1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 // The main idea in Courgette is to do patching *under a tranformation*. The
6 // input is transformed into a new representation, patching occurs in the new
7 // repesentation, and then the tranform is reversed to get the patched data.
9 // The idea is applied to pieces (or 'Elements') of the whole (or 'Ensemble').
10 // Each of the elements has to go through the same set of steps in lock-step,
11 // but there may be many different kinds of elements, which have different
14 // This file declares all the main types involved in creating and applying a
15 // patch with this structure.
17 #ifndef COURGETTE_ENSEMBLE_H_
18 #define COURGETTE_ENSEMBLE_H_
26 #include "base/macros.h"
27 #include "courgette/courgette.h"
28 #include "courgette/region.h"
29 #include "courgette/streams.h"
33 // Forward declarations:
36 // An Element is a region of an Ensemble with an identifyable kind.
40 Element(ExecutableType kind,
42 const Region& region);
46 ExecutableType kind() const { return kind_; }
47 const Region& region() const { return region_; }
49 // The name is used only for debugging and logging.
50 virtual std::string Name() const;
52 // Returns the byte position of this Element relative to the start of
53 // containing Ensemble.
54 size_t offset_in_ensemble() const;
61 DISALLOW_COPY_AND_ASSIGN(Element);
67 Ensemble(const Region& region, const char* name)
68 : region_(region), name_(name) {}
71 const Region& region() const { return region_; }
72 const std::string& name() const { return name_; }
74 // Scans the region to find Elements within the region().
75 Status FindEmbeddedElements();
77 // Returns the elements found by 'FindEmbeddedElements'.
78 const std::vector<Element*>& elements() const { return elements_; }
82 Region region_; // The memory, owned by caller, containing the
84 std::string name_; // A debugging/logging name for the Ensemble.
86 std::vector<Element*> elements_; // Embedded elements discovered.
87 std::vector<Element*> owned_elements_; // For deallocation.
89 DISALLOW_COPY_AND_ASSIGN(Ensemble);
92 inline size_t Element::offset_in_ensemble() const {
93 return region().start() - ensemble_->region().start();
96 // The 'CourgettePatchFile' is class is a 'namespace' for the constants that
97 // appear in a Courgette patch file.
98 struct CourgettePatchFile {
100 // The Courgette patch format interleaves the data for N embedded Elements.
102 // Format of a patch file:
108 // final-patch-input-size (an allocation hint)
111 // number-of-transformed-elements (N) - varint32
112 // transformation-1-method-id
113 // transformation-2-method-id
115 // transformation-1-initial-parameters
116 // transformation-2-initial-parameters
120 // transformation-1-parameters
121 // transformation-2-parameters
125 // transformed-element-1
126 // transformed-element-2
135 static const uint32_t kMagic = 'C' | ('o' << 8) | ('u' << 16);
137 static const uint32_t kVersion = 20110216;
140 // For any transform you would implement both a TransformationPatcher and a
141 // TransformationPatchGenerator.
143 // TransformationPatcher is the interface which abstracts out the actual
144 // transformation used on an Element. The patching itself happens outside the
145 // actions of a TransformationPatcher. There are four steps.
147 // The first step is an Init step. The parameters to the Init step identify the
148 // element, for example, range of locations within the original ensemble that
149 // correspond to the element.
151 // PredictTransformParameters, explained below.
153 // The two final steps are 'Transform' - to transform the element into a new
154 // representation, and to 'Reform' - to transform from the new representation
155 // back to the original form.
157 // The Transform step takes some parameters. This allows the transform to be
158 // customized to the particular element, or to receive some assistance in the
159 // analysis required to perform the transform. The transform parameters might
160 // be extensive but mostly predicable, so preceeding Transform is a
161 // PredictTransformParameters step.
163 class TransformationPatcher {
165 virtual ~TransformationPatcher() {}
167 // First step: provides parameters for the patching. This would at a minimum
168 // identify the element within the ensemble being patched.
169 virtual Status Init(SourceStream* parameter_stream) = 0;
171 // Second step: predicts transform parameters.
172 virtual Status PredictTransformParameters(
173 SinkStreamSet* predicted_parameters) = 0;
175 // Third step: transforms element from original representation into alternate
177 virtual Status Transform(SourceStreamSet* corrected_parameters,
178 SinkStreamSet* transformed_element) = 0;
180 // Final step: transforms element back from alternate representation into
181 // original representation.
182 virtual Status Reform(SourceStreamSet* transformed_element,
183 SinkStream* reformed_element) = 0;
186 // TransformationPatchGenerator is the interface which abstracts out the actual
187 // transformation used (and adjustment used) when differentially compressing one
188 // Element from the |new_ensemble| against a corresponding element in the
191 // This is not a pure interface. There is a small amount of inheritance
192 // implementation for the fields and actions common to all
193 // TransformationPatchGenerators.
195 // When TransformationPatchGenerator is subclassed, there will be a
196 // corresponding subclass of TransformationPatcher.
198 class TransformationPatchGenerator {
200 TransformationPatchGenerator(Element* old_element,
201 Element* new_element,
202 TransformationPatcher* patcher);
204 virtual ~TransformationPatchGenerator();
206 // Returns the TransformationMethodId that identies this transformation.
207 virtual ExecutableType Kind() = 0;
209 // Writes the parameters that will be passed to TransformationPatcher::Init.
210 virtual Status WriteInitialParameters(SinkStream* parameter_stream) = 0;
212 // Predicts the transform parameters for the |old_element|. This must match
213 // exactly the output that will be produced by the PredictTransformParameters
214 // method of the corresponding subclass of TransformationPatcher. This method
215 // is not pure. The default implementation delegates to the patcher to
216 // guarantee matching output.
217 virtual Status PredictTransformParameters(SinkStreamSet* prediction);
219 // Writes the desired parameters for the transform of the old element from the
220 // file representation to the alternate representation.
221 virtual Status CorrectedTransformParameters(SinkStreamSet* parameters) = 0;
223 // Writes both |old_element| and |new_element| in the new representation.
224 // |old_corrected_parameters| will match the |corrected_parameters| passed to
225 // the Transform method of the corresponding sublcass of
226 // TransformationPatcher.
228 // The output written to |old_transformed_element| must match exactly the
229 // output written by the Transform method of the corresponding subclass of
230 // TransformationPatcher.
231 virtual Status Transform(SourceStreamSet* old_corrected_parameters,
232 SinkStreamSet* old_transformed_element,
233 SinkStreamSet* new_transformed_element) = 0;
235 // Transforms the new transformed_element back from the alternate
236 // representation into the original file format. This must match exactly the
237 // output that will be produced by the corresponding subclass of
238 // TransformationPatcher::Reform. This method is not pure. The default
239 // implementation delegates to the patcher.
240 virtual Status Reform(SourceStreamSet* transformed_element,
241 SinkStream* reformed_element);
244 Element* old_element_;
245 Element* new_element_;
246 TransformationPatcher* patcher_;
250 #endif // COURGETTE_ENSEMBLE_H_