Merge "Allow to set the minimum required match length."

bsdiff.cc

@@ -50,12 +50,20 @@ int bsdiff(const uint8_t* old_buf, size_t oldsize, const uint8_t* new_buf,
            size_t newsize, const char* patch_filename,
            SuffixArrayIndexInterface** sai_cache) {
 	BsdiffPatchWriter patch(patch_filename);
-	return bsdiff(old_buf, oldsize, new_buf, newsize, &patch, sai_cache);
+	return bsdiff(old_buf, oldsize, new_buf, newsize, 0, &patch,
+	              sai_cache);
 }
 
 int bsdiff(const uint8_t* old_buf, size_t oldsize, const uint8_t* new_buf,
            size_t newsize, PatchWriterInterface* patch,
            SuffixArrayIndexInterface** sai_cache) {
+	return bsdiff(old_buf, oldsize, new_buf, newsize, 0, patch,
+	              sai_cache);
+}
+
+int bsdiff(const uint8_t* old_buf, size_t oldsize, const uint8_t* new_buf,
+           size_t newsize, size_t min_length, PatchWriterInterface* patch,
+           SuffixArrayIndexInterface** sai_cache) {
 	size_t scsc, scan;
 	uint64_t pos=0;
 	size_t len;
@@ -112,7 +120,7 @@ int bsdiff(const uint8_t* old_buf, size_t oldsize, const uint8_t* new_buf,
 				oldscore++;
 
 			if(((len==oldscore) && (len!=0)) ||
-				(len>oldscore+8)) break;
+				(len>oldscore+8 && len>=min_length)) break;
 
 			if((scan+lastoffset<oldsize) &&
 				(old_buf[scan+lastoffset] == new_buf[scan]))

bsdiff_arguments.cc

@@ -24,6 +24,7 @@ constexpr char kBsdiff40String[] = "bsdiff40";
 
 const struct option OPTIONS[] = {
     {"format", required_argument, nullptr, 0},
+    {"minlen", required_argument, nullptr, 0},
     {"type", required_argument, nullptr, 0},
     {"quality", required_argument, nullptr, 0},
     {nullptr, 0, nullptr, 0},
@@ -58,11 +59,15 @@ bool BsdiffArguments::ParseCommandLine(int argc, char** argv) {
       return false;
     }
 
-    std::string name = OPTIONS[option_index].name;
+    string name = OPTIONS[option_index].name;
     if (name == "format") {
       if (!ParseBsdiffFormat(optarg, &format_)) {
         return false;
       }
+    } else if (name == "minlen") {
+      if (!ParseMinLength(optarg, &min_length_)) {
+        return false;
+      }
     } else if (name == "type") {
       if (!ParseCompressorType(optarg, &compressor_type_)) {
         return false;
@@ -110,6 +115,24 @@ bool BsdiffArguments::ParseCompressorType(const string& str,
   return false;
 }
 
+bool BsdiffArguments::ParseMinLength(const string& str, size_t* len) {
+  errno = 0;
+  char* end;
+  const char* s = str.c_str();
+  long result = strtol(s, &end, 10);
+  if (errno != 0 || s == end || *end != '\0') {
+    return false;
+  }
+
+  if (result < 0) {
+    std::cerr << "Minimum length must be non-negative: " << str << endl;
+    return false;
+  }
+
+  *len = result;
+  return true;
+}
+
 bool BsdiffArguments::ParseBsdiffFormat(const string& str,
                                         BsdiffFormat* format) {
   string format_string = str;

bsdiff_arguments.h

@@ -35,6 +35,8 @@ class BsdiffArguments {
   // Getter functions.
   BsdiffFormat format() const { return format_; }
 
+  int min_length() const { return min_length_; }
+
   CompressorType compressor_type() const { return compressor_type_; }
 
   int compression_quality() const { return compression_quality_; }
@@ -46,6 +48,9 @@ class BsdiffArguments {
   // Parse the compression type from string.
   static bool ParseCompressorType(const string& str, CompressorType* type);
 
+  // Parse the minimum length parameter from string.
+  static bool ParseMinLength(const string& str, size_t* len);
+
   // Parse the bsdiff format from string.
   static bool ParseBsdiffFormat(const string& str, BsdiffFormat* format);
 
@@ -62,8 +67,10 @@ class BsdiffArguments {
   // The quality of compression, only valid when using brotli as the
   // compression algorithm.
   int compression_quality_;
+
+  size_t min_length_{0};
 };
 
 }  // namespace bsdiff
 
-#endif  //_BSDIFF_BSDIFF_ARGUMENTS_H_
+#endif  // _BSDIFF_BSDIFF_ARGUMENTS_H_

bsdiff_arguments_unittest.cc

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "bsdiff_arguments.h"
+#include "bsdiff/bsdiff_arguments.h"
 
 #include <vector>
 
@@ -46,6 +46,16 @@ TEST(BsdiffArgumentsTest, ParseQualityTest) {
   EXPECT_FALSE(BsdiffArguments::ParseQuality("aabb", &quality));
 }
 
