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* [PATCH v2] attempt multibyte-aware truncation of database names
@ 2024-11-20 22:30 Nathan Bossart <nathan@postgresql.org>
0 siblings, 0 replies; 1+ messages in thread
From: Nathan Bossart @ 2024-11-20 22:30 UTC (permalink / raw)
---
src/backend/utils/init/postinit.c | 76 +++++++++++++++++++++++++++++--
1 file changed, 73 insertions(+), 3 deletions(-)
100.0% src/backend/utils/init/
inline patch 1: src/backend/utils/init/postinit.c (+73/-3 lines) download inline-1.patch
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 5b657a3f13..a594c0d4f3 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -1003,14 +1003,84 @@ InitPostgres(const char *in_dbname, Oid dboid,
{
HeapTuple tuple;
Form_pg_database dbform;
+ char trunc_dbname[NAMEDATALEN];
+
+ /* truncate to NAMEDATALEN-1 bytes first */
+ strncpy(trunc_dbname, in_dbname, NAMEDATALEN - 1);
+ trunc_dbname[NAMEDATALEN - 1] = '\0';
+
+ tuple = GetDatabaseTuple(trunc_dbname);
+ if (HeapTupleIsValid(tuple))
+ strcpy(dbname, trunc_dbname);
+
+ /*
+ * If the original name is too long and we see two consecutive bytes
+ * with their high bits set at the truncation point, we might have
+ * truncated in the middle of a multibyte character. In multibyte
+ * encodings, every byte of a multibyte character has its high bit
+ * set. So if IS_HIGHBIT_SET is true for both NAMEDATALEN-1 and
+ * NAMEDATALEN-2, we know we're in the middle of a multibyte
+ * character. We need to try truncating one more byte back to find the
+ * start of the next character.
+ */
+ if (strlen(in_dbname) >= NAMEDATALEN &&
+ IS_HIGHBIT_SET(in_dbname[NAMEDATALEN - 1]) &&
+ IS_HIGHBIT_SET(in_dbname[NAMEDATALEN - 2]))
+ {
+ /*
+ * Try progressively shorter truncations to find a character
+ * boundary. We check at most MAX_MULTIBYTE_CHAR_LEN-1 bytes back.
+ */
+ for (int i = 1; i < MAX_MULTIBYTE_CHAR_LEN - 1; i++)
+ {
+ HeapTuple tmp;
+
+ /* truncate one more byte back */
+ trunc_dbname[NAMEDATALEN - 1 - i] = '\0';
+ tmp = GetDatabaseTuple(trunc_dbname);
+
+ /*
+ * If we already had a match then the name is ambiguous and we
+ * must fail.
+ */
+ if (HeapTupleIsValid(tmp))
+ {
+ if (HeapTupleIsValid(tuple))
+ ereport(FATAL,
+ (errmsg("ambiguous database name")));
+ tuple = tmp;
+ strcpy(dbname, trunc_dbname);
+ }
+
+ /*
+ * If we've hit a byte with high bit clear (an ASCII byte), we
+ * know we can't be in the middle of a multibyte character,
+ * because all bytes of a multibyte character must have their
+ * high bits set. Any following byte must therefore be the
+ * start of a new character, so we can stop looking for
+ * earlier truncation points.
+ */
+ 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 +1137,12 @@ 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,
--
2.34.1
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2024-11-20 22:30 [PATCH v2] attempt multibyte-aware truncation of database names Nathan Bossart <nathan@postgresql.org>
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