Add pg_encoding_set_invalid()

There are cases where we cannot / do not want to error out for invalidly
encoded input. In such cases it can be useful to replace e.g. an incomplete
multi-byte characters with bytes that will trigger an error when getting
validated as part of a larger string.

Unfortunately, until now, for some encoding no such sequence existed. For
those encodings this commit removes one previously accepted input combination
- we consider that to be ok, as the chosen bytes are outside of the valid
ranges for the encodings, we just previously failed to detect that.

As we cannot add a new field to pg_wchar_table without breaking ABI, this is
implemented "in-line" in the newly added function.

Author: Noah Misch <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Backpatch-through: 13
Security: CVE-2025-1094

1 files changed, 1 insertions, 0 deletions

diff --git a/src/include/mb/pg_wchar.h b/src/include/mb/pg_wchar.h
index e50c45c018a..ff7983ee90a 100644
--- a/src/include/mb/pg_wchar.h
+++ b/src/include/mb/pg_wchar.h
@@ -662,6 +662,7 @@ extern int	pg_valid_server_encoding_id(int encoding);
  * (in addition to the ones just above).  The constant tables declared
  * earlier in this file are also available from libpgcommon.
  */
+extern void pg_encoding_set_invalid(int encoding, char *dst);
 extern int	pg_encoding_mblen(int encoding, const char *mbstr);
 extern int	pg_encoding_mblen_bounded(int encoding, const char *mbstr);
 extern int	pg_encoding_dsplen(int encoding, const char *mbstr);