db/log_test: add recycle log test

This currently fails because we do not properly map a
corrupt header to the logical end of the log.

Signed-off-by: Sage Weil <sage@redhat.com>

db/log_test.cc

@@ -174,6 +174,8 @@ class LogTest : public ::testing::TestWithParam<int> {
                                              3 * header_size;
   }
 
+  Slice* get_reader_contents() { return &reader_contents_; }
+
   void Write(const std::string& msg) {
     writer_.AddRecord(Slice(msg));
   }
@@ -690,6 +692,29 @@ TEST_P(LogTest, ClearEofError2) {
   ASSERT_EQ("OK", MatchError("read error"));
 }
 
+TEST_P(LogTest, Recycle) {
+  if (!GetParam()) {
+    return;  // test is only valid for recycled logs
+  }
+  Write("foo");
+  Write("bar");
+  Write("baz");
+  Write("bif");
+  Write("blitz");
+  while (get_reader_contents()->size() < log::kBlockSize * 2) {
+    Write("xxxxxxxxxxxxxxxx");
+  }
+  unique_ptr<WritableFileWriter> dest_holder(test::GetWritableFileWriter(
+      new test::OverwritingStringSink(get_reader_contents())));
+  Writer recycle_writer(std::move(dest_holder), 123, true);
+  recycle_writer.AddRecord(Slice("foooo"));
+  recycle_writer.AddRecord(Slice("bar"));
+  ASSERT_GE(get_reader_contents()->size(), log::kBlockSize * 2);
+  ASSERT_EQ("foooo", Read());
+  ASSERT_EQ("bar", Read());
+  ASSERT_EQ("EOF", Read());
+}
+
 INSTANTIATE_TEST_CASE_P(bool, LogTest, ::testing::Values(0, 2));
 
 }  // namespace log

util/testutil.h

@@ -230,6 +230,49 @@ class StringSink: public WritableFile {
   size_t last_flush_;
 };
 
+// Like StringSink, this writes into a string.  Unlink StringSink, it
+// has some initial content and overwrites it, just like a recycled
+// log file.
+class OverwritingStringSink : public WritableFile {
+ public:
+  explicit OverwritingStringSink(Slice* reader_contents)
+      : WritableFile(),
+        contents_(""),
+        reader_contents_(reader_contents),
+        last_flush_(0) {}
+
+  const std::string& contents() const { return contents_; }
+
+  virtual Status Truncate(uint64_t size) override {
+    contents_.resize(static_cast<size_t>(size));
+    return Status::OK();
+  }
+  virtual Status Close() override { return Status::OK(); }
+  virtual Status Flush() override {
+    if (last_flush_ < contents_.size()) {
+      assert(reader_contents_->size() >= contents_.size());
+      memcpy((char*)reader_contents_->data() + last_flush_,
+             contents_.data() + last_flush_, contents_.size() - last_flush_);
+      last_flush_ = contents_.size();
+    }
+    return Status::OK();
+  }
+  virtual Status Sync() override { return Status::OK(); }
+  virtual Status Append(const Slice& slice) override {
+    contents_.append(slice.data(), slice.size());
+    return Status::OK();
+  }
+  void Drop(size_t bytes) {
+    contents_.resize(contents_.size() - bytes);
+    if (last_flush_ > contents_.size()) last_flush_ = contents_.size();
+  }
+
+ private:
+  std::string contents_;
+  Slice* reader_contents_;
+  size_t last_flush_;
+};
+
 class StringSource: public RandomAccessFile {
  public:
   explicit StringSource(const Slice& contents, uint64_t uniq_id = 0,