[英]Go: Copy data from io.Reader to io.Writer implementations with sleep timeout, empty Writes
我正在嘗試將數據從 io.Reader 實現復制到 io.Writer 實現,並在下一次迭代之前延遲(time.Sleep)。 理想情況下,我想控制該過程(即 io.Copy 並不理想,因為我可能想在讀取和寫入之間執行一些操作)。
無論如何,在下面的代碼中嘗試了 4 種方法,它應該在go.dev/play
中運行。 除了空字符串之外,我無法獲得任何寫入任何內容的方法,盡管所有寫入方法確實報告了正確的寫入字節數(與讀取報告的相同)。 我可能缺少一些基本的東西,但任何幫助/解釋都非常感謝,因為我很困惑。
以下代碼包含 4 種不同方法的注釋和函數,用於在下一次迭代之前以指定的延遲 (time.Sleep) 從 io.Reader 的自定義實現到 io.Writer 復制和記錄數據。 您可以在下方評論/取消評論所需的 function 以觀察結果。
package main
import (
"bufio"
"fmt"
"io"
"log"
"math/rand"
"time"
)
// READ
type MyReader struct{}
func (r *MyReader) Read(p []byte) (read int, err error) {
someString := fmt.Sprintf("testing-%d", rand.Int())
p = []byte(someString)
read = len(p)
log.Printf("io read %d bytes: %s\n", read, string(p))
return read, io.EOF
}
// WRITE
type MyWriter struct{}
func (w *MyWriter) Write(p []byte) (wrote int, err error) {
wrote = len(p)
log.Printf("io wrote %d bytes: %s\n", wrote, string(p))
return
}
// MAIN
func main() {
// The following contains comments and functions for 4 different approaches to copying and logging data from
// custom implementations of io.Reader to an io.Writer with a specified delay (time.Sleep) before the next
// iteration. You may comment/uncomment the desired function below to observe the results.
// AutoIoCopy - Approach 1) io.Copy
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called and the MyWriter.Write method of the io.Writer implementation
// is executed, but the output logged by MyWriter.Write is empty instead of the expected string reported by the
// MyReader.Read log.
//
AutoIoCopy()
// ReadBytesApproach - Approach 2) Using ReadBytes('\n')
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called and reports written bytes, but the Write method of MyWriter
// io.Writer implementation is never executed, it is skipped and another Read occurs
//
//ReadBytesApproach()
// ReadLineApproach - Approach 3) Using ReadLine()
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called and reports written bytes, but the Write method of MyWriter
// io.Writer implementation is never executed, it is skipped and another Read occurs
//
//ReadLineApproach()
// WriteToApproach - Approach 4) Using WriteTo()
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called and reports written bytes, but the Write method of MyWriter
// io.Writer implementation is never executed, it is skipped and another Read occurs
//
//WriteToApproach()
}
// Approaches:
// AutoIoCopy - Approach 1) io.Copy
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called and the MyWriter.Write method of the io.Writer implementation
// is executed, but the output logged by MyWriter.Write is empty instead of the expected string reported by the
// MyReader.Read log.
//
func AutoIoCopy() {
reader := MyReader{}
writer := MyWriter{}
for {
_, _ = io.Copy(&writer, &reader)
time.Sleep(1000 * time.Millisecond)
}
}
// ReadBytesApproach - Approach 2) Using ReadBytes('\n')
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called but the Write method of MyWriter io.Writer implementation
// is never executed, it is skipped and another Read occurs
//
func ReadBytesApproach() {
reader := MyReader{}
writer := MyWriter{}
bufRead := bufio.NewReader(&reader)
bufWrite := bufio.NewWriter(&writer)
for {
// Using ReadBytes('\n')
readBytes, err := bufRead.ReadBytes('\n')
if err != nil {
switch err {
case io.EOF:
log.Printf("io.EOF detected\n")
wrote, err := bufWrite.Write(readBytes)
if err != nil {
log.Printf("error writing: %s\n", err)
}
convertedValue := string(readBytes)
log.Printf("bufio wrote %d bytes: %s\n", wrote, convertedValue)
break
default:
log.Printf("bufio error reading: %s\n", err.Error())
break
}
} else {
log.Printf("no error, continue to read\n")
}
time.Sleep(1000 * time.Millisecond)
}
}
// ReadLineApproach - Approach 3) Using ReadLine()
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that the bufio.Write method is called but the Write method of MyWriter io.Writer implementation
// is never executed, it is skipped and another Read occurs
//
func ReadLineApproach() {
reader := MyReader{}
writer := MyWriter{}
bufRead := bufio.NewReader(&reader)
bufWrite := bufio.NewWriter(&writer)
for {
// Using ReadLine()
readBytes, _, err := bufRead.ReadLine()
if err != nil {
switch err {
case io.EOF:
log.Printf("io.EOF detected\n")
wrote, err := bufWrite.Write(readBytes)
if err != nil {
log.Printf("error writing: %s\n", err)
}
convertedValue := string(readBytes)
log.Printf("bufio wrote %d bytes: %s\n", wrote, convertedValue)
break
default:
log.Printf("bufio error reading: %s\n", err.Error())
break
}
} else {
log.Printf("no error, continue to read\n")
}
time.Sleep(1000 * time.Millisecond)
}
}
// WriteToApproach - Approach 4) Using WriteTo()
//
// Expected is to read and log the correct value (generated in the method)
// then write the value (output another log)
//
// Actual is that neither the bufio.Write or the Write method of MyWriter io.Writer implementation is executed,
// it is skipped and another Read occurs
//
func WriteToApproach() {
reader := MyReader{}
writer := MyWriter{}
bufRead := bufio.NewReader(&reader)
bufWrite := bufio.NewWriter(&writer)
for {
wrote, _ := bufRead.WriteTo(bufWrite)
log.Printf("bufio wrote %d bytes\n", wrote)
time.Sleep(1000 * time.Millisecond)
}
}
問題出在MyReader.Read
方法中
線
p = []byte(someString)
應該
read = copy(p, someString)
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