Difference between revisions of "Fetch Module"

From BaseX Documentation
Jump to navigation Jump to search
m (Text replacement - "<syntaxhighlight lang="xquery">" to "<pre lang='xquery'>")
Tags: Mobile web edit Mobile edit
 
(68 intermediate revisions by 3 users not shown)
Line 1: Line 1:
−
This [[Module Library|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 {{Code|file://}} or {{Code|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.
+
This [[Module Library|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 {{Code|file://}} or {{Code|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.
  
−
The module has initially been inspired by [http://www.zorba-xquery.com/html/modules/zorba/io/fetch Zorba’s Fetch Module].
+
=Conventions=
  
−
=Conventions=
+
All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/fetch</nowiki></code> namespace, which is statically bound to the {{Code|fetch}} prefix.<br/>
  
−
All functions in this module are assigned to the {{Code|http://basex.org/modules/fetch}} namespace, which is statically bound to the {{Code|fetch}} prefix.<br/>
+
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#File Paths|File Module]]).
−
All errors are assigned to the {{Code|http://basex.org/errors}} namespace, which is statically bound to the {{Code|bxerr}} prefix.
 
  
 
=Functions=
 
=Functions=
 +
 +
==fetch:binary==
 +
 +
{| width='100%'
 +
|- valign="top"
 +
| width='120' | '''Signature'''
 +
|<pre>fetch:binary(
 +
  $href  as xs:string
 +
) as xs:base64Binary</pre>
 +
|- valign="top"
 +
| '''Summary'''
 +
|Fetches the resource referred to by the given {{Code|href}} string and returns it as [[Lazy Module|lazy]] {{Code|xs:base64Binary}} item.
 +
|- valign="top"
 +
| '''Errors'''
 +
|{{Error|open|#Errors}} the URI could not be resolved, or the resource could not be retrieved.
 +
|- valign="top"
 +
| '''Examples'''
 +
|
 +
* <code><nowiki>fetch:binary("http://images.trulia.com/blogimg/c/5/f/4/679932_1298401950553_o.jpg")</nowiki></code> returns the addressed image.
 +
* <code><nowiki>lazy:cache(fetch:binary("http://en.wikipedia.org"))</nowiki></code> enforces the fetch operation (otherwise, it will be delayed until requested first).
 +
|}
  
 
==fetch:text==
 
==fetch:text==
 +
 
{| width='100%'
 
{| width='100%'
−
|-
+
|- valign="top"
−
| width='90' | '''Signatures'''
+
| width='120' | '''Signature'''
−
|{{Func|fetch:text|$uri as xs:string|xs:string}}<br/>{{Func|fetch:text|$uri as xs:string, $encoding as xs:string|xs:string}}<br/>
+
|<pre>fetch:text(
−
|-
+
  $href      as xs:string,
 +
  $encoding  as xs:string   := (),
 +
  $fallback  as xs:boolean?  := false()
 +
) as xs:string</pre>
 +
|- valign="top"
 
| '''Summary'''
 
| '''Summary'''
−
|Fetches the resource referred to by the given URI and returns it as a streamable string.
+
|Fetches the resource referred to by the given {{Code|href}} string and returns it as [[Lazy Module|lazy]] {{Code|xs:string}} item:
−
|-
+
* The UTF-8 default encoding can be overwritten with the optional {{Code|$encoding}} argument.
 +
* By default, invalid characters will be rejected. If {{Code|$fallback}} is set to true, these characters will be replaced with the Unicode replacement character <code>FFFD</code> (&#xFFFD;).
 +
|- valign="top"
 
| '''Errors'''
 
| '''Errors'''
−
|{{Error|BXFE0001|XQuery Errors#Functions Errors}} the URI could not be resolved, or the resource could not be retrieved.<br/>{{Error|BXFE0002|XQuery Errors#Functions Errors}} the specified encoding is not supported, or unknown.
+
|{{Error|open|#Errors}} the URI could not be resolved, or the resource could not be retrieved.<br/>{{Error|encoding|#Errors}} the specified encoding is not supported, or unknown.
−
|-
+
|- valign="top"
 
| '''Examples'''
 
| '''Examples'''
 
|
 
|
 
* <code><nowiki>fetch:text("http://en.wikipedia.org")</nowiki></code> returns a string representation of the English Wikipedia main HTML page.
 
