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// Copyright 2021 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package filebuffer
import (
"bytes"
"errors"
"io"
"os"
)
const maxInt = int(^uint(0) >> 1) // taken from bytes.Buffer
var (
// ErrInvalidMemorySize occurs if the memory size is not in a valid range
ErrInvalidMemorySize = errors.New("Memory size must be greater 0 and lower math.MaxInt32")
// ErrWriteAfterRead occurs if Write is called after a read operation
ErrWriteAfterRead = errors.New("Write is unsupported after a read operation")
)
type readAtSeeker interface {
io.ReadSeeker
io.ReaderAt
}
// FileBackedBuffer uses a memory buffer with a fixed size.
// If more data is written a temporary file is used instead.
// It implements io.ReadWriteCloser, io.ReadSeekCloser and io.ReaderAt
type FileBackedBuffer struct {
maxMemorySize int64
size int64
buffer bytes.Buffer
file *os.File
reader readAtSeeker
}
// New creates a file backed buffer with a specific maximum memory size
func New(maxMemorySize int) (*FileBackedBuffer, error) {
if maxMemorySize < 0 || maxMemorySize > maxInt {
return nil, ErrInvalidMemorySize
}
return &FileBackedBuffer{
maxMemorySize: int64(maxMemorySize),
}, nil
}
// CreateFromReader creates a file backed buffer and copies the provided reader data into it.
func CreateFromReader(r io.Reader, maxMemorySize int) (*FileBackedBuffer, error) {
b, err := New(maxMemorySize)
if err != nil {
return nil, err
}
_, err = io.Copy(b, r)
if err != nil {
return nil, err
}
return b, nil
}
// Write implements io.Writer
func (b *FileBackedBuffer) Write(p []byte) (int, error) {
if b.reader != nil {
return 0, ErrWriteAfterRead
}
var n int
var err error
if b.file != nil {
n, err = b.file.Write(p)
} else {
if b.size+int64(len(p)) > b.maxMemorySize {
b.file, err = os.CreateTemp("", "gitea-buffer-")
if err != nil {
return 0, err
}
_, err = io.Copy(b.file, &b.buffer)
if err != nil {
return 0, err
}
return b.Write(p)
}
n, err = b.buffer.Write(p)
}
if err != nil {
return n, err
}
b.size += int64(n)
return n, nil
}
// Size returns the byte size of the buffered data
func (b *FileBackedBuffer) Size() int64 {
return b.size
}
func (b *FileBackedBuffer) switchToReader() error {
if b.reader != nil {
return nil
}
if b.file != nil {
if _, err := b.file.Seek(0, io.SeekStart); err != nil {
return err
}
b.reader = b.file
} else {
b.reader = bytes.NewReader(b.buffer.Bytes())
}
return nil
}
// Read implements io.Reader
func (b *FileBackedBuffer) Read(p []byte) (int, error) {
if err := b.switchToReader(); err != nil {
return 0, err
}
return b.reader.Read(p)
}
// ReadAt implements io.ReaderAt
func (b *FileBackedBuffer) ReadAt(p []byte, off int64) (int, error) {
if err := b.switchToReader(); err != nil {
return 0, err
}
return b.reader.ReadAt(p, off)
}
// Seek implements io.Seeker
func (b *FileBackedBuffer) Seek(offset int64, whence int) (int64, error) {
if err := b.switchToReader(); err != nil {
return 0, err
}
return b.reader.Seek(offset, whence)
}
// Close implements io.Closer
func (b *FileBackedBuffer) Close() error {
if b.file != nil {
err := b.file.Close()
os.Remove(b.file.Name())
return err
}
return nil
}
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