add http head based digest comparison to avoid dockerhub rate limits

pkg/registry/manifest/manifest.go

@@ -0,0 +1,64 @@
+package manifest
+
+import (
+	"fmt"
+	"github.com/containrrr/watchtower/pkg/registry/helpers"
+	"github.com/containrrr/watchtower/pkg/types"
+	ref "github.com/docker/distribution/reference"
+	"github.com/sirupsen/logrus"
+	url2 "net/url"
+	"strings"
+)
+
+// BuildManifestURL from raw image data
+func BuildManifestURL(container types.Container) (string, error) {
+
+	normalizedName, err := ref.ParseNormalizedNamed(container.ImageName())
+	if err != nil {
+		return "", err
+	}
+
+	host, err := helpers.NormalizeRegistry(normalizedName.String())
+	img, tag := extractImageAndTag(strings.TrimPrefix(container.ImageName(), host+"/"))
+
+	logrus.WithFields(logrus.Fields{
+		"image":      img,
+		"tag":        tag,
+		"normalized": normalizedName,
+		"host":       host,
+	}).Debug("Parsing image ref")
+
+	if err != nil {
+		return "", err
+	}
+	img = strings.TrimPrefix(img, fmt.Sprintf("%s/", host))
+	if !strings.Contains(img, "/") {
+		img = "library/" + img
+	}
+	url := url2.URL{
+		Scheme: "https",
+		Host:   host,
+		Path:   fmt.Sprintf("/v2/%s/manifests/%s", img, tag),
+	}
+	return url.String(), nil
+}
+
+func extractImageAndTag(imageName string) (string, string) {
+	var img string
+	var tag string
+
+	if strings.Contains(imageName, ":") {
+		parts := strings.Split(imageName, ":")
+		if len(parts) > 2 {
+			img = fmt.Sprintf("%s%s", parts[0], parts[1])
+			tag = parts[3]
+		} else {
+			img = parts[0]
+			tag = parts[1]
+		}
+	} else {
+		img = imageName
+		tag = "latest"
+	}
+	return img, tag
+}