1 // Copyright 2017 The Chromium OS 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. 4 5 #ifndef _BSDIFF_ENDSLEY_PATCH_WRITER_H_ 6 #define _BSDIFF_ENDSLEY_PATCH_WRITER_H_ 7 8 #include <memory> 9 #include <string> 10 #include <vector> 11 12 #include "bsdiff/compressor_interface.h" 13 #include "bsdiff/constants.h" 14 #include "bsdiff/patch_writer_interface.h" 15 16 namespace bsdiff { 17 18 // A PatchWriterInterface class compatible with the format used by Android Play 19 // Store's bsdiff implementation, which is based on Matthew Endsley's bsdiff 20 // implementation. See https://github.com/mendsley/bsdiff for the original 21 // implementation of this format. See also Google's APK patch size estimator for 22 // more information on the file-by-file format used by Play Store: 23 // https://github.com/googlesamples/apk-patch-size-estimator 24 25 // This format, identified by the "ENDSLEY/BSDIFF43" magic string, uses a single 26 // stream with the control entries, diff data and extra data interleaved. After 27 // the header, each Control Entry is stored in 24 bytes followed by the diff 28 // stream data for that entry only, and then followed by the extra stream data 29 // for that entry only. The format doesn't handle the compression of the data, 30 // instead, the whole file (including the magic string) is compressed with any 31 // compression algorithm. 32 33 // This format is easier to parse and allows the patch to be streamed, but by 34 // mixing the diff and extra data into the same compression context offers a 35 // slightly worse compression ratio (about 3.5% compared to upstream's format). 36 37 class EndsleyPatchWriter : public PatchWriterInterface { 38 public: 39 // Create the patch writer that will write the data to the passed vector 40 // |patch|, resizing it as needed. The |patch| vector must be valid until 41 // Close() is called or this patch is destroyed. The data in |patch| will be 42 // compressed using the compressor type |type|. 43 EndsleyPatchWriter(std::vector<uint8_t>* patch, 44 CompressorType type, 45 int quality) 46 : patch_(patch), compressor_type_(type), quality_(quality) {} 47 48 // PatchWriterInterface overrides. 49 bool Init(size_t new_size) override; 50 bool WriteDiffStream(const uint8_t* data, size_t size) override; 51 bool WriteExtraStream(const uint8_t* data, size_t size) override; 52 bool AddControlEntry(const ControlEntry& entry) override; 53 bool Close() override; 54 55 private: 56 // Emit at the end of the |patch_| vector the passed control entry. 57 void EmitControlEntry(const ControlEntry& entry); 58 59 // Emit at the end of the |patch_| vector the passed buffer. 60 void EmitBuffer(const uint8_t* data, size_t size); 61 62 // Flush as much as possible of the pending data. 63 void Flush(); 64 65 // The vector we are writing to, owned by the caller. 66 std::vector<uint8_t>* patch_; 67 68 // The compressor type to use and its quality (if any). 69 CompressorType compressor_type_; 70 int quality_; 71 72 std::unique_ptr<CompressorInterface> compressor_; 73 74 // The pending diff and extra data to be encoded in the file. These vectors 75 // would not be used whenever is possible to the data directly to the patch_ 76 // vector; namely when the control, diff and extra stream data are provided in 77 // that order for each control entry. 78 std::vector<uint8_t> diff_data_; 79 std::vector<uint8_t> extra_data_; 80 std::vector<ControlEntry> control_; 81 82 // Defined as the sum of all the diff_size and extra_size values in 83 // |control_|. This is used to determine whether it is worth Flushing the 84 // pending data. 85 size_t pending_control_data_{0}; 86 87 // Number of bytes in the diff and extra stream that are pending in the 88 // last control entry encoded in the |patch_|. If both are zero the last 89 // control entry was completely emitted. 90 size_t pending_diff_{0}; 91 size_t pending_extra_{0}; 92 }; 93 94 } // namespace bsdiff 95 96 #endif // _BSDIFF_ENDSLEY_PATCH_WRITER_H_ 97
