SERVER-25868 Incomplete FTDC files on Windows

(cherry picked from commit b5277068ff66e7fe2b2a98144aa6993ca6e17f5c)

3 files changed, 53 insertions, 7 deletions

diff --git a/src/mongo/db/ftdc/file_writer.cpp b/src/mongo/db/ftdc/file_writer.cpp
index 576f946700a..1f290249c67 100644
--- a/src/mongo/db/ftdc/file_writer.cpp
+++ b/src/mongo/db/ftdc/file_writer.cpp
@@ -57,9 +57,6 @@ Status FTDCFileWriter::open(const boost::filesystem::path& file) {
 
     _archiveFile = file;
 
-    // Disable file buffering
-    _archiveStream.rdbuf()->pubsetbuf(0, 0);
-
     // Ideally, we create a file from scratch via O_CREAT but there is not portable way via C++
     // iostreams to do this.
     _archiveStream.open(_archiveFile.c_str(),
@@ -87,9 +84,6 @@ Status FTDCFileWriter::writeInterimFileBuffer(ConstDataRange buf) {
     // Fixed size interim stream
     std::ofstream interimStream;
 
-    // Disable file buffering
-    interimStream.rdbuf()->pubsetbuf(0, 0);
-
     // Open up a temporary interim file
     interimStream.open(_interimTempFile.c_str(),
                        std::ios_base::out | std::ios_base::binary | std::ios_base::trunc);
@@ -134,6 +128,18 @@ Status FTDCFileWriter::writeArchiveFileBuffer(ConstDataRange buf) {
                 << _archiveFile.generic_string()};
     }
 
+    // Flush the stream explictly, this is preferred over "pubsetbuf(0,0)" which has implementation
+    // defined behavior of "before any I/O has occurred".
+    _archiveStream.flush();
+
+    if (_archiveStream.fail()) {
+        return {
+            ErrorCodes::FileStreamFailed,
+            str::stream()
+                << "Failed to flush to archive file buffer for full-time diagnostic data capture: "
+                << _archiveFile.generic_string()};
+    }
+
     _size += buf.length();
 
     return Status::OK();
diff --git a/src/mongo/db/ftdc/file_writer_test.cpp b/src/mongo/db/ftdc/file_writer_test.cpp
index 6555a13c115..719f1ee87bd 100644
--- a/src/mongo/db/ftdc/file_writer_test.cpp
+++ b/src/mongo/db/ftdc/file_writer_test.cpp
@@ -45,6 +45,7 @@
 namespace mongo {
 
 const char* kTestFile = "metrics.test";
+const char* kTestFileCopy = "metrics.test.copy";
 
 // File Sanity check
 TEST(FTDCFileTest, TestFileBasicMetadata) {
@@ -160,7 +161,27 @@ public:
     }
 
 private:
-    void validate(bool forceCompress = true) {
+    void validate() {
+        // Verify we are flushing writes correctly by copying the file, and then reading it.
+        auto tempfile(boost::filesystem::path(_tempdir.path()) / kTestFileCopy);
+        boost::filesystem::copy_file(_path, tempfile);
+
+        // Read the file to make sure it is correct.
+        // We do not verify contents because the compressor may not have flushed the final records
+        // which is expected.
+        {
+            FTDCFileReader reader;
+
+            ASSERT_OK(reader.open(tempfile));
+
+            auto sw = reader.hasNext();
+            while (sw.isOK() && sw.getValue()) {
+                sw = reader.hasNext();
+            }
+
+            ASSERT_OK(sw);
+        }
+
         _writer.close();
 
         ValidateDocumentList(_path, _docs);
@@ -244,6 +265,23 @@ TEST(FTDCFileTest, TestFull) {
     }
 }
 
+// Test a large documents so that we cause multiple 4kb buffers to flush on Windows.
+TEST(FTDCFileTest, TestLargeDocuments) {
+    FileTestTie c;
+
+    for (int j = 0; j < 5; j++) {
+        for (size_t i = 0; i <= FTDCConfig::kMaxSamplesPerArchiveMetricChunkDefault; i++) {
+            BSONObjBuilder b;
+            b.append("name", "joe");
+            for (size_t k = 0; k < 200; k++) {
+                b.appendNumber("num", static_cast<long long int>(i * j + 5000 - (sin(k) * 100)));
+            }
+
+            c.addSample(b.obj());
+        }
+    }
+}
+
 // Test a bad file
 TEST(FTDCFileTest, TestBadFile) {
     unittest::TempDir tempdir("metrics_testpath");
diff --git a/src/mongo/db/ftdc/ftdc_test.cpp b/src/mongo/db/ftdc/ftdc_test.cpp
index 33fcce62eff..28910def1a1 100644
--- a/src/mongo/db/ftdc/ftdc_test.cpp
+++ b/src/mongo/db/ftdc/ftdc_test.cpp
@@ -58,6 +58,8 @@ void ValidateDocumentList(const boost::filesystem::path& p, const std::vector<BS
         sw = reader.hasNext();
     }
 
+    ASSERT_OK(sw);
+
     ValidateDocumentList(list, docs);
 }