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copy.go
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copy.go
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/*
* umoci: Umoci Modifies Open Containers' Images
* Copyright (C) 2016-2022 SUSE LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package system
import (
"errors"
"io"
"golang.org/x/sys/unix"
)
// Copy has identical semantics to io.Copy except it will automatically resume
// the copy after it receives an EINTR error.
func Copy(dst io.Writer, src io.Reader) (int64, error) {
// Make a buffer so io.Copy doesn't make one for each iteration.
var buf []byte
size := 32 * 1024
if lr, ok := src.(*io.LimitedReader); ok && lr.N < int64(size) {
if lr.N < 1 {
size = 1
} else {
size = int(lr.N)
}
}
buf = make([]byte, size)
var written int64
for {
n, err := io.CopyBuffer(dst, src, buf)
written += n // n is always non-negative
if errors.Is(err, unix.EINTR) {
continue
}
return written, err
}
}
// CopyN has identical semantics to io.CopyN except it will automatically
// resume the copy after it receives an EINTR error.
func CopyN(dst io.Writer, src io.Reader, n int64) (written int64, err error) {
// This is based on the stdlib io.CopyN implementation.
written, err = Copy(dst, io.LimitReader(src, n))
if written == n {
err = nil // somewhat confusing io.CopyN semantics
}
if written < n && err == nil {
err = io.EOF // if the source ends prematurely, io.EOF
}
return
}