Fetch Module

From BaseX Documentation
Revision as of 13:17, 20 July 2022 by CG (talk | contribs)
Jump to navigation Jump to search

This XQuery Module provides simple functions to fetch the content of resources identified by URIs. Resources can be stored locally or remotely and e.g. use the file:// or http:// scheme. If more control over HTTP requests is required, the HTTP Client Module can be used. With the HTML Module, retrieved HTML documents can be converted to XML.

Conventions

All functions and errors in this module are assigned to the http://basex.org/modules/fetch namespace, which is statically bound to the fetch prefix.

URI arguments can point be URLs or point to local files. Relative file paths will be resolved against the current working directory (for more details, have a look at the File Module).

Functions

fetch:binary

Signatures fetch:binary($uri as xs:string) as xs:base64Binary
Summary Fetches the resource referred to by the given URI and returns it as lazy xs:base64Binary item.
Errors open: the URI could not be resolved, or the resource could not be retrieved.
Examples
  • fetch:binary("http://images.trulia.com/blogimg/c/5/f/4/679932_1298401950553_o.jpg") returns the addressed image.
  • lazy:cache(fetch:binary("http://en.wikipedia.org")) enforces the fetch operation (otherwise, it will be delayed until requested first).

fetch:text

Signatures fetch:text($uri as xs:string) as xs:string
fetch:text($uri as xs:string, $encoding as xs:string) as xs:string
fetch:text($uri as xs:string, $encoding as xs:string, $fallback as xs:boolean) as xs:string
Summary Fetches the resource referred to by the given $uri and returns it as lazy xs:string item:
  • The UTF-8 default encoding can be overwritten with the optional $encoding argument.
  • By default, invalid characters will be rejected. If $fallback is set to true, these characters will be replaced with the Unicode replacement character FFFD (�).
Errors open: the URI could not be resolved, or the resource could not be retrieved.
encoding: the specified encoding is not supported, or unknown.
Examples
  • fetch:text("http://en.wikipedia.org") returns a string representation of the English Wikipedia main HTML page.
  • fetch:text("http://www.bbc.com","US-ASCII",true()) returns the BBC homepage in US-ASCII with all non-US-ASCII characters replaced with �.
  • lazy:cache(fetch:text("http://en.wikipedia.org")) enforces the fetch operation (otherwise, it will be delayed until requested first).

fetch:doc

Signatures fetch:doc($uri as xs:string) as document-node()
fetch:doc($uri as xs:string, $options as map(*)?) as document-node()
Summary Fetches the resource referred to by the given $uri and returns it as a document node.
The $options argument can be used to change the parsing behavior. Allowed options are all parsing and XML parsing options in lower case.
The function differs from fn:doc in various aspects:
  • It is non-deterministic, i.e., a new document node will be created by each call of this function.
  • A document created by this function will be garbage-collected as soon as it is not referenced anymore.
  • URIs will not be resolved against existing databases. As a result, it will not trigger any locks (see limitations of database locking for more details).
Errors open: the URI could not be resolved, or the resource could not be retrieved.
Examples
  • Retrieve an XML representation of the English Wikipedia main HTML page with whitespace stripped:

<syntaxhighlight lang="xquery"> fetch:doc("http://en.wikipedia.org", map { 'stripws': true() }) </syntaxhighlight>

  • Return a web page as XML, preserve namespaces:

<syntaxhighlight lang="xquery"> fetch:doc(

 'http://basex.org/',
 map {
   'parser': 'html',
   'htmlparser': map { 'nons': false() }
 }

) </syntaxhighlight>

fetch:binary-doc

Signatures fetch:binary-doc($input as xs:anyAtomicType) as document-node()
fetch:binary-doc($data as xs:anyAtomicType, $options as map(*)?) as document-node()
Summary Converts the specified $input (xs:base64Binary, xs:hexBinary) to XML and returns it as a document node.
In contrast to fn:parse-xml, which expects a string, the input can be arbitrarily encoded. The encoding will be derived from the XML declaration or (in case of UTF-16 or UTF-32) from the first bytes of the input.
The $options argument can be used to change the parsing behavior. Allowed options are all parsing and XML parsing options in lower case.
Examples
  • Retrieves file input as binary data and parses it as XML:

<syntaxhighlight lang="xquery"> fetch:binary-doc(file:read-binary('doc.xml')) </syntaxhighlight>

  • Encodes a string as CP1252 and parses it as XML. The input and the string touché will be correctly decoded because of the XML declaration:

<syntaxhighlight lang="xquery"> fetch:binary-doc(convert:string-to-base64(

 "<?xml version='1.0' encoding='CP1252'?><xml>touché</xml>",
 "CP1252"

)) </syntaxhighlight>

  • Encodes a string as UTF-16 and parses it as XML. The document will be correctly decoded, as the first bytes of the data indicate that the input must be UTF-16:

<syntaxhighlight lang="xquery"> fetch:binary-doc(convert:string-to-base64("<xml/>", "UTF16")) </syntaxhighlight>

Errors open: the input could not be parsed.

fetch:content-type

Signatures fetch:content-type($uri as xs:string) as xs:string
Summary Returns the content-type (also called mime-type) of the resource specified by $uri:
  • If a remote resource is addressed, the request header will be evaluated.
  • If the addressed resource is locally stored, the content-type will be guessed based on the file extension.
Errors open: the URI could not be resolved, or the resource could not be retrieved.
Examples
  • fetch:content-type("http://docs.basex.org/skins/vector/images/wiki.png") returns image/png.

Errors

Code Description
encoding The specified encoding is not supported, or unknown.
open The URI could not be resolved, or the resource could not be retrieved.

Changelog

Version 10.0
Version 9.0
  • Added: fetch:xml-binary
  • Updated: error codes updated; errors now use the module namespace
Version 8.5
Version 8.0
  • Added: fetch:xml

The module was introduced with Version 7.6.