Clean up some code related to file checksums (#6861)

Summary:
* Add missing unit test for schema stability of FileChecksumGenCrc32c
  (previously was only comparing to itself)
* A lot of clarifying comments
* Add some assertions for preconditions
* Rename WritableFileWriter::CalculateFileChecksum -> UpdateFileChecksum
* Simplify FileChecksumGenCrc32c with shared functions
* Implement EndianSwapValue to replace unused EndianTransform

And incidentally since I had trouble with 'make check-format' GitHub action disagreeing with local run,
* Output full diagnostic information when 'make check-format' fails in CI
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6861

Test Plan: new unit test passes before & after other changes

Reviewed By: zhichao-cao

Differential Revision: D21667115

Pulled By: pdillinger

fbshipit-source-id: 6a99970f87605aa024fa540c78cd519ff322c3e6

.github/workflows/sanity_check.yml

@@ -35,7 +35,7 @@ jobs:
         args: https://raw.githubusercontent.com/llvm-mirror/clang/master/tools/clang-format/clang-format-diff.py
 
     - name: Check format
-      run: make check-format
+      run: VERBOSE_CHECK=1 make check-format
 
     - name: Compare buckify output
       run: make check-buck-targets

build_tools/format-diff.sh

@@ -124,6 +124,10 @@ then
 elif [ $CHECK_ONLY ]
 then
   echo "Your change has unformatted code. Please run make format!"
+  if [ $VERBOSE_CHECK ]; then
+    clang-format --version
+    echo "$diffs"
+  fi
   exit 1
 fi
 

file/writable_file_writer.cc

@@ -31,7 +31,7 @@ IOStatus WritableFileWriter::Append(const Slice& data) {
                    rocksdb_kill_odds * REDUCE_ODDS2);
 
   // Calculate the checksum of appended data
-  CalculateFileChecksum(data);
+  UpdateFileChecksum(data);
 
   {
     IOSTATS_TIMER_GUARD(prepare_write_nanos);
@@ -225,6 +225,7 @@ IOStatus WritableFileWriter::Flush() {
 
 std::string WritableFileWriter::GetFileChecksum() {
   if (checksum_generator_ != nullptr) {
+    assert(checksum_finalized_);
     return checksum_generator_->GetChecksum();
   } else {
     return kUnknownFileChecksum;
@@ -346,7 +347,7 @@ IOStatus WritableFileWriter::WriteBuffered(const char* data, size_t size) {
   return s;
 }
 
-void WritableFileWriter::CalculateFileChecksum(const Slice& data) {
+void WritableFileWriter::UpdateFileChecksum(const Slice& data) {
   if (checksum_generator_ != nullptr) {
     checksum_generator_->Update(data.data(), data.size());
   }

file/writable_file_writer.h

@@ -51,7 +51,7 @@ class WritableFileWriter {
 #endif  // ROCKSDB_LITE
 
   bool ShouldNotifyListeners() const { return !listeners_.empty(); }
-  void CalculateFileChecksum(const Slice& data);
+  void UpdateFileChecksum(const Slice& data);
 
   std::unique_ptr<FSWritableFile> writable_file_;
   std::string file_name_;

include/rocksdb/file_checksum.h

@@ -24,6 +24,10 @@ struct FileChecksumGenContext {
 
 // FileChecksumGenerator is the class to generates the checksum value
 // for each file when the file is written to the file system.
+// Implementations may assume that
+// * Finalize is called at most once during the life of the object
+// * All calls to Update come before Finalize
+// * All calls to GetChecksum come after Finalize
 class FileChecksumGenerator {
  public:
   virtual ~FileChecksumGenerator() {}
@@ -36,7 +40,8 @@ class FileChecksumGenerator {
   // Generate the final results if no further new data will be updated.
   virtual void Finalize() = 0;
 
-  // Get the checksum
+  // Get the checksum. The result should not be the empty string and may
+  // include arbitrary bytes, including non-printable characters.
   virtual std::string GetChecksum() const = 0;
 
   // Returns a name that identifies the current file checksum function.
@@ -97,9 +102,13 @@ class FileChecksumList {
 // Create a new file checksum list.
 extern FileChecksumList* NewFileChecksumList();
 
