DockMV/internal/sshx/docker.go

package sshx

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"strings"

	"github.com/arescom/dockmv/internal/spec"
)

// RemoteDocker drives the docker CLI on a target host over SSH. It assumes
// nothing beyond sshd, docker and a POSIX shell; gzip is used only when
// compression is enabled and is probed for first.
type RemoteDocker struct {
	c      *Client
	binary string
	sudo   bool
}

// NewRemoteDocker wraps a connection.
func NewRemoteDocker(c *Client) *RemoteDocker {
	cfg := c.Config()
	bin := cfg.DockerCmd
	if bin == "" {
		bin = "docker"
	}
	return &RemoteDocker{c: c, binary: bin, sudo: cfg.Sudo}
}

// Cmd renders a docker invocation as a shell command line, correctly quoted.
func (r *RemoteDocker) Cmd(args ...string) string {
	var b strings.Builder
	if r.sudo {
		b.WriteString("sudo -n ")
	}
	b.WriteString(spec.ShellQuote(r.binary))
	if len(args) > 0 {
		b.WriteString(" ")
		b.WriteString(spec.ShellQuoteAll(args))
	}
	return b.String()
}

// Run executes a docker command and returns its stdout, failing on non-zero.
func (r *RemoteDocker) Run(ctx context.Context, args ...string) (string, error) {
	return r.c.RunCheck(ctx, r.Cmd(args...))
}

// Try executes a docker command and reports success without treating a
// non-zero exit as an error. Used for existence probes.
func (r *RemoteDocker) Try(ctx context.Context, args ...string) (string, bool, error) {
	res, err := r.c.Run(ctx, r.Cmd(args...))
	if err != nil {
		return "", false, err
	}
	return res.Stdout, res.ExitCode == 0, nil
}

// Feed pipes a local reader into a docker command's stdin. When decompress is
// set the remote side runs `gzip -dc` ahead of docker, so the bytes on the
// wire are compressed.
func (r *RemoteDocker) Feed(ctx context.Context, src io.Reader, decompress bool, args ...string) error {
	cmd := r.Cmd(args...)
	if decompress {
		cmd = "gzip -dc | " + cmd
	}
	_, err := r.c.Stream(ctx, cmd, src, nil)
	return err
}

// Preflight is what the target host was found to support.
type Preflight struct {
	DockerVersion string   `json:"dockerVersion"`
	ServerVersion string   `json:"serverVersion"`
	OS            string   `json:"os"`
	Arch          string   `json:"arch"`
	HasGzip       bool     `json:"hasGzip"`
	DiskFreeBytes int64    `json:"diskFreeBytes"`
	DockerRoot    string   `json:"dockerRoot"`
	Problems      []string `json:"problems,omitempty"`
}

// Preflight checks everything the migration depends on before any data moves.
func (r *RemoteDocker) Preflight(ctx context.Context) (*Preflight, error) {
	p := &Preflight{}

	out, ok, err := r.Try(ctx, "version", "--format", "{{.Client.Version}}|{{.Server.Version}}|{{.Server.Os}}|{{.Server.Arch}}")
	if err != nil {
		return nil, err
	}
	if !ok {
		res, _ := r.c.Run(ctx, r.Cmd("version"))
		msg := strings.TrimSpace(res.Stderr)
		if strings.Contains(msg, "permission denied") {
			p.Problems = append(p.Problems,
				"the login user cannot talk to the docker daemon; add it to the docker group or enable sudo for this connection")
		} else if msg != "" {
			p.Problems = append(p.Problems, "docker is not usable on the target: "+firstLine(msg))
		} else {
			p.Problems = append(p.Problems, "docker is not installed or not on PATH on the target")
		}
		return p, nil
	}
	parts := strings.Split(strings.TrimSpace(out), "|")
	if len(parts) == 4 {
		p.DockerVersion, p.ServerVersion, p.OS, p.Arch = parts[0], parts[1], parts[2], parts[3]
	}
	if p.OS != "" && p.OS != "linux" {
		p.Problems = append(p.Problems, "target daemon runs "+p.OS+" containers; only linux targets are supported")
	}

	res, err := r.c.Run(ctx, "command -v gzip >/dev/null 2>&1")
	if err != nil {
		return nil, err
	}
	p.HasGzip = res.ExitCode == 0
	if !p.HasGzip {
		p.Problems = append(p.Problems, "gzip is missing on the target; transfers will run uncompressed")
	}

	if root, err2 := r.Run(ctx, "info", "--format", "{{.DockerRootDir}}"); err2 == nil {
		p.DockerRoot = strings.TrimSpace(root)
		if p.DockerRoot != "" {
			// POSIX df in 1K blocks; the fourth column is available space.
			cmd := "df -Pk " + spec.ShellQuote(p.DockerRoot) + " | awk 'NR==2 {print $4}'"
			if dres, derr := r.c.Run(ctx, cmd); derr == nil && dres.ExitCode == 0 {
				var kb int64
				if _, serr := fmt.Sscanf(strings.TrimSpace(dres.Stdout), "%d", &kb); serr == nil {
					p.DiskFreeBytes = kb * 1024
				}
			}
		}
	}
	return p, nil
}

