英文:
How to stop io.CopyN
问题
我有一些代码，从文件复制到tcp套接字（类似于ftp服务器），如果需要，希望能够中止此复制。
我只是使用io.CopyN(socket, file, size)，看不到任何中止信号的方法。有什么想法吗？
英文:
I have some code that copies from a file to a tcp socket (like an ftp server) and want to be able to abort this copy if needed.
Im just using io.CopyN(socket, file, size) and cant see a way to signal an abort. Any ideas?
答案1
得分: 6
如何只关闭输入文件？io.CopyN将返回一个错误并中止。
这是一个演示（如果不在Linux上运行，请将/dev/zero和/dev/null更改为您的操作系统等效物！）
package main
import (
"fmt"
"io"
"log"
"os"
"time"
)
func main() {
in, err := os.Open("/dev/zero")
if err != nil {
log.Fatal(err)
}
out, err := os.Create("/dev/null")
if err != nil {
log.Fatal(err)
}
go func() {
time.Sleep(time.Second)
in.Close()
}()
written, err := io.CopyN(out, in, 1E12)
fmt.Printf("%d 字节已写入，错误为 %s\n", written, err)
}
运行时，它将打印类似以下内容：
9756147712 字节已写入，错误为 read /dev/zero: bad file descriptor
英文:
How about just closing the input file? io.CopyN will then return an error and abort.
Here is a demonstration (If not running on Linux change /dev/zero & /dev/null for your OS equivalent!)
package main
import (
"fmt"
"io"
"log"
"os"
"time"
)
func main() {
in, err := os.Open("/dev/zero")
if err != nil {
log.Fatal(err)
}
out, err := os.Create("/dev/null")
if err != nil {
log.Fatal(err)
}
go func() {
time.Sleep(time.Second)
in.Close()
}()
written, err := io.CopyN(out, in, 1E12)
fmt.Printf("%d bytes written with error %s\n", written, err)
}
When run it will print something like
9756147712 bytes written with error read /dev/zero: bad file descriptor
答案2
得分: 4
CopyN努力复制N个字节。如果您想选择性地复制少于N个字节，则首先不要使用CopyN。我可能会将原始代码改为以下内容（未经测试的代码）：
func copyUpToN(dst Writer, src Reader, n int64, signal chan int) (written int64, err error) {
buf := make([]byte, 32*1024)
for written < n {
select {
default:
case <-signal:
return 0, fmt.Errorf("Aborted") // 或其他适当的错误信息
}
l := len(buf)
if d := n - written; d < int64(l) {
l = int(d)
}
nr, er := src.Read(buf[0:l])
if nr > 0 {
nw, ew := dst.Write(buf[0:nr])
if nw > 0 {
written += int64(nw)
}
if ew != nil {
err = ew
break
}
if nr != nw {
err = io.ErrShortWrite
break
}
}
if er != nil {
err = er
break
}
}
return written, err
}
英文:
CopyN tries hard to copy N bytes. If you want to optionally copy less than N bytes then don't use CopyN in the first place. I would probably adapt the original code to something like (untested code):
func copyUpToN(dst Writer, src Reader, n int64, signal chan int) (written int64, err error) {
buf := make([]byte, 32*1024)
for written < n {
select {
default:
case <-signal:
return 0, fmt.Errorf("Aborted") // or whatever
}
l := len(buf)
if d := n - written; d < int64(l) {
l = int(d)
}
nr, er := src.Read(buf[0:l])
if nr > 0 {
nw, ew := dst.Write(buf[0:nr])
if nw > 0 {
written += int64(nw)
}
if ew != nil {
err = ew
break
}
if nr != nw {
err = io.ErrShortWrite
break
}
}
if er != nil {
err = er
break
}
}
return written, err
}
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