* <code><nowiki>fetch:text("http://en.wikipedia.org")</nowiki></code> returns a string representation of the English Wikipedia main HTML page.
−
* <code><nowiki>data(fetch:text("http://en.wikipedia.org"))</nowiki></code> returns a materialized representation of the streamable string.
+
* <code><nowiki>fetch:text("http://www.bbc.com","US-ASCII",true())</nowiki></code> returns the BBC homepage in US-ASCII with all non-US-ASCII characters replaced with &#xFFFD;.
 +
* <code><nowiki>lazy:cache(fetch:text("http://en.wikipedia.org"))</nowiki></code> enforces the fetch operation (otherwise, it will be delayed until requested first).
 
|}
 
|}
  
−
==fetch:binary==
+
==fetch:doc==
 +
 
 
{| width='100%'
 
{| width='100%'
−
|-
+
|- valign="top"
−
| width='90' | '''Signatures'''
+
| width='120' | '''Signature'''
−
|{{Func|fetch:binary|$uri as xs:string|xs:base64Binary}}<br/>
+
|<pre>fetch:doc(
−
|-
+
  $href    as xs:string,
 +
  $options  as map(*)?    := map { }
 +
) as document-node()</pre>
 +
|- valign="top"
 
| '''Summary'''
 
| '''Summary'''
−
|Fetches the resource referred to by the given URI and returns it as streamable base64Binary.
+
|Fetches the resource referred to by the given {{Code|href}} string and returns it as a document node.<br/>The {{Code|$options}} argument can be used to change the parsing behavior. Allowed options are all [[Options#Parsing|parsing]] and [[Options#XML Parsing|XML parsing]] options in lower case.<br/>The function differs from {{Code|fn:doc}} in various aspects:
−
|-
+
* It is ''nondeterministic'', 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 [[Transaction Management#Limitations|limitations of database locking]] for more details).
 +
|- valign="top"
 
| '''Errors'''
 
| '''Errors'''
−
|{{Error|BXFE0001|XQuery Errors#Functions Errors}} the URI could not be resolved, or the resource could not be retrieved.
+
|{{Error|open|#Errors}} the URI could not be resolved, or the resource could not be retrieved.
−
|-
+
|- valign="top"
 +
| '''Examples'''
 +
|
 +
* Retrieve an XML representation of the English Wikipedia main HTML page with whitespace stripped:
 +
<pre lang='xquery'>
 +
fetch:doc("http://en.wikipedia.org", map { 'stripws': true() })
 +
</pre>
 +
* Return a web page as XML, preserve namespaces:
 +
<pre lang='xquery'>
 +
fetch:doc(
 +
  'http://basex.org/',
 +
  map {
 +
    'parser': 'html',
 +
    'htmlparser': map { 'nons': false() }
 +
  }
 +
)
 +
</pre>
 +
|}
 +
 
 +
==fetch:binary-doc==
 +
 
 +
{| width='100%'
 +
|- valign="top"
 +
| width='120' | '''Signature'''
 +
|<pre>fetch:binary-doc(
 +
  $input    as xs:anyAtomicType,
 +
  $options  as map(*)?          := map { }
 +
) as document-node()</pre>
 +
|- valign="top"
 +
| '''Summary'''
 +
|Converts the specified {{Code|$input}} ({{Code|xs:base64Binary}}, {{Code|xs:hexBinary}}) to XML and returns it as a document node.<br/>In contrast to {{Code|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.<br/>The {{Code|$options}} argument can be used to change the parsing behavior. Allowed options are all [[Options#Parsing|parsing]] and [[Options#XML Parsing|XML parsing]] options in lower case.
 +
|- valign="top"
 
| '''Examples'''
 
| '''Examples'''
 
|
 
|
−
* <code><nowiki>fetch:binary("http://images.trulia.com/blogimg/c/5/f/4/679932_1298401950553_o.jpg")</nowiki></code> returns the addressed image.
+
* Retrieves file input as binary data and parses it as XML:
 +
<pre lang='xquery'>
 +
fetch:binary-doc(file:read-binary('doc.xml'))
 +
</pre>
 +
* Encodes a string as CP1252 and parses it as XML. The input and the string {{Code|touché}} will be correctly decoded because of the XML declaration:
 +
<pre lang='xquery'>
 +
fetch:binary-doc(convert:string-to-base64(
 +
  "<?xml version='1.0' encoding='CP1252'?><xml>touché</xml>",
 +
  "CP1252"
 +
))
 +
</pre>
 +
* 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:
 +
<pre lang='xquery'>
 +
fetch:binary-doc(convert:string-to-base64("<xml/>", "UTF16"))
 +
</pre>
 +
|- valign="top"
 +
| '''Errors'''
 +
|{{Error|open|#Errors}} the input could not be parsed.
 
|}
 
|}
  
 
==fetch:content-type==
 
==fetch:content-type==
 +
 
{| width='100%'
 
{| width='100%'
−
|-
+
|- valign="top"
−
| width='90' | '''Signatures'''
+
| width='120' | '''Signature'''
−
|{{Func|fetch:content-type|$uri as xs:string|xs:string}}<br/>
+
|<pre>fetch:content-type(
−
|-
+
  $href  as xs:string
 +
) as xs:string</pre>
 +
|- valign="top"
 
| '''Summary'''
 
| '''Summary'''
−
|Returns the content-type (also called mime-type) of the resource specified by {{Code|$uri}}:
+
|Returns the content-type (also called mime-type) of the resource specified by {{Code|href}} string:
 
* If a remote resource is addressed, the request header will be evaluated.
 
