--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/internal/Preview.java	Tue Dec 06 12:57:21 2011 +0100
@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2011 TMate Software Ltd
+ *  
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * 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 General Public License for more details.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.internal;
+
+import java.nio.ByteBuffer;
+import java.nio.channels.ByteChannel;
+
+/**
+ * Filters may need to look into data stream before actual processing takes place,
+ * for example, to find out whether filter shall be applied at all.
+ * 
+ * {@link ByteChannel ByteChannels} that may use filters shall be checked for {@link Preview} adaptable before writing to them. 
+ * 
+ * E.g. newline filter handles streams with mixed newline endings according to configuration option 
+ * (either process or ignore), hence, need to check complete stream first.
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+public interface Preview {
+	/**
+	 * Supplied buffer may be shared between few Preview filter instances, hence implementers shall NOT consume (move position)
+	 * of the buffer. Caller enforces this reseting buffer position between calls to previewers.
+	 * <p>
+	 * XXX if this approach turns out to impose a great burden on filter implementations, FilterByteChannel may be modified to keep
+	 * record of how far each filter had read it's buffer. 
+	 */
+	void preview(ByteBuffer src);
+}
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