使用Go Docker API从装入的文件中获取文件上下文

Question

I'm trying to get mounted file content using Go docker API:

File secret.txt stores a line TOKEN=MY_TOKEN

Code:

cli, err := client.NewEnvClient()
if err != nil {
    panic(err)
}
defer cli.Close()

ctx := context.Background()

_, err = cli.ImagePull(ctx, "alpine", types.ImagePullOptions{})
if err != nil {
    panic(err)

}

containerConfig := &container.Config{
    Image: "alpine",
    Cmd:   []string{"echo", "hello world"},
}

// mounted file
h := container.HostConfig{
    Binds: []string{"/etc/secret.txt"},
}

resp, err := cli.ContainerCreate(ctx, containerConfig, &h, nil, "")
if err != nil {
    panic(err)
}

rc, _, err := cli.CopyFromContainer(context.Background(), resp.ID, "/etc/secret.txt")
if err != nil {
    fmt.Println(err.Error())
}
b, err := ioutil.ReadAll(rc)
if err != nil {
    fmt.Println(err.Error())
}
rc.Close()
fmt.Println(string(b), "  len=", len(string(b)))

I'm getting secret.txt file with additional information:

secret.txt/0040755000000000000000000000000013204637420011354 5ustar0000000000000000 len= 153

How to get actual data from text file? Thank you

Answer 1

First, the Binds parameter is of the format "source:target[:ro]", so you should have it "/etc/secret.txt:/etc/secret.txt", or "/etc/secret.txt:/etc/secret.txt:ro" if you want it to be read-only.

Second, the format of the data from the reader returned by CopyFromContainer() is a tar archive. Here is a small modification to your code that fixes Binds, and uses tar from the stdlib to extract the bytes from /etc/secret.

func main() {
        cli, err := client.NewEnvClient()
        if err != nil {
                panic(err)
        }
        defer cli.Close()

        ctx := context.Background()

        _, err = cli.ImagePull(ctx, "alpine", types.ImagePullOptions{})
        if err != nil {
                panic(err)

        }

        containerConfig := &container.Config{
                Image: "alpine",
                Cmd:   []string{"sleep", "1h"},
        }

        // mounted file
        h := container.HostConfig{
                Binds: []string{"/etc/secret.txt:/etc/secret.txt"},
        }

        resp, err := cli.ContainerCreate(ctx, containerConfig, &h, nil, "")
        if err != nil {
                panic(err)
        }

        rc, _, err := cli.CopyFromContainer(context.Background(), resp.ID, "/etc/secret.txt")
        if err != nil {
                fmt.Println(err.Error())
        }

        tr := tar.NewReader(rc)
        var b []byte
        for {
                hdr, err := tr.Next()
                if err == io.EOF {
                        break
                }
                if err != nil {
                        break
                }
                if hdr.Name == "secret.txt" {
                        b, err = ioutil.ReadAll(tr)
                        break
                }
                fmt.Println("Name:", hdr.Name)
                if err != nil {
                        break
                }
        }
        if err != nil {
                fmt.Println(err.Error())
        }
        rc.Close()
        fmt.Printf("%q (len=%d)
", b, len(string(b)))
}