-// Return a shared_ptr of the builtin Crc32 based file checksum generatory
+// Return a shared_ptr of the builtin Crc32c based file checksum generatory
 // factory object, which can be shared to create the Crc32c based checksum
 // generator object.
+// Note: this implementation is compatible with many other crc32c checksum
+// implementations and uses big-endian encoding of the result, unlike most
+// other crc32c checksums in RocksDB, which alter the result with
+// crc32c::Mask and use little-endian encoding.
 extern std::shared_ptr<FileChecksumGenFactory>
 GetFileChecksumGenCrc32cFactory();
 

include/rocksdb/utilities/backupable_db.h

@@ -89,7 +89,7 @@ struct BackupableDBOptions {
 
   // Only used if share_table_files is set to true. If true, will consider that
   // backups can come from different databases, hence a sst is not uniquely
-  // identifed by its name, but by the triple (file name, crc32, file length)
+  // identifed by its name, but by the triple (file name, crc32c, file length)
   // Default: false
   // Note: this is an experimental option, and you'll need to set it manually
   // *turn it on only if you know what you're doing*

table/table_test.cc

@@ -3297,7 +3297,7 @@ TEST_P(BlockBasedTableTest, NoFileChecksum) {
   ASSERT_STREQ(f.GetFileChecksum().c_str(), kUnknownFileChecksum.c_str());
 }
 
-TEST_P(BlockBasedTableTest, Crc32FileChecksum) {
+TEST_P(BlockBasedTableTest, Crc32cFileChecksum) {
   FileChecksumGenCrc32cFactory* file_checksum_gen_factory =
       new FileChecksumGenCrc32cFactory();
   Options options;
@@ -3322,12 +3322,12 @@ TEST_P(BlockBasedTableTest, Crc32FileChecksum) {
 
   FileChecksumGenContext gen_context;
   gen_context.file_name = "db/tmp";
-  std::unique_ptr<FileChecksumGenerator> checksum_crc32_gen1 =
+  std::unique_ptr<FileChecksumGenerator> checksum_crc32c_gen1 =
       options.file_checksum_gen_factory->CreateFileChecksumGenerator(
           gen_context);
   FileChecksumTestHelper f(true);
   f.CreateWriteableFile();
-  f.SetFileChecksumGenerator(checksum_crc32_gen1.release());
+  f.SetFileChecksumGenerator(checksum_crc32c_gen1.release());
   std::unique_ptr<TableBuilder> builder;
   builder.reset(ioptions.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, *comparator,
@@ -3342,12 +3342,22 @@ TEST_P(BlockBasedTableTest, Crc32FileChecksum) {
   f.WriteKVAndFlushTable();
   ASSERT_STREQ(f.GetFileChecksumFuncName(), "FileChecksumCrc32c");
 
-  std::unique_ptr<FileChecksumGenerator> checksum_crc32_gen2 =
+  std::unique_ptr<FileChecksumGenerator> checksum_crc32c_gen2 =
       options.file_checksum_gen_factory->CreateFileChecksumGenerator(
           gen_context);
   std::string checksum;
-  ASSERT_OK(f.CalculateFileChecksum(checksum_crc32_gen2.get(), &checksum));
+  ASSERT_OK(f.CalculateFileChecksum(checksum_crc32c_gen2.get(), &checksum));
   ASSERT_STREQ(f.GetFileChecksum().c_str(), checksum.c_str());
+
+  // Unit test the generator itself for schema stability
+  std::unique_ptr<FileChecksumGenerator> checksum_crc32c_gen3 =
+      options.file_checksum_gen_factory->CreateFileChecksumGenerator(
+          gen_context);
+  const char data[] = "here is some data";
+  checksum_crc32c_gen3->Update(data, sizeof(data));
+  checksum_crc32c_gen3->Finalize();
+  checksum = checksum_crc32c_gen3->GetChecksum();
+  ASSERT_STREQ(checksum.c_str(), "\345\245\277\110");
 }
 
 // Plain table is not supported in ROCKSDB_LITE
@@ -3441,7 +3451,7 @@ TEST_F(PlainTableTest, NoFileChecksum) {
   EXPECT_EQ(f.GetFileChecksum(), kUnknownFileChecksum.c_str());
 }
 
-TEST_F(PlainTableTest, Crc32FileChecksum) {
+TEST_F(PlainTableTest, Crc32cFileChecksum) {
   PlainTableOptions plain_table_options;
   plain_table_options.user_key_len = 20;
   plain_table_options.bloom_bits_per_key = 8;
@@ -3462,12 +3472,12 @@ TEST_F(PlainTableTest, Crc32FileChecksum) {
 
