How to decode XML entities?

Question

To encode a string to XML, the xmerl_lib:export_text function does the job, but which function does the opposite job, i.e. converts < to >?

I want to convert a complete string like:

<foo="bar">

To:

<foo="bar">

Answer 1

I never was able to find a good library for this, so I've created my own decode function.

decode(">" ++ Rest) ->
 ">" ++ decode(Rest);
decode("<" ++ Rest) ->
 "<" ++ decode(Rest);
decode("&quot;" ++ Rest) ->
 "\"" ++ decode(Rest);
decode([]) ->
 [].

According to wikipedia, there are only five character references for XML, so you should be ok with supporting these five:

& → & (ampersand, U+0026)
&lt; → < (less-than sign, U+003C)
&gt; → > (greater-than sign, U+003E)
&quot; → " (quotation mark, U+0022)
&apos; → ' (apostrophe, U+0027)

Answer 2

The exml package has support for this:

https://github.com/paulgray/exml/blob/master/src/exml.erl#L54

In general, consider exml over xmerl, but be aware it is a NIF-based parser.