From ced9fccddc033de98709a6e93dc6530ce68149db Mon Sep 17 00:00:00 2001
From: Jim Jones <jim.jones@uni-muenster.de>
Date: Thu, 2 Feb 2023 21:27:16 +0100
Subject: [PATCH v1] Add pretty-printed XML output option

This small patch introduces a XML pretty print function.
It basically takes advantage of the indentation feature
of xmlDocDumpFormatMemory from libxml2 to format XML strings.
---
 doc/src/sgml/func.sgml            |  34 ++++++++++
 src/backend/utils/adt/xml.c       |  30 +++++++++
 src/include/catalog/pg_proc.dat   |   3 +
 src/test/regress/expected/xml.out | 107 ++++++++++++++++++++++++++++++
 src/test/regress/sql/xml.sql      |  34 ++++++++++
 5 files changed, 208 insertions(+)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index e09e289a43..e8b5e581f0 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -14293,6 +14293,40 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
 ]]></screen>
     </para>
    </sect3>
+   
+     <sect3 id="functions-xml-xmlpretty">
+    <title><literal>xmlpretty</literal></title>
+    
+     <indexterm>
+     <primary>xmlpretty</primary>
+     </indexterm>
+     
+<synopsis>
+<function>xmlpretty</function> ( <type>xml</type> ) <returnvalue>xml</returnvalue>
+</synopsis>
+     
+     <para>
+     Converts the given XML value to pretty-printed, indented text.
+     </para>
+     
+     <para>
+     Example:
+     <screen><![CDATA[
+SELECT xmlpretty('<foo id="x"><bar id="y"><var id="z">42</var></bar></foo>');
+        xmlpretty         
+--------------------------
+ <foo id="x">            
+   <bar id="y">          
+     <var id="z">42</var>
+   </bar>                
+ </foo>                  
+ 
+(1 row)
+
+]]></screen>
+     </para>
+   </sect3>
+   
    </sect2>
 
    <sect2 id="functions-xml-predicates">
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 079bcb1208..6409133137 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -473,6 +473,36 @@ xmlBuffer_to_xmltype(xmlBufferPtr buf)
 }
 #endif
 
+Datum
+xmlpretty(PG_FUNCTION_ARGS)
+{
+#ifdef USE_LIBXML
+
+    xmlDocPtr  doc;
+    xmlChar    *buf = NULL;
+    text       *arg = PG_GETARG_TEXT_PP(0);
+
+    doc = xml_parse(arg, XMLOPTION_DOCUMENT, false, GetDatabaseEncoding(), NULL);
+
+    /**
+    * xmlDocDumpFormatMemory (
+    *   xmlDocPtr doc,  # the XML document.
+    *   xmlChar ** buf, # buffer where the formatted XML document will be stored.
+    *   int *size,      # this could store the size of the created buffer
+    *                     but as we do not need it, we can leave it NULL.
+    *   int format)     # 1 = node indenting.
+    */
+    xmlDocDumpFormatMemory(doc, &buf, NULL, 1);
+
+    xmlFreeDoc(doc);
+    PG_RETURN_XML_P(cstring_to_xmltype((char*)buf));
+
+#else
+    NO_XML_SUPPORT();
+    return 0;
+#endif
+}
+
 
 Datum
 xmlcomment(PG_FUNCTION_ARGS)
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index c0f2a8a77c..3224dc3e76 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -8842,6 +8842,9 @@
 { oid => '3053', descr => 'determine if a string is well formed XML content',
   proname => 'xml_is_well_formed_content', prorettype => 'bool',
   proargtypes => 'text', prosrc => 'xml_is_well_formed_content' },
+  { oid => '4642', descr => 'Indented text from xml',
+  proname => 'xmlpretty', prorettype => 'xml',
+  proargtypes => 'xml', prosrc => 'xmlpretty' },
 
 # json
 { oid => '321', descr => 'I/O',
diff --git a/src/test/regress/expected/xml.out b/src/test/regress/expected/xml.out
index 3c357a9c7e..98a338ad8d 100644
--- a/src/test/regress/expected/xml.out
+++ b/src/test/regress/expected/xml.out
@@ -1599,3 +1599,110 @@ SELECT * FROM XMLTABLE('.' PASSING XMLELEMENT(NAME a) columns a varchar(20) PATH
  <foo/> | &lt;foo/&gt;
 (1 row)
 
