feat(pdk/log): Add upstream status code

CHANGELOG.md

@@ -137,6 +137,11 @@
   errors to a single array via the optional `flatten_errors` query parameter.
   [#10161](https://github.com/Kong/kong/pull/10161)
 
+#### PDK
+
+- Support for `upstream_status` field in log serializer.
+  [#10296](https://github.com/Kong/kong/pull/10296)
+
 ### Fixes
 
 #### Core

kong/pdk/log.lua

@@ -802,6 +802,11 @@ do
         end
       end
 
+      -- The value of upstream_status is a string, and status codes may be 
+      -- seperated by comma or grouped by colon, according to
+      -- the nginx doc: http://nginx.org/en/docs/http/ngx_http_upstream_module.html#upstream_status
+      local upstream_status = var.upstream_status or ""
+
       local root = {
         request = {
           uri = request_uri,
@@ -813,6 +818,7 @@ do
           tls = build_tls_info(var, ctx.CLIENT_VERIFY_OVERRIDE),
         },
         upstream_uri = upstream_uri,
+        upstream_status = upstream_status,
         response = {
           status = ongx.status,
           headers = ongx.resp.get_headers(),
@@ -822,7 +828,7 @@ do
           kong = (ctx.KONG_PROXY_LATENCY or ctx.KONG_RESPONSE_LATENCY or 0) +
                  (ctx.KONG_RECEIVE_TIME or 0),
           proxy = ctx.KONG_WAITING_TIME or -1,
-          request = var.request_time * 1000
+          request = tonumber(var.request_time) * 1000,
         },
         tries = (ctx.balancer_data or {}).tries,
         authenticated_entity = build_authenticated_entity(ctx),

spec/01-unit/10-log_serializer_spec.lua

@@ -30,7 +30,10 @@ describe("kong.log.serialize", function()
           request_length = "200",
           bytes_sent = "99",
           request_time = "2",
-          remote_addr = "1.1.1.1"
+          remote_addr = "1.1.1.1",
+          -- may be a non-numeric string, 
+          -- see http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_addr
+          upstream_status = "500, 200 : 200, 200",
         },
         update_time = ngx.update_time,
         sleep = ngx.sleep,
@@ -74,6 +77,7 @@ describe("kong.log.serialize", function()
         assert.same({"arg1", "arg2"}, res.request.querystring)
         assert.equal("http://test.com:80/request_uri", res.request.url)
         assert.equal("/upstream_uri", res.upstream_uri)
+        assert.equal("500, 200 : 200, 200", res.upstream_status)
         assert.equal(200, res.request.size)
         assert.equal("/request_uri", res.request.uri)