How can I extract the node names for fragmented XML document using Ruby?

Question

I an XML-like document which is pre-processed by a system out of my control. The format of the document is like this:

 <template>
Hello, there <RECALL>first_name</RECALL>.  Thanks for giving me your email.  
<SETPROFILE><NAME>email</NAME><VALUE><star/></VALUE></SETPROFILE>.  I have just sent you something.
</template>

However, I only get as a text string what is between the <template> tags.

I would like to be able to extract without specifying the tags ahead of time when parsing. I can do this with the Crack gem but only if the tags are at the end of the string and there is only one.

With Crack, I can put a string like

string = "<SETPROFILE><NAME>email</NAME><VALUE>[email protected]</VALUE></SETPROFILE>"

and my output from Crack is:

{"SETPROFILE"=>{"NAME"=>"email", "VALUE"=>"[email protected]"}}

Then I can use a case statement for the possible values I care about.

Given that I need to have multiple <tags> in the string and they cannot be at the end of the string, how can I parse out the node names and the values easily, similar to what I do with crack?

These tags also need to be removed. I would like to continue to use the excellent suggestion from @TinMan.

It works perfectly once I know the name of the tag. The number of tags will be finite. I send the tag to the appropriate method once I know it, but it needs to get parsed out easily first.

Output similar to crack would be a great. Parsed keys and associated values — Satchel
– Satchel, Commented Dec 28, 2014 at 22:32

the Tin Man · Accepted Answer · 2014-12-29 18:39:44Z

Using Nokogiri, you can treat the string as a DocumentFragment, then find the embedded nodes:

require 'nokogiri'

doc = Nokogiri::XML::DocumentFragment.parse(<<EOT)
Hello, there <RECALL>first_name</RECALL>.  Thanks for giving me your email.  
<SETPROFILE><NAME>email</NAME><VALUE><star/></VALUE></SETPROFILE>.  I have just sent you something.
EOT

nodes = doc.search('*').each_with_object({}){ |n, h|
  h[n] = n.text
}

nodes # => {#<Nokogiri::XML::Element:0x3ff96083b744 name="RECALL" children=[#<Nokogiri::XML::Text:0x3ff96083a09c "first_name">]>=>"first_name", #<Nokogiri::XML::Element:0x3ff96083b5c8 name="SETPROFILE" children=[#<Nokogiri::XML::Element:0x3ff96083a678 name="NAME" children=[#<Nokogiri::XML::Text:0x3ff960836884 "email">]>, #<Nokogiri::XML::Element:0x3ff96083a650 name="VALUE" children=[#<Nokogiri::XML::Element:0x3ff96083a5c4 name="star">]>]>=>"email", #<Nokogiri::XML::Element:0x3ff96083a678 name="NAME" children=[#<Nokogiri::XML::Text:0x3ff960836884 "email">]>=>"email", #<Nokogiri::XML::Element:0x3ff96083a650 name="VALUE" children=[#<Nokogiri::XML::Element:0x3ff96083a5c4 name="star">]>=>"", #<Nokogiri::XML::Element:0x3ff96083a5c4 name="star">=>""}

Or, more legibly:

nodes = doc.search('*').each_with_object({}){ |n, h|
  h[n.name] = n.text
}

nodes # => {"RECALL"=>"first_name", "SETPROFILE"=>"email", "NAME"=>"email", "VALUE"=>"", "star"=>""}

Getting the content of a particular tag is easy then:

nodes['RECALL'] # => "first_name"

Iterating over all the tags is also easy:

nodes.keys.each do |k| 
  ... 
end

You can even replace a tag and its content with text:

doc.at('RECALL').replace('Fred')
doc.to_xml # => "Hello, there Fred.  Thanks for giving me your email.  \n<SETPROFILE>\n  <NAME>email</NAME>\n  <VALUE>\n    <star/>\n  </VALUE>\n</SETPROFILE>.  I have just sent you something.\n"

How to replace the nested tags is left to you as an exercise.

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