Fix transform_cypher_param to pass agtype_access_operator a VARIADIC array

regress/expected/cypher_create.out

@@ -467,6 +467,46 @@ EXECUTE p_2('{"var_name": "Hello Prepared Statements 2"}');
  {"id": 2533274790395908, "label": "new_vertex", "properties": {"key": "Hello Prepared Statements 2"}}::vertex
 (1 row)
 
+-- prepared statement with scalar parameters used in MATCH and CREATE EDGE.
+-- Regression test: transform_cypher_param() previously called the VARIADIC
+-- agtype_access_operator without building the agtype[] ArrayExpr argument
+-- and without setting funcvariadic = true. Under the extended query
+-- protocol this caused agtype_access_operator to read past its argument
+-- at execution time, corrupting error messages with random bytes and
+-- producing client-side UnicodeDecodeError / invalid-start-byte errors.
+PREPARE p_create_edge(agtype) AS
+SELECT * FROM cypher('cypher_create', $$
+    MATCH (source:v {id: $src_id}), (target:v {id: $tgt_id})
+    CREATE (source)-[r:e {id: $edge_id}]->(target)
+    RETURN r
+$$, $1) AS (r agtype);
+-- seed vertices to match against
+SELECT * FROM cypher('cypher_create', $$
+    CREATE (:v {id: 'a'}), (:v {id: 'b'})
+$$) AS (a agtype);
+ a 
+---
+(0 rows)
+
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge1"}');
+                                                                  r                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------
+ {"id": 1125899906842635, "label": "e", "end_id": 844424930131990, "start_id": 844424930131989, "properties": {"id": "edge1"}}::edge
+(1 row)
+
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge2"}');
+                                                                  r                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------
+ {"id": 1125899906842636, "label": "e", "end_id": 844424930131990, "start_id": 844424930131989, "properties": {"id": "edge2"}}::edge
+(1 row)
+
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge3"}');
+                                                                  r                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------
+ {"id": 1125899906842637, "label": "e", "end_id": 844424930131990, "start_id": 844424930131989, "properties": {"id": "edge3"}}::edge
+(1 row)
+
+DEALLOCATE p_create_edge;
 -- pl/pgsql
 CREATE FUNCTION create_test()
 RETURNS TABLE(vertex agtype)

regress/sql/cypher_create.sql

@@ -194,6 +194,31 @@ PREPARE p_2 AS SELECT * FROM cypher('cypher_create', $$CREATE (v:new_vertex {key
 EXECUTE p_2('{"var_name": "Hello Prepared Statements"}');
 EXECUTE p_2('{"var_name": "Hello Prepared Statements 2"}');
 
+-- prepared statement with scalar parameters used in MATCH and CREATE EDGE.
+-- Regression test: transform_cypher_param() previously called the VARIADIC
+-- agtype_access_operator without building the agtype[] ArrayExpr argument
+-- and without setting funcvariadic = true. Under the extended query
+-- protocol this caused agtype_access_operator to read past its argument
+-- at execution time, corrupting error messages with random bytes and
+-- producing client-side UnicodeDecodeError / invalid-start-byte errors.
+PREPARE p_create_edge(agtype) AS
+SELECT * FROM cypher('cypher_create', $$
+    MATCH (source:v {id: $src_id}), (target:v {id: $tgt_id})
+    CREATE (source)-[r:e {id: $edge_id}]->(target)
+    RETURN r
+$$, $1) AS (r agtype);
+
+-- seed vertices to match against
+SELECT * FROM cypher('cypher_create', $$
+    CREATE (:v {id: 'a'}), (:v {id: 'b'})
+$$) AS (a agtype);
+
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge1"}');
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge2"}');
+EXECUTE p_create_edge('{"src_id": "a", "tgt_id": "b", "edge_id": "edge3"}');
+
+DEALLOCATE p_create_edge;
+
 -- pl/pgsql
 CREATE FUNCTION create_test()
 RETURNS TABLE(vertex agtype)

src/backend/parser/cypher_expr.c

@@ -848,6 +848,7 @@ static Node *transform_cypher_param(cypher_parsestate *cpstate,
                                     cypher_param *cp)
 {
     ParseState *pstate = (ParseState *)cpstate;
+    ArrayExpr  *newa;
     Const *const_str;
     FuncExpr *func_expr;
     Oid func_access_oid;
@@ -867,15 +868,42 @@ static Node *transform_cypher_param(cypher_parsestate *cpstate,
     func_access_oid = get_ag_func_oid("agtype_access_operator", 1,
                                       AGTYPEARRAYOID);
 
+    /*
+     * agtype_access_operator is declared VARIADIC agtype[] and expects a
+     * single agtype[] ArrayExpr with funcvariadic = true. Every other call
+     * site in this file (see transform_cypher_map_projection,
+     * transform_cypher_indirection) assembles its arguments via
+     * make_agtype_array_expr() and sets funcvariadic; only this function was
+     * passing the Param and the key Const as separate list elements directly.
+     *
+     * With the Simple Query protocol PostgreSQL implicitly forms the variadic
+     * array from separate arguments at execution time, masking the bug. But
+     * under the Extended Query protocol (prepared statements /
+     * Parse-Bind-Execute) the executor does not perform that implicit
+     * assembly, so agtype_access_operator read past its single agtype
+     * argument treating adjacent memory as additional array elements. The
+     * resulting out-of-bounds read surfaced as corrupted relation names in
+     * error responses (random bytes mixed with fragments of property values
+     * such as "November", "customer", "communication"; control bytes such as
+     * 0x01), which client drivers then failed to UTF-8 decode:
+     *
+     *     UnicodeDecodeError: 'utf-8' ... invalid start byte
+     *
+     * The fix matches every other call site: pack the arguments into an
+     * agtype[] ArrayExpr and set funcvariadic = true.
+     */
     args = lappend(args, copyObject(cpstate->params));
 
     const_str = makeConst(AGTYPEOID, -1, InvalidOid, -1,
                           string_to_agtype(cp->name), false, false);
 
     args = lappend(args, const_str);
 
-    func_expr = makeFuncExpr(func_access_oid, AGTYPEOID, args, InvalidOid,
-                             InvalidOid, COERCE_EXPLICIT_CALL);
+    newa = make_agtype_array_expr(args);
+
+    func_expr = makeFuncExpr(func_access_oid, AGTYPEOID, list_make1(newa),
+                             InvalidOid, InvalidOid, COERCE_EXPLICIT_CALL);
+    func_expr->funcvariadic = true;
     func_expr->location = cp->location;
 
     return (Node *)func_expr;