1 files changed, 143 insertions, 0 deletions
diff --git a/src/backend/nodes/extensible.c b/src/backend/nodes/extensible.c
new file mode 100644
index 0000000..1489df0
--- /dev/null
+++ b/src/backend/nodes/extensible.c
@@ -0,0 +1,143 @@
+/*-------------------------------------------------------------------------
+ *
+ * extensible.c
+ *	  Support for extensible node types
+ *
+ * Loadable modules can define what are in effect new types of nodes using
+ * the routines in this file.  All such nodes are flagged T_ExtensibleNode,
+ * with the extnodename field distinguishing the specific type.  Use
+ * RegisterExtensibleNodeMethods to register a new type of extensible node,
+ * and GetExtensibleNodeMethods to get information about a previously
+ * registered type of extensible node.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/nodes/extensible.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "nodes/extensible.h"
+#include "utils/hsearch.h"
+
+static HTAB *extensible_node_methods = NULL;
+static HTAB *custom_scan_methods = NULL;
+
+typedef struct
+{
+	char		extnodename[EXTNODENAME_MAX_LEN];
+	const void *extnodemethods;
+} ExtensibleNodeEntry;
+
+/*
+ * An internal function to register a new callback structure
+ */
+static void
+RegisterExtensibleNodeEntry(HTAB **p_htable, const char *htable_label,
+							const char *extnodename,
+							const void *extnodemethods)
+{
+	ExtensibleNodeEntry *entry;
+	bool		found;
+
+	if (*p_htable == NULL)
+	{
+		HASHCTL		ctl;
+
+		ctl.keysize = EXTNODENAME_MAX_LEN;
+		ctl.entrysize = sizeof(ExtensibleNodeEntry);
+
+		*p_htable = hash_create(htable_label, 100, &ctl,
+								HASH_ELEM | HASH_STRINGS);
+	}
+
+	if (strlen(extnodename) >= EXTNODENAME_MAX_LEN)
+		elog(ERROR, "extensible node name is too long");
+
+	entry = (ExtensibleNodeEntry *) hash_search(*p_htable,
+												extnodename,
+												HASH_ENTER, &found);
+	if (found)
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("extensible node type \"%s\" already exists",
+						extnodename)));
+
+	entry->extnodemethods = extnodemethods;
+}
+
+/*
+ * Register a new type of extensible node.
+ */
+void
+RegisterExtensibleNodeMethods(const ExtensibleNodeMethods *methods)
+{
+	RegisterExtensibleNodeEntry(&extensible_node_methods,
+								"Extensible Node Methods",
+								methods->extnodename,
+								methods);
+}
+
+/*
+ * Register a new type of custom scan node
+ */
+void
+RegisterCustomScanMethods(const CustomScanMethods *methods)
+{
+	RegisterExtensibleNodeEntry(&custom_scan_methods,
+								"Custom Scan Methods",
+								methods->CustomName,
+								methods);
+}
+
+/*
+ * An internal routine to get an ExtensibleNodeEntry by the given identifier
+ */
+static const void *
+GetExtensibleNodeEntry(HTAB *htable, const char *extnodename, bool missing_ok)
+{
+	ExtensibleNodeEntry *entry = NULL;
+
+	if (htable != NULL)
+		entry = (ExtensibleNodeEntry *) hash_search(htable,
+													extnodename,
+													HASH_FIND, NULL);
+	if (!entry)
+	{
+		if (missing_ok)
+			return NULL;
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("ExtensibleNodeMethods \"%s\" was not registered",
+						extnodename)));
+	}
+
+	return entry->extnodemethods;
+}
+
+/*
+ * Get the methods for a given type of extensible node.
+ */
+const ExtensibleNodeMethods *
+GetExtensibleNodeMethods(const char *extnodename, bool missing_ok)
+{
+	return (const ExtensibleNodeMethods *)
+		GetExtensibleNodeEntry(extensible_node_methods,
+							   extnodename,
+							   missing_ok);
+}
+
+/*
+ * Get the methods for a given name of CustomScanMethods
+ */
+const CustomScanMethods *
+GetCustomScanMethods(const char *CustomName, bool missing_ok)
+{
+	return (const CustomScanMethods *)
+		GetExtensibleNodeEntry(custom_scan_methods,
+							   CustomName,
+							   missing_ok);
+}