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server/internal/library/queue/disk/reader.go

@@ -0,0 +1,176 @@
+package disk
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"path/filepath"
+	"sort"
+	"strconv"
+)
+
+var (
+	errorQueueEmpty = errors.New("queue is empty")
+)
+
+type reader struct {
+	file       *os.File
+	index      int64
+	offset     int64
+	reader     *bufio.Reader
+	checkpoint checkpoint
+	config     *Config
+}
+
+type checkpoint struct {
+	Index  int64 `json:"index"`
+	Offset int64 `json:"offset"`
+}
+
+// read data
+func (r *reader) read() (int64, int64, []byte, error) {
+	if err := r.check(); err != nil {
+		return r.index, r.offset, nil, err
+	}
+
+	// read a line
+	data, err := r.reader.ReadBytes('\n')
+	if err != nil {
+		return r.index, r.offset, nil, err
+	}
+	data = bytes.TrimRight(data, "\n")
+
+	r.offset += int64(len(data)) + 1
+	return r.index, r.offset, data, err
+}
+
+// check a new segment
+func (r *reader) check() error {
+	if r.file != nil {
+		return nil
+	}
+
+	file, err := r.next()
+	if err != nil {
+		return err
+	}
+
+	return r.open(file)
+}
+
+func (r *reader) open(file string) (err error) {
+	if r.file, err = os.OpenFile(file, os.O_RDONLY, filePerm); err != nil {
+		return err
+	}
+
+	// get file index
+	r.index = r.getIndex(file)
+
+	// seek read offset
+	if _, err = r.file.Seek(r.offset, 0); err != nil {
+		return err
+	}
+
+	r.reader = bufio.NewReader(r.file)
+	return nil
+}
+
+// safeRotate to next segment
+func (r *reader) safeRotate() error {
+	// if there is no next file, it is not cleared
+	if _, err := r.next(); err == errorQueueEmpty {
+		return nil
+	}
+
+	return r.rotate()
+}
+
+// rotate to next segment
+func (r *reader) rotate() error {
+	if r.file == nil {
+		return nil
+	}
+
+	// close segment
+	_ = r.file.Close()
+	r.file, r.offset, r.reader = nil, 0, nil
+	return nil
+}
+
+// close reader
+func (r *reader) close() {
+	if r.file == nil {
+		return
+	}
+
+	if err := r.file.Close(); err != nil {
+		return
+	}
+
+	r.file, r.reader, r.index, r.offset = nil, nil, 0, 0
+}
+
+// sync index and offset
+func (r *reader) sync() {
+	name := path.Join(r.config.Path, indexFile)
+	data, _ := json.Marshal(&r.checkpoint)
+	_ = ioutil.WriteFile(name, data, filePerm)
+}
+
+// restore index and offset
+func (r *reader) restore() (err error) {
+	name := path.Join(r.config.Path, indexFile)
+
+	// uninitialized
+	if _, err1 := os.Stat(name); err1 != nil {
+		r.sync()
+	}
+
+	data, _ := ioutil.ReadFile(name)
+
+	_ = json.Unmarshal(data, &r.checkpoint)
+	r.index, r.offset = r.checkpoint.Index, r.checkpoint.Offset
+	if r.index == 0 {
+		return
+	}
+
+	if err = r.open(fmt.Sprintf("%s/%d.data", r.config.Path, r.index)); err != nil {
+		r.offset = 0
+	}
+	return
+}
+
+// next segment
+func (r *reader) next() (string, error) {
+	files, err := filepath.Glob(filepath.Join(r.config.Path, "*.data"))
+	if err != nil {
+		return "", err
+	}
+	sort.Strings(files)
+
+	for _, file := range files {
+		index := r.getIndex(file)
+		if index < r.checkpoint.Index {
+			_ = os.Remove(file) // remove expired segment
+		}
+
+		if index > r.index {
+			return file, nil
+		}
+	}
+
+	return "", errorQueueEmpty
+}
+
+// get segment index
+func (r *reader) getIndex(filename string) int64 {
+	base := filepath.Base(filename)
+	name := base[0 : len(base)-len(path.Ext(filename))]
+	index, _ := strconv.ParseInt(name, 10, 64)
+	return index
+}