XSLT-1.0 to read a specific substring from a message - xslt

Question

I've below message in a variable .
7c
 {"code":3001,"message":"issued"}
 0
I would like to take the message starting with '{' and ending with '}' using XSLT. I tried using sub-string() and starts-with functions, but without success.
My final out put should be
{"code":3001,"message":"issued"}

Answer 1

In XSLT 2.0 you could use analyze-string with matching-substring inside, to process the captured regex.
Let's move to an example. Start with a source XML given below:
<?xml version="1.0" encoding="UTF-8"?>
<main>
<message>7c {"code":3001,"message":"issued"} 0</message>
</main>
Then we can use such XSLT:
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
<xsl:output method="xml" encoding="UTF-8" indent="yes" />
<xsl:template match="message">
<xsl:copy>
<xsl:analyze-string select="." regex="\{{(.*)\}}">
<xsl:matching-substring>
<xsl:value-of select="regex-group(1)"/>
</xsl:matching-substring>
</xsl:analyze-string>
</xsl:copy>
</xsl:template>
<xsl:template match="#*|node()">
<xsl:copy><xsl:apply-templates select="#*|node()"/></xsl:copy>
</xsl:template>
</xsl:transform>
Note the content of regex attribute.
In XSLT curly braces must be doubled in order to tell them apart from
an attribute value template.
But these curly braces are here literal curly braces, i.e. we are looking
just for { and } chars (they are not here as delimiters of repetition
counts for the preceding regex). For this reason we have to precede
each of them with a backslash.
Between these curly braces we have a capturing group (...).
We refer to the content of the captured group in regex-group(1) below.
If you need, you can put more capturing groups in the regex, to capture
individual parts of the message and then make some use of them.
But if you are really limited to XSLT 1.0 you can:
Start from substring-before to cut off } and everything after.
Then use substring-after to cut off { and everything before.
Or maybe you need the text with surrounding curly braces?
Then use concat to prepend { and append }.

Answer 2

I tried substring-after and before which give me text after '{' and
before '}'
If you're using XSLT 1.0, then do exactly that, and add the missing separators as text - for example:
<xsl:variable name="var">7c {"code":3001,"message":"issued"} 0 </xsl:variable>
<xsl:text>{</xsl:text>
<xsl:value-of select="substring-before(substring-after($var, '{'), '}')"/>
<xsl:text>}</xsl:text>
returns:
{"code":3001,"message":"issued"}
In XSLT 2.0, you could do simply:
<xsl:value-of select="replace($var, '.*(\{.*\}).*', '$1')"/>
to get the same result.