Change method of resolving hashes

Different repositories might not always have the same
metadata hash digest. Use a list of repo hashes instead.

README.md

@@ -40,12 +40,32 @@ chart-name-here:
 $ helm plugin install https://github.com/balboah/helm-hashtag --version master
 
 # Update tag hash digest values
-$ helm hashtag -f values.yaml --tagfile hashtags.yaml --gcp-repo="eu.gcr.io/foobar"
- 
+$ helm hashtag -f values.yaml --tagfile hashtags.yaml --resolver="https://foobar/path"
+
 # Use the override values
 $ helm install -f values.yaml -f hashtags.yaml ...
 ```
 
-## Dependencies
+## Resolver format:
+
+The resolver is any http server which serves the correct format.
+
+#### http GET `<resolver-url>/<image>/<tag>`
+
+```
+some-other-registry.com/foobar/my-image@sha256:7639a940c07f15c0f842faccd2f0973da9875f02ac1139b72a704e206bdc4e8c
+eu.gcr.io/foobar/my-image@sha256:3867e93f2ad17b12cda5e4dede5c21311826de2b022ab65804e53de3c401b7a1
+```
+
+This file content can be generated with:
+
+`docker inspect eu.gcr.io/foobar/my-image:tagname -f '{{range .RepoDigests}}{{. | printf "%s\n"}}{{end}}'`
+
+Which could be saved in Google Cloud Storage to be used as the resolver:
+
+```
+docker inspect eu.gcr.io/foobar/my-image:tagname -f '{{range .RepoDigests}}{{. | printf "%s\n"}}{{end}}' \
+  | gsutil cp - gs://your-bucket-of-tags/my-image/tagname
+```
 
-This plugin uses gcloud for looking up tags and thus requires the source of truth to be a Google Container Registry.
+This will typically be ran in the CI platform that creates the original image.

cmd/helm-hashtag/main.go

@@ -1,10 +1,11 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"io/ioutil"
+	"net/http"
 	"os"
-	"os/exec"
 	"strings"
 
 	flag "github.com/spf13/pflag"
@@ -24,24 +25,24 @@ const header = `# Values will be overwritten by helm hashtag.
 
 func main() {
 	var (
-		gcpRepo string
-		tf      string
-		vf      valueFiles
-		vs      []string
+		resolver string
+		tf       string
+		vf       valueFiles
+		vs       []string
 	)
 	flag.VarP(&vf, "values", "f", "specify values in a YAML file or a URL(can specify multiple)")
 	flag.StringArrayVar(
 		&vs, "set", []string{},
 		"set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)",
 	)
 	flag.StringVar(&tf, "tagfile", "hashtags.yaml", "the hash tag value file to use for repository overrides")
-	flag.StringVar(&gcpRepo, "gcp-repo", "", "the source of truth for looking up docker tags, must be configured with gcloud cli")
+	flag.StringVar(&resolver, "resolver", "", "the source of truth for resolving docker tags into digest hashes")
 	flag.Parse()
 
-	if gcpRepo == "" {
+	if resolver == "" {
 		fmt.Println(
-			"A GCP repository must be set. This should be accessible via the gcloud command as it will be used",
-			"for looking up the docker tag digest.")
+			"A resolver URL must be set. This should serve http GET <alias-url>/<tag>",
+			"for resolving the docker tag digest. See the README for further information.")
 		os.Exit(1)
 	}
 
@@ -66,7 +67,7 @@ func main() {
 		fmt.Println(err)
 		os.Exit(1)
 	}
-	if err := tags.updateFrom(gcpRepo, values); err != nil {
+	if err := tags.updateFrom(resolver, values); err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
@@ -85,7 +86,7 @@ func main() {
 
 type hashtags map[string]interface{}
 
-func (t *hashtags) updateFrom(gcpRepo string, values map[string]interface{}) error {
+func (t *hashtags) updateFrom(resolver string, values map[string]interface{}) error {
 	// Find the intersection of which charts we know about and which are available.
 	updates := 0
 	total := 0
@@ -123,7 +124,7 @@ func (t *hashtags) updateFrom(gcpRepo string, values map[string]interface{}) err
 
 			fmt.Printf("updating hash digest for tag %s of %s image %s\n", tag, chart, imageName)
 			updates++
-			if err := t.update(chart, imageRef.(string), repo, gcpRepo, imageName, tag); err != nil {
+			if err := t.update(chart, imageRef.(string), repo, resolver, imageName, tag); err != nil {
 				fmt.Println(err)
 				os.Exit(1)
 			}
@@ -133,31 +134,46 @@ func (t *hashtags) updateFrom(gcpRepo string, values map[string]interface{}) err
 	return nil
 }
 
-func (t *hashtags) update(chart, imageRef, origRepo, gcpRepo, imageName, tag string) error {
-	cmd := exec.Command(
-		"gcloud", "container", "images", "list-tags",
-		fmt.Sprintf("%s/%s", gcpRepo, imageName),
-		"--limit", "1", "--filter", fmt.Sprintf("tags:%s", tag),
-		"--format", "get(digest)",
-	)
-	out, err := cmd.CombinedOutput()
+func (t *hashtags) update(chart, imageRef, origRepo, resolver, imageName, tag string) error {
+	url := fmt.Sprintf("%s/%s/%s", resolver, imageName, tag)
+	resp, err := http.Get(url)
 	if err != nil {
-		fmt.Println(string(out))
 		return err
 	}
-	// On no error, we hopefully got the hash digest in format
-	// <digest type>:<long hash>
-	parts := strings.Split(string(out), ":")
-	if len(parts) != 2 {
-		return fmt.Errorf("unknown digest format: %q", string(out))
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unexpected resolver status code %d for %q", resp.StatusCode, url)
 	}
-	digest, hash := parts[0], parts[1]
+	scanner := bufio.NewScanner(resp.Body)
+	for scanner.Scan() {
+		line := scanner.Text()
+		parts := strings.Split(line, "@")
+		if len(parts) != 2 {
+			return fmt.Errorf("unknown resolver format: %q", line)
+		}
+		// On no error, we hopefully got the hash digest in format
+		// <repo>@<digest type>:<long hash>
+		repo, digest := parts[0], parts[1]
 
-	m := map[string]interface{}(*t)
-	m[chart].(map[interface{}]interface{})[imageRef] = map[string]string{
-		"repository": fmt.Sprintf("%s@%s", origRepo, digest),
-		"tag":        hash,
+		// Use this digest if this entry is about our original repository.
+		if strings.HasPrefix(repo, origRepo) {
+			if parts = strings.Split(digest, ":"); len(parts) != 2 {
+				return fmt.Errorf("unknown digest format: %q", digest)
+			}
+			hashType, hash := parts[0], parts[1]
+			m := map[string]interface{}(*t)
+			m[chart].(map[interface{}]interface{})[imageRef] = map[string]string{
+				"repository": fmt.Sprintf("%s@%s", origRepo, hashType),
+				"tag":        hash,
+			}
+			*t = m
+			return nil
+		}
 	}
-	*t = m
-	return nil
+	if err := scanner.Err(); err != nil {
+		return err
+	}
+
+	return fmt.Errorf("could not resolve %s", origRepo)
 }