Add push-only support

card.go

@@ -17,8 +17,14 @@ import (
 	"github.com/inhies/go-bytesize"
 )
 
+// writeCard maintains backward compatibility by using TempTag
 func (p Plugin) writeCard() error {
-	cmd := exec.Command(dockerExe, "inspect", p.Build.TempTag)
+	return p.writeCardForImage(p.Build.TempTag)
+}
+
+// writeCardForImage generates card for any image reference
+func (p Plugin) writeCardForImage(imageRef string) error {
+	cmd := exec.Command(dockerExe, "inspect", imageRef)
 	data, err := cmd.CombinedOutput()
 	if err != nil {
 		return err
@@ -38,7 +44,11 @@ func (p Plugin) writeCard() error {
 	for _, tag := range inspect.RepoTags {
 		sliceTagStruct = append(sliceTagStruct, TagStruct{Tag: tag})
 	}
-	inspect.ParsedRepoTags = sliceTagStruct[1:] // remove the first tag which is always "hash:latest"
+	if len(sliceTagStruct) > 1 {
+		inspect.ParsedRepoTags = sliceTagStruct[1:] // remove the first tag which is always "hash:latest"
+	} else {
+		inspect.ParsedRepoTags = sliceTagStruct
+	}
 	// create the url from repo and registry
 	inspect.URL = mapRegistryToURL(p.Daemon.Registry, p.Build.Repo)
 	cardData, _ := json.Marshal(inspect)

cmd/drone-docker/main.go

@@ -339,6 +339,16 @@ func main() {
 			Usage:  "additional cosign parameters (e.g., annotations, flags)",
 			EnvVar: "PLUGIN_COSIGN_PARAMS",
 		},
+		cli.BoolFlag{
+			Name:   "push-only",
+			Usage:  "skip build and only push images",
+			EnvVar: "PLUGIN_PUSH_ONLY",
+		},
+		cli.StringFlag{
+			Name:   "source-image",
+			Usage:  "source image to tag and push (format: repo:tag)",
+			EnvVar: "PLUGIN_SOURCE_IMAGE",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -419,6 +429,8 @@ func run(c *cli.Context) error {
 			Password:   c.String("cosign.password"),
 			Params:     c.String("cosign.params"),
 		},
+		PushOnly:    c.Bool("push-only"),
+		SourceImage: c.String("source-image"),
 	}
 
 	if c.Bool("tags.auto") {

docker.go

@@ -96,6 +96,8 @@ type (
 		BaseImageRegistry string       // Docker registry to pull base image
 		BaseImageUsername string       // Docker registry username to pull base image
 		BaseImagePassword string       // Docker registry password to pull base image
+		PushOnly          bool         // Push only mode, skips build process
+		SourceImage       string       // Source image to push (optional)
 	}
 
 	Card []struct {
@@ -201,7 +203,8 @@ func (p Plugin) Exec() error {
 			fmt.Println(out)
 			return fmt.Errorf("Error authenticating base connector: exit status 1")
 		}
-	} else {
+	} else if !p.PushOnly {
+		// Skip base image connector warning in push-only mode (not pulling anything)
 		fmt.Println("\033[33mTo ensure consistent and reliable pipeline execution, we recommend setting up a Base Image Connector.\033[0m\n" +
 			"\033[33mWhile optional at this time, configuring it helps prevent failures caused by Docker Hub's rate limits.\033[0m")
 	}
@@ -229,6 +232,16 @@ func (p Plugin) Exec() error {
 		}
 	}
 
+	// Enforce mutual exclusivity: push-only and dry-run cannot be used together
+	if p.PushOnly && p.Dryrun {
+		return fmt.Errorf("conflict: push-only and dry-run cannot be used together")
+	}
+
+	// Handle push-only mode if requested
+	if p.PushOnly {
+		return p.pushOnly()
+	}
+
 	if p.Build.Squash && !p.Daemon.Experimental {
 		fmt.Println("Squash build flag is only available when Docker deamon is started with experimental flag. Ignoring...")
 		p.Build.Squash = false
@@ -742,6 +755,22 @@ func getDigest(buildName string) (string, error) {
 	return "", errors.New("unable to fetch digest")
 }
 
+// imageExists checks if an image exists in local daemon
+func imageExists(tag string) bool {
+	cmd := exec.Command(dockerExe, "image", "inspect", tag)
+	return cmd.Run() == nil
+}
+
+// getDigestAfterPush gets digest from a pushed image
+func getDigestAfterPush(tag string) (string, error) {
+	cmd := exec.Command(dockerExe, "inspect", "--format", "{{ index (split (index .RepoDigests 0) \"@\") 1 }}", tag)
+	output, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("failed to get digest for %s: %w", tag, err)
+	}
+	return strings.TrimSpace(string(output)), nil
+}
+
 // shouldSignWithCosign determines if cosign signing should be performed
 func (p Plugin) shouldSignWithCosign() bool {
 	return p.Cosign.PrivateKey != ""
@@ -845,4 +874,164 @@ func executeCosignCommand(cmd *exec.Cmd) {
 	}
 }
 
+// pushOnly handles pushing images without building them
+func (p Plugin) pushOnly() error {
+	// Check if source image is specified
+	sourceImageName := p.SourceImage
+	var sourceTags []string
 
