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+/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
+ *
+ * librsync -- dynamic caching and delta update in HTTP
+ * $Id$
+ * 
+ * Copyright (C) 2000, 2001 by Martin Pool <mbp@samba.org>
+ * 
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+                     /*
+                      * Programming languages should be designed not
+                      * by piling feature on top of feature, but by
+                      * removing the weaknesses and restrictions that
+                      * make additional features appear necessary.
+                      *    -- Revised^5 Report on Scheme
+                      */
+
+
+/*
+ * OK, so I'll admit IO here is a little complex.  The most important
+ * player here is the stream, which is an object for managing filter
+ * operations.  It has both input and output sides, both of which is
+ * just a (pointer,len) pair into a buffer provided by the client.
+ * The code controlling the stream handles however much data it wants,
+ * and the client provides or accepts however much is convenient.
+ *
+ * At the same time as being friendly to the client, we also try to be
+ * very friendly to the internal code.  It wants to be able to ask for
+ * arbitrary amounts of input or output and get it without having to
+ * keep track of partial completion.  So there are functions which
+ * either complete, or queue whatever was not sent and return
+ * RS_BLOCKED.
+ *
+ * The output buffer is a little more clever than simply a data
+ * buffer.  Instead it knows that we can send either literal data, or
+ * data copied through from the input of the stream.
+ *
+ * In buf.c you will find functions that then map buffers onto stdio
+ * files.
+ *
+ * So on return from an encoding function, either the input or the
+ * output or possibly both will have no more bytes available.
+ */
+
+/*
+ * Manage librsync streams of IO.  See scoop.c and tube.c for related
+ * code for input and output respectively.
+ *
+ * librsync never does IO or memory allocation, but relies on the
+ * caller.  This is very nice for integration, but means that we have
+ * to be fairly flexible as to when we can `read' or `write' stuff
+ * internally.
+ *
+ * librsync basically does two types of IO.  It reads network integers
+ * of various lengths which encode command and control information
+ * such as versions and signatures.  It also does bulk data transfer.
+ *
+ * IO of network integers is internally buffered, because higher
+ * levels of the code need to see them transmitted atomically: it's no
+ * good to read half of a uint32.  So there is a small and fixed
+ * length internal buffer which accumulates these.  Unlike previous
+ * versions of the library, we don't require that the caller hold the
+ * start until the whole thing has arrived, which guarantees that we
+ * can always make progress.
+ *
+ * On each call into a stream iterator, it should begin by trying to
+ * flush output.  This may well use up all the remaining stream space,
+ * in which case nothing else can be done.
+ */
+
+/* TODO: Return errors rather than aborting if something goes wrong.  */
+
+
+#include <config_rsync.h>
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "rsync.h"
+#include "stream.h"
+#include "util.h"
+#include "trace.h"
+
+static const int RS_STREAM_DOGTAG = 2001125;
+
+
+/**
+ * \brief Copy up to \p max_len bytes from input of \b stream to its output.
+ *
+ * Return the number of bytes actually copied, which may be less than
+ * LEN if there is not enough space in one or the other stream.
+ *
+ * This always does the copy immediately.  Most functions should call
+ * rs_tube_copy() to cause the copy to happen gradually as space
+ * becomes available.
+ */
+int rs_buffers_copy(rs_buffers_t *stream, int max_len)
+{
+    int len = max_len;
+    
+    assert(len > 0);
+
+    if ((unsigned) len > stream->avail_in) {
+        rs_trace("copy limited to %d available input bytes",
+                 stream->avail_in);
+        len = stream->avail_in;
+    }
+
+
+    if ((unsigned) len > stream->avail_out) {
+        rs_trace("copy limited to %d available output bytes",
+                 stream->avail_out);
+        len = stream->avail_out;
+    }
+
+    if (!len)
+        return 0;
+/*     rs_trace("stream copied chunk of %d bytes", len); */
+
+    memcpy(stream->next_out, stream->next_in, len);
+    
+    stream->next_out += len;
+    stream->avail_out -= len;
+
+    stream->next_in += len;
+    stream->avail_in -= len;
+
+    return len;
+}
+
+
+/**
+ * Whenever a stream processing function exits, it should have done so
+ * because it has either consumed all the input or has filled the
+ * output buffer.  This function checks that simple postcondition.
+ */
+void rs_buffers_check_exit(rs_buffers_t const *stream)
+{
+    assert(stream->avail_in == 0  ||  stream->avail_out == 0);
+}