   FileChecksumGenContext gen_context;
   gen_context.file_name = "db/tmp";
-  std::unique_ptr<FileChecksumGenerator> checksum_crc32_gen1 =
+  std::unique_ptr<FileChecksumGenerator> checksum_crc32c_gen1 =
       options.file_checksum_gen_factory->CreateFileChecksumGenerator(
           gen_context);
   FileChecksumTestHelper f(true);
   f.CreateWriteableFile();
-  f.SetFileChecksumGenerator(checksum_crc32_gen1.release());
+  f.SetFileChecksumGenerator(checksum_crc32c_gen1.release());
 
   std::unique_ptr<TableBuilder> builder(factory.NewTableBuilder(
       TableBuilderOptions(
@@ -3481,11 +3491,11 @@ TEST_F(PlainTableTest, Crc32FileChecksum) {
   f.WriteKVAndFlushTable();
   ASSERT_STREQ(f.GetFileChecksumFuncName(), "FileChecksumCrc32c");
 
-  std::unique_ptr<FileChecksumGenerator> checksum_crc32_gen2 =
+  std::unique_ptr<FileChecksumGenerator> checksum_crc32c_gen2 =
       options.file_checksum_gen_factory->CreateFileChecksumGenerator(
           gen_context);
   std::string checksum;
-  ASSERT_OK(f.CalculateFileChecksum(checksum_crc32_gen2.get(), &checksum));
+  ASSERT_OK(f.CalculateFileChecksum(checksum_crc32c_gen2.get(), &checksum));
   EXPECT_STREQ(f.GetFileChecksum().c_str(), checksum.c_str());
 }
 

util/coding.h

@@ -7,8 +7,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 //
-// Endian-neutral encoding:
+// Encoding independent of machine byte order:
 // * Fixed-length numbers are encoded with least-significant byte first
+//   (little endian, native order on Intel and others)
 // * In addition we support variable length "varint" encoding
 // * Strings are encoded prefixed by their length in varint format
 
@@ -402,13 +403,34 @@ inline bool GetVarsignedint64(Slice* input, int64_t* value) {
   }
 }
 
-// Provide an interface for platform independent endianness transformation
-inline uint64_t EndianTransform(uint64_t input, size_t size) {
-  char* pos = reinterpret_cast<char*>(&input);
-  uint64_t ret_val = 0;
-  for (size_t i = 0; i < size; ++i) {
-    ret_val |= (static_cast<uint64_t>(static_cast<unsigned char>(pos[i]))
-                << ((size - i - 1) << 3));
+// Swaps between big and little endian. Can be used to in combination
+// with the little-endian encoding/decoding functions to encode/decode
+// big endian.
+template <typename T>
+inline T EndianSwapValue(T v) {
+  static_assert(std::is_integral<T>::value, "non-integral type");
+
+#ifdef _MSC_VER
+  if (sizeof(T) == 2) {
+    return static_cast<T>(_byteswap_ushort(static_cast<uint16_t>(v)));
+  } else if (sizeof(T) == 4) {
+    return static_cast<T>(_byteswap_ulong(static_cast<uint32_t>(v)));
+  } else if (sizeof(T) == 8) {
+    return static_cast<T>(_byteswap_uint64(static_cast<uint64_t>(v)));
+  }
+#else
+  if (sizeof(T) == 2) {
+    return static_cast<T>(__builtin_bswap16(static_cast<uint16_t>(v)));
+  } else if (sizeof(T) == 4) {
+    return static_cast<T>(__builtin_bswap32(static_cast<uint32_t>(v)));
+  } else if (sizeof(T) == 8) {
+    return static_cast<T>(__builtin_bswap64(static_cast<uint64_t>(v)));
+  }
+#endif
+  // Recognized by clang as bswap, but not by gcc :(
+  T ret_val = 0;
+  for (size_t i = 0; i < sizeof(T); ++i) {
+    ret_val |= ((v >> (8 * i)) & 0xff) << (8 * (sizeof(T) - 1 - i));
   }
   return ret_val;
 }

util/file_checksum_helper.h

@@ -6,11 +6,12 @@
 #pragma once
 #include <cassert>
 #include <unordered_map>
+
 #include "port/port.h"
 #include "rocksdb/file_checksum.h"
 #include "rocksdb/status.h"
+#include "util/coding.h"
 #include "util/crc32c.h"
-#include "util/string_util.h"
 
 namespace ROCKSDB_NAMESPACE {
 
@@ -26,60 +27,19 @@ class FileChecksumGenCrc32c : public FileChecksumGenerator {
     checksum_ = crc32c::Extend(checksum_, data, n);
   }
 
