a temporary directory:

declare
  %rest:POST
  %rest:path("/upload")
  %rest:form-param("files", "{$files}")
function page:upload($files) {
  for $name    in map:keys($files)
  let $content := $files($name)
  let $path    := file:temp-dir() || $name
  return (
    file:write-binary($path, $content),
    <file name="{ $name }" size="{ file:size($path) }"/>
  )
};

HTTP Headers[edit]

Header parameters are specified the same way as query parameters:

%rest:header-param("User-Agent", "{$user-agent}")
%rest:header-param("Referer", "{$referer}", "none")

Cookies[edit]

Cookie parameters are specified the same way as query parameters:

%rest:cookie-param("username", "{$user}")
%rest:cookie-param("authentication", "{$auth}", "no_auth")

Query Execution[edit]

In many web search scenarios, user input from browser forms is processed and search results are returned. Such operations can be made more interactive by sending a new search request to the server with each key click. However, this may lead to many parallel server-side requests, from which only the result of the last request will be relevant for the client.

With the %rest:single annotation, it can be enforced that only one instance of a function will run at the same time and for the same client. If the same function will be called for the second time, a currently executed query will be stopped, and the HTTP error code 460 will be returned instead:

(: If fast enough, returns the result. Otherwise, if called again, raises 460 :)
declare
  %rest:path("/search")
  %rest:query-param("term", "{$term}")
  %rest:single
function page:search($term as xs:string) {
  <ul>{
    for $result in db:open('large-db')//*[text() = $term]
    return <li>{ $result }</li>
  }</ul>
};

By adding a string value to with the annotation, functions can be bundled together, and a running query can be canceled by calling another one that has the same annotation value. This is shown by another example, in which the first function can be interrupted by the second one. If you call both functions in separate browser tabs, you will note that the first tab will return 460, and the second one will return <xml>stopped</xml>.

declare 
  %rest:path("/compute")
  %rest:single("EXPENSIVE")
function local:compute() {
  (1 to 100000000000000)[. = 0]
};

declare 
  %rest:path("/stop")
  %rest:single("EXPENSIVE")
function local:stop() {
  <xml>stopped</xml>
};

The following things should be noted:

  • If a query will be canceled, there will be no undesirable side effects. For example, it won’t be possible to abort a query if it is currently updating the database or performing any other I/O operations. As a result, the termination of a running query can take some more time as expected.
  • The currently executed function is bound to the current session. This way, a client will not be able to cancel requests from other clients. As a result, functions can only be stopped if there was at least one previous successful response, in which initial session data was returned to the client.

Response[edit]

By default, a successful request is answered with the HTTP status code 200 (OK) and is followed by the given content. An erroneous request leads to an error code and an optional error message (e.g. 404 for “resource not found”).

With Version 9.6, the Server-Timing HTTP header will be attached to the response. It indicates how much time was spent for parsing, compiling, evaluating and serializing the query. The last value will not necessarily reflect the full time for serializing the result, as the header is generated before the result is sent to the client. Server-side serialization can be enforced by annotating a function with the %rest:single annotation.

Custom Response[edit]

Custom responses can be generated in XQuery by returning an rest:response element, an http:response child node that matches the syntax of the EXPath HTTP Client Module specification, and optional child nodes that will be serialized as usual. A function that yields a response on an unknown resource may look as follows:

declare %output:method("text") %rest:path("") function page:error404() {
  <rest:response>
    <http:response status="404">
      <http:header name="Content-Language" value="en"/>
      <http:header name="Content-Type" value="text/plain; charset=utf-8"/>
    </http:response>
  </rest:response>,
  "The requested resource is not available."
};

Forwards and Redirects[edit]

Redirects[edit]

The server can invite the client (e.g., the web browser) to make a second request to another URL by sending a 302 response:

<rest:response>
  <http:response status="302">
    <http:header name="Location" value="new-location"/>
  </http:response>
</rest:response>

The convenience function web:redirect can be called to create such a response.

In the XQuery context, redirects are particularly helpful if Updates are performed. An updating request may send a redirect to a second function that generates a success message, or evaluates an updated database:

declare %updating %rest:path('/app/init') function local:create() {
  db:create('app', <root/>, 'root.xml'),
  db:output(web:redirect('/app/ok'))
};

declare %rest:path('/app/ok') function local:ok() {
  'Stored documents: ' || count(db:open('app'))
};

Forwards[edit]

A server-side redirect is called forwarding. It reduces traffic among client and server, and the forwarding will not change the URL seen from the client’s perspective:

<rest:forward>new-location</rest:forward>

The fragment can also be created with the convenience function web:forward.

Output[edit]

The content-type of a response can be influenced by the user via Serialization Parameters. The steps are described in the REST chapter. In RESTXQ, serialization parameters can be specified in the query prolog, via annotations, or within the REST response element:

Query Prolog[edit]

In main modules, serialization parameters may be specified in the query prolog. These parameters will then apply to all functions in a module. In the following example, the content type of the response is overwritten with the media-type parameter:

declare option output:media-type 'text/plain';

declare %rest:path("version1") function page:version1() {
  'Keep it simple, stupid'
};

Annotations[edit]

Global serialization parameters can be overwritten via %output annotations. The following example serializes XML nodes as JSON, using the JsonML format:

declare
  %rest:path("cities")
  %output:method("json")
  %output:json("format=jsonml")
function page:cities() {
  element cities {
    db:open('factbook')//city/name
  }
};

The next function, when called, generates XHTML headers, and text/html will be set as content type:

declare
  %rest:path("done")
  %output:method("xhtml")
  %output:omit-xml-declaration("no")
  %output:doctype-public("-//W3C//DTD XHTML 1.0 Transitional//EN")  
  %output:doctype-system("http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd")
function page:html() {
  <html xmlns="http://www.w3.org/1999/xhtml">
    <body>done</body>
  </html>
};

Response Element[edit]

Serialization parameters can also be specified in a REST reponse element in a query. Serialization parameters will be overwritten:

declare %rest:path("version3") function page:version3() {
  <rest:response>
    <output:serialization-parameters>
      <output:media-type value='text/plain'/>
    </output:serialization-parameters>
  </rest:response>,
  'Not that simple anymore'
};

Error Handling[edit]

If an error is raised when RESTXQ code is parsed, compiled or evaluated, an HTTP response with the status code 500 is generated.

