From aa0cc332c6fbadfa6f49ab072dd97c5c8d78fdf8 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Tue, 11 Mar 2025 11:01:32 -0500
Subject: [PATCH v2 1/1] Add reverse() for bytea.

This commit introduces a function for reversing the order of the
bytes in binary strings.

NEEDS CATVERSION BUMP

Author: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://postgr.es/m/CAJ7c6TMe0QVRuNssUArbMi0bJJK32%2BzNA3at5m3osrBQ25MHuw%40mail.gmail.com
---
 doc/src/sgml/func.sgml                | 17 +++++++++++++++++
 src/backend/utils/adt/varlena.c       | 21 +++++++++++++++++++++
 src/include/catalog/pg_proc.dat       |  3 +++
 src/test/regress/expected/strings.out | 18 ++++++++++++++++++
 src/test/regress/sql/strings.sql      |  4 ++++
 5 files changed, 63 insertions(+)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 51dd8ad6571..1c3810e1a04 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -4660,6 +4660,23 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>reverse</primary>
+        </indexterm>
+        <function>reverse</function> ( <type>bytea</type> )
+        <returnvalue>bytea</returnvalue>
+       </para>
+       <para>
+        Reverses the order of the bytes in the binary string.
+       </para>
+       <para>
+        <literal>reverse('\xabcd'::bytea)</literal>
+        <returnvalue>\xcdab</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index cdf185ea00b..95631eb2099 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -3398,6 +3398,27 @@ byteaSetBit(PG_FUNCTION_ARGS)
 	PG_RETURN_BYTEA_P(res);
 }
 
+/*
+ * Return reversed bytea
+ */
+Datum
+bytea_reverse(PG_FUNCTION_ARGS)
+{
+	bytea	   *v = PG_GETARG_BYTEA_PP(0);
+	const char *p = VARDATA_ANY(v);
+	int			len = VARSIZE_ANY_EXHDR(v);
+	const char *endp = p + len;
+	bytea	   *result = palloc(len + VARHDRSZ);
+	char	   *dst = (char *) VARDATA(result) + len;
+
+	SET_VARSIZE(result, len + VARHDRSZ);
+
+	while (p < endp)
+		*(--dst) = *p++;
+
+	PG_RETURN_BYTEA_P(result);
+}
+
 
 /* text_name()
  * Converts a text type to a Name type.
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 42e427f8fe8..890822eaf79 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -1518,6 +1518,9 @@
 { oid => '6163', descr => 'number of set bits',
   proname => 'bit_count', prorettype => 'int8', proargtypes => 'bytea',
   prosrc => 'bytea_bit_count' },
+{ oid => '8694', descr => 'reverse bytea',
+  proname => 'reverse', prorettype => 'bytea', proargtypes => 'bytea',
+  prosrc => 'bytea_reverse' },
 
 { oid => '725',
   proname => 'dist_pl', prorettype => 'float8', proargtypes => 'point line',
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index f8cba9f5b24..fbe7d7be71f 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -236,6 +236,24 @@ SELECT E'De\\678dBeEf'::bytea;
 ERROR:  invalid input syntax for type bytea
 LINE 1: SELECT E'De\\678dBeEf'::bytea;
                ^
+SELECT reverse(''::bytea);
+ reverse 
+---------
+ \x
+(1 row)
+
+SELECT reverse('\xaa'::bytea);
+ reverse 
+---------
+ \xaa
+(1 row)
+
+SELECT reverse('\xabcd'::bytea);
+ reverse 
+---------
+ \xcdab
+(1 row)
+
 SET bytea_output TO escape;
 SELECT E'\\xDeAdBeEf'::bytea;
       bytea       
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 4deb0683d57..ed054e6e99c 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -77,6 +77,10 @@ SELECT E'De\123dBeEf'::bytea;
 SELECT E'De\\123dBeEf'::bytea;
 SELECT E'De\\678dBeEf'::bytea;
 
+SELECT reverse(''::bytea);
+SELECT reverse('\xaa'::bytea);
+SELECT reverse('\xabcd'::bytea);
+
 SET bytea_output TO escape;
 SELECT E'\\xDeAdBeEf'::bytea;
 SELECT E'\\x De Ad Be Ef '::bytea;
-- 
2.39.5 (Apple Git-154)