Add a test for seek data right after writing to mmap and not syncing

diff --git a/storage/file-io-mmap_test.go b/storage/file-io-mmap_test.go
new file mode 100644 (file)
index 0000000..316dce5
--- /dev/null
+++ b/storage/file-io-mmap_test.go
@@ -0,0 +1,69 @@
+package storage
+
+import (
+       "bytes"
+       "os"
+       "path/filepath"
+       "testing"
+
+       "github.com/go-quicktest/qt"
+)
+
+// Note this is AI slop with some modifications. Test if writes to mmap without sync or flush are
+// detected by a subsequent seek data. It would appear they are since the mmap is created from the
+// file descriptor used for the seek, and probably because we're in the same process so MAP_SHARED
+// kicks in.
+func TestFileIoImplementationsSeekDataDetection(t *testing.T) {
+       testData := []byte{0x42}
+       writeOffset := int64(1234567) // Large enough for sparse files to kick in.
+       const fileSize = 12345678
+
+       implementations := []struct {
+               name   string
+               fileIo fileIo
+       }{
+               {"classic", classicFileIo{}},
+               {"mmap", &mmapFileIo{}},
+       }
+
+       for _, impl := range implementations {
+               t.Run(impl.name, func(t *testing.T) {
+                       // Create temporary directory and file
+                       tempDir := t.TempDir()
+                       t.Logf("tempDir: %s", tempDir)
+                       testFile := filepath.Join(tempDir, "test.dat")
+
+                       // Create empty file
+                       f, err := os.Create(testFile)
+                       qt.Assert(t, qt.IsNil(err))
+                       f.Close()
+
+                       // Open for write and write a byte without flushing
+                       writer, err := impl.fileIo.openForWrite(testFile, fileSize)
+                       qt.Assert(t, qt.IsNil(err))
+
+                       _, err = writer.WriteAt(testData, writeOffset)
+                       qt.Assert(t, qt.IsNil(err))
+
+                       // Close writer (but note: we didn't call flush)
+                       err = writer.Close()
+                       qt.Assert(t, qt.IsNil(err))
+
+                       // Open for read and test seekData detection
+                       reader, err := impl.fileIo.openForRead(testFile)
+                       qt.Assert(t, qt.IsNil(err))
+                       defer reader.Close()
+
+                       // Use seekDataOrEof to detect data
+                       dataPos, err := reader.seekDataOrEof(writeOffset)
+                       qt.Assert(t, qt.IsNil(err))
+                       qt.Assert(t, qt.Equals(dataPos, writeOffset))
+
+                       var buf bytes.Buffer
+                       written, err := reader.writeToN(&buf, 1)
+                       qt.Assert(t, qt.IsNil(err))
+                       qt.Assert(t, qt.Equals(written, 1))
+                       qt.Assert(t, qt.DeepEquals(buf.Bytes(), testData))
+               })
+       }
+}