Handle unexpected query results, especially NULLs, safely in connectby().

connectby() didn't adequately check that the constructed SQL query returns
what it's expected to; in fact, since commit 08c33c426b it wasn't
checking that at all.  This could result in a null-pointer-dereference
crash if the constructed query returns only one column instead of the
expected two.  Less excitingly, it could also result in surprising data
conversion failures if the constructed query returned values that were
not I/O-conversion-compatible with the types specified by the query
calling connectby().

In all branches, insist that the query return at least two columns;
this seems like a minimal sanity check that can't break any reasonable
use-cases.

In HEAD, insist that the constructed query return the types specified by
the outer query, including checking for typmod incompatibility, which the
code never did even before it got broken.  This is to hide the fact that
the implementation does a conversion to text and back; someday we might
want to improve that.

In back branches, leave that alone, since adding a type check in a minor
release is more likely to break things than make people happy.  Type
inconsistencies will continue to work so long as the actual type and
declared type are I/O representation compatible, and otherwise will fail
the same way they used to.

Also, in all branches, be on guard for NULL results from the constructed
query, which formerly would cause null-pointer dereference crashes.
We now print the row with the NULL but don't recurse down from it.

In passing, get rid of the rather pointless idea that
build_tuplestore_recursively() should return the same tuplestore that's
passed to it.

Michael Paquier, adjusted somewhat by me

contrib/tablefunc/expected/tablefunc.out

@@ -377,6 +377,37 @@ SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 4, '~') A
     11 |           10 |     4 | 2~5~9~10~11
 (8 rows)
 
+-- should fail as first two columns must have the same type
+SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 0, '~') AS t(keyid text, parent_keyid int, level int, branch text);
+ERROR:  invalid return type
+DETAIL:  First two columns must be the same type.
+-- should fail as key field datatype should match return datatype
+SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 0, '~') AS t(keyid float8, parent_keyid float8, level int, branch text);
+ERROR:  infinite recursion detected
+-- tests for values using custom queries
+-- query with one column - failed
+SELECT * FROM connectby('connectby_int', '1; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+ERROR:  invalid return type
+DETAIL:  Query must return at least two columns.
+-- query with two columns first value as NULL
+SELECT * FROM connectby('connectby_int', 'NULL::int, 1::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+ keyid | parent_keyid | level 
+-------+--------------+-------
+     2 |              |     0
+       |            1 |     1
+(2 rows)
+
+-- query with two columns second value as NULL
+SELECT * FROM connectby('connectby_int', '1::int, NULL::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+ERROR:  infinite recursion detected
+-- query with two columns, both values as NULL
+SELECT * FROM connectby('connectby_int', 'NULL::int, NULL::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+ keyid | parent_keyid | level 
+-------+--------------+-------
+     2 |              |     0
+       |              |     1
+(2 rows)
+
 -- test for falsely detected recursion
 DROP TABLE connectby_int;
 CREATE TABLE connectby_int(keyid int, parent_keyid int);

contrib/tablefunc/sql/tablefunc.sql

@@ -179,6 +179,22 @@ SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 0, '~') A
 -- infinite recursion failure avoided by depth limit
 SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 4, '~') AS t(keyid int, parent_keyid int, level int, branch text);
 
+-- should fail as first two columns must have the same type
+SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 0, '~') AS t(keyid text, parent_keyid int, level int, branch text);
+
+-- should fail as key field datatype should match return datatype
+SELECT * FROM connectby('connectby_int', 'keyid', 'parent_keyid', '2', 0, '~') AS t(keyid float8, parent_keyid float8, level int, branch text);
+
+-- tests for values using custom queries
+-- query with one column - failed
+SELECT * FROM connectby('connectby_int', '1; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+-- query with two columns first value as NULL
+SELECT * FROM connectby('connectby_int', 'NULL::int, 1::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+-- query with two columns second value as NULL
+SELECT * FROM connectby('connectby_int', '1::int, NULL::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+-- query with two columns, both values as NULL
+SELECT * FROM connectby('connectby_int', 'NULL::int, NULL::int; --', 'parent_keyid', '2', 0) AS t(keyid int, parent_keyid int, level int);
+
 -- test for falsely detected recursion
 DROP TABLE connectby_int;
 CREATE TABLE connectby_int(keyid int, parent_keyid int);