+-- XML pretty print: single line XML string
+SELECT xmlpretty('<breakfast_menu id="42"><food type="discounter"><name>Belgian Waffles</name><price>$5.95</price><description>Two of our famous Belgian Waffles with plenty of real maple syrup</description><calories>650</calories></food></breakfast_menu>')::xml;
+                                            xmlpretty                                             
+--------------------------------------------------------------------------------------------------
+ <breakfast_menu id="42">                                                                        +
+   <food type="discounter">                                                                      +
+     <name>Belgian Waffles</name>                                                                +
+     <price>$5.95</price>                                                                        +
+     <description>Two of our famous Belgian Waffles with plenty of real maple syrup</description>+
+     <calories>650</calories>                                                                    +
+   </food>                                                                                       +
+ </breakfast_menu>                                                                               +
+ 
+(1 row)
+
+-- XML pretty print: XML string with space, tabs and newline between nodes
+SELECT xmlpretty('<breakfast_menu id="73"> <food type="organic" class="fancy">    <name>Belgian Waffles</name> <price>$15.95</price>
+                                 <description>Two of our famous Belgian Waffles with plenty of real maple syrup</description>
+<calories>650</calories>       </food>           </breakfast_menu>  ')::xml;
+                                            xmlpretty                                             
+--------------------------------------------------------------------------------------------------
+ <breakfast_menu id="73">                                                                        +
+   <food type="organic" class="fancy">                                                           +
+     <name>Belgian Waffles</name>                                                                +
+     <price>$15.95</price>                                                                       +
+     <description>Two of our famous Belgian Waffles with plenty of real maple syrup</description>+
+     <calories>650</calories>                                                                    +
+   </food>                                                                                       +
+ </breakfast_menu>                                                                               +
+ 
+(1 row)
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using a namespace
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" id="73"> <meal:food type="organic" class="fancy">   <meal:name>Belgian Waffles</meal:name>      <meal:price>$15.95</meal:price>
+                                 <meal:description>Two of our famous Belgian Waffles with plenty of real maple syrup</meal:description>
+<meal:calories>650</meal:calories>     </meal:food></meal:breakfast_menu>')::xml;
+                                                 xmlpretty                                                  
+------------------------------------------------------------------------------------------------------------
+ <meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" id="73">                                      +
+   <meal:food type="organic" class="fancy">                                                                +
+     <meal:name>Belgian Waffles</meal:name>                                                                +
+     <meal:price>$15.95</meal:price>                                                                       +
+     <meal:description>Two of our famous Belgian Waffles with plenty of real maple syrup</meal:description>+
+     <meal:calories>650</meal:calories>                                                                    +
+   </meal:food>                                                                                            +
+ </meal:breakfast_menu>                                                                                    +
+ 
+(1 row)
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using multiple namespaces and a comment
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73"> <meal:food type="organic" class="fancy"> <meal:name>Belgian Waffles</meal:name> <!-- eat this --> <meal:price>$15.95</meal:price>
+                                 <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description>
+<meal:calories>650</meal:calories> </meal:food></meal:breakfast_menu>')::xml;
+                                                  xmlpretty                                                  
+-------------------------------------------------------------------------------------------------------------
+ <meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73">+
+   <meal:food type="organic" class="fancy">                                                                 +
+     <meal:name>Belgian Waffles</meal:name>                                                                 +
+     <!-- eat this -->                                                                                      +
+     <meal:price>$15.95</meal:price>                                                                        +
+     <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description> +
+     <meal:calories>650</meal:calories>                                                                     +
+   </meal:food>                                                                                             +
+ </meal:breakfast_menu>                                                                                     +
+ 
+(1 row)
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using multiple namespaces and CDATA
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73"> <meal:food type="organic" class="fancy"> <meal:name>Belgian Waffles</meal:name> <meal:price>$15.95</meal:price>
+                                 <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description>
+<meal:calories><c><![CDATA[<unknown> &"<>!<a>foo</a>]]></c></meal:calories> </meal:food></meal:breakfast_menu>')::xml;
+                                                  xmlpretty                                                  
+-------------------------------------------------------------------------------------------------------------
+ <meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73">+
+   <meal:food type="organic" class="fancy">                                                                 +
+     <meal:name>Belgian Waffles</meal:name>                                                                 +
+     <meal:price>$15.95</meal:price>                                                                        +
+     <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description> +
+     <meal:calories>                                                                                        +
+       <c><![CDATA[<unknown> &"<>!<a>foo</a>]]></c>                                                         +
+     </meal:calories>                                                                                       +
+   </meal:food>                                                                                             +
+ </meal:breakfast_menu>                                                                                     +
+ 
+(1 row)
+
+-- XML pretty print: invalid XML string (not well balanced)
+SELECT xmlpretty('<foo>')::xml;
+ERROR:  invalid XML content
+LINE 1: SELECT xmlpretty('<foo>')::xml;
+                         ^
+DETAIL:  line 1: chunk is not well balanced
+<foo>
+     ^
+-- XML pretty print: invalid parameter
+SELECT xmlpretty(42)::xml;
+ERROR:  function xmlpretty(integer) does not exist
+LINE 1: SELECT xmlpretty(42)::xml;
+               ^
+HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
+-- XML pretty print: NULL parameter
+SELECT xmlpretty(NULL)::xml;
+ xmlpretty 
+-----------
+ 
+(1 row)
+
diff --git a/src/test/regress/sql/xml.sql b/src/test/regress/sql/xml.sql
index ddff459297..2b40c90966 100644
--- a/src/test/regress/sql/xml.sql
+++ b/src/test/regress/sql/xml.sql
@@ -624,3 +624,37 @@ SELECT * FROM XMLTABLE('*' PASSING '<e>pre<!--c1--><?pi arg?><![CDATA[&ent1]]><n
 \x
 