+	if sourceImageName == "" {
+		// If no source image specified, use the repo and first tag
+		fmt.Println("source_image not provided, using repo and tag value")
+		sourceImageName = p.Build.Repo
+		sourceTags = p.Build.Tags
+	} else {
+		// If source image is specified, check if it has a tag
+		lastColonIndex := strings.LastIndex(sourceImageName, ":")
+		if lastColonIndex > 0 && lastColonIndex < len(sourceImageName) {
+			// Check if there's a slash after the last colon (indicating it's a port, not a tag)
+			// For example: registry:5000/image (has slash after colon - port not tag)
+			// vs image:tag (no slash after colon - it's a tag)
+			if strings.LastIndex(sourceImageName, "/") > lastColonIndex {
+				// The last colon is part of the registry:port, not a tag separator
+				sourceTags = []string{"latest"}
+			} else {
+				// The last colon separates the tag
+				tag := sourceImageName[lastColonIndex+1:]
+				sourceImageName = sourceImageName[:lastColonIndex]
+
+				if tag == "" {
+					fmt.Printf("No tag specified in source image (or empty tag). Using 'latest' as the default tag.\n")
+					tag = "latest"
+				}
+				sourceTags = []string{tag}
+			}
+		} else {
+			// Default to "latest" if no tag specified
+			sourceTags = []string{"latest"}
+		}
+		fmt.Printf("Using source image: %s with tag(s): %s\n", sourceImageName, strings.Join(sourceTags, ", "))
+	}
+
+	// For each source tag and target tag combination
+	var digest string
+	var firstPushedImage string
+
+	for _, sourceTag := range sourceTags {
+		sourceFullImageName := fmt.Sprintf("%s:%s", sourceImageName, sourceTag)
+
+		// Check if the source image exists in local daemon
+		if !imageExists(sourceFullImageName) {
+			fmt.Printf("Warning: Source image %s not found\n", sourceFullImageName)
+			// Continue to the next source tag if available, otherwise return error
+			if len(sourceTags) > 1 {
+				continue
+			}
+			return fmt.Errorf("source image %s not found, cannot push", sourceFullImageName)
+		}
+
+		// For each target tag, tag and push
+		for _, targetTag := range p.Build.Tags {
+			targetFullImageName := fmt.Sprintf("%s:%s", p.Build.Repo, targetTag)
+
+			// Skip if source and target are identical
+			if sourceFullImageName == targetFullImageName {
+				fmt.Printf("Source and target image names are identical: %s\n", sourceFullImageName)
+			} else {
+				// Tag the source image with the target name
+				fmt.Printf("Tagging %s as %s\n", sourceFullImageName, targetFullImageName)
+				tagCmd := exec.Command(dockerExe, "tag", sourceFullImageName, targetFullImageName)
+				tagCmd.Stdout = os.Stdout
+				tagCmd.Stderr = os.Stderr
+				trace(tagCmd)
+				if err := tagCmd.Run(); err != nil {
+					return fmt.Errorf("failed to tag image %s as %s: %w", sourceFullImageName, targetFullImageName, err)
+				}
+			}
+		}
+	}
+
+	// Push all target images
+	for _, tag := range p.Build.Tags {
+		fullImageName := fmt.Sprintf("%s:%s", p.Build.Repo, tag)
+
+		// Check if image exists in local daemon
+		if !imageExists(fullImageName) {
+			return fmt.Errorf("image %s not found, cannot push", fullImageName)
+		}
+
+		// Push image
+		fmt.Println("Pushing image:", fullImageName)
+		pushCmd := commandPush(p.Build, tag)
+		pushCmd.Stdout = os.Stdout
+		pushCmd.Stderr = os.Stderr
+		trace(pushCmd)
+		if err := pushCmd.Run(); err != nil {
+			return fmt.Errorf("failed to push image %s: %w", fullImageName, err)
+		}
+
+		// Track the first pushed image for card generation
+		if firstPushedImage == "" {
+			firstPushedImage = fullImageName
+		}
+
+		// Get the digest after push (we only need one)
+		if digest == "" {
+			d, err := getDigestAfterPush(fullImageName)
+			if err == nil {
+				digest = d
+			} else {
+				fmt.Printf("Warning: Could not get digest for %s: %v\n", fullImageName, err)
+			}
+		}
+	}
+
+	// Output the adaptive card
+	if firstPushedImage != "" {
+		if err := p.writeCardForImage(firstPushedImage); err != nil {
+			fmt.Printf("Could not create adaptive card. %s\n", err)
+		}
+	}
+
+	// Write to artifact file
+	if p.ArtifactFile != "" && digest != "" {
+		if err := drone.WritePluginArtifactFile(
+			p.Daemon.RegistryType,
+			p.ArtifactFile,
+			p.Daemon.Registry,
+			p.Build.Repo,
+			digest,
+			p.Build.Tags,
+		); err != nil {
+			fmt.Printf("Failed to write plugin artifact file at path: %s with error: %s\n",
+				p.ArtifactFile, err)
+		}
+	}
+
+	// Handle cosign signing after push
+	if p.shouldSignWithCosign() {
+		// Set up environment variables for cosign
+		os.Setenv("COSIGN_YES", "true")
+
+		if digest != "" {
+			fmt.Printf("🔐 Found image digest: %s\n", digest)
+
+			// Sign with digest reference
+			imageRef := fmt.Sprintf("%s@%s", p.Build.Repo, digest)
+			cosignCmd := createCosignCommand(imageRef, p.Cosign)
+			executeCosignCommand(cosignCmd)
+		} else {
+			fmt.Printf("⚠️  WARNING: Could not get image digest for cosign signing\n")
+			fmt.Printf("   Falling back to tag-based signing\n")
+
+			// Fall back to tag-based signing for each tag
+			for _, tag := range p.Build.Tags {
+				imageRef := fmt.Sprintf("%s:%s", p.Build.Repo, tag)
+				cosignCmd := createCosignCommand(imageRef, p.Cosign)
+				executeCosignCommand(cosignCmd)
+			}
+		}
+	}
+
+	return nil
+}