From ce45404bba80d6f85057b596cd716d6c4759dcad Mon Sep 17 00:00:00 2001
From: Mike Wiacek <mjwiacek@google.com>
Date: Tue, 11 Aug 2015 15:36:45 -0700
Subject: [PATCH] Suppress error reporting after seeking but before a valid
 First or Full record is encountered.

Fix a spelling mistake.
---
 db/log_reader.cc | 14 +++++++++++++-
 db/log_reader.h  |  5 +++++
 db/log_test.cc   | 33 +++++++++++++++++++++++++++------
 3 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/db/log_reader.cc b/db/log_reader.cc
index e44b66c..6d4a5b2 100644
--- a/db/log_reader.cc
+++ b/db/log_reader.cc
@@ -25,7 +25,8 @@ Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
       eof_(false),
       last_record_offset_(0),
       end_of_buffer_offset_(0),
-      initial_offset_(initial_offset) {
+      initial_offset_(initial_offset),
+      resyncing_(initial_offset > 0) {
 }
 
 Reader::~Reader() {
@@ -74,6 +75,17 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
   while (true) {
     uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size();
     const unsigned int record_type = ReadPhysicalRecord(&fragment);
+    if (resyncing_) {
+      if (record_type == kMiddleType) {
+        continue;
+      } else if (record_type == kLastType) {
+        resyncing_ = false;
+        continue;
+      } else {
+        resyncing_ = false;
+      }
+    }
+
     switch (record_type) {
       case kFullType:
         if (in_fragmented_record) {
diff --git a/db/log_reader.h b/db/log_reader.h
index 6aff791..8389d61 100644
--- a/db/log_reader.h
+++ b/db/log_reader.h
@@ -73,6 +73,11 @@ class Reader {
   // Offset at which to start looking for the first record to return
   uint64_t const initial_offset_;
 
+  // True if we are resynchronizing after a seek (initial_offset_ > 0). In
+  // particular, a run of kMiddleType and kLastType records can be silently
+  // skipped in this mode
+  bool resyncing_;
+
   // Extend record types with the following special values
   enum {
     kEof = kMaxRecordType + 1,
diff --git a/db/log_test.cc b/db/log_test.cc
index 11e4a47..7b08c26 100644
--- a/db/log_test.cc
+++ b/db/log_test.cc
@@ -79,7 +79,7 @@ class LogTest {
     virtual Status Skip(uint64_t n) {
       if (n > contents_.size()) {
         contents_.clear();
-        return Status::NotFound("in-memory file skipepd past end");
+        return Status::NotFound("in-memory file skipped past end");
       }
 
       contents_.remove_prefix(n);
@@ -105,7 +105,7 @@ class LogTest {
   ReportCollector report_;
   bool reading_;
   Writer* writer_;
-  Reader reader_;
+  Reader* reader_;
 
   // Record metadata for testing initial offset functionality
   static size_t initial_offset_record_sizes_[];
@@ -114,12 +114,13 @@ class LogTest {
  public:
   LogTest() : reading_(false),
               writer_(new Writer(&dest_)),
-              reader_(&source_, &report_, true/*checksum*/,
-                      0/*initial_offset*/) {
+              reader_(new Reader(&source_, &report_, true/*checksum*/,
+                      0/*initial_offset*/)) {
   }
 
   ~LogTest() {
     delete writer_;
+    delete reader_;
   }
 
   void ReopenForAppend() {
@@ -143,7 +144,7 @@ class LogTest {
     }
     std::string scratch;
     Slice record;
-    if (reader_.ReadRecord(&record, &scratch)) {
+    if (reader_->ReadRecord(&record, &scratch)) {
       return record.ToString();
     } else {
       return "EOF";
@@ -198,6 +199,11 @@ class LogTest {
     }
   }
 
+  void StartReadingAt(uint64_t initial_offset) {
+    delete reader_;
+    reader_ = new Reader(&source_, &report_, true/*checksum*/, initial_offset);
+  }
+
   void CheckOffsetPastEndReturnsNoRecords(uint64_t offset_past_end) {
     WriteInitialOffsetLog();
     reading_ = true;
@@ -227,7 +233,6 @@ class LogTest {
     ASSERT_EQ((char)('a' + expected_record_offset), record.data()[0]);
     delete offset_reader;
   }
-
 };
 
 size_t LogTest::initial_offset_record_sizes_[] =
@@ -463,6 +468,22 @@ TEST(LogTest, PartialLastIsIgnored) {
   ASSERT_EQ(0, DroppedBytes());
 }
 
+TEST(LogTest, SkipIntoMultiRecord) {
+  // Consider a fragmented record:
+  //    first(R1), middle(R1), last(R1), first(R2)
+  // If initial_offset points to a record after first(R1) but before first(R2)
+  // incomplete fragment errors are not actual errors, and must be suppressed
+  // until a new first or full record is encountered.
+  Write(BigString("foo", 3*kBlockSize));
+  Write("correct");
+  StartReadingAt(kBlockSize);
+
+  ASSERT_EQ("correct", Read());
+  ASSERT_EQ("", ReportMessage());
+  ASSERT_EQ(0, DroppedBytes());
+  ASSERT_EQ("EOF", Read());
+}
+
 TEST(LogTest, ErrorJoinsRecords) {
   // Consider two fragmented records:
   //    first(R1) last(R1) first(R2) last(R2)