 SELECT * FROM XMLTABLE('.' PASSING XMLELEMENT(NAME a) columns a varchar(20) PATH '"<foo/>"', b xml PATH '"<foo/>"');
+
+
+-- XML pretty print: single line XML string
+SELECT xmlpretty('<breakfast_menu id="42"><food type="discounter"><name>Belgian Waffles</name><price>$5.95</price><description>Two of our famous Belgian Waffles with plenty of real maple syrup</description><calories>650</calories></food></breakfast_menu>')::xml;
+
+-- XML pretty print: XML string with space, tabs and newline between nodes
+SELECT xmlpretty('<breakfast_menu id="73"> <food type="organic" class="fancy">    <name>Belgian Waffles</name> <price>$15.95</price>
+                                 <description>Two of our famous Belgian Waffles with plenty of real maple syrup</description>
+<calories>650</calories>       </food>           </breakfast_menu>  ')::xml;
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using a namespace
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" id="73"> <meal:food type="organic" class="fancy">   <meal:name>Belgian Waffles</meal:name>      <meal:price>$15.95</meal:price>
+                                 <meal:description>Two of our famous Belgian Waffles with plenty of real maple syrup</meal:description>
+<meal:calories>650</meal:calories>     </meal:food></meal:breakfast_menu>')::xml;
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using multiple namespaces and a comment
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73"> <meal:food type="organic" class="fancy"> <meal:name>Belgian Waffles</meal:name> <!-- eat this --> <meal:price>$15.95</meal:price>
+                                 <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description>
+<meal:calories>650</meal:calories> </meal:food></meal:breakfast_menu>')::xml;
+
+-- XML pretty print: XML string with space, tabs and newline between nodes, using multiple namespaces and CDATA
+SELECT xmlpretty('<meal:breakfast_menu xmlns:meal="http://fancycafe.im/meal/" xmlns:desc="http://fancycafe.mn/meal/" id="73"> <meal:food type="organic" class="fancy"> <meal:name>Belgian Waffles</meal:name> <meal:price>$15.95</meal:price>
+                                 <desc:description>Two of our famous Belgian Waffles with plenty of real maple syrup</desc:description>
+<meal:calories><c><![CDATA[<unknown> &"<>!<a>foo</a>]]></c></meal:calories> </meal:food></meal:breakfast_menu>')::xml;
+
+-- XML pretty print: invalid XML string (not well balanced)
+SELECT xmlpretty('<foo>')::xml;
+
+-- XML pretty print: invalid parameter
+SELECT xmlpretty(42)::xml;
+
+-- XML pretty print: NULL parameter
+SELECT xmlpretty(NULL)::xml;
+
-- 
2.25.1

