From aba3f35c496d3edd0f56bb4a2d446494ad54ba93 Mon Sep 17 00:00:00 2001
From: Robin Xiang <liverpool8056@163.com>
Date: Mon, 18 Mar 2024 14:34:29 +0800
Subject: [PATCH] fix(core): fix a bug that `X-Kong-Upstream-Status` header is
 not set when the response is returned from the cache of `proxy-cache` plugin.

FTI-5827
---
 .../kong/fix-upstream-status-unset.yml        |  3 ++
 kong/runloop/handler.lua                      |  2 +-
 .../15-upstream-status-header_spec.lua        | 35 +++++++++++++++++--
 3 files changed, 36 insertions(+), 4 deletions(-)
 create mode 100644 changelog/unreleased/kong/fix-upstream-status-unset.yml

diff --git a/changelog/unreleased/kong/fix-upstream-status-unset.yml b/changelog/unreleased/kong/fix-upstream-status-unset.yml
new file mode 100644
index 000000000000..eefb1e02bcf4
--- /dev/null
+++ b/changelog/unreleased/kong/fix-upstream-status-unset.yml
@@ -0,0 +1,3 @@
+message: fix a bug that `X-Kong-Upstream-Status` will not appear in the response headers even if it is set in the `headers` parameter in the kong.conf when the response is hit and returned by proxy cache plugin.
+scope: Core
+type: bugfix
diff --git a/kong/runloop/handler.lua b/kong/runloop/handler.lua
index 1a5f3a00a00c..4ef16da3e827 100644
--- a/kong/runloop/handler.lua
+++ b/kong/runloop/handler.lua
@@ -1438,7 +1438,7 @@ return {
 
       local upstream_status_header = constants.HEADERS.UPSTREAM_STATUS
       if kong.configuration.enabled_headers[upstream_status_header] then
-        local upstream_status = ctx.buffered_status or tonumber(sub(var.upstream_status or "", -3))
+        local upstream_status = ctx.buffered_status or tonumber(sub(var.upstream_status or "", -3)) or ngx.status
         header[upstream_status_header] = upstream_status
         if not header[upstream_status_header] then
           log(ERR, "failed to set ", upstream_status_header, " header")
diff --git a/spec/02-integration/05-proxy/15-upstream-status-header_spec.lua b/spec/02-integration/05-proxy/15-upstream-status-header_spec.lua
index 8b67a077f124..b7c24e51360e 100644
--- a/spec/02-integration/05-proxy/15-upstream-status-header_spec.lua
+++ b/spec/02-integration/05-proxy/15-upstream-status-header_spec.lua
@@ -18,7 +18,7 @@ local function setup_db()
     protocol = helpers.mock_upstream_protocol,
   }
 
-  bp.routes:insert {
+  local route1 = bp.routes:insert {
     protocols = { "http" },
     paths = { "/status/200" },
     service = service,
@@ -49,6 +49,19 @@ local function setup_db()
     route = { id = route3.id },
   }
 
+  bp.plugins:insert {
+    name = "proxy-cache",
+    route = { id = route1.id },
+    config = {
+      response_code = { 200 },
+      request_method = { "GET" },
+      content_type = { "application/json" },
+      cache_ttl = 300,
+      storage_ttl = 300,
+      strategy = "memory",
+    }
+  }
+
   return bp
 end
 
@@ -65,8 +78,6 @@ describe(constants.HEADERS.UPSTREAM_STATUS .. " header", function()
         headers = "server_tokens,latency_tokens,x-kong-upstream-status",
         plugins = "bundled,dummy",
       })
-
-      client = helpers.proxy_client()
     end)
 
     lazy_teardown(function()
@@ -77,6 +88,11 @@ describe(constants.HEADERS.UPSTREAM_STATUS .. " header", function()
       helpers.stop_kong()
     end)
 
+    before_each(function()
+      if client then client:close() end
+      client = helpers.proxy_client()
+    end)
+
     it("when no plugin changes status code", function()
       local res = assert(client:send {
         method  = "GET",
@@ -101,6 +117,19 @@ describe(constants.HEADERS.UPSTREAM_STATUS .. " header", function()
       assert.res_status(500, res)
       assert.equal("200", res.headers[constants.HEADERS.UPSTREAM_STATUS])
     end)
+
+    it("should be set when proxy-cache is enabled", function()
+      local res = assert(client:send {
+        method  = "GET",
+        path    = "/status/200",
+        headers = {
+          host = helpers.mock_upstream_host,
+        }
+      })
+      assert.res_status(200, res)
+      assert.equal("Hit", res.headers["X-Cache-Status"])
+      assert.equal("200", res.headers[constants.HEADERS.UPSTREAM_STATUS])
+    end)
   end)
 
   describe("is not injected with default configuration", function()