contrib/tablefunc/tablefunc.c

@@ -56,7 +56,7 @@ static Tuplestorestate *get_crosstab_tuplestore(char *sql,
 						bool randomAccess);
 static void validateConnectbyTupleDesc(TupleDesc tupdesc, bool show_branch, bool show_serial);
 static bool compatCrosstabTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
-static bool compatConnectbyTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
+static void compatConnectbyTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
 static void get_normal_pair(float8 *x1, float8 *x2);
 static Tuplestorestate *connectby(char *relname,
 		  char *key_fld,
@@ -70,7 +70,7 @@ static Tuplestorestate *connectby(char *relname,
 		  MemoryContext per_query_ctx,
 		  bool randomAccess,
 		  AttInMetadata *attinmeta);
-static Tuplestorestate *build_tuplestore_recursively(char *key_fld,
+static void build_tuplestore_recursively(char *key_fld,
 							 char *parent_key_fld,
 							 char *relname,
 							 char *orderby_fld,
@@ -1180,7 +1180,7 @@ connectby(char *relname,
 	MemoryContextSwitchTo(oldcontext);
 
 	/* now go get the whole tree */
-	tupstore = build_tuplestore_recursively(key_fld,
+	build_tuplestore_recursively(key_fld,
 								 parent_key_fld,
 								 relname,
 								 orderby_fld,
@@ -1201,7 +1201,7 @@ connectby(char *relname,
 	return tupstore;
 }
 
-static Tuplestorestate *
+static void
 build_tuplestore_recursively(char *key_fld,
 							 char *parent_key_fld,
 							 char *relname,
@@ -1232,7 +1232,7 @@ build_tuplestore_recursively(char *key_fld,
 	HeapTuple	tuple;
 
 	if (max_depth > 0 && level > max_depth)
-		return tupstore;
+		return;
 
 	initStringInfo(&sql);
 
@@ -1318,22 +1318,11 @@ build_tuplestore_recursively(char *key_fld,
 		StringInfoData chk_branchstr;
 		StringInfoData chk_current_key;
 
-		/* First time through, do a little more setup */
-		if (level == 0)
-		{
 		/*
-			 * Check that return tupdesc is compatible with the one we got
+		 * Check that return tupdesc is compatible with the one we got from
-			 * from the query, but only at level 0 -- no need to check more
+		 * the query.
-			 * than once
 		 */
-
+		compatConnectbyTupleDescs(tupdesc, spi_tupdesc);
-			if (!compatConnectbyTupleDescs(tupdesc, spi_tupdesc))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("invalid return type"),
-						 errdetail("Return and SQL tuple descriptions are " \
-								   "incompatible.")));
-		}
 
 		initStringInfo(&branchstr);
 		initStringInfo(&chk_branchstr);
@@ -1348,24 +1337,31 @@ build_tuplestore_recursively(char *key_fld,
 			/* get the next sql result tuple */
 			spi_tuple = tuptable->vals[i];
 
-			/* get the current key and parent */
+			/* get the current key (might be NULL) */
 			current_key = SPI_getvalue(spi_tuple, spi_tupdesc, 1);
-			appendStringInfo(&chk_current_key, "%s%s%s", branch_delim, current_key, branch_delim);
+
-			current_key_parent = pstrdup(SPI_getvalue(spi_tuple, spi_tupdesc, 2));
+			/* get the parent key (might be NULL) */
+			current_key_parent = SPI_getvalue(spi_tuple, spi_tupdesc, 2);
 
