Execute powershell command in running container via Docker API

Question

I want to execute a powershell command in a docker container running on a windows host.

The specific command I want to execute is "powershell Get-PSDrive C | Select-Object Used,Free"

I have implemented this using the Docker API for python and it is simple like calling:

cmd = "powershell Get-PSDrive C | Select-Object Used,Free"
output = container.exec_run(cmd)

This works as intended, but I need to implement this in golang.

But somehow, it is not clear for me how to interact with the Docker API for golang. I looked into the API and was confused by the hijackedSession. How do I have to setup the calls for ContainerExecCreate, ContainerExecAttach and ContainerExecStart ?

I expect the golang script to deliver the same results like the python code does:

        Used         Free
        ----         ----
199181606912 307151622144

Which then can be parsed by me.

Just a quick info for users trying to interface windows containers using powershell. The nanoserver docker image does not include powershell. I used servercore. — semaph0r
– semaph0r, Commented Apr 22, 2019 at 9:11

aristotll · Accepted Answer · 2019-04-21 15:03:50Z

1

+50

The HijackedResponse struct:

type HijackedResponse struct {
    Conn   net.Conn
    Reader *bufio.Reader
}

You need to copy the response from the resp.Reader,here is my code:

package main

import (
    "bytes"
    "context"
    "fmt"
    "github.com/docker/docker/api/types"
    "github.com/docker/docker/client"
    "github.com/docker/docker/pkg/stdcopy"
    "strings"
)

func readFromCommand() (string, error) {
    cli, err := client.NewEnvClient()
    if err != nil {
        return "", err
    }
    ctx := context.Background()
    config := types.ExecConfig{
        Cmd:          strings.Split("powershell Get-PSDrive C | Select-Object Used,Free", " "),
        AttachStdout: true,
        AttachStderr: true,
    }
    response, err := cli.ContainerExecCreate(ctx,
        // container id
        "cf59d65ab1", config)
    if err != nil {
        return "", err
    }
    execID := response.ID

    resp, err := cli.ContainerExecAttach(ctx, execID, config)
    if err != nil {
        return "", err
    }
    defer resp.Close()
    stdout := new(bytes.Buffer)
    stderr := new(bytes.Buffer)
    _, err = stdcopy.StdCopy(stdout, stderr, resp.Reader)
    if err != nil {
        return "", err
    }
    s := stdout.String()
    fmt.Println(s)
    i := stderr.String()
    fmt.Println(i)
    return s, nil

}

Do remember to change the container id.

answered Apr 21, 2019 at 15:03

aristotll

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3 Comments

semaph0r Over a year ago

Thank you for your example. But, is there something missing?

func (cli *Client) ContainerExecAttach(ctx context.Context, execID string, config types.ExecStartCheck) (types.HijackedResponse, error)

says that the configuration is of type ExecStartCheck. In the above example a config of type ExecConfig is passed.

aristotll Over a year ago

@semaph0r In my docker client version docker v1.13.1, it is

func (cli *Client) ContainerExecAttach(ctx context.Context, execID string, config types.ExecConfig) (types.HijackedResponse, error) {

, of course you can modify the code to satisfy your api version need.

semaph0r Over a year ago

Thank you for your comment. I have added execConfig := types.ExecStartCheck{Tty: false, Detach: false} and passed it to ContainerExecAttach. Good job, thank you for your work. This bounty is well deserved!

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