Fetch Module

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Revision as of 18:23, 11 March 2017 by CG (talk | contribs) (→‎fetch:xml)
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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 Module can be used. With the HTML Module, retrieved HTML documents can be converted to XML.

Conventions

All functions in this module are assigned to the http://basex.org/modules/fetch namespace, which is statically bound to the fetch prefix.
All errors are assigned to the http://basex.org/errors namespace, which is statically bound to the bxerr 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 streamable xs:base64Binary.
Errors BXFE0001: 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.
  • stream:materialize(fetch:binary("http://en.wikipedia.org")) returns a materialized representation of the streamable result.

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 streamable xs:string:
  • 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 BXFE0001: the URI could not be resolved, or the resource could not be retrieved.
BXFE0002: 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.
  • stream:materialize(fetch:text("http://en.wikipedia.org")) returns a materialized representation of the streamable result.

fetch:xml

Signatures fetch:xml($uri as xs:string) as document-node()
fetch:xml($uri as xs:string, $options as map(*)) as document-node()
Summary Fetches the resource referred to by the given $uri and returns it as an XML document.
In contrast to fn:doc, each function call returns a different document node. As a consequence, document instances created by this function will not be kept in memory until the end of query evaluation.
The $options argument can be used to change the parsing behavior. Allowed options are all parsing and XML parsing options in lower case.
Errors BXFE0001: 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, chop all whitespace nodes:
fetch:xml("http://en.wikipedia.org", map { 'chop': true() })
* Return a document located in the current base directory:
fetch:xml(file:base-dir() || "example.xml")

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 BXFE0001: 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
BXFE0001 The URI could not be resolved, or the resource could not be retrieved.
BXFE0002 The specified encoding is not supported, or unknown.

Changelog

Version 8.5
Version 8.0

The module was introduced with Version 7.6.