/
reader.go
121 lines (100 loc) · 2.57 KB
/
reader.go
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// (c) 2021 Jacek Olszak
// This code is licensed under MIT license (see LICENSE for details)
package store
import (
"fmt"
"hash"
"io"
"io/ioutil"
"os"
"time"
)
func (s *Store) openReader(options []ReaderOption, areChecksumsEqual func(expected, actual []byte) bool) (Reader, error) {
opts := &ReaderOptions{
chooseVersion: func(versions []Version) (Version, error) {
return versions[len(versions)-1], nil
},
}
for _, apply := range options {
if apply == nil {
continue
}
if err := apply(opts); err != nil {
return nil, fmt.Errorf("error applying option: %w", err)
}
}
versions, err := s.Versions()
if err != nil {
return nil, fmt.Errorf("error reading versions in directory %s: %w", s.dir, err)
}
if len(versions) == 0 {
return nil, versionNotFoundError{msg: "no version found"}
}
version, err := opts.chooseVersion(versions)
if err != nil {
return nil, err
}
name := s.dataFilename(version.Time)
file, err := os.Open(name)
if err != nil {
return nil, fmt.Errorf("error opening file %s for reading: %w", name, err)
}
r := &reader{
file: file,
version: version,
checksum: newHash(),
areChecksumsEqual: areChecksumsEqual,
metrics: &s.metrics.Read,
}
return r, nil
}
type ReaderOptions struct {
chooseVersion func([]Version) (Version, error)
}
type reader struct {
file *os.File
version Version
checksum hash.Hash
areChecksumsEqual func(expected, actual []byte) bool
metrics *ReadMetrics
}
func (r *reader) Read(p []byte) (int, error) {
defer r.addElapsedTime(time.Now())
n, err := r.file.Read(p)
if err == io.EOF {
if err2 := r.validateChecksum(); err2 != nil {
return n, err2
}
}
r.checksum.Write(p[:n])
r.metrics.TotalBytesRead += n
return n, err
}
func (r *reader) validateChecksum() error {
actual := r.checksum.Sum([]byte{})
expected, err := r.readChecksum()
if err != nil {
return fmt.Errorf("error reading checksum: %w", err)
}
if !r.areChecksumsEqual(expected, actual) {
return fmt.Errorf("invalid checksum when reading file %s", r.file.Name())
}
return nil
}
func (r *reader) readChecksum() ([]byte, error) {
checksumFile := checksumFileForDataFile(r.file.Name())
return ioutil.ReadFile(checksumFile)
}
func (r *reader) Close() error {
defer r.addElapsedTime(time.Now())
if err := r.file.Close(); err != nil {
return fmt.Errorf("error closing file: %w", err)
}
return r.validateChecksum()
}
func (r *reader) Version() Version {
return r.version
}
func (r *reader) addElapsedTime(start time.Time) {
r.metrics.TotalTime += time.Since(start)
}