fix(router) ensure reducers respect matching priorities

This patch ensures that when reducing categories, we always consider
higher-priority categories first.

kong/router.lua

@@ -72,6 +72,16 @@ local MATCH_RULES = {
   DST             = 0x00000001,
 }
 
+local SORTED_MATCH_RULES = {}
+
+for _, v in pairs(MATCH_RULES) do
+  insert(SORTED_MATCH_RULES, v)
+end
+
+sort(SORTED_MATCH_RULES, function(a, b)
+  return a > b
+end)
+
 local MATCH_SUBRULES = {
   HAS_REGEX_URI    = 0x01,
   PLAIN_HOSTS_ONLY = 0x02,
@@ -851,7 +861,7 @@ do
 
     local reducers_set = {}
 
-    for _, bit_match_rule in pairs(MATCH_RULES) do
+    for _, bit_match_rule in ipairs(SORTED_MATCH_RULES) do
       if band(bit_category, bit_match_rule) ~= 0 then
         reducers_set[#reducers_set + 1] = reducers[bit_match_rule]
       end

spec/01-unit/08-router_spec.lua

@@ -1088,6 +1088,54 @@ describe("Router", function()
         assert.truthy(route_t)
         assert.equal(use_case[2].route, route_t.route)
       end)
+
+      it("more [headers] has priority over longer [paths]", function()
+        local use_case = {
+          {
+            service = service,
+            route   = {
+              headers = {
+                version = { "v1" },
+              },
+              paths = { "/my-route/hello" },
+            },
+          },
+          {
+            service = service,
+            route   = {
+              headers = {
+                version = { "v1" },
+                location = { "us-east" },
+              },
+              paths = { "/my-route" },
+            },
+          },
+        }
+
+        local router = assert(Router.new(use_case))
+
+        local match_t = router.select("GET", "/my-route/hello", "domain.org",
+                                      nil, nil, nil, nil, nil, {
+                                        version = "v1",
+                                        location = "us-east",
+                                      })
+        assert.truthy(match_t)
+        assert.equal(use_case[2].route, match_t.route)
+        assert.same("/my-route", match_t.matches.uri)
+        assert.same({ version = "v1", location = "us-east" },
+                    match_t.matches.headers)
+
+        local match_t = router.select("GET", "/my-route/hello/world",
+                                      "domain.org", nil, nil, nil, nil, nil, {
+                                        version = "v1",
+                                        location = "us-east",
+                                      })
+        assert.truthy(match_t)
+        assert.equal(use_case[2].route, match_t.route)
+        assert.same("/my-route", match_t.matches.uri)
+        assert.same({ version = "v1", location = "us-east" },
+                    match_t.matches.headers)
+      end)
     end)
 
     describe("misses", function()