Add push support

README.md

@@ -118,6 +118,20 @@ Next, any of the following optional parameters may be specified:
 * `$TARGET_FILE` (default empty): path to a file containing the name of the
   target build stage to build.
 
+* `$PUSH` (default empty): If non-empty the image will use the PUSH variable
+  as name and push the image. If credentials is required, they can be supplied
+  as three seperate parameters `$DOCKER_USERNAME`, `DOCKER_PASSWORD` and 
+  `DOCKER_REGISTRY`
+
+  Example here would push the image to docker.io/concourse/oci-build.task
+  ```
+  DOCKER_USERNAME: ((docker_username.secret))
+  DOCKER_PASSWORD: ((docker_password.secret))
+  DOCKER_REGISTRY: ((docker_registry.secret))
+  PUSH: docker.io/concourse/oci-build.task
+
+  ```
+
 * `$ADDITIONAL_TARGETS` (default empty): a comma-separated (`,`) list of
   additional target build stages to build.
 

cmd/build/main.go

@@ -60,6 +60,12 @@ func main() {
 		}
 	}
 
+	//CheckForDockerCredentials only returns an error, if there
+	//was a problem saving the credentials
+	//No credentials will just be ignored
+	err = task.CheckForDockerCredentials()
+	failIf("docker auth check", err)
+
 	logrus.Debugf("read config from env: %#v\n", req.Config)
 
 	reqPayload, err := json.Marshal(req)

docker_auth.go

@@ -0,0 +1,55 @@
+package task
+
+import (
+	"encoding/json"
+	"os"
+
+	"github.com/docker/cli/cli/config/configfile"
+	"github.com/docker/cli/cli/config/types"
+	"github.com/sirupsen/logrus"
+)
+
+func CheckForDockerCredentials() error {
+	username := os.Getenv("DOCKER_USERNAME")
+	password := os.Getenv("DOCKER_PASSWORD")
+	registry := os.Getenv("DOCKER_REGISTRY")
+
+	if username == "" || password == "" || registry == "" {
+		logrus.Debugf("No docker credentials in environment variables")
+		return nil
+	}
+
+	config := configfile.ConfigFile{
+		AuthConfigs: map[string]types.AuthConfig{
+			registry: types.AuthConfig{
+				Username: username,
+				Password: password,
+			},
+		},
+	}
+
+	fileContents, err := json.MarshalIndent(config, "", " ")
+	if err != nil {
+		return err
+
+	}
+
+	fileMode := os.FileMode(0444)
+
+	homedir, err := os.UserHomeDir()
+	if err != nil {
+		return err
+	}
+
+	configPath := homedir + "/.docker"
+	if err := os.MkdirAll(configPath, fileMode); err != nil {
+		return err
+	}
+
+	filePath := configPath + "/config.json"
+	if err := os.WriteFile(filePath, fileContents, fileMode); err != nil {
+		return err
+	}
+
+	return nil
+}

task.go

@@ -136,6 +136,11 @@ func Build(buildkitd *Buildkitd, outputsDir string, req Request) (Response, erro
 		)
 	}
 
+	if cfg.Push != "" {
+		buildctlArgs = append(buildctlArgs,
+			"--output", fmt.Sprintf("type=image,name=%s,push=true", cfg.Push))
+	}
+
 	if cfg.AddHosts != "" {
 		buildctlArgs = append(buildctlArgs,
 			"--opt", "add-hosts="+cfg.AddHosts,

types.go

@@ -53,6 +53,7 @@ type Config struct {
 	Target            string   `json:"target"      envconfig:"optional"`
 	TargetFile        string   `json:"target_file" envconfig:"optional"`
 	AdditionalTargets []string `json:"additional_targets" envconfig:"ADDITIONAL_TARGETS,optional"`
+	Push              string   `json:"push" envconfig:"optional"`
 
 	BuildArgs     []string `json:"build_args"      envconfig:"optional"`
 	BuildArgsFile string   `json:"build_args_file" envconfig:"optional"`