From 685643d506b7593cfe2b66c066f7f9a68655a2ff Mon Sep 17 00:00:00 2001
From: chrislu <chris.lu@gmail.com>
Date: Sat, 4 Jun 2022 19:10:52 -0700
Subject: [PATCH] needle read into a writer

---
 weed/storage/needle/needle_read_page.go | 26 +++++++++++++++++++++++++
 weed/storage/needle/needle_read_test.go | 20 ++-----------------
 2 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/weed/storage/needle/needle_read_page.go b/weed/storage/needle/needle_read_page.go
index 4600f4314..300b415c9 100644
--- a/weed/storage/needle/needle_read_page.go
+++ b/weed/storage/needle/needle_read_page.go
@@ -9,6 +9,32 @@ import (
 	"io"
 )
 
+// ReadNeedleDataInto uses a needle without n.Data to read the content into an io.Writer
+func (n *Needle) ReadNeedleDataInto(r backend.BackendStorageFile, offset int64, buf []byte, writer io.Writer, expectedChecksumValue uint32) (err error) {
+	crc := CRC(0)
+	for x := 0; ; x += len(buf) {
+		count, err := n.ReadNeedleData(r, offset, buf, int64(x))
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return fmt.Errorf("ReadNeedleData: %v", err)
+		}
+		if count > 0 {
+			crc = crc.Update(buf[0:count])
+			if _, err = writer.Write(buf[0:count]); err != nil {
+				return fmt.Errorf("ReadNeedleData write: %v", err)
+			}
+		} else {
+			break
+		}
+	}
+	if expectedChecksumValue != crc.Value() {
+		return fmt.Errorf("ReadNeedleData checksum %v expected %v", crc.Value(), expectedChecksumValue)
+	}
+	return nil
+}
+
 // ReadNeedleData uses a needle without n.Data to read the content
 // volumeOffset: the offset within the volume
 // needleOffset: the offset within the needle Data
diff --git a/weed/storage/needle/needle_read_test.go b/weed/storage/needle/needle_read_test.go
index b519b0241..688df0d53 100644
--- a/weed/storage/needle/needle_read_test.go
+++ b/weed/storage/needle/needle_read_test.go
@@ -3,7 +3,6 @@ package needle
 import (
 	"fmt"
 	"github.com/chrislusf/seaweedfs/weed/storage/backend"
-	"github.com/stretchr/testify/assert"
 	"io"
 	"os"
 	"testing"
@@ -75,24 +74,9 @@ func TestPageRead(t *testing.T) {
 		fmt.Printf("Checksum value %d\n", checksumValue)
 
 		buf := make([]byte, 1024)
-		crc := CRC(0)
-		for x := int64(0); ; x += 1024 {
-			count, err := n.ReadNeedleData(datBackend, offset, buf, x)
-			if err != nil {
-				if err == io.EOF {
-					break
-				}
-				t.Fatalf("ReadNeedleData: %v", err)
-			}
-			if count > 0 {
-				crc = crc.Update(buf[0:count])
-			} else {
-				break
-			}
+		if err = n.ReadNeedleDataInto(datBackend, offset, buf, io.Discard, checksumValue); err != nil {
+			t.Fatalf("ReadNeedleDataInto: %v", err)
 		}
-		fmt.Printf("read checksum value %d\n", crc.Value())
-
-		assert.Equal(t, checksumValue, crc.Value(), "validate checksum value")
 
 	}