feat(server): implement tags/list endpoint

When a git source is used branch names are exposed in the tags list.

For other source types, only "latest" is exposed.

Fixes: #85

config/pkgsource.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -32,13 +33,16 @@ type PkgSource interface {
 	// for calling Nix.
 	Render(tag string) (string, string)
 
-	// Create a key by which builds for this source and iamge
+	// Create a key by which builds for this source and image
 	// combination can be cached.
 	//
 	// The empty string means that this value is not cacheable due
 	// to the package source being a moving target (such as a
 	// channel).
 	CacheKey(pkgs []string, tag string) string
+
+	// Return available docker tags for the current PkgSource
+	Tags() ([]string, error)
 }
 
 type GitSource struct {
@@ -91,6 +95,25 @@ func (g *GitSource) CacheKey(pkgs []string, tag string) string {
 	return hashed
 }
 
+// Regex to determine valid docker tags
+var tagRegex = regexp.MustCompile(`^[\w][\w.-]{0,127}$`)
+
+func (g *GitSource) Tags() ([]string, error) {
+	tags := []string{"latest"}
+	heads := filepath.Join(g.repository, ".git/refs/heads")
+	err := filepath.Walk(heads, func(path string, info os.FileInfo, err error) error {
+		if info.IsDir() {
+			return nil
+		}
+		// latest tag is always present and represent the master branch
+		if tagRegex.MatchString(info.Name()) && info.Name() != "master" {
+			tags = append(tags, info.Name())
+		}
+		return nil
+	})
+	return tags, err
+}
+
 type NixChannel struct {
 	channel string
 }
@@ -113,6 +136,10 @@ func (n *NixChannel) CacheKey(pkgs []string, tag string) string {
 	return hashed
 }
 
+func (n *NixChannel) Tags() ([]string, error) {
+	return []string{"latest"}, nil
+}
+
 type PkgsPath struct {
 	path string
 }
@@ -128,6 +155,10 @@ func (p *PkgsPath) CacheKey(pkgs []string, tag string) string {
 	return ""
 }
 
+func (n *PkgsPath) Tags() ([]string, error) {
+	return []string{"latest"}, nil
+}
+
 // Retrieve a package source from the environment. If no source is
 // specified, the Nix code will default to a recent NixOS channel.
 func pkgSourceFromEnv() (PkgSource, error) {
@@ -140,7 +171,7 @@ func pkgSourceFromEnv() (PkgSource, error) {
 	}
 
 	if git := os.Getenv("NIXERY_PKGS_REPO"); git != "" {
-		log.WithField("repo", git).Info("using NIx package set from git repository")
+		log.WithField("repo", git).Info("using Nix package set from git repository")
 
 		return &GitSource{
 			repository: git,

main.go

@@ -55,6 +55,7 @@ var version string = "devel"
 var (
 	manifestRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/manifests/([\w|\-|\.|\_]+)$`)
 	layerRegex    = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/blobs/sha256:(\w+)$`)
+	tagsRegex     = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/tags/list$`)
 )
 
 // Downloads the popularity information for the package set from the
@@ -184,6 +185,27 @@ func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	tagsMatches := tagsRegex.FindStringSubmatch(r.RequestURI)
+	if len(tagsMatches) == 2 {
+		tags, err := h.state.Cfg.Pkgs.Tags()
+		if err != nil {
+			writeError(w, 500, "UNKNOWN", "failed to list tags")
+
+			log.WithError(err).WithFields(log.Fields{
+				"image": tagsMatches[1],
+			}).Error(err)
+
+			return
+		}
+		manifest, _ := json.Marshal(map[string]interface{}{
+			"name": tagsMatches[1],
+			"tags": tags,
+		})
+		w.Header().Add("Content-Type", manifestMediaType)
+		w.Write(manifest)
+		return
+	}
+
 	log.WithField("uri", r.RequestURI).Info("unsupported registry route")
 
 	w.WriteHeader(404)