add Peek method supporting pagination

filefanoutqueue.go

@@ -180,6 +180,18 @@ func (q *FileFanoutQueue) PeekAll(fanoutID int64) ([][]byte, []int64, error) {
 	return q.fileQueue.peekAll(index, q.Size(fanoutID))
 }
 
+// PeekPagination to peek data from queue by paing feature.
+func (q *FileFanoutQueue) PeekPagination(fanoutID int64, page, pagesize uint64) ([][]byte, []int64, error) {
+
+	qf, err := q.getQueueFront(fanoutID)
+	if err != nil {
+		return nil, nil, err
+	}
+	index := qf.frontIndex
+
+	return q.fileQueue.peekPagination(index, q.fileQueue.size(index), page, pagesize)
+}
+
 // Skip To skip deqeue target number of items
 func (q *FileFanoutQueue) Skip(fanoutID int64, count int64) error {
 	if count <= 0 {

filefanoutqueue_test.go

@@ -368,3 +368,63 @@ func TestFanoutQueue_Status(t *testing.T) {
 	})
 
 }
+
+func TestFanoutQueue_PeekPagination(t *testing.T) {
+	Convey("Test PeekPagination", t, func() {
+		path := Tempfile()
+		defer clearFiles(path, "fanoutqueue")
+		fanoutID := int64(100)
+
+		defer clearFrontIndexFiles(path, "fanoutqueue", fanoutID)
+
+		queue := FileFanoutQueue{}
+		err := queue.Open(path, "fanoutqueue", nil)
+		if err != nil {
+			t.Error(err)
+		}
+		defer queue.Close()
+
+		Convey("test PeekPagination on empty queue", func() {
+			data, indexs, err := queue.PeekPagination(fanoutID, 0, 0)
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+
+			data, indexs, err = queue.PeekPagination(fanoutID, 1, 1)
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+		})
+
+		Convey("test PeekPagination on items small than pagesize", func() {
+			for i := 0; i < 5; i++ { // add value
+				_, err := queue.Enqueue([]byte("hello matthew " + strconv.Itoa(i)))
+				So(err, ShouldBeNil)
+			}
+
+			data, indexs, err := queue.PeekPagination(fanoutID, 0, 0)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 5)
+			So(string(data[4]), ShouldEqual, "hello matthew 4")
+			So(len(indexs), ShouldEqual, 5)
+
+			data, indexs, err = queue.PeekPagination(fanoutID, 1, 10)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 5)
+			So(string(data[4]), ShouldEqual, "hello matthew 4")
+			So(len(indexs), ShouldEqual, 5)
+
+			data, indexs, err = queue.PeekPagination(fanoutID, 2, 10) // large paing
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+
+			data, indexs, err = queue.PeekPagination(fanoutID, 2, 2)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 2)
+			So(string(data[1]), ShouldEqual, "hello matthew 3")
+			So(len(indexs), ShouldEqual, 2)
+		})
+
+	})
+}

filequeue.go

@@ -40,6 +40,8 @@ const (
 	fileSuffix = ".dat"
 
 	defaultFileMode = 0666
+
+	Default_Page_Size = 10
 )
 
 // DefaultOptions default options
@@ -435,6 +437,52 @@ func (q *FileQueue) PeekAll() ([][]byte, []int64, error) {
 	return q.peekAll(index, q.Size())
 }
 
+// PeekPagination to peek data from queue by paing feature.
+func (q *FileQueue) PeekPagination(page, pagesize uint64) ([][]byte, []int64, error) {
+	return q.peekPagination(q.frontIndex, q.Size(), page, pagesize)
+}
+
+// peekPagination to peek data from queue by paing feature.
+func (q *FileQueue) peekPagination(frontindex int64, size int64, page, pagesize uint64) ([][]byte, []int64, error) {
+	if page == 0 {
+		page = 1
+	}
+	if pagesize == 0 {
+		pagesize = Default_Page_Size
+	}
+
+	begin := (page - 1) * pagesize
+	end := begin + pagesize
+
+	if begin > uint64(size) { // no data return
+		return [][]byte{}, []int64{}, nil
+	}
+
+	if end > uint64(size) {
+		end = uint64(size)
+		pagesize = end - begin
+	}
+
+	// fix the offset
+	begin = begin + uint64(frontindex)
+	end = end + uint64(frontindex)
+
+	result := make([][]byte, pagesize)
+	indexs := make([]int64, pagesize)
+
+	var index int = 0
+	for i := begin; i < end; i++ {
+		bb, err := q.peek(int64(i))
+		if err != nil {
+			return nil, nil, err
+		}
+		result[index] = bb
+		indexs[index] = int64(i)
+		index++
+	}
+	return result, indexs, nil
+}
+
 // Skip the target n items to front index
 func (q *FileQueue) Skip(count int64) error {
 	if q.IsEmpty() {

filequeue_test.go

@@ -2,6 +2,7 @@ package bigqueue
 
 import (
 	"fmt"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -431,6 +432,66 @@ func TestFileQueue_Status(t *testing.T) {
 
 }
 
+// TestFileQueue_PeekPagination
+func TestFileQueue_PeekPagination(t *testing.T) {
+	Convey("Test PeekPagination", t, func() {
+
+		path := Tempfile()
+		defer clearFiles(path, "testqueue")
+
+		var queue = new(FileQueue)
+
+		err := queue.Open(path, "testqueue", nil)
+		if err != nil {
+			t.Error(err)
+		}
+		defer queue.Close()
+
+		Convey("test PeekPagination on empty queue", func() {
+			data, indexs, err := queue.PeekPagination(0, 0)
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+
+			data, indexs, err = queue.PeekPagination(1, 1)
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+		})
+
+		Convey("test PeekPagination on items small than pagesize", func() {
+			for i := 0; i < 5; i++ { // add value
+				_, err := queue.Enqueue([]byte("hello matthew " + strconv.Itoa(i)))
+				So(err, ShouldBeNil)
+			}
+
+			data, indexs, err := queue.PeekPagination(0, 0)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 5)
+			So(string(data[4]), ShouldEqual, "hello matthew 4")
+			So(len(indexs), ShouldEqual, 5)
+
+			data, indexs, err = queue.PeekPagination(1, 10)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 5)
+			So(string(data[4]), ShouldEqual, "hello matthew 4")
+			So(len(indexs), ShouldEqual, 5)
+
+			data, indexs, err = queue.PeekPagination(2, 10) // large paing
+			So(err, ShouldBeNil)
+			So(data, ShouldBeEmpty)
+			So(indexs, ShouldBeEmpty)
+
+			data, indexs, err = queue.PeekPagination(2, 2)
+			So(err, ShouldBeNil)
+			So(len(data), ShouldEqual, 2)
+			So(string(data[1]), ShouldEqual, "hello matthew 3")
+			So(len(indexs), ShouldEqual, 2)
+		})
+
+	})
+}
+
 // tempfile returns a temporary file path.
 func Tempfile() string {
 	return "./bin/temp"