Create Repositories method

This change removes the Catalog Service and replaces it with a more
simplistic Repositories() method for obtaining a catalog of all
repositories.  The Repositories method takes a pre-allocated slice
and fills it up to the size of the slice and returns the amount
filled.  The catalog is returned lexicographically and will start
being filled from the last entry passed to Repositories().  If there
are no more entries to fill, io.EOF will be returned.

Signed-off-by: Patrick Devine <patrick.devine@docker.com>

Conflicts:
	registry/client/repository.go
	registry/handlers/api_test.go

docs/client/repository.go

@@ -445,34 +445,7 @@ func (bs *blobStatter) Stat(ctx context.Context, dgst digest.Digest) (distributi
 	}
 }
 
-// NewCatalog can be used to get a list of repositories
-func NewCatalog(ctx context.Context, baseURL string, transport http.RoundTripper) (distribution.CatalogService, error) {
-	ub, err := v2.NewURLBuilderFromString(baseURL)
-	if err != nil {
-		return nil, err
-	}
-
-	client := &http.Client{
-		Transport: transport,
-		Timeout:   1 * time.Minute,
-	}
-
-	return &catalog{
-		client:  client,
-		ub:      ub,
-		context: ctx,
-	}, nil
-}
-
-type catalog struct {
-	client  *http.Client
-	ub      *v2.URLBuilder
-	context context.Context
-}
-
-func (c *catalog) Get(maxEntries int, last string) ([]string, bool, error) {
-	var repos []string
-
+func buildCatalogValues(maxEntries int, last string) url.Values {
 	values := url.Values{}
 
 	if maxEntries > 0 {
@@ -483,14 +456,35 @@ func (c *catalog) Get(maxEntries int, last string) ([]string, bool, error) {
 		values.Add("last", last)
 	}
 
-	u, err := c.ub.BuildCatalogURL(values)
+	return values
+}
+
+// Repositories returns a lexigraphically sorted catalog given a base URL.  The 'entries' slice will be filled up to the size
+// of the slice, starting at the value provided in 'last'.  The number of entries will be returned along with io.EOF if there
+// are no more entries
+func Repositories(ctx context.Context, baseURL string, entries []string, last string, transport http.RoundTripper) (int, error) {
+	var numFilled int
+	var returnErr error
+
+	ub, err := v2.NewURLBuilderFromString(baseURL)
 	if err != nil {
-		return nil, false, err
+		return 0, err
 	}
 
-	resp, err := c.client.Get(u)
+	client := &http.Client{
+		Transport: transport,
+		Timeout:   1 * time.Minute,
+	}
+
+	values := buildCatalogValues(len(entries), last)
+	u, err := ub.BuildCatalogURL(values)
 	if err != nil {
-		return nil, false, err
+		return 0, err
+	}
+
+	resp, err := client.Get(u)
+	if err != nil {
+		return 0, err
 	}
 	defer resp.Body.Close()
 
@@ -502,13 +496,22 @@ func (c *catalog) Get(maxEntries int, last string) ([]string, bool, error) {
 		decoder := json.NewDecoder(resp.Body)
 
 		if err := decoder.Decode(&ctlg); err != nil {
-			return nil, false, err
+			return 0, err
+		}
+
+		for cnt := range ctlg.Repositories {
+			entries[cnt] = ctlg.Repositories[cnt]
+		}
+		numFilled = len(ctlg.Repositories)
+
+		link := resp.Header.Get("Link")
+		if link == "" {
+			returnErr = io.EOF
 		}
 
-		repos = ctlg.Repositories
 	default:
-		return nil, false, handleErrorResponse(resp)
+		return 0, handleErrorResponse(resp)
 	}
 
-	return repos, false, nil
+	return numFilled, returnErr
 }