hxt-8.5.2: A collection of tools for processing XML with Haskell.

MaintainerUwe Schmidt (uwe@fh-wedel.de)



Version : $Id: ReadDocument.hs,v 1.10 20061124 07:41:37 hxml Exp $

Compound arrows for reading an XML/HTML document or an XML/HTML string



readDocument :: Attributes -> String -> IOStateArrow s b XmlTreeSource

the main document input filter

this filter can be configured by an option list, a value of type Text.XML.HXT.DOM.TypeDefs.Attributes

available options:

  • a_parse_html: use HTML parser, else use XML parser (default)
  • a_tagsoup : use light weight and lazy parser based on tagsoup lib
  • a_parse_by_mimetype : select the parser by the mime type of the document (pulled out of the HTTP header). When the mime type is set to "text/html" the HTML parser (parsec or tagsoup) is taken, when it's set to "text/xml" or "text/xhtml" the XML parser (parsec or tagsoup) is taken. If the mime type is something else no further processing is performed, the contents is given back to the application in form of a single text node. If the default document encoding (a_encoding) is set to isoLatin1, this even enables processing of arbitray binary data.
  • a_validate : validate document againsd DTD (default), else skip validation
  • a_relax_schema : validate document with Relax NG, the options value is the schema URI this implies using XML parser, no validation against DTD, and canonicalisation
  • a_check_namespaces : check namespaces, else skip namespace processing (default)
  • a_canonicalize : canonicalize document (default), else skip canonicalization
  • a_preserve_comment : preserve comments during canonicalization, else remove comments (default)
  • a_remove_whitespace : remove all whitespace, used for document indentation, else skip this step (default)
  • a_indent : indent document by inserting whitespace, else skip this step (default)
  • a_issue_warnings : issue warnings, when parsing HTML (default), else ignore HTML parser warnings
  • a_issue_errors : issue all error messages on stderr (default), or ignore all error messages
  • a_ignore_encoding_errors: ignore all encoding errors, default is issue all encoding errors
  • a_ignore_none_xml_contents: ignore document contents of none XML/HTML documents. This option can be useful for implementing crawler like applications, e.g. an URL checker. In those cases net traffic can be reduced.
  • a_trace : trace level: values: 0 - 4
  • a_proxy : proxy for http access, e.g. www-cache:3128
  • a_redirect : automatically follow redirected URIs, default is yes
  • a_use_curl : obsolete and ignored, HTTP acccess is always done with curl bindings for libcurl
  • a_strict_input : file input is done strictly using the Data.ByteString input functions. This ensures correct closing of files, especially when working with the tagsoup parser and not processing the whole input data. Default is off. The ByteString input usually is not faster than the buildin hGetContents for strings.
  • a_options_curl : deprecated but for compatibility reasons still supported. More options passed to the curl binding. Instead of using this option to set a whole bunch of options at once for curl it is recomended to use the curl-.* options syntax described below.
  • a_encoding : default document encoding (utf8, isoLatin1, usAscii, iso8859_2, ... , iso8859_16, ...). Only XML, HTML and text documents are decoded, default decoding for XML/HTML is utf8, for text iso latin1 (no decoding). The whole content is returned in a single text node.
  • a_mime_types : set the mime type table for file input with given file. The format of this config file must be in the syntax of a debian linux "mime.types" config file
  • a_if_modified_since : read document conditionally, only if the document is newer than the given date and time argument, the contents is delivered, else just the root node with the meta data is returned. The date and time must be given in System.Locale.rfc822DateFormat.
  • curl options : the HTTP interface with libcurl can be configured with a lot of options. To support these options in an easy way, there is a naming convetion: Every option, which has the prefix curl and the rest of the name forms an option as described in the curl man page, is passed to the curl binding lib. See Text.XML.HXT.IO.GetHTTPLibCurl.getCont for examples. Currently most of the options concerning HTTP requests are implemented.

All attributes not evaluated by readDocument are stored in the created document root node for easy access of the various options in e.g. the input/output modules

If the document name is the empty string or an uri of the form "stdin:", the document is read from standard input.


 readDocument [ ] "test.xml"

reads and validates a document "test.xml", no namespace propagation, only canonicalization is performed

 readDocument [ (a_validate, "0")
              , (a_encoding, isoLatin1)
              , (a_parse_by_mimetype, "1")
              ] "http://localhost/test.php"

reads document "test.php", parses it as HTML or XML depending on the mimetype given from the server, but without validation, default encoding isoLatin1.

 readDocument [ (a_parse_html, "1")
              , (a_encoding, isoLatin1)
              ] ""

reads a HTML document from standard input, no validation is done when parsing HTML, default encoding is isoLatin1, parsing is done with tagsoup parser, but input is read strictly

 readDocument [ (a_encoding, isoLatin1)
              , (a_mime_type,    "/etc/mime.types")
              , (a_tagsoup,      "1")
              , (a_strict_input, "1")
              ] "test.svg"

reads an SVG document from standard input, sets the mime type by looking in the system mimetype config file, default encoding is isoLatin1, parsing is done with the lightweight tagsoup parser, which implies no validation.

 readDocument [ (a_parse_html,     "1")
              , (a_proxy,          "www-cache:3128")
              , (a_curl,           "1")
              , (a_issue_warnings, "0")
              ] "http://www.haskell.org/"

reads Haskell homepage with HTML parser ignoring any warnings, with http access via external program curl and proxy "www-cache" at port 3128

 readDocument [ (a_validate,          "1")
              , (a_check_namespace,   "1")
              , (a_remove_whitespace, "1")
              , (a_trace,             "2")
              ] "http://www.w3c.org/"

read w3c home page (xhtml), validate and check namespaces, remove whitespace between tags, trace activities with level 2

for minimal complete examples see Text.XML.HXT.Arrow.WriteDocument.writeDocument and runX, the main starting point for running an XML arrow.

readFromDocument :: Attributes -> IOStateArrow s String XmlTreeSource

the arrow version of readDocument, the arrow input is the source URI

readString :: Attributes -> String -> IOStateArrow s b XmlTreeSource

read a document that is stored in a normal Haskell String

the same function as readDocument, but the parameter forms the input. All options available for readDocument are applicable for readString.

Default encoding: No encoding is done, the String argument is taken as Unicode string

readFromString :: Attributes -> IOStateArrow s String XmlTreeSource

the arrow version of readString, the arrow input is the source URI

hread :: ArrowXml a => a String XmlTreeSource

parse a string as HTML content, substitute all HTML entity refs and canonicalize tree (substitute char refs, ...). Errors are ignored.

A simpler version of readFromString but with less functionality. Does not run in the IO monad

xread :: ArrowXml a => a String XmlTreeSource

parse a string as XML content, substitute all predefined XML entity refs and canonicalize tree (substitute char refs, ...)