英文:
Why os.Open returns nil error when opening a directory?
问题
我花了一些时间查找我的代码中的错误，结果发现在一个地方，我试图像读取文件一样读取目录的内容。请考虑以下代码：
import (
"fmt"
"os"
)
func init() {
file, err := os.Open("/tmp/")
fmt.Println(file, err) // 这里 err == nil
var b []byte
n, err := file.Read(b)
fmt.Println(n, err) // 这里 err == "read /tmp/: is a directory"
}
我想知道为什么 os.Open 允许无错误地“打开”一个目录，但无法“读取”它呢？文档中说：
Open 打开指定的文件用于读取。如果成功，返回的文件可以用于读取；关联的文件描述符具有 O_RDONLY 模式。如果出现错误，它将是 *PathError 类型。[参考链接]
对于这个“目录”是否是“文件”的问题可以有争议，但对我来说，它看起来有点误导。这种行为有什么用途吗？
英文:
I've spend some time looking for an error in my code and it appeared that at one place I was trying to read contents of a directory like it was the file. Consider the following code:
import (
"fmt"
"os"
)
func init() {
file, err := os.Open("/tmp/")
fmt.Println(file, err) //err == nil here
var b []byte
n, err := file.Read(b)
fmt.Println(n, err) //err == "read /tmp/: is a directory"
}
I am wondering, why os.Open allows to 'open' a directory without an error if I cannot 'read' it anyway? The documentation says
> Open opens the named file for reading. If successful, methods on the
> returned file can be used for reading; the associated file descriptor
> has mode O_RDONLY. If there is an error, it will be of type
> *PathError. [reference]
If the 'directory' is a 'file' is disputable but for me it looks a bit misleading. Is there any usage for that behavior?
答案1
得分: 4
"Reading"有更多的含义，其中之一是读取文件的内容。
另一个含义是，如果文件表示一个目录，你可以读取它的内容，也就是其中的文件列表或子文件夹列表，可以使用File.Readdir()或File.Readdirnames()。对于表示目录的已打开文件，这是完全有效的。
此外，即使文件表示一个文件夹，你也可以对已打开的os.File执行更多操作，例如调用其File.Chdir()（仅适用于目录）或File.Chmod()方法，或者使用File.Stat()获取有关它的统计信息。我不明白为什么应该禁止“打开”一个文件夹。文档中的措辞可能不完美（或者可以扩展以提及这一点）。
英文:
"Reading" has more meanings, one of which is reading the contents of a file.
Another meaning is if the file denotes a directory, you may read its content, which is the list of the files / subfolders in it, using File.Readdir() or File.Readdirnames(). This is perfectly valid for an opened file whose name denotes a directory.
Also you may do a lot more with an opened os.File even if it denotes a folder, e.g. call its File.Chdir() (exclusive for directories) or File.Chmod() methods, or get statistics about it using File.Stat(). I don't see why "opening" a folder should be disallowed. The wording in the doc may not be perfect (or it could be extended to mention this though).
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