1 files changed, 145 insertions, 0 deletions
diff --git a/src/backend/utils/adt/expandeddatum.c b/src/backend/utils/adt/expandeddatum.c
new file mode 100644
index 0000000..cb0adfa
--- /dev/null
+++ b/src/backend/utils/adt/expandeddatum.c
@@ -0,0 +1,145 @@
+/*-------------------------------------------------------------------------
+ *
+ * expandeddatum.c
+ *	  Support functions for "expanded" value representations.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/adt/expandeddatum.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "utils/expandeddatum.h"
+#include "utils/memutils.h"
+
+/*
+ * DatumGetEOHP
+ *
+ * Given a Datum that is an expanded-object reference, extract the pointer.
+ *
+ * This is a bit tedious since the pointer may not be properly aligned;
+ * compare VARATT_EXTERNAL_GET_POINTER().
+ */
+ExpandedObjectHeader *
+DatumGetEOHP(Datum d)
+{
+	varattrib_1b_e *datum = (varattrib_1b_e *) DatumGetPointer(d);
+	varatt_expanded ptr;
+
+	Assert(VARATT_IS_EXTERNAL_EXPANDED(datum));
+	memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
+	Assert(VARATT_IS_EXPANDED_HEADER(ptr.eohptr));
+	return ptr.eohptr;
+}
+
+/*
+ * EOH_init_header
+ *
+ * Initialize the common header of an expanded object.
+ *
+ * The main thing this encapsulates is initializing the TOAST pointers.
+ */
+void
+EOH_init_header(ExpandedObjectHeader *eohptr,
+				const ExpandedObjectMethods *methods,
+				MemoryContext obj_context)
+{
+	varatt_expanded ptr;
+
+	eohptr->vl_len_ = EOH_HEADER_MAGIC;
+	eohptr->eoh_methods = methods;
+	eohptr->eoh_context = obj_context;
+
+	ptr.eohptr = eohptr;
+
+	SET_VARTAG_EXTERNAL(eohptr->eoh_rw_ptr, VARTAG_EXPANDED_RW);
+	memcpy(VARDATA_EXTERNAL(eohptr->eoh_rw_ptr), &ptr, sizeof(ptr));
+
+	SET_VARTAG_EXTERNAL(eohptr->eoh_ro_ptr, VARTAG_EXPANDED_RO);
+	memcpy(VARDATA_EXTERNAL(eohptr->eoh_ro_ptr), &ptr, sizeof(ptr));
+}
+
+/*
+ * EOH_get_flat_size
+ * EOH_flatten_into
+ *
+ * Convenience functions for invoking the "methods" of an expanded object.
+ */
+
+Size
+EOH_get_flat_size(ExpandedObjectHeader *eohptr)
+{
+	return eohptr->eoh_methods->get_flat_size(eohptr);
+}
+
+void
+EOH_flatten_into(ExpandedObjectHeader *eohptr,
+				 void *result, Size allocated_size)
+{
+	eohptr->eoh_methods->flatten_into(eohptr, result, allocated_size);
+}
+
+/*
+ * If the Datum represents a R/W expanded object, change it to R/O.
+ * Otherwise return the original Datum.
+ *
+ * Caller must ensure that the datum is a non-null varlena value.  Typically
+ * this is invoked via MakeExpandedObjectReadOnly(), which checks that.
+ */
+Datum
+MakeExpandedObjectReadOnlyInternal(Datum d)
+{
+	ExpandedObjectHeader *eohptr;
+
+	/* Nothing to do if not a read-write expanded-object pointer */
+	if (!VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)))
+		return d;
+
+	/* Now safe to extract the object pointer */
+	eohptr = DatumGetEOHP(d);
+
+	/* Return the built-in read-only pointer instead of given pointer */
+	return EOHPGetRODatum(eohptr);
+}
+
+/*
+ * Transfer ownership of an expanded object to a new parent memory context.
+ * The object must be referenced by a R/W pointer, and what we return is
+ * always its "standard" R/W pointer, which is certain to have the same
+ * lifespan as the object itself.  (The passed-in pointer might not, and
+ * in any case wouldn't provide a unique identifier if it's not that one.)
+ */
+Datum
+TransferExpandedObject(Datum d, MemoryContext new_parent)
+{
+	ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
+
+	/* Assert caller gave a R/W pointer */
+	Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
+
+	/* Transfer ownership */
+	MemoryContextSetParent(eohptr->eoh_context, new_parent);
+
+	/* Return the object's standard read-write pointer */
+	return EOHPGetRWDatum(eohptr);
+}
+
+/*
+ * Delete an expanded object (must be referenced by a R/W pointer).
+ */
+void
+DeleteExpandedObject(Datum d)
+{
+	ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
+
+	/* Assert caller gave a R/W pointer */
+	Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
+
+	/* Kill it */
+	MemoryContextDelete(eohptr->eoh_context);
+}