next

fs/util/bufioutil/buffer_seeker.go

@@ -0,0 +1,34 @@
+package bufioutil
+
+import (
+	"bufio"
+	"io"
+)
+
+type BufferedSeeker struct {
+	rs io.ReadSeeker
+	br *bufio.Reader
+}
+
+func NewBufferedSeeker(rs io.ReadSeeker, size int) *BufferedSeeker {
+	return &BufferedSeeker{
+		rs: rs,
+		br: bufio.NewReaderSize(rs, size),
+	}
+}
+
+func (b *BufferedSeeker) Read(p []byte) (int, error) {
+	return b.br.Read(p)
+}
+
+func (b *BufferedSeeker) Seek(offset int64, whence int) (int64, error) {
+	if whence == io.SeekCurrent {
+		offset -= int64(b.br.Buffered())
+	}
+	n, err := b.rs.Seek(offset, whence)
+	if err != nil {
+		return 0, err
+	}
+	b.br.Reset(b.rs)
+	return n, nil
+}

fs/util/bufioutil/buffer_seeker_test.go

@@ -0,0 +1,64 @@
+package bufioutil
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestBufferedSeeker(t *testing.T) {
+	const alphabet = "abcdefghijklmnopqrstuvwxyz"
+
+	bs := NewBufferedSeeker(strings.NewReader(alphabet), 0) // minReadBufferSize = 16
+
+	checkRead := func(buf []byte, expected string) {
+		t.Helper()
+		_, err := bs.Read(buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !bytes.Equal(buf, []byte(expected)) {
+			t.Fatalf("expected %s, got %s", expected, buf)
+		}
+	}
+
+	// Read the first 5 bytes
+	buf := make([]byte, 5)
+
+	checkRead(buf, "abcde")
+
+	// Seek back to the beginning
+	_, err := bs.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// read 'a'
+	checkRead(buf[:1], "a")
+
+	if bs.br.Buffered() == 0 {
+		t.Fatalf("totally unexpected sanity check failed")
+	}
+
+	// Seek past 'b'
+	_, err = bs.Seek(1, io.SeekCurrent)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkRead(buf, "cdefg")
+
+	// Seek back to the beginning
+	_, err = bs.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkRead(buf, "abcde")
+
+	// Seek to the end
+	_, err = bs.Seek(-5, io.SeekEnd)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkRead(buf, "vwxyz")
+}