fix(queue): function Queue.can_enqueue should handle non-existing queue instance correctly

kong/tools/queue.lua

@@ -297,8 +297,18 @@ end
 function Queue.can_enqueue(queue_conf, entry)
   local queue = queues[_make_queue_key(queue_conf.name)]
   if not queue then
-    -- treat non-existing queues as not full as they will be created on demand
-    return false
+    -- treat non-existing queues having enough capacity.
+    -- WARNING: The limitation is that if the `entry` is a string and the `queue.max_bytes` is set,
+    --          and also the `#entry` is larger than `queue.max_bytes`,
+    --          this function will incorrectly return `true` instead of `false`.
+    --          This is a limitation of the current implementation.
+    --          All capacity checking functions need a Queue instance to work correctly.
+    --          constructing a Queue instance just for this function is not efficient,
+    --          so we just return `true` here.
+    --          This limitation should not happen in normal usage,
+    --          as user should be aware of the queue capacity settings
+    --          to avoid such situation.
+    return true
   end
 
   return _can_enqueue(queue, entry)

spec/01-unit/27-queue_spec.lua

@@ -812,8 +812,11 @@ describe("plugin queue", function()
       )
     end
 
+    -- should be true if the queue does not exist
+    assert.is_true(Queue.can_enqueue(queue_conf))
+
     assert.is_false(Queue.is_full(queue_conf))
-    assert.is_false(Queue.can_enqueue(queue_conf, "One"))
+    assert.is_true(Queue.can_enqueue(queue_conf, "One"))
     enqueue(queue_conf, "One")
     assert.is_false(Queue.is_full(queue_conf))
 
@@ -835,8 +838,11 @@ describe("plugin queue", function()
       max_retry_delay = 60,
     }
 
+    -- should be true if the queue does not exist
+    assert.is_true(Queue.can_enqueue(queue_conf))
+
     assert.is_false(Queue.is_full(queue_conf))
-    assert.is_false(Queue.can_enqueue(queue_conf, "1"))
+    assert.is_true(Queue.can_enqueue(queue_conf, "1"))
     enqueue(queue_conf, "1")
     assert.is_false(Queue.is_full(queue_conf))
 
@@ -857,6 +863,9 @@ describe("plugin queue", function()
       max_retry_delay = 60,
     }
 
+    -- should be true if the queue does not exist
+    assert.is_true(Queue.can_enqueue(queue_conf))
+
     enqueue(queue_conf, "1")
 
     assert.is_false(Queue.is_full(queue_conf))