-  void Finalize() override { checksum_str_ = Uint32ToString(checksum_); }
-
-  std::string GetChecksum() const override { return checksum_str_; }
-
-  const char* Name() const override { return "FileChecksumCrc32c"; }
-
-  // Convert a uint32_t type data into a 4 bytes string.
-  static std::string Uint32ToString(uint32_t v) {
-    std::string s;
-    if (port::kLittleEndian) {
-      s.append(reinterpret_cast<char*>(&v), sizeof(v));
-    } else {
-      char buf[sizeof(v)];
-      buf[0] = v & 0xff;
-      buf[1] = (v >> 8) & 0xff;
-      buf[2] = (v >> 16) & 0xff;
-      buf[3] = (v >> 24) & 0xff;
-      s.append(buf, sizeof(v));
-    }
-    size_t i = 0, j = s.size() - 1;
-    while (i < j) {
-      char tmp = s[i];
-      s[i] = s[j];
-      s[j] = tmp;
-      ++i;
-      --j;
-    }
-    return s;
+  void Finalize() override {
+    assert(checksum_str_.empty());
+    // Store as big endian raw bytes
+    PutFixed32(&checksum_str_, EndianSwapValue(checksum_));
   }
 
-  // Convert a 4 bytes size string into a uint32_t type data.
-  static uint32_t StringToUint32(std::string s) {
-    assert(s.size() == sizeof(uint32_t));
-    size_t i = 0, j = s.size() - 1;
-    while (i < j) {
-      char tmp = s[i];
-      s[i] = s[j];
-      s[j] = tmp;
-      ++i;
-      --j;
-    }
-    uint32_t v = 0;
-    if (port::kLittleEndian) {
-      memcpy(&v, s.c_str(), sizeof(uint32_t));
-    } else {
-      const char* buf = s.c_str();
-      v |= static_cast<uint32_t>(buf[0]);
-      v |= (static_cast<uint32_t>(buf[1]) << 8);
-      v |= (static_cast<uint32_t>(buf[2]) << 16);
-      v |= (static_cast<uint32_t>(buf[3]) << 24);
-    }
-    return v;
+  std::string GetChecksum() const override {
+    assert(!checksum_str_.empty());
+    return checksum_str_;
   }
 
+  const char* Name() const override { return "FileChecksumCrc32c"; }
+
  private:
   uint32_t checksum_;
   std::string checksum_str_;

utilities/backupable/backupable_db.cc

@@ -1197,7 +1197,7 @@ Status BackupEngineImpl::RestoreDBFromBackup(const RestoreOptions& options,
     std::string dst;
     // 1. extract the filename
     size_t slash = file.find_last_of('/');
-    // file will either be shared/<file>, shared_checksum/<file_crc32_size>
+    // file will either be shared/<file>, shared_checksum/<file_crc32c_size>
     // or private/<number>/<file>
     assert(slash != std::string::npos);
     dst = file.substr(slash + 1);
@@ -1759,8 +1759,8 @@ Slice kMetaDataPrefix("metadata ");
 // <seq number>
 // <metadata(literal string)> <metadata> (optional)
 // <number of files>
-// <file1> <crc32(literal string)> <crc32_value>
-// <file2> <crc32(literal string)> <crc32_value>
+// <file1> <crc32(literal string)> <crc32c_value>
+// <file2> <crc32(literal string)> <crc32c_value>
 // ...
 Status BackupEngineImpl::BackupMeta::LoadFromFile(
     const std::string& backup_dir,
@@ -1808,6 +1808,7 @@ Status BackupEngineImpl::BackupMeta::LoadFromFile(
 
   std::vector<std::shared_ptr<FileInfo>> files;
 
+  // WART: The checksums are crc32c, not original crc32
   Slice checksum_prefix("crc32 ");
 
   for (uint32_t i = 0; s.ok() && i < num_files; ++i) {
@@ -1921,7 +1922,8 @@ Status BackupEngineImpl::BackupMeta::StoreToFile(bool sync) {
   }
 
   for (const auto& file : files_) {
-    // use crc32 for now, switch to something else if needed
+    // use crc32c for now, switch to something else if needed
+    // WART: The checksums are crc32c, not original crc32
 
     size_t newlen = len + file->filename.length() + snprintf(writelen_temp,
       sizeof(writelen_temp), " crc32 %u\n", file->checksum_value);