fix(proxy-cache): set Header Accept-Encoding as default values of v…

…ary_headers

Currently, proxy-cache might mix the compression and uncompression
values while cacheing, and return runexpected compression response to
the request if users didn't specify the vary_headers.

kong/plugins/proxy-cache/schema.lua

@@ -72,6 +72,7 @@ return {
             elements = { type = "string" },
           }},
           { vary_headers = { description = "Relevant headers considered for the cache key. If undefined, none of the headers are taken into consideration.", type = "array",
+            default = { "Accept-Encoding" },
             elements = { type = "string" },
           }},
           { response_headers = {

spec/03-plugins/31-proxy-cache/01-schema_spec.lua

@@ -112,6 +112,13 @@ describe("proxy-cache schema", function()
     assert.is_truthy(entity)
   end)
 
+  it("defines default vary_headers values", function()
+    local config = { strategy = "memory" }
+    local entity, err = v(config, proxy_cache_schema)
+    assert.is_nil(err)
+    assert.is_truthy(entity)
+    assert.same(entity.config.vary_headers, { "Accept-Encoding" })
+  end)
   it("supports vary_headers values", function()
     local entity, err = v({
       strategy = "memory",

spec/03-plugins/31-proxy-cache/03-api_spec.lua

@@ -259,6 +259,17 @@ describe("Plugin: proxy-cache", function()
         assert.res_status(200, res)
         assert.same("Miss", res.headers["X-Cache-Status"])
       end)
+      it("miss if pass the Accept-Encoding", function()
+        local res = assert(proxy_client:get("/get", {
+          headers = {
+            host = "route-1.test",
+            ["kong-debug"] = 1,
+            ["Accept-Encoding"] = "gzip",
+          }
+        }))
+        assert.res_status(200, res)
+        assert.same("Miss", res.headers["X-Cache-Status"])
+      end)
       it("purge all the cache entries", function()
         -- make a `Hit` request to `route-1`
         local res = assert(proxy_client:get("/get", {