fix(dao): page size 1 does not work for lmdb

Fix KAG-5875

kong/db/strategies/off/init.lua

@@ -131,6 +131,12 @@ local function page_for_prefix(self, prefix, size, offset, options, follow)
     return nil, err_or_more
   end
 
+  -- special handling for page size 1.
+  -- drop other results
+  if size == 1 then
+    res = { res[1] }
+  end
+
   local ret = {}
   local ret_idx = 0
   local schema = self.schema

spec/02-integration/04-admin_api/07-upstreams_routes_spec.lua

@@ -663,6 +663,18 @@ describe("Admin API: #" .. strategy, function()
           assert.same({ data = {}, next = ngx.null }, json)
         end)
       end)
+
+      describe("#regression", function()
+        it("page size 1", function()
+          local res = assert(client:send {
+            method = "GET",
+            path = "/upstreams?size=1"
+          })
+          assert.response(res).has.status(200)
+          local json = assert.response(res).has.jsonbody()
+          assert.equal(1, #json.data)
+        end)
+      end)
     end)
 
     describe("DELETE", function()