读取超时。
我想做一些类似 unix 的东西tail -f，但是在通过 Go 的Cmd设施运行的进程产生的输出上。
显然，我的 google-fu 没有达到标准，但我确实找到了这篇文章，它引导我编写以下代码，几乎可以正常工作，但我希望能得到帮助。
如果重要的话，我会在 Mac 上运行它。
首先，这是编译为slowroll可执行文件的最小程序：
package main
import (
"fmt"
"time"
)
func main() {
line := 1
for {
fmt.Println("This is line", line)
line += 1
time.Sleep(2 * time.Second)
}
}
运行时，它会产生以下输出，每 2 秒一行：
> ./slowroll
This is line 1
This is line 2
This is line 3
This is line 4
等等。
这是尝试读取此内容的包代码，但允许超时以便可以完成其他操作：
package timeout_io
import (
"bufio"
"bytes"
"context"
"errors"
"time"
)
const BufferSize = 4096
var ErrTimeout = errors.New("timeout")
type TimeoutReader struct {
b *bufio.Reader
t time.Duration
}
func NewTimeoutReader(stdOut *bytes.Buffer) *TimeoutReader {
return &TimeoutReader{b: bufio.NewReaderSize(stdOut, BufferSize), t: 0}
}
func (r *TimeoutReader) SetTimeout(t time.Duration) time.Duration {
prev := r.t
r.t = t
return prev
}
type CallResponse struct {
Resp string
Err error
}
func helper(r *bufio.Reader) <-chan *CallResponse {
respChan := make(chan *CallResponse, 1)
go func() {
resp, err := r.ReadString('\n')
if err != nil {
respChan <- &CallResponse{resp, err}
} else {
respChan <- &CallResponse{resp, nil}
}
return
}()
return respChan
}
func (r *TimeoutReader) ReadLineCtx(ctx context.Context) (string, error) {
select {
case <-ctx.Done():
return "", ErrTimeout
case respChan := <-helper(r.b):
return respChan.Resp, respChan.Err
}
}
交互式爱情3回答
-
慕姐4208626
通过创建管道并从该管道读取来简化代码：cmd := exec.Command("./slowroll")stdout, _ := cmd.StdoutPipe()if err := cmd.Start(); err != nil { log.Fatal(err)}s := bufio.NewScanner(stdout)for s.Scan() { fmt.Printf("%s\n", s.Bytes())}如果您的目标是监视 stderr 和 stdin 的组合输出，则对两者使用相同的管道：cmd := exec.Command("./slowroll")combined, _ := cmd.StdoutPipe()cmd.Stderr = cmd.Stdout // <-- use stdout pipe for stderrif err := cmd.Start(); err != nil { log.Fatal(err)}s := bufio.NewScanner(combined)for s.Scan() { fmt.Printf("%s\n", s.Bytes())}问题中的代码在 stdOut bytes.Buffer 上有数据竞争。 -
一只斗牛犬
if err != timeout_io.ErrTimeout && err != io.EOF { ...; break; }在这样的条件下， anErrTimeout将被默默地忽略并且不会中断您的阅读循环。另请注意，到达io.EOF会在无限循环中发送您的程序（尝试使用echo "Hello"而不是./slowroll作为命令）。您可能希望将break指令放在if 块之后：if err != timeout_io.ErrTimeout && err != io.EOF { fmt.Println("ReadLine got error", err)}break -
缥缈止盈
昨晚深夜意识到我有点像围棋的标准行为。应该解释说目标是能够同时观看标准输出和标准错误。接受上面@Zombo 的建议，我切换到cmd.StdoutPipeand cmd.StderrPipe。主要思想是只有 goroutines 读取管道并将找到的内容放入通道，然后select在通道之间。所以slowroll.go不会产生无限输出，以表明 EOF 不会导致无限循环：package mainimport ( "fmt" "os" "time")func main() { line := 1 for { fmt.Println("This is line", line) line += 1 time.Sleep(2 * time.Second) if line%3 == 0 { fmt.Fprintf(os.Stderr, "This is error %d\n", line) } if line > 10 { break } }}现在更简单的工作watcher.go是：package mainimport ( "bufio" "fmt" "os" "os/exec" "sync")func main() { runCommand := &exec.Cmd{ Path: "./slowroll", } stdOut, err := runCommand.StdoutPipe() if err != nil { fmt.Println("Can't create StdoutPipe:", err) os.Exit(1) } stdErr, err := runCommand.StderrPipe() if err != nil { fmt.Println("Can't create StderrPipe:", err) os.Exit(1) } var wg sync.WaitGroup go func(wg *sync.WaitGroup) { defer wg.Done() err := runCommand.Run() if err != nil { fmt.Println("failed due to error:", err) os.Exit(1) } }(&wg) wg.Add(1) stdOutChan := make(chan string, 1) go func(wg *sync.WaitGroup) { defer wg.Done() scanner := bufio.NewScanner(stdOut) for scanner.Scan() { stdOutChan <- string(scanner.Bytes()) } fmt.Println("Ran out of stdout input, read thread bailing.") close(stdOutChan) }(&wg) wg.Add(1) stdErrChan := make(chan string, 1) go func(wg *sync.WaitGroup) { defer wg.Done() scanner := bufio.NewScanner(stdErr) for scanner.Scan() { stdErrChan <- string(scanner.Bytes()) } fmt.Println("Ran out of stderr input, read thread bailing.") close(stdErrChan) }(&wg) wg.Add(1) index := 1 keepGoing := true for keepGoing { select { case res, isOpen := <-stdOutChan: if !isOpen { fmt.Println("stdOutChan is no longer open, main bailing.") keepGoing = false } else { fmt.Println(index, "s:", res) index += 1 } case res, isOpen := <-stdErrChan: if !isOpen { fmt.Println("stdErrChan is no longer open, main bailing.") keepGoing = false } else { fmt.Println(index, "error s:", res) index += 1 } } } wg.Wait() fmt.Println("Done!")}输出： > go run watcher.go 1 s: This is line 1 2 s: This is line 2 3 error s: This is error 3 4 s: This is line 3 5 s: This is line 4 6 s: This is line 5 7 s: This is line 6 8 error s: This is error 6 9 s: This is line 7 10 s: This is line 8 11 s: This is line 9 12 error s: This is error 9 13 s: This is line 10 Ran out of stdout input, read thread bailing. stdOutChan is no longer open, main bailing. Ran out of stderr input, read thread bailing. Done!显然，可以进行一些重构，但它可以工作，这就是目标。
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