R's XML package throws error on correct XML document

Question

I should parse many XML documents using the R software using the XML package (Duncan Temple Lang, 2013). Here is an example: http://musicbrainz.org/ws/2/release?query=%22A%20Is%20for%20Alpine%22%20AND%20artist:%22Alpine%22

If the link is copy-pasted in the address bar of a browser, an XML page is displayed and its correctness has been checked with one of the many online validators. The http://validator.w3.org has been chosen and the markup of the XML document seems valid.

However using this code:

library(XML)
url = "http://musicbrainz.org/ws/2/release?query=%22A%20Is%20for%20Alpine%22%20AND%20artist:%22Alpine%22"
data = xmlTreeParse(url, asTree = TRUE)

the following error is reported:

Blank needed here
Error: 1: Blank needed here

Now, the error is similar to the one discussed here Validation problem with XML declaration, but can't see how the error applies to the XML document I would to parse.

Software: R version 3.0.2 (2013-09-25) -- "Frisbee Sailing"

Platform: x86_64-unknown-linux-gnu (64-bit)

XML package version 3.98-1.1

Answer 1

Download the file first using RCurl, then you should have no problem:

library(RCurl)
u <- getURL(url)

> xmlTreeParse(u, asTree=TRUE)
$doc
$file
[1] "<buffer>"

$version
[1] "1.0"

$children
$children$metadata
<metadata created="2013-12-17T04:49:41.807Z" xmlns="http://musicbrainz.org/ns/mmd-2.0#" xmlns:ext="http://musicbrainz.org/ns/ext#-2.0">
 <release-list count="1" offset="0">
  <release id="d1e75e7b-fe4a-4cd6-b0d9-8ccf04a62406" score="100">
   <title>A Is for Alpine by Alpine</title>
   <status>Official</status>
   <text-representation>
    <language>eng</language>
    <script>Latn</script>
   </text-representation>
   <artist-credit>
    <name-credit>
     <artist id="d7f0c2fe-00fb-4248-995a-dbfd5a87331a">
      <name>Alpine</name>
      <sort-name>Alpine</sort-name>
     </artist>
    </name-credit>
   </artist-credit>
   <release-group id="7ea67d40-8819-4059-a9be-e1115cdf0ddb" type="Album">
    <primary-type>Album</primary-type>
   </release-group>
   <date>2012-08-10</date>
   <country>AU</country>
   <release-event-list>
    <release-event>
     <date>2012-08-10</date>
     <area id="106e0bec-b638-3b37-b731-f53d507dc00e">
      <name>Australia</name>
      <sort-name>Australia</sort-name>
      <iso-3166-1-code-list>
       <iso-3166-1-code>AU</iso-3166-1-code>
      </iso-3166-1-code-list>
     </area>
    </release-event>
   </release-event-list>
   <label-info-list>
    <label-info>
     <catalog-number>IVY166</catalog-number>
     <label id="96e57a7b-c481-41e5-a0d4-111604210207">
      <name>Ivy League Records</name>
     </label>
    </label-info>
   </label-info-list>
   <medium-list count="1">
    <track-count>12</track-count>
    <medium>
     <format>CD</format>
     <disc-list count="1"/>
     <track-list count="12"/>
    </medium>
   </medium-list>
  </release>
 </release-list>
</metadata>


attr(,"class")
[1] "XMLDocumentContent"

$dtd
$external
NULL

$internal
NULL

attr(,"class")
[1] "DTDList"

attr(,"class")
[1] "XMLDocument"         "XMLAbstractDocument"