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diff --git a/sdch/open-vcdiff/src/codetablewriter_interface.h b/sdch/open-vcdiff/src/codetablewriter_interface.h
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+// Copyright 2008 Google Inc. All Rights Reserved.
+// Author: ajenjo@google.com (Lincoln Smith)
+//
+// Definition of an abstract class that describes the interface between the
+// encoding engine (which finds the best string matches between the source and
+// target data) and the code table writer.  The code table writer is passed a
+// series of Add, Copy, and Run instructions and produces an output file in the
+// desired format.
+
+#ifndef OPEN_VCDIFF_CODETABLEWRITER_INTERFACE_H_
+#define OPEN_VCDIFF_CODETABLEWRITER_INTERFACE_H_
+
+#include <stddef.h>  // size_t
+
+namespace open_vcdiff {
+
+class OutputStringInterface;
+
+// The method calls after construction should follow this pattern:
+//    {{Add|Copy|Run}* Output}*
+//
+// Output() will produce an encoding using the given series of Add, Copy,
+// and/or Run instructions.  One implementation of the interface
+// (VCDiffCodeTableWriter) produces a VCDIFF delta window, but other
+// implementations may be used to produce other output formats, or as test
+// mocks, or to gather encoding statistics.
+//
+class CodeTableWriterInterface {
+ public:
+  virtual ~CodeTableWriterInterface() { }
+
+  // Encode an ADD opcode with the "size" bytes starting at data
+  virtual void Add(const char* data, size_t size) = 0;
+
+  // Encode a COPY opcode with args "offset" (into dictionary) and "size" bytes.
+  virtual void Copy(int32_t offset, size_t size) = 0;
+
+  // Encode a RUN opcode for "size" copies of the value "byte".
+  virtual void Run(size_t size, unsigned char byte) = 0;
+
+  // Finishes encoding and appends the encoded delta window to the output
+  // string.  The output string is not null-terminated and may contain embedded
+  // '\0' characters.
+  virtual void Output(OutputStringInterface* out) = 0;
+
+  // Returns the number of target bytes processed, which is the sum of all the
+  // size arguments passed to Add(), Copy(), and Run().
+  virtual size_t target_length() const = 0;
+};
+
+}  // namespace open_vcdiff
+
+#endif  // OPEN_VCDIFF_CODETABLEWRITER_INTERFACE_H_