From aae0f061f2b417df36630a151f2be041f4aab81e Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 20 Nov 2024 16:30:11 -0600
Subject: [PATCH v1 1/1] attempt multibyte-aware truncation of database names

---
 src/backend/utils/init/postinit.c | 46 +++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 5b657a3f13..c64e8ac849 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -1003,14 +1003,54 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	{
 		HeapTuple	tuple;
 		Form_pg_database dbform;
+		char		trunc_dbname[NAMEDATALEN];
+
+		strncpy(trunc_dbname, in_dbname, NAMEDATALEN - 1);
+		trunc_dbname[NAMEDATALEN - 1] = '\0';
+
+		tuple = GetDatabaseTuple(trunc_dbname);
+		if (HeapTupleIsValid(tuple))
+			strcpy(dbname, trunc_dbname);
+
+		if (strlen(in_dbname) >= NAMEDATALEN &&
+			IS_HIGHBIT_SET(in_dbname[NAMEDATALEN - 1]) &&
+			IS_HIGHBIT_SET(in_dbname[NAMEDATALEN - 2]))
+		{
+			for (int i = 1; i < MAX_MULTIBYTE_CHAR_LEN - 1; i++)
+			{
+				HeapTuple	tmp;
+
+				trunc_dbname[NAMEDATALEN - 1 - i] = '\0';
+				tmp = GetDatabaseTuple(trunc_dbname);
+				if (HeapTupleIsValid(tmp))
+				{
+					if (HeapTupleIsValid(tuple))
+						ereport(FATAL,
+								(errmsg("ambiguous database name")));
+					tuple = tmp;
+					strcpy(dbname, trunc_dbname);
+				}
+
+				if (!IS_HIGHBIT_SET(dbname[NAMEDATALEN - 2 - i]))
+					break;
+			}
+		}
 
-		tuple = GetDatabaseTuple(in_dbname);
 		if (!HeapTupleIsValid(tuple))
 			ereport(FATAL,
 					(errcode(ERRCODE_UNDEFINED_DATABASE),
 					 errmsg("database \"%s\" does not exist", in_dbname)));
 		dbform = (Form_pg_database) GETSTRUCT(tuple);
 		dboid = dbform->oid;
+
+		if (MyProcPort && MyProcPort->database_name &&
+			strcmp(MyProcPort->database_name, dbname) != 0)
+		{
+			pfree(MyProcPort->database_name);
+			MyProcPort->database_name = pstrdup(dbname);
+
+			/* XXX: should we fix process title? */
+		}
 	}
 	else if (!OidIsValid(dboid))
 	{
@@ -1067,12 +1107,12 @@ InitPostgres(const char *in_dbname, Oid dboid,
 			datform = (Form_pg_database) GETSTRUCT(tuple);
 
 		if (!HeapTupleIsValid(tuple) ||
-			(in_dbname && namestrcmp(&datform->datname, in_dbname)))
+			(in_dbname && namestrcmp(&datform->datname, dbname)))
 		{
 			if (in_dbname)
 				ereport(FATAL,
 						(errcode(ERRCODE_UNDEFINED_DATABASE),
-						 errmsg("database \"%s\" does not exist", in_dbname),
+						 errmsg("database \"%s\" does not exist", dbname),
 						 errdetail("It seems to have just been dropped or renamed.")));
 			else
 				ereport(FATAL,
-- 
2.39.5 (Apple Git-154)