Avoid producing over-length specific_name outputs in information_schema.

information_schema output columns that are declared as being type
sql_identifier are supposed to conform to the implementation's rules
for valid identifiers, in particular the identifier length limit.
Several places potentially violated this limit by concatenating a
function's name and OID.  (The OID is added to ensure name uniqueness
within a schema, since the spec doesn't expect function name overloading.)

Simply truncating the concatenation result to fit in "name" won't do,
since losing part of the OID might wind up giving non-unique results.
Instead, let's truncate the function name as necessary.

The most practical way to do that is to do it in a C function; the
information_schema.sql script doesn't have easy access to the value
of NAMEDATALEN, nor does it have an easy way to truncate on the basis
of resulting byte-length rather than number of characters.

(There are still a couple of places that cast concatenation results to
sql_identifier, but as far as I can see they are guaranteed not to produce
over-length strings, at least with the normal value of NAMEDATALEN.)

Discussion: https://postgr.es/m/23817.1545283477@sss.pgh.pa.us

1 files changed, 35 insertions, 0 deletions

diff --git a/src/backend/utils/adt/name.c b/src/backend/utils/adt/name.c
index 0cf8b9d46b5..eb35188e06f 100644
--- a/src/backend/utils/adt/name.c
+++ b/src/backend/utils/adt/name.c
@@ -364,3 +364,38 @@ current_schemas(PG_FUNCTION_ARGS)
 
 	PG_RETURN_POINTER(array);
 }
+
+/*
+ * SQL-function nameconcatoid(name, oid) returns name
+ *
+ * This is used in the information_schema to produce specific_name columns,
+ * which are supposed to be unique per schema.  We achieve that (in an ugly
+ * way) by appending the object's OID.  The result is the same as
+ *		($1::text || '_' || $2::text)::name
+ * except that, if it would not fit in NAMEDATALEN, we make it do so by
+ * truncating the name input (not the oid).
+ */
+Datum
+nameconcatoid(PG_FUNCTION_ARGS)
+{
+	Name		nam = PG_GETARG_NAME(0);
+	Oid			oid = PG_GETARG_OID(1);
+	Name		result;
+	char		suffix[20];
+	int			suflen;
+	int			namlen;
+
+	suflen = snprintf(suffix, sizeof(suffix), "_%u", oid);
+	namlen = strlen(NameStr(*nam));
+
+	/* Truncate oversize input by truncating name part, not suffix */
+	if (namlen + suflen >= NAMEDATALEN)
+		namlen = pg_mbcliplen(NameStr(*nam), namlen, NAMEDATALEN - 1 - suflen);
+
+	/* We use palloc0 here to ensure result is zero-padded */
+	result = (Name) palloc0(NAMEDATALEN);
+	memcpy(NameStr(*result), NameStr(*nam), namlen);
+	memcpy(NameStr(*result) + namlen, suffix, suflen);
+
+	PG_RETURN_NAME(result);
+}