英文:
Read contents from what io.Writer writes
问题
有一个库可以导出一个文件，但我想捕获文件的内容。我想传递一个写入器给库，并能够读取写入器写入文件的内容。最终，我想修改库以跳过写入这个文件。使用io.Copy或io.Pipe可以实现这个吗？
库的代码创建了一个*File，并将其作为io.Writer使用。
我尝试使用io.Copy，但只读取了0字节。
func TestFileCopy(t *testing.T) {
codeFile, err := os.Create("test.txt")
if err != nil {
t.Error(err)
}
defer codeFile.Close()
codeFile.WriteString("Hello World")
n, err := io.Copy(os.Stdout, codeFile)
if err != nil {
t.Error(err)
}
log.Println(n, "bytes")
}
英文:
There's a library that exports a file but I'd like to capture the contents of the file. I'd like to pass a writer to the library and be able to read what the writer wrote to the file. Eventually i want to augment the library to skip writing this file.
Is this possible with io.Copy or io.Pipe?
The library code creates a *File and uses this handle as an io.Writer.
I tried using io.Copy but only 0 bytes were read.
func TestFileCopy(t *testing.T) {
codeFile, err := os.Create("test.txt")
if err != nil {
t.Error(err)
}
defer codeFile.Close()
codeFile.WriteString("Hello World")
n, err := io.Copy(os.Stdout, codeFile)
if err != nil {
t.Error(err)
}
log.Println(n, "bytes")
}
答案1
得分: 6
如果你想按原样捕获字节流，可以使用io.MultiWriter，并将bytes.Buffer作为第二个写入器。
var buf bytes.Buffer
w := io.MultiWriter(codeFile, &buf)
或者如果你想在写入时将文件内容显示在标准输出中：
w := io.MultiWriter(codeFile, os.Stdout)
否则，如果你想重新读取同一个文件，在写入后需要将文件指针定位回开头：
codeFile.Seek(0, 0)
英文:
If you want to capture the bytes as they are written, use an io.MultiWriter with a bytes.Buffer as the second writer.
var buf bytes.Buffer
w := io.MultiWriter(codeFile, &buf)
or to see the file on stdout as it's written:
w := io.MultiWriter(codeFile, os.Stdout)
Otherwise, if you want to re-read the same file, you need to seek back to the start after writing:
codeFile.Seek(0, 0)
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论