Function send_subtag

src/backend/executor/nodeModifyTable.c:3869–3902

* send_subtag * Send the data of subtag, the format is: * subtag + length + data * while length is the length of data followed. */

 * while length is the length of data followed.
 */
static void
send_subtag(StringInfoData *buf, ExtendProtocolSubTag subtag, List *relids)
{
	bytea	*res;
	int 	rlen;
	char	*ptr;
	int		rcount;
	Oid		relid;
	ListCell	*lc;

	pq_sendint32(buf, subtag); /* subtag */

	rcount = list_length(relids);
	rlen = sizeof(int)/* count of relids */ + sizeof(Oid) * rcount;

	pq_sendint32(buf, rlen); /* length */

	res = palloc(rlen + VARHDRSZ);
	ptr = VARDATA(res);

	memcpy(ptr, &rcount, sizeof(int));
	ptr += sizeof(int);

	foreach(lc, relids)
	{
		relid = lfirst_oid(lc);
		memcpy(ptr, &relid, sizeof(Oid));
		ptr += sizeof(Oid);
	}

	SET_VARSIZE(res, rlen + VARHDRSZ);

	pq_sendbytes(buf, VARDATA(res),	VARSIZE(res) - VARHDRSZ);
}

/*
 * notify_modified_relations_local