Add APIv2 CLI example POC

* Add ReadMe, CLI and unit files to support socket activation, both for
  system and rootless

Signed-off-by: Jhon Honce <jhonce@redhat.com>

cmd/cli/main.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+
+	"golang.org/x/crypto/ssh"
+)
+
+// remote PODMAN_HOST=ssh://<user>@<host>[:port]/run/podman/podman.sock
+// local  PODMAN_HOST=unix://run/podman/podman.sock
+
+var (
+	DefaultURL = "unix://root@localhost/run/podman/podman.sock"
+)
+
+func main() {
+	connectionURL := DefaultURL
+	if value, found := os.LookupEnv("PODMAN_HOST"); found {
+		connectionURL = value
+	}
+
+	_url, err := url.Parse(connectionURL)
+	if err != nil {
+		die("Value of PODMAN_HOST is not a valid url: %s\n", connectionURL)
+	}
+
+	if _url.Scheme != "ssh" && _url.Scheme != "unix" {
+		die("Scheme from PODMAN_HOST is not supported: %s\n", _url.Scheme)
+	}
+
+	// Now we setup the http client to use the connection above
+	client := &http.Client{}
+	if _url.Scheme == "ssh" {
+		var auth ssh.AuthMethod
+		if value, found := os.LookupEnv("PODMAN_SSHKEY"); found {
+			auth, err = publicKey(value)
+			if err != nil {
+				die("Failed to parse %s: %v\n", value, err)
+			}
+		} else {
+			die("PODMAN_SSHKEY was not defined\n")
+		}
+
+		// Connect to sshd
+		bastion, err := ssh.Dial("tcp",
+			net.JoinHostPort(_url.Hostname(), _url.Port()),
+			&ssh.ClientConfig{
+				User:            _url.User.Username(),
+				Auth:            []ssh.AuthMethod{auth},
+				HostKeyCallback: ssh.InsecureIgnoreHostKey(),
+			},
+		)
+		if err != nil {
+			die("Failed to build ssh tunnel")
+		}
+		defer bastion.Close()
+
+		client.Transport = &http.Transport{
+			DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+				// Now we make the connection to the unix domain socket on the server using the ssh tunnel
+				return bastion.Dial("unix", _url.Path)
+			},
+		}
+	} else {
+		client.Transport = &http.Transport{
+			DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+				d := net.Dialer{}
+				return d.DialContext(ctx, "unix", _url.Path)
+			},
+			DisableCompression: true,
+		}
+	}
+
+	resp, err := client.Get("http://localhost/v1.24/images/json")
+	if err != nil {
+		die(err.Error())
+	}
+	defer resp.Body.Close()
+	body, _ := ioutil.ReadAll(resp.Body)
+
+	var output bytes.Buffer
+	_ = json.Indent(&output, body, "", "  ")
+	fmt.Printf("%s\n", output.String())
+	os.Exit(0)
+}
+
+func die(format string, a ...interface{}) {
+	fmt.Fprintf(os.Stderr, format, a...)
+	fmt.Fprintf(os.Stderr, "\n")
+	os.Exit(1)
+}
+
+func publicKey(path string) (ssh.AuthMethod, error) {
+	key, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	signer, err := ssh.ParsePrivateKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	return ssh.PublicKeys(signer), nil
+}