Catalog V2 API specification proposal

This contains a proposal for a catalog API, provided access to the internal
contents of a registry instance. The API endpoint is prefixed with an
underscore, which is illegal in images names, to prevent collisions with
repositories names. To avoid issues with large result sets, a paginated version
of the API is proposed. We make an addition to the tags API to support
pagination to ensure the specification is conistent.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/api/v2/descriptors.go

@@ -87,6 +87,23 @@ var (
 		Format:      "<digest>",
 	}
 
+	paginationParameters = []ParameterDescriptor{
+		{
+			Name:        "n",
+			Type:        "integer",
+			Description: "Limit the number of entries in each response. It not present, all entries will be returned.",
+			Format:      "<integer>",
+			Required:    false,
+		},
+		{
+			Name:        "last",
+			Type:        "string",
+			Description: "Result set will include values lexically after last.",
+			Format:      "<integer>",
+			Required:    false,
+		},
+	}
+
 	unauthorizedResponse = ResponseDescriptor{
 		Description: "The client does not have access to the repository.",
 		StatusCode:  http.StatusUnauthorized,
@@ -269,6 +286,9 @@ type ResponseDescriptor struct {
 	// Headers covers any headers that may be returned from the response.
 	Headers []ParameterDescriptor
 
+	// Fields describes any fields that may be present in the response.
+	Fields []ParameterDescriptor
+
 	// ErrorCodes enumerates the error codes that may be returned along with
 	// the response.
 	ErrorCodes []errcode.ErrorCode
@@ -427,6 +447,44 @@ var routeDescriptors = []RouteDescriptor{
 							},
 						},
 					},
+					{
+						Description:     "Return a portion of the tags for the specified repository.",
+						PathParameters:  []ParameterDescriptor{nameParameterDescriptor},
+						QueryParameters: paginationParameters,
+						Successes: []ResponseDescriptor{
+							{
+								StatusCode:  http.StatusOK,
+								Description: "A list of tags for the named repository.",
+								Headers: []ParameterDescriptor{
+									{
+										Name:        "Content-Length",
+										Type:        "integer",
+										Description: "Length of the JSON response body.",
+										Format:      "<length>",
+									},
+								},
+								Fields: []ParameterDescriptor{
+									{
+										Name:        "next",
+										Type:        "url",
+										Description: "Provides the URL to get the next set of results, if available.",
+										Format:      "<url>",
+									},
+								},
+								Body: BodyDescriptor{
+									ContentType: "application/json; charset=utf-8",
+									Format: `{
+    "name": <name>,
+    "tags": [
+        <tag>,
+        ...
+    ],
+    "next": "<url>?last=<name>&n=<last value of n>"
+}`,
+								},
+							},
+						},
+					},
 				},
 			},
 		},
@@ -1320,6 +1378,83 @@ var routeDescriptors = []RouteDescriptor{
 			},
 		},
 	},
+	{
+		Name:        RouteNameCatalog,
+		Path:        "/v2/_catalog",
+		Entity:      "Catalog",
+		Description: "List a set of available repositories in the local registry cluster. Does not provide any indication of what may be available upstream. Applications can only determine if a repository is available but not if it is not available.",
+		Methods: []MethodDescriptor{
+			{
+				Method:      "GET",
+				Description: "Retrieve a sorted, json list of repositories available in the registry.",
+				Requests: []RequestDescriptor{
+					{
+						Name:        "Catalog Fetch Complete",
+						Description: "Request an unabridged list of repositories available.",
+						Successes: []ResponseDescriptor{
+							{
+								Description: "Returns the unabridged list of repositories as a json response.",
+								StatusCode:  http.StatusOK,
+								Headers: []ParameterDescriptor{
+									{
+										Name:        "Content-Length",
+										Type:        "integer",
+										Description: "Length of the JSON response body.",
+										Format:      "<length>",
+									},
+								},
+								Body: BodyDescriptor{
+									ContentType: "application/json; charset=utf-8",
+									Format: `{
+	"repositories": [
+		<name>,
+		...
+	]
+}`,
+								},
+							},
+						},
+					},
+					{
+						Name:            "Catalog Fetch Paginated",
+						Description:     "Return the specified portion of repositories.",
+						QueryParameters: paginationParameters,
+						Successes: []ResponseDescriptor{
+							{
+								StatusCode: http.StatusOK,
+								Body: BodyDescriptor{
+									ContentType: "application/json; charset=utf-8",
+									Format: `{
+	"repositories": [
+		<name>,
+		...
+	]
+	"next": "<url>?last=<name>&n=<last value of n>"
+}`,
+								},
+								Headers: []ParameterDescriptor{
+									{
+										Name:        "Content-Length",
+										Type:        "integer",
+										Description: "Length of the JSON response body.",
+										Format:      "<length>",
+									},
+								},
+								Fields: []ParameterDescriptor{
+									{
+										Name:        "next",
+										Type:        "url",
+										Description: "Provides the URL to get the next set of results, if available.",
+										Format:      "<url>",
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+	},
 }
 
 var routeDescriptorsMap map[string]RouteDescriptor

docs/api/v2/routes.go

@@ -11,6 +11,7 @@ const (
 	RouteNameBlob            = "blob"
 	RouteNameBlobUpload      = "blob-upload"
 	RouteNameBlobUploadChunk = "blob-upload-chunk"
+	RouteNameCatalog         = "catalog"
 )
 
 var allEndpoints = []string{