如何使用Untar内置的golang（golang.org/x/build/internal/untar）

Question

This seems like a really simple issue but for the life of me I cannot figure it out.

All I want to do is unzip and extract the contents of a tar.gz file. On godoc there seems to be a reference to a function that does exactly this. (https://godoc.org/golang.org/x/build/internal/untar).

There are no examples though and I can't seem to figure it out. Worse yet, though, I can't even figure out how to get access to the function.

Right now I have:

package main

import (
    "io"
    "os"
    //???
)

func main() {

    f, err := os.Open("foo.tar.gz")

    if err != nil {
        panic(err)
    }
    defer f.Close()

    var freader io.ReadCloser = f


    err = untar.Untar(freader, ".")    // <- Compiler doesn't recognize

    if err != nil {
        panic(err)
    }

    freader.Close()

}

Answer 1

You can't. Packages with internal as part of their name can't be used by any package outside of the same repo. In other words, golang.org/x/build/internal/untar is for golang.org/x/build only, and the compiler won't allow you to reference it from anywhere else.

You can, if you really like, copy the source of that package into a new file, and use it from there, but you can't use it directly. This gives the developers of the internal untar package complete freedom to break their interface without having to worry about other users.