+TEST(BsdiffArgumentsTest, ParseMinLengthTest) {
+  size_t len;
+  EXPECT_TRUE(BsdiffArguments::ParseMinLength("11", &len));
+  EXPECT_EQ(11U, len);
+
+  // Check the out of range quality values.
+  EXPECT_FALSE(BsdiffArguments::ParseMinLength("-1", &len));
+  EXPECT_FALSE(BsdiffArguments::ParseMinLength("aabb", &len));
+}
+
 TEST(BsdiffArgumentsTest, ArgumentsValidTest) {
   // Default arguments using BsdiffFormat::kLegacy and CompressorType::kBZ2
   // should be valid.
@@ -67,14 +77,16 @@ TEST(BsdiffArgumentsTest, ArgumentsValidTest) {
 
 TEST(BsdiffArgumentsTest, ParseArgumentsSmokeTest) {
   std::vector<const char*> args = {"bsdiff", "--format=bsdf2", "--type=brotli",
-                                   "--quality=9"};
+                                   "--quality=9", "--minlen=12"};
 
   BsdiffArguments arguments;
-  EXPECT_TRUE(arguments.ParseCommandLine(4, const_cast<char**>(args.data())));
+  EXPECT_TRUE(
+      arguments.ParseCommandLine(args.size(), const_cast<char**>(args.data())));
 
   EXPECT_EQ(BsdiffFormat::kBsdf2, arguments.format());
   EXPECT_EQ(CompressorType::kBrotli, arguments.compressor_type());
   EXPECT_EQ(9, arguments.compression_quality());
+  EXPECT_EQ(12, arguments.min_length());
 }
 
 }  // namespace bsdiff

bsdiff_main.cc

@@ -85,8 +85,8 @@ int GenerateBsdiffFromFiles(const char* old_filename,
     return 1;
   }
 
-  return bsdiff::bsdiff(old_buf, oldsize, new_buf, newsize, patch_writer.get(),
-                        nullptr);
+  return bsdiff::bsdiff(old_buf, oldsize, new_buf, newsize,
+                        arguments.min_length(), patch_writer.get(), nullptr);
 }
 
 void PrintUsage(const std::string& proc_name) {
@@ -94,6 +94,8 @@ void PrintUsage(const std::string& proc_name) {
             << " [options] oldfile newfile patchfile\n";
   std::cerr << "  --format <legacy|bsdiff40|bsdf2>  The format of the bsdiff"
                " patch.\n"
+            << "  --minlen LEN             The minimum match length required "
+               "to consider a match in the algorithm.\n"
             << "  --type <bz2|brotli>      The algorithm to compress the "
                "patch, bsdf2 format only.\n"
             << "  --quality                Quality of the patch compression,"

bsdiff_unittest.cc

@@ -33,11 +33,12 @@ class BsdiffTest : public testing::Test {
 
   void RunBsdiff() {
     EXPECT_EQ(0, bsdiff(old_file_.data(), old_file_.size(), new_file_.data(),
-                        new_file_.size(), &patch_writer_, nullptr));
+                        new_file_.size(), min_len_, &patch_writer_, nullptr));
   }
 
   std::vector<uint8_t> old_file_;
   std::vector<uint8_t> new_file_;
+  size_t min_len_ = 0;  // 0 means the default.
   FakePatchWriter patch_writer_;
 };
 
@@ -81,4 +82,25 @@ TEST_F(BsdiffTest, FileWithSmallErrorsTest) {
   EXPECT_EQ(0U, entry.extra_size);
 }
 
+TEST_F(BsdiffTest, MinLengthConsideredTest) {
+  old_file_.resize(100);
+  GenerateRandomBuffer(&old_file_);
+  new_file_ = old_file_;
+  // Copy the first 10 bytes to the middle.
+  for (size_t i = 0; i < 10; i++) {
+    new_file_[50 + i] = old_file_[i];
+  }
+
+  min_len_ = 12;
+  RunBsdiff();
+
+  // We expect that the 10 bytes in the middle that match the beginning are
+  // ignored and just emitted as diff data because the min_len is bigger than
+  // 10.
+  EXPECT_EQ(1U, patch_writer_.entries().size());
+  ControlEntry entry = patch_writer_.entries()[0];
+  EXPECT_EQ(100U, entry.diff_size);
+  EXPECT_EQ(0U, entry.extra_size);
+}
+
 }  // namespace bsdiff

include/bsdiff/bsdiff.h

@@ -34,6 +34,23 @@ int bsdiff(const uint8_t* old_buf,
            PatchWriterInterface* patch,
            SuffixArrayIndexInterface** sai_cache);
 
+// The |min_length| parameter determines the required minimum length of a match
+// to be considered instead of emitting mismatches. The minimum value is 9,
+// since smaller matches are always ignored. If a smaller value is passed, the
+// minimum value of 9 will be used instead. A very large value (past 30) will
+// give increasingly bad results as you increase the minimum length since legit
+// matches between the old and new data will be ignored. The exact best value
+// depends on the data, but the sweet spot should be between 9 and 20 for the
+// examples tested.
+BSDIFF_EXPORT
+int bsdiff(const uint8_t* old_buf,
+           size_t oldsize,
+           const uint8_t* new_buf,
+           size_t newsize,
+           size_t min_length,
+           PatchWriterInterface* patch,
+           SuffixArrayIndexInterface** sai_cache);
+
 }  // namespace bsdiff
 
 #endif  // _BSDIFF_BSDIFF_H_