Add a new DestReceiver for printing tuples without catalog access.

If you create a DestReciver of type DestRemote and try to use it from
a replication connection that is not bound to a specific daabase, or
any other hypothetical type of backend that is not bound to a specific
database, it will fail because it doesn't have a pg_proc catalog to
look up properties of the types being printed.  In general, that's
an unavoidable problem, but we can hardwire the properties of a few
builtin types in order to support utility commands.  This new
DestReceiver of type DestRemoteSimple does just that.

Patch by me, reviewed by Michael Paquier.

Discussion: http://postgr.es/m/CA+TgmobNo4qz06wHEmy9DszAre3dYx-WNhHSCbU9SAwf+9Ft6g@mail.gmail.com

1 files changed, 110 insertions, 0 deletions

diff --git a/src/backend/access/common/printsimple.c b/src/backend/access/common/printsimple.c
new file mode 100644
index 00000000000..420de65e207
--- /dev/null
+++ b/src/backend/access/common/printsimple.c
@@ -0,0 +1,110 @@
+/*-------------------------------------------------------------------------
+ *
+ * printsimple.c
+ *	  Routines to print out tuples containing only a limited range of
+ *	  builtin types without catalog access.  This is intended for
+ *	  backends that don't have catalog access because they are not bound
+ *	  to a specific database, such as some walsender processes.  It
+ *	  doesn't handle standalone backends or protocol versions other than
+ *	  3.0, because we don't need such handling for current applications.
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/common/printsimple.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/printsimple.h"
+#include "catalog/pg_type.h"
+#include "fmgr.h"
+#include "libpq/pqformat.h"
+
+/*
+ * At startup time, send a RowDescription message.
+ */
+void
+printsimple_startup(DestReceiver *self, int operation, TupleDesc tupdesc)
+{
+	StringInfoData buf;
+	int			i;
+
+	pq_beginmessage(&buf, 'T'); /* RowDescription */
+	pq_sendint(&buf, tupdesc->natts, 2);
+
+	for (i = 0; i < tupdesc->natts; ++i)
+	{
+		Form_pg_attribute attr = tupdesc->attrs[i];
+
+		pq_sendstring(&buf, NameStr(attr->attname));
+		pq_sendint(&buf, 0, 4); /* table oid */
+		pq_sendint(&buf, 0, 2); /* attnum */
+		pq_sendint(&buf, (int) attr->atttypid, 4);
+		pq_sendint(&buf, attr->attlen, 2);
+		pq_sendint(&buf, attr->atttypmod, 4);
+		pq_sendint(&buf, 0, 2); /* format code */
+	}
+
+	pq_endmessage(&buf);
+}
+
+/*
+ * For each tuple, send a DataRow message.
+ */
+bool
+printsimple(TupleTableSlot *slot, DestReceiver *self)
+{
+	TupleDesc	tupdesc = slot->tts_tupleDescriptor;
+	StringInfoData buf;
+	int			i;
+
+	/* Make sure the tuple is fully deconstructed */
+	slot_getallattrs(slot);
+
+	/* Prepare and send message */
+	pq_beginmessage(&buf, 'D');
+	pq_sendint(&buf, tupdesc->natts, 2);
+
+	for (i = 0; i < tupdesc->natts; ++i)
+	{
+		Form_pg_attribute attr = tupdesc->attrs[i];
+		Datum		value;
+
+		if (slot->tts_isnull[i])
+		{
+			pq_sendint(&buf, -1, 4);
+			continue;
+		}
+
+		value = slot->tts_values[i];
+
+		/*
+		 * We can't call the regular type output functions here because we
+		 * might not have catalog access.  Instead, we must hard-wire
+		 * knowledge of the required types.
+		 */
+		switch (attr->atttypid)
+		{
+			case TEXTOID:
+				{
+					text	   *t = DatumGetTextPP(value);
+
+					pq_sendcountedtext(&buf,
+									   VARDATA_ANY(t),
+									   VARSIZE_ANY_EXHDR(t),
+									   false);
+				}
+				break;
+
+			default:
+				elog(ERROR, "unsupported type OID: %u", attr->atttypid);
+		}
+	}
+
+	pq_endmessage(&buf);
+
+	return true;
+}