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lazyfile.go
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/
lazyfile.go
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package main
import (
"os"
"bytes"
"fmt"
)
const CHUNK_SIZE int64 = 4096
type LazyFile struct {
os.FileInfo
file *os.File
data []byte
}
func (fi *LazyFile) String() string {
return fmt.Sprintf("{\"%s\", %d}", fi.FileInfo.Name(), len(fi.data))
}
func (fi *LazyFile) Open() (err error) {
if fi.file != nil {
return
}
file, err := os.Open(fi.Name())
if err == nil {
fi.file = file
}
return
}
func (fi *LazyFile) Close() (err error) {
if fi.file == nil {
return nil
}
return fi.file.Close()
}
func (fi *LazyFile) Slurp() (n int, err error) {
if err := fi.Open(); err != nil {
return 0, err
}
buffer := make([]byte, CHUNK_SIZE)
n, err = fi.file.Read(buffer)
if err == nil {
fi.data = append(fi.data, buffer...)
}
return
}
func (fi *LazyFile) Equal(other *LazyFile) (equal bool, err error) {
// Check both files' length first
if fi.Size() != other.Size() {
return false, nil
}
size := fi.Size()
var i int64 = 0
for i < size {
// Slurp when necessary
if i + CHUNK_SIZE > int64(len(fi.data)) {
if _, err := fi.Slurp(); err != nil {
return false, err
}
}
if i + CHUNK_SIZE > int64(len(other.data)) {
if _, err := other.Slurp(); err != nil {
return false, err
}
}
x, y := fi.data[i:i+CHUNK_SIZE], other.data[i:i+CHUNK_SIZE]
if !bytes.Equal(x, y) {
return false, nil
}
i += CHUNK_SIZE
}
return true, nil
}