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package parser
import (
"encoding/binary"
"io"
"io/ioutil"
"os"
)
// This cache implementation is using a temp file to provide key-value data storage
// It allows to avoid storing intermediate calculations in RAM
// The stored data must be a fixed-size value or a slice of fixed-size values, or a pointer to such data
type cache struct {
file *os.File
chunkSize int64
}
func newCache(tempDir, filename string, data interface{}) (*cache, error) {
f, err := ioutil.TempFile(tempDir, filename)
if err != nil {
return nil, err
}
if err := os.Remove(f.Name()); err != nil {
return nil, err
}
return &cache{file: f, chunkSize: int64(binary.Size(data))}, nil
}
func (c *cache) SetEntry(id Id, data interface{}) error {
if err := c.setOffset(id); err != nil {
return err
}
return binary.Write(c.file, binary.LittleEndian, data)
}
func (c *cache) Entry(id Id, data interface{}) error {
if err := c.setOffset(id); err != nil {
return err
}
return binary.Read(c.file, binary.LittleEndian, data)
}
func (c *cache) Close() error {
return c.file.Close()
}
func (c *cache) setOffset(id Id) error {
offset := int64(id) * c.chunkSize
_, err := c.file.Seek(offset, io.SeekStart)
return err
}
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