golang http.Dir()

Question

使用FileServer看到需要传一个FileSystem类型
http.FileServer(http.Dir("/public"))
FileSystem是个interface

然后http.Dir实现了FileSystem

不应该是http.Dir.Open("public")
为何可以直接http.Dir("public")?不解，有人给解答下？

Answer 1

Dir实际上是string

type Dir string

http.Dir("/public")可以认为是类型转换，不是函数

Answer 2

因为Dir实现了Open接口,http.Dir("/public")将/public字符串转换为了Dir.

Answer 3

// A Dir implements FileSystem using the native file system restricted to a
// specific directory tree.
//
// While the FileSystem.Open method takes '/'-separated paths, a Dir's string
// value is a filename on the native file system, not a URL, so it is separated
// by filepath.Separator, which isn't necessarily '/'.
//
// Note that Dir will allow access to files and directories starting with a
// period, which could expose sensitive directories like a .git directory or
// sensitive files like .htpasswd. To exclude files with a leading period,
// remove the files/directories from the server or create a custom FileSystem
// implementation.
//
// An empty Dir is treated as ".".
type Dir string

func (d Dir) Open(name string) (File, error) {
    ....
}

// A FileSystem implements access to a collection of named files.
// The elements in a file path are separated by slash ('/', U+002F)
// characters, regardless of host operating system convention.
type FileSystem interface {
    Open(name string) (File, error)
}

这样看应该比较清楚吧

http.Dir("/public")是利用本地tmp目录实现一个文件系统；
http.FileServer(http.Dir("/public"))返回一个Handler，其用来处理访问本地"/tmp"文件夹的HTTP请求；