v2: add pagination decorator

endpoints/v2/__init__.py

@@ -2,13 +2,14 @@ import logging
 
 from functools import wraps
 from urlparse import urlparse
+from urllib import urlencode
 
 from flask import Blueprint, make_response, url_for, request, jsonify
 from semantic_version import Spec
 
 import features
 
-from app import app, metric_queue
+from app import app, metric_queue, get_app_url
 from auth.auth_context import get_grant_context
 from auth.permissions import (ReadRepositoryPermission, ModifyRepositoryPermission,
                               AdministerRepositoryPermission)
@@ -19,12 +20,53 @@ from endpoints.v2.errors import V2RegistryException, Unauthorized
 from util.http import abort
 from util.registry.dockerver import docker_version
 from util.metrics.metricqueue import time_blueprint
+from util.pagination import encrypt_page_token, decrypt_page_token
 
 logger = logging.getLogger(__name__)
 v2_bp = Blueprint('v2', __name__)
 
 time_blueprint(v2_bp, metric_queue)
 
+
+_MAX_RESULTS_PER_PAGE = 50
+
+
+def _paginate(limit_kwarg_name='limit', offset_kwarg_name='offset',
+              callback_kwarg_name='pagination_callback'):
+  def wrapper(func):
+    @wraps(func)
+    def wrapped(*args, **kwargs):
+      try:
+        requested_limit = int(request.args.get('n', _MAX_RESULTS_PER_PAGE))
+      except ValueError:
+        requested_limit = 0
+
+      limit = max(min(requested_limit, _MAX_RESULTS_PER_PAGE), 1)
+      next_page_token = request.args.get('next_page', None)
+
+      # Decrypt the next page token, if any.
+      offset = 0
+      page_info = decrypt_page_token(next_page_token)
+      if page_info is not None:
+        # Note: we use offset here instead of ID >= n because one of the V2 queries is a UNION.
+        offset = page_info.get('offset', 0)
+
+      def callback(num_results, response):
+        if num_results <= limit:
+          return
+        next_page_token = encrypt_page_token({'offset': limit+offset})
+        link = get_app_url() + url_for(request.endpoint, **request.view_args)
+        link += '?%s; rel="next"' % urlencode({'n': limit, 'next_page': next_page_token})
+        response.headers['Link'] = link
+
+      kwargs[limit_kwarg_name] = limit
+      kwargs[offset_kwarg_name] = offset
+      kwargs[callback_kwarg_name] = callback
+      func(*args, **kwargs)
+    return wrapped
+  return wrapper
+
+
 @v2_bp.app_errorhandler(V2RegistryException)
 def handle_registry_v2_exception(error):
   response = jsonify({
@@ -104,8 +146,10 @@ def v2_support_enabled():
   return response
 
 
-from endpoints.v2 import v2auth
-from endpoints.v2 import manifest
-from endpoints.v2 import blob
-from endpoints.v2 import tag
-from endpoints.v2 import catalog
+from endpoints.v2 import (
+  blob,
+  catalog,
+  manifest,
+  tag,
+  v2auth,
+)