feat: look up latest caddy version tag when deploying caddy service

internal/cli/client/caddy.go

@@ -1,18 +1,35 @@
 package client
 
 import (
+	"fmt"
+	"github.com/Masterminds/semver"
+	"github.com/distribution/reference"
+	"regexp"
 	"uncloud/internal/api"
+
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1/remote"
 )
 
-const CaddyServiceName = "caddy"
+const (
+	CaddyServiceName = "caddy"
+	// CaddyImage is the official Caddy Docker image on Docker Hub: https://hub.docker.com/_/caddy
+	CaddyImage = "caddy"
+)
+
+var caddyImageTagRegex = regexp.MustCompile(`^2\.\d+\.\d+$`)
 
 // NewCaddyDeployment creates a new deployment for a Caddy reverse proxy service.
 // The service is deployed in global mode to all machines in the cluster. If the image is not provided, the latest
 // version of the official Caddy Docker image is used.
 func (cli *Client) NewCaddyDeployment(image string) (*Deployment, error) {
+	latest, err := latestCaddyImage()
+	if err != nil {
+		return nil, fmt.Errorf("look up latest Caddy image: %w", err)
+	}
+
 	if image == "" {
-		// TODO: fetch the latest version tag from the Docker Hub registry.
-		image = "caddy:latest"
+		image = reference.FamiliarString(latest)
 	}
 
 	spec := api.ServiceSpec{
@@ -41,3 +58,45 @@ func (cli *Client) NewCaddyDeployment(image string) (*Deployment, error) {
 
 	return cli.NewDeployment(spec, &RollingStrategy{})
 }
+
+// latestCaddyImage returns the latest image of the official Caddy Docker image on Docker Hub.
+// The latest image is determined by the latest version tag 2.x.x.
+func latestCaddyImage() (reference.NamedTagged, error) {
+	repo, err := name.NewRepository(CaddyImage)
+	if err != nil {
+		return nil, fmt.Errorf("parse image: %w", err)
+	}
+	tags, err := remote.List(repo)
+	if err != nil {
+		return nil, fmt.Errorf("list image tags: %w", err)
+	}
+
+	// Default to the 'latest' tag but try to find the latest version tag 2.x.x.
+	latestTag := "latest"
+	var latestVersion *semver.Version
+	for _, t := range tags {
+		if !caddyImageTagRegex.MatchString(t) {
+			continue
+		}
+
+		v, err := semver.NewVersion(t)
+		if err != nil {
+			continue
+		}
+		if latestVersion == nil || v.GreaterThan(latestVersion) {
+			latestVersion = v
+			latestTag = t
+		}
+	}
+
+	image, err := reference.ParseDockerRef(CaddyImage)
+	if err != nil {
+		return nil, fmt.Errorf("parse image: %w", err)
+	}
+	imageWithTag, err := reference.WithTag(image, latestTag)
+	if err != nil {
+		return nil, fmt.Errorf("set image tag: %w", err)
+	}
+
+	return imageWithTag, nil
+}