 			/* get the current level */
 			sprintf(current_level, "%d", level);
 
 			/* check to see if this key is also an ancestor */
+			if (current_key)
+			{
+				appendStringInfo(&chk_current_key, "%s%s%s",
+								 branch_delim, current_key, branch_delim);
 				if (strstr(chk_branchstr.data, chk_current_key.data))
 					elog(ERROR, "infinite recursion detected");
+			}
 
 			/* OK, extend the branch */
+			if (current_key)
 				appendStringInfo(&branchstr, "%s%s", branch_delim, current_key);
 			current_branch = branchstr.data;
 
 			/* build a tuple */
-			values[0] = pstrdup(current_key);
+			values[0] = current_key;
 			values[1] = current_key_parent;
 			values[2] = current_level;
 			if (show_branch)
@@ -1381,21 +1377,19 @@ build_tuplestore_recursively(char *key_fld,
 
 			tuple = BuildTupleFromCStrings(attinmeta, values);
 
-			xpfree(current_key);
-			xpfree(current_key_parent);
-
 			/* store the tuple for later use */
 			tuplestore_puttuple(tupstore, tuple);
 
 			heap_freetuple(tuple);
 
-			/* recurse using current_key_parent as the new start_with */
+			/* recurse using current_key as the new start_with */
-			tupstore = build_tuplestore_recursively(key_fld,
+			if (current_key)
+				build_tuplestore_recursively(key_fld,
 											 parent_key_fld,
 											 relname,
 											 orderby_fld,
 											 branch_delim,
-													values[0],
+											 current_key,
 											 current_branch,
 											 level + 1,
 											 serial,
@@ -1406,6 +1400,9 @@ build_tuplestore_recursively(char *key_fld,
 											 attinmeta,
 											 tupstore);
 
+			xpfree(current_key);
+			xpfree(current_key_parent);
+
 			/* reset branch for next pass */
 			resetStringInfo(&branchstr);
 			resetStringInfo(&chk_branchstr);
@@ -1416,8 +1413,6 @@ build_tuplestore_recursively(char *key_fld,
 		xpfree(chk_branchstr.data);
 		xpfree(chk_current_key.data);
 	}
-
-	return tupstore;
 }
 
 /*
@@ -1490,34 +1485,25 @@ validateConnectbyTupleDesc(TupleDesc tupdesc, bool show_branch, bool show_serial
 /*
  * Check if spi sql tupdesc and return tupdesc are compatible
  */
-static bool
+static void
 compatConnectbyTupleDescs(TupleDesc ret_tupdesc, TupleDesc sql_tupdesc)
 {
-	Oid			ret_atttypid;
+	/*
-	Oid			sql_atttypid;
+	 * Result must have at least 2 columns.
-
+	 */
-	/* check the key_fld types match */
+	if (sql_tupdesc->natts < 2)
-	ret_atttypid = ret_tupdesc->attrs[0]->atttypid;
-	sql_atttypid = sql_tupdesc->attrs[0]->atttypid;
-	if (ret_atttypid != sql_atttypid)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("invalid return type"),
-				 errdetail("SQL key field datatype does " \
+				 errdetail("Query must return at least two columns.")));
-						   "not match return key field datatype.")));
 
-	/* check the parent_key_fld types match */
+	/*
-	ret_atttypid = ret_tupdesc->attrs[1]->atttypid;
+	 * We have failed to check datatype match since 2003, so we don't do that
-	sql_atttypid = sql_tupdesc->attrs[1]->atttypid;
+	 * here.  The call will work as long as the datatypes are I/O
-	if (ret_atttypid != sql_atttypid)
+	 * representation compatible.
-		ereport(ERROR,
+	 */
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("invalid return type"),
-				 errdetail("SQL parent key field datatype does " \
-						   "not match return parent key field datatype.")));
 
 	/* OK, the two tupdescs are compatible for our purposes */
-	return true;
 }
 
 /*