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

cmd/drone-docker/main.go

@@ -248,6 +248,11 @@ func main() {
 			Usage:  "additional host:IP mapping",
 			EnvVar: "PLUGIN_ADD_HOST",
 		},
+		cli.StringSliceFlag{
+			Name:   "ssh-agent",
+			Usage:  "mount ssh agent",
+			EnvVar: "PLUGIN_SSH_AGENT",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -267,26 +272,27 @@ func run(c *cli.Context) error {
 			Config:   c.String("docker.config"),
 		},
 		Build: docker.Build{
-			Remote:        c.String("remote.url"),
-			Name:          c.String("commit.sha"),
-			Dockerfile:    c.String("dockerfile"),
-			Context:       c.String("context"),
-			Tags:          c.StringSlice("tags"),
-			Args:          c.StringSlice("args"),
-			ArgsEnv:       c.StringSlice("args-from-env"),
-			Target:        c.String("target"),
-			Squash:        c.Bool("squash"),
-			Pull:          c.BoolT("pull-image"),
-			CacheFrom:     c.StringSlice("cache-from"),
-			Compress:      c.Bool("compress"),
-			Repo:          c.String("repo"),
-			Labels:        c.StringSlice("custom-labels"),
-			LabelSchema:   c.StringSlice("label-schema"),
-			AutoLabel:     c.BoolT("auto-label"),
-			Link:          c.String("link"),
-			NoCache:       c.Bool("no-cache"),
-			AddHost:       c.StringSlice("add-host"),
-			Quiet:         c.Bool("quiet"),
+			Remote:      c.String("remote.url"),
+			Name:        c.String("commit.sha"),
+			Dockerfile:  c.String("dockerfile"),
+			Context:     c.String("context"),
+			Tags:        c.StringSlice("tags"),
+			Args:        c.StringSlice("args"),
+			ArgsEnv:     c.StringSlice("args-from-env"),
+			Target:      c.String("target"),
+			Squash:      c.Bool("squash"),
+			Pull:        c.BoolT("pull-image"),
+			CacheFrom:   c.StringSlice("cache-from"),
+			Compress:    c.Bool("compress"),
+			Repo:        c.String("repo"),
+			Labels:      c.StringSlice("custom-labels"),
+			LabelSchema: c.StringSlice("label-schema"),
+			AutoLabel:   c.BoolT("auto-label"),
+			Link:        c.String("link"),
+			NoCache:     c.Bool("no-cache"),
+			AddHost:     c.StringSlice("add-host"),
+			Quiet:       c.Bool("quiet"),
+			SSHAgent:    c.String("ssh-agent"),
 		},
 		Daemon: docker.Daemon{
 			Registry:      c.String("docker.registry"),

docker.go

@@ -59,6 +59,7 @@ type (
 		NoCache     bool     // Docker build no-cache
 		AddHost     []string // Docker build add-host
 		Quiet       bool     // Docker build quiet
+		SSHAgent    string   // Docker build ssh
 	}
 
 	// Plugin defines the Docker plugin parameters.
@@ -264,6 +265,9 @@ func commandBuild(build Build) *exec.Cmd {
 	if build.Quiet {
 		args = append(args, "--quiet")
 	}
+	if build.SSHAgent != "" {
+		args = append(args, "--ssh", build.SSHAgent)
+	}
 
 	if build.AutoLabel {
 		labelSchema := []string{