* If a remote resource is addressed, the request header will be evaluated.
−
* If the addressed resource is locally stored, the file extension will be guessed based on the file extension.
+
* If the addressed resource is locally stored, the content-type will be guessed based on the file extension.
−
|-
+
|- valign="top"
 
| '''Errors'''
 
| '''Errors'''
−
|{{Error|BXFE0001|XQuery Errors#Functions Errors}} the URI could not be resolved, or the resource could not be retrieved.
+
|{{Error|open|#Errors}} the URI could not be resolved, or the resource could not be retrieved.
−
|-
+
|- valign="top"
 
| '''Examples'''
 
| '''Examples'''
 
|
 
|
Line 66: Line 152:
 
=Errors=
 
=Errors=
  
−
{| width='100%' class="wikitable" width="100%"
+
{| class="wikitable" width="100%"
−
! width="5%"|Code
+
! width="110"|Code
−
! width="95%"|Description
+
|Description
−
|-
+
|- valign="top"
−
|{{Code|BXFE0001}}
+
|{{Code|encoding}}
 +
|The specified encoding is not supported, or unknown.
 +
|- valign="top"
 +
|{{Code|open}}
 
|The URI could not be resolved, or the resource could not be retrieved.
 
|The URI could not be resolved, or the resource could not be retrieved.
−
|-
 
−
|{{Code|BXFE0002}}
 
−
|The specified encoding is not supported, or unknown.
 
 
|}
 
|}
  
 
=Changelog=
 
=Changelog=
  
−
The module was introduced with Version 7.5.1.
+
;Version 10.0
 +
* Updated: {{Function||fetch:doc}} renamed (before: {{Code|fetch:xml}}).
 +
* Updated: {{Function||fetch:binary-doc}} renamed (before: {{Code|fetch:xml-binary}}).
 +
 
 +
;Version 9.0
 +
* Added: {{Code|fetch:xml-binary}}
 +
* Updated: error codes updated; errors now use the module namespace
 +
 
 +
;Version 8.5
 +
* Updated: {{Function||fetch:text}}: <code>$fallback</code> argument added.
 +
 
 +
;Version 8.0
 +
* Added: {{Code|fetch:xml}}
  
−
[[Category:XQuery]]
+
The module was introduced with Version 7.6.

Latest revision as of 18:34, 1 December 2023

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[edit]

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[edit]

fetch:binary[edit]

Signature 
fetch:binary(
  $href  as xs:string
) as xs:base64Binary
Summary Fetches the resource referred to by the given href string 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[edit]

Signature 
fetch:text(
  $href      as xs:string,
  $encoding  as xs:string    := (),
  $fallback  as xs:boolean?  := false()
) as xs:string
Summary Fetches the resource referred to by the given href string 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[edit]

Signature 
fetch:doc(
  $href     as xs:string,
  $options  as map(*)?    := map { }
) as document-node()
Summary Fetches the resource referred to by the given href string 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 nondeterministic, 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:
fetch:doc("http://en.wikipedia.org", map { 'stripws': true() })
  • Return a web page as XML, preserve namespaces:
fetch:doc(
  'http://basex.org/',
  map {
    'parser': 'html',
    'htmlparser': map { 'nons': false() }
  }
)

fetch:binary-doc[edit]

Signature 
fetch:binary-doc(
  $input    as xs:anyAtomicType,
  $options  as map(*)?           := 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:
fetch:binary-doc(file:read-binary('doc.xml'))
  • 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:
fetch:binary-doc(convert:string-to-base64(
  "<?xml version='1.0' encoding='CP1252'?><xml>touché</xml>",
  "CP1252"
))
  • 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:
fetch:binary-doc(convert:string-to-base64("<xml/>", "UTF16"))
Errors open: the input could not be parsed.

fetch:content-type[edit]

Signature 
fetch:content-type(
  $href  as xs:string
) as xs:string
Summary Returns the content-type (also called mime-type) of the resource specified by href string:
  • 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[edit]

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[edit]

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.

Retrieved from "http://docs.basex.org/index.php?title=Fetch_Module&oldid=16815"