From 1ef47968fd1852f7a409764db2c4b35f0eb948b6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dagfinn=20Ilmari=20Manns=C3=A5ker?= <ilmari@ilmari.org>
Date: Tue, 28 Oct 2025 16:33:17 +0000
Subject: [PATCH] Allow explicit casting between bytea and UUID

This enables using encode() and decode() to convert UUIDs to and from
alternative formats, such as base64.
---
 src/backend/utils/adt/bytea.c      | 26 ++++++++++++++++++++++++++
 src/include/catalog/pg_cast.dat    |  6 ++++++
 src/include/catalog/pg_proc.dat    |  7 +++++++
 src/test/regress/expected/uuid.out | 15 +++++++++++++++
 src/test/regress/sql/uuid.sql      |  4 ++++
 5 files changed, 58 insertions(+)

diff --git a/src/backend/utils/adt/bytea.c b/src/backend/utils/adt/bytea.c
index 6e7b914c563..e51190d2cb2 100644
--- a/src/backend/utils/adt/bytea.c
+++ b/src/backend/utils/adt/bytea.c
@@ -26,6 +26,7 @@
 #include "utils/fmgrprotos.h"
 #include "utils/memutils.h"
 #include "utils/sortsupport.h"
+#include "utils/uuid.h"
 #include "utils/varlena.h"
 #include "varatt.h"
 
@@ -1112,3 +1113,28 @@ int8_bytea(PG_FUNCTION_ARGS)
 {
 	return int8send(fcinfo);
 }
+
+/* Cast bytea -> uuid */
+Datum
+bytea_uuid(PG_FUNCTION_ARGS)
+{
+	bytea	   *v = PG_GETARG_BYTEA_PP(0);
+	int			len = VARSIZE_ANY_EXHDR(v);
+	pg_uuid_t  *uuid;
+
+	if (len != UUID_LEN)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("invalid uuid length"));
+
+	uuid = (pg_uuid_t *) palloc(UUID_LEN);
+	memcpy(uuid->data, VARDATA_ANY(v), UUID_LEN);
+	PG_RETURN_POINTER(uuid);
+}
+
+/* Cast uuid -> bytea; can just use uuid_send() */
+Datum
+uuid_bytea(PG_FUNCTION_ARGS)
+{
+	return uuid_send(fcinfo);
+}
diff --git a/src/include/catalog/pg_cast.dat b/src/include/catalog/pg_cast.dat
index fbfd669587f..913c55ef869 100644
--- a/src/include/catalog/pg_cast.dat
+++ b/src/include/catalog/pg_cast.dat
@@ -348,6 +348,12 @@
 { castsource => 'bytea', casttarget => 'int8', castfunc => 'int8(bytea)',
   castcontext => 'e', castmethod => 'f' },
 
+# Allow explicit coercions between bytea and uuid type
+{ castsource => 'bytea', casttarget => 'uuid', castfunc => 'uuid(bytea)',
+  castcontext => 'e', castmethod => 'f' },
+{ castsource => 'uuid', casttarget => 'bytea', castfunc => 'bytea(uuid)',
+  castcontext => 'e', castmethod => 'f' },
+
 # Allow explicit coercions between int4 and "char"
 { castsource => 'char', casttarget => 'int4', castfunc => 'int4(char)',
   castcontext => 'e', castmethod => 'f' },
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 9121a382f76..110593eb399 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -1199,6 +1199,13 @@
   proname => 'int8', prorettype => 'int8', proargtypes => 'bytea',
   prosrc => 'bytea_int8' },
 
+{ oid => '9880', descr => 'convert uuid to bytea',
+  proname => 'bytea', prorettype => 'bytea', proargtypes => 'uuid',
+  prosrc => 'uuid_bytea' },
+{ oid => '9881', descr => 'convert bytea to uuid',
+  proname => 'uuid', prorettype => 'uuid', proargtypes => 'bytea',
+  prosrc => 'bytea_uuid' },
+
 { oid => '449', descr => 'hash',
   proname => 'hashint2', prorettype => 'int4', proargtypes => 'int2',
   prosrc => 'hashint2' },
diff --git a/src/test/regress/expected/uuid.out b/src/test/regress/expected/uuid.out
index 95392003b86..44f58454d19 100644
--- a/src/test/regress/expected/uuid.out
+++ b/src/test/regress/expected/uuid.out
@@ -305,5 +305,20 @@ SELECT uuid_extract_timestamp('11111111-1111-1111-1111-111111111111');  -- null
  
 (1 row)
 
+-- casts
+SELECT '11111111-1111-1111-1111-111111111111'::uuid::bytea;
+               bytea                
+------------------------------------
+ \x11111111111111111111111111111111
+(1 row)
+
+SELECT '\xffffffffffffffffffffffffffffffff'::bytea::uuid;
+                 uuid                 
+--------------------------------------
+ ffffffff-ffff-ffff-ffff-ffffffffffff
+(1 row)
+
+SELECT '\x12345678'::bytea::uuid; -- error
+ERROR:  invalid uuid length
 -- clean up
 DROP TABLE guid1, guid2, guid3 CASCADE;
diff --git a/src/test/regress/sql/uuid.sql b/src/test/regress/sql/uuid.sql
index 465153a0341..ef81be93670 100644
--- a/src/test/regress/sql/uuid.sql
+++ b/src/test/regress/sql/uuid.sql
@@ -146,6 +146,10 @@ SELECT uuid_extract_timestamp('017F22E2-79B0-7CC3-98C4-DC0C0C07398F') = 'Tuesday
 SELECT uuid_extract_timestamp(gen_random_uuid());  -- null
 SELECT uuid_extract_timestamp('11111111-1111-1111-1111-111111111111');  -- null
 
+-- casts
+SELECT '11111111-1111-1111-1111-111111111111'::uuid::bytea;
+SELECT '\xffffffffffffffffffffffffffffffff'::bytea::uuid;
+SELECT '\x12345678'::bytea::uuid; -- error
 
 -- clean up
 DROP TABLE guid1, guid2, guid3 CASCADE;
-- 
2.51.1