// TargetContainer is a container that already exists on the target host.
type TargetContainer struct {
	ID     string `json:"id"`
	Name   string `json:"name"`
	Image  string `json:"image"`
	State  string `json:"state"`
	Status string `json:"status"`
	Ports  string `json:"ports"`
}

// TargetInventory is the current state of the target host, used to show it
// side by side with the source and to detect name conflicts up front.
type TargetInventory struct {
	Host       string            `json:"host"`
	Containers []TargetContainer `json:"containers"`
	Volumes    []string          `json:"volumes"`
	Networks   []string          `json:"networks"`
	Preflight  *Preflight        `json:"preflight"`
}

// Inventory reads the target host's containers, volumes and networks.
func (r *RemoteDocker) Inventory(ctx context.Context) (*TargetInventory, error) {
	pre, err := r.Preflight(ctx)
	if err != nil {
		return nil, err
	}
	inv := &TargetInventory{Preflight: pre}
	if pre.ServerVersion == "" {
		return inv, nil
	}

	if host, err := r.c.RunCheck(ctx, "hostname"); err == nil {
		inv.Host = strings.TrimSpace(host)
	}

	out, err := r.Run(ctx, "ps", "-a", "--no-trunc", "--format", "{{json .}}")
	if err != nil {
		return nil, err
	}
	for _, line := range strings.Split(out, "\n") {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		var raw struct {
			ID, Names, Image, State, Status, Ports string
		}
		if json.Unmarshal([]byte(line), &raw) != nil {
			continue
		}
		// A container attached to several networks is reported with a
		// comma-separated name list; the first is its real name.
		name := raw.Names
		if i := strings.Index(name, ","); i >= 0 {
			name = name[:i]
		}
		inv.Containers = append(inv.Containers, TargetContainer{
			ID: raw.ID, Name: name, Image: raw.Image,
			State: raw.State, Status: raw.Status, Ports: raw.Ports,
		})
	}

	if out, err := r.Run(ctx, "volume", "ls", "--format", "{{.Name}}"); err == nil {
		inv.Volumes = nonEmptyLines(out)
	}
	if out, err := r.Run(ctx, "network", "ls", "--format", "{{.Name}}"); err == nil {
		inv.Networks = nonEmptyLines(out)
	}
	return inv, nil
}

// Exists reports whether an object of the given kind is present on the target.
func (r *RemoteDocker) Exists(ctx context.Context, kind, name string) (bool, error) {
	var args []string
	switch kind {
	case "container":
		args = []string{"container", "inspect", name}
	case "volume":
		args = []string{"volume", "inspect", name}
	case "network":
		args = []string{"network", "inspect", name}
	case "image":
		args = []string{"image", "inspect", name}
	default:
		return false, fmt.Errorf("unknown object kind %q", kind)
	}
	res, err := r.c.Run(ctx, r.Cmd(args...)+" >/dev/null 2>&1")
	if err != nil {
		return false, err
	}
	return res.ExitCode == 0, nil
}

// MkdirAll creates a directory on the target host, for bind mount sources that
// need to exist with the right ownership before the container starts.
func (r *RemoteDocker) MkdirAll(ctx context.Context, path string) error {
	cmd := "mkdir -p " + spec.ShellQuote(path)
	if r.sudo {
		cmd = "sudo -n " + cmd
	}
	_, err := r.c.RunCheck(ctx, cmd)
	return err
}

// Client exposes the underlying SSH connection for raw shell work.
func (r *RemoteDocker) Client() *Client { return r.c }

func nonEmptyLines(s string) []string {
	var out []string
	for _, l := range strings.Split(s, "\n") {
		if l = strings.TrimSpace(l); l != "" {
			out = append(out, l)
		}
	}
	return out
}

func firstLine(s string) string {
	if i := strings.IndexByte(s, '\n'); i >= 0 {
		return s[:i]
	}
	return s
}