Add option to mount host ssh agent (--ssh)

.gitignore

@@ -1,3 +1,5 @@
 release
 coverage.out
 vendor
+.vscode/
+Dockerfile

cmd/drone-docker/main.go

@@ -274,6 +274,11 @@ func main() {
 			Usage:  "platform value to pass to docker",
 			EnvVar: "PLUGIN_PLATFORM",
 		},
+		cli.StringFlag{
+			Name:   "ssh-agent-key",
+			Usage:  "ssh agent key to use",
+			EnvVar: "PLUGIN_SSH_AGENT_KEY",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -318,6 +323,7 @@ func run(c *cli.Context) error {
 			AddHost:     c.StringSlice("add-host"),
 			Quiet:       c.Bool("quiet"),
 			Platform:    c.String("platform"),
+			SSHAgentKey: c.String("ssh-agent-key"),
 		},
 		Daemon: docker.Daemon{
 			Registry:      c.String("docker.registry"),

daemon.go

@@ -1,9 +1,10 @@
+//go:build !windows
 // +build !windows
 
 package docker
 
 import (
-	"io/ioutil"
+	"io"
 	"os"
 )
 
@@ -17,8 +18,8 @@ func (p Plugin) startDaemon() {
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
 	} else {
-		cmd.Stdout = ioutil.Discard
-		cmd.Stderr = ioutil.Discard
+		cmd.Stdout = io.Discard
+		cmd.Stderr = io.Discard
 	}
 	go func() {
 		trace(cmd)

docker.go

@@ -2,7 +2,6 @@ package docker
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -64,6 +63,8 @@ type (
 		AddHost     []string // Docker build add-host
 		Quiet       bool     // Docker build quiet
 		Platform    string   // Docker build platform
+		SSHAgentKey string   // Docker build ssh agent key
+		SSHKeyPath  string   // Docker build ssh key path
 	}
 
 	// Plugin defines the Docker plugin parameters.
@@ -106,6 +107,7 @@ type (
 
 // Exec executes the plugin step
 func (p Plugin) Exec() error {
+
 	// start the Docker daemon server
 	if !p.Daemon.Disabled {
 		p.startDaemon()
@@ -144,7 +146,7 @@ func (p Plugin) Exec() error {
 		os.MkdirAll(dockerHome, 0600)
 
 		path := filepath.Join(dockerHome, "config.json")
-		err := ioutil.WriteFile(path, []byte(p.Login.Config), 0600)
+		err := os.WriteFile(path, []byte(p.Login.Config), 0600)
 		if err != nil {
 			return fmt.Errorf("Error writing config.json: %s", err)
 		}
@@ -179,6 +181,15 @@ func (p Plugin) Exec() error {
 		cmds = append(cmds, commandPull(img))
 	}
 
+	// setup for using ssh agent (https://docs.docker.com/develop/develop-images/build_enhancements/#using-ssh-to-access-private-data-in-builds)
+	if p.Build.SSHAgentKey != "" {
+		var sshErr error
+		p.Build.SSHKeyPath, sshErr = writeSSHPrivateKey(p.Build.SSHAgentKey)
+		if sshErr != nil {
+			return sshErr
+		}
+	}
+
 	cmds = append(cmds, commandBuild(p.Build)) // docker build
 
 	for _, tag := range p.Build.Tags {
@@ -328,6 +339,9 @@ func commandBuild(build Build) *exec.Cmd {
 	if build.Platform != "" {
 		args = append(args, "--platform", build.Platform)
 	}
+	if build.SSHKeyPath != "" {
+		args = append(args, "--ssh", build.SSHKeyPath)
+	}
 
 	if build.AutoLabel {
 		labelSchema := []string{
@@ -353,8 +367,8 @@ func commandBuild(build Build) *exec.Cmd {
 		}
 	}
 
-	// we need to enable buildkit, for secret support
-	if build.Secret != "" || len(build.SecretEnvs) > 0 || len(build.SecretFiles) > 0 {
+	// we need to enable buildkit, for secret support and ssh agent support
+	if build.Secret != "" || len(build.SecretEnvs) > 0 || len(build.SecretFiles) > 0 || build.SSHAgentKey != "" {
 		os.Setenv("DOCKER_BUILDKIT", "1")
 	}
 	return exec.Command(dockerExe, args...)
@@ -507,6 +521,23 @@ func commandRmi(tag string) *exec.Cmd {
 	return exec.Command(dockerExe, "rmi", tag)
 }
 
+func writeSSHPrivateKey(key string) (path string, err error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("unable to determine home directory: %s", err)
+	}
+	if err := os.MkdirAll(filepath.Join(home, ".ssh"), 0700); err != nil {
+		return "", fmt.Errorf("unable to create .ssh directory: %s", err)
+	}
+	pathToKey := filepath.Join(home, ".ssh", "id_rsa")
+	if err := os.WriteFile(pathToKey, []byte(key), 0400); err != nil {
+		return "", fmt.Errorf("unable to write ssh key %s: %s", pathToKey, err)
+	}
+	path = fmt.Sprintf("default=%s", pathToKey)
+
+	return path, nil
+}
+
 // trace writes each command to stdout with the command wrapped in an xml
 // tag so that it can be extracted and displayed in the logs.
 func trace(cmd *exec.Cmd) {

docker_test.go

@@ -135,6 +135,26 @@ func TestCommandBuild(t *testing.T) {
 				"test/platform",
 			),
 		},
+		{
+			name: "ssh agent",
+			build: Build{
+				Name:       "plugins/drone-docker:latest",
+				Dockerfile: "Dockerfile",
+				Context:    ".",
+				SSHKeyPath: "id_rsa=/root/.ssh/id_rsa",
+			},
+			want: exec.Command(
+				dockerExe,
+				"build",
+				"--rm=true",
+				"-f",
+				"Dockerfile",
+				"-t",
+				"plugins/drone-docker:latest",
+				".",
+				"--ssh id_rsa=/root/.ssh/id_rsa",
+			),
+		},
 	}
 
 	for _, tc := range tcs {