Catalog for V2 API Implementation

This change adds a basic catalog endpoint to the API, which returns a list,
or partial list, of all of the repositories contained in the registry.  Calls
to this endpoint are somewhat expensive, as every call requires walking a
large part of the registry.

Instead, to maintain a list of repositories, you would first call the catalog
endpoint to get an initial list, and then use the events API to maintain
any future repositories.

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

docs/client/repository_test.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -77,6 +78,23 @@ func addTestFetch(repo string, dgst digest.Digest, content []byte, m *testutil.R
 	})
 }
 
+func addTestCatalog(content []byte, m *testutil.RequestResponseMap) {
+	*m = append(*m, testutil.RequestResponseMapping{
+		Request: testutil.Request{
+			Method: "GET",
+			Route:  "/v2/_catalog",
+		},
+		Response: testutil.Response{
+			StatusCode: http.StatusOK,
+			Body:       content,
+			Headers: http.Header(map[string][]string{
+				"Content-Length": {strconv.Itoa(len(content))},
+				"Content-Type":   {"application/json; charset=utf-8"},
+			}),
+		},
+	})
+}
+
 func TestBlobFetch(t *testing.T) {
 	d1, b1 := newRandomBlob(1024)
 	var m testutil.RequestResponseMap
@@ -732,3 +750,26 @@ func TestManifestUnauthorized(t *testing.T) {
 		t.Fatalf("Unexpected message value: %q, expected %q", v2Err.Message, expected)
 	}
 }
+
+func TestCatalog(t *testing.T) {
+	var m testutil.RequestResponseMap
+	addTestCatalog([]byte("{\"repositories\":[\"foo\", \"bar\", \"baz\"]}"), &m)
+
+	e, c := testServer(m)
+	defer c()
+
+	ctx := context.Background()
+	ctlg, err := NewCatalog(ctx, e, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	repos, _, err := ctlg.Get(0, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(repos) != 3 {
+		t.Fatalf("Got wrong number of repos")
+	}
+}