Update Storage options to support rolling buffer (#798)

Add new storage options:
- `WithBuffer`:  WithBuffer sets the buffer size. The value must be a factorial of 4KiB.
- `WithMinimumBuffer`: WithMinimumBuffer sets the threshold to enforce when the buffer expands back to its original size.

internal/storage/options.go

@@ -52,6 +52,8 @@ func getDefaultOptions() Options {
 		WithCloseSyncMode:  Asynchronous,
 		WithFileAccessMode: ReadOnly,
 		WithCreateFile:     false,
+		WithBuffer:         0,
+		WithMinimumBuffer:  0,
 	}
 }
 
@@ -60,6 +62,8 @@ type Options struct {
 	WithCloseSyncMode  SyncMode
 	WithFileAccessMode AccessMode
 	WithCreateFile     bool
+	WithBuffer         uint64
+	WithMinimumBuffer  uint64
 }
 
 // Option is a storage option.
@@ -85,3 +89,19 @@ func WithFileAccessMode(m AccessMode) Option {
 		o.WithFileAccessMode = m
 	}
 }
+
+// WithBuffer sets the buffer size.
+// The value must be a factorial of 4KiB.
+func WithBuffer(b uint64) Option {
+	return func(o *Options) {
+		o.WithBuffer = b
+	}
+}
+
+// WithMinimumBuffer sets the threshold to enforce when the
+// buffer expands back to its original size.
+func WithMinimumBuffer(m uint64) Option {
+	return func(o *Options) {
+		o.WithMinimumBuffer = m
+	}
+}

internal/storage/options_test.go

@@ -59,4 +59,24 @@ func Test_getOpts(t *testing.T) {
 		testOpts.WithCreateFile = true
 		assert.Equal(opts, testOpts)
 	})
+	t.Run("WithBuffer", func(t *testing.T) {
+		testOpts := getDefaultOptions()
+		opts := GetOpts(WithBuffer(0))
+		assert.Equal(testOpts, opts)
+
+		testOpts = getDefaultOptions()
+		opts = GetOpts(WithBuffer(4096))
+		testOpts.WithBuffer = 4096
+		assert.Equal(opts, testOpts)
+	})
+	t.Run("WithMinimumBuffer", func(t *testing.T) {
+		testOpts := getDefaultOptions()
+		opts := GetOpts(WithMinimumBuffer(0))
+		assert.Equal(testOpts, opts)
+
+		testOpts = getDefaultOptions()
+		opts = GetOpts(WithMinimumBuffer(88))
+		testOpts.WithMinimumBuffer = 88
+		assert.Equal(opts, testOpts)
+	})
 }