By default, all server-side errors will be passed on to the client. This is particularly helpful during the development process. In a productive environment, however, it is advisable not to expose errors to the client. This can be realized via the RESTXQERRORS option. If disabled,

  • XQuery modules that cannot be parsed will be ignored and
  • full error messages and stack traces will be suppressed and not included in the HTTP response.

The full error information can still be looked up in the database logs.

Raise Errors[edit]

With web:error, you can abort query evaluation, enforce a premature HTTP response and report errors back to the client:

declare
  %rest:path("/teapot")
function page:teapot() {
  web:error(418, "I'm a pretty teapot")
};

In contrast to the standard fn:error function, a status code can be supplied, and the response body will only contain the specified error message and no stack trace.

Catch XQuery Errors[edit]

XQuery runtime errors can be processed via error annotations. Error annotations have one or more arguments, which represent the error codes to be caught. The codes equal the names of the try/catch construct:

Precedence Syntax Example
1 prefix:name
Q{uri}name
err:FORG0001
Q{http://www.w3.org/2005/xqt-errors}FORG0001
2 prefix:*
Q{uri}*
err:*
Q{http://www.w3.org/2005/xqt-errors}*
3 *:name *:FORG0001
4 * *

All error codes that are specified for a function must have the same precedence. The following rules apply when catching errors:

  • Codes with a higher precedence (smaller number) will be given preference.
  • A global RESTXQ error will be raised if two functions with conflicting codes are found.

Similar to try/catch, the pre-defined variables (code, description, value, module, line-number, column-number, additional) can be bound to variables via error parameter annotations, which are specified the same way as query parameters.

Errors may occur unexpectedly. However, they can also be triggered by a query, as demonstrated by the following example:

declare
  %rest:path("/check/{$user}")
function page:check($user) {
  if($user = ('jack', 'lisa'))
  then 'User exists'
  else fn:error(xs:QName('err:user'), $user)
};

declare 
  %rest:error("err:user")
  %rest:error-param("description", "{$user}")
function page:user-error($user) {
  'User "' || $user || '" is unknown'
};

Catch HTTP Errors[edit]

Errors that occur outside RESTXQ can be caught by adding error-page elements with an error code and a target location to the web.xml configuration file (find more details in the Jetty Documentation):

<error-page>
  <error-code>404</error-code>
  <location>/error404</location>
</error-page>

The target location may be another RESTXQ function. The request:attribute function can be used to request details on the caught error:

declare %rest:path("/error404") function page:error404() {
  "URL: " || request:attribute("javax.servlet.error.request_uri") || ", " || 
  "Error message: " || request:attribute("javax.servlet.error.message")
};

User Authentication[edit]

If you want to provide restricted access to parts of a web applications, you will need to check permissions before returning a response to the client. The Permissions layer is a nice abstraction for defining permission checks.

Functions[edit]

The Request Module contains functions for accessing data related to the current HTTP request. Two modules exist for setting and retrieving server-side session data of the current user (Session Module) and all users known to the HTTP server (Sessions Module). The RESTXQ Module provides functions for requesting RESTXQ base URIs and generating a WADL description of all services. Please note that the namespaces of all of these modules must be explicitly specified via module imports in the query prolog.

The following example returns the current host name:

import module namespace request = "http://exquery.org/ns/request";

declare %rest:path("/host-name") function page:host() {
  'Remote host name: ' || request:remote-hostname()
};

References[edit]

Documentation:

Examples:

  • Sample code combining XQuery and JavaScript: Materials and paper from Amanda Galtman, Balisage 2016.
  • DBA: The Database Administration interface, bundled with the full distributions of BaseX.

Changelog[edit]

Version 9.6
  • Updated: Response: Server-Timing HTTP header.
Version 9.5
  • Updated: Raise Errors: Status code 400 changed to 500, omit stack trace.
Version 9.3
  • Updated: Custom Methods: Better support for the OPTIONS and HEAD methods.
  • Updated: XQuery Errors: Suppress stack trace and error code in the HTTP response.
  • Removed: rest:redirect element (web:redirect can be used instead)
Version 9.2
  • Updated: Ignore XQuery modules that cannot be parsed
Version 9.0
  • Added: Support for server-side quality factors in the %rest:produces annotation
  • Updated: Status code 410 was replaced with 460
  • Removed: restxq prefix
Version 8.4
  • Added: %rest:single annotation
Version 8.1
  • Added: support for input-specific content-type parameters
  • Added: %input annotations
Version 8.0
Version 7.9
  • Updated: XQuery Errors, extended error annotations
  • Added: %rest:method
Version 7.7
  • Added: Error Handling, File Uploads, Multipart Types
  • Updated: RESTXQ function may now also be specified in main modules (suffix: *.xq).
  • Updated: the RESTXQ prefix has been changed from restxq to rest.
  • Updated: parameters are implicitly cast to the type of the function argument
  • Updated: the RESTXQ root url has been changed to http://localhost:8984/
Version 7.5
  • Added: new XML elements <rest:redirect/> and <rest:forward/>