usability: add driver API check

In addition to the core queue drivers, customer drivers are exists.
In the commit a check for a driver API implementation was added.
Now, the consumer will be informed about the missing methods in
the driver implementation.

Closes #126

Author: LeonidVas

queue/abstract.lua

@@ -75,6 +75,12 @@ local function tube_release_all_tasks(tube)
         return
     end
 
+    -- Custom drivers may not have an implementation of
+    -- the "tasks_by_state" method.
+    if tube.raw["tasks_by_state"] == nil then
+        return
+    end
+
     log.info(prefix .. 'releasing all taken task (may take a while)')
     local released = 0
     for _, task in tube.raw:tasks_by_state(state.TAKEN) do
@@ -308,6 +314,45 @@ end
 -- methods
 local method = {}
 
+-- Original list of required driver methods.
+local required_driver_methods = {
+    'normalize_task',
+    'put',
+    'take',
+    'delete',
+    'release',
+    'bury',
+    'kick',
+    'peek',
+    'truncate'
+}
+
+-- List of driver methods that were added to the original list.
+local new_driver_methods = {
+    'tasks_by_state'
+}
+
+-- gh-126 Check the driver API.
+local function check_driver_api(tube_impl, tube_type)
+    for _, v in pairs(required_driver_methods) do
+        if tube_impl[v] == nil then
+            error('The "' .. tube_type ..'" driver does not have an'
+                  .. ' implementation of method "' .. v ..'".')
+        end
+    end
+
+    for _, v in pairs(new_driver_methods) do
+        if tube_impl[v] == nil then
+            log.warn('The "' .. tube_type ..'" driver doesn\'t have an'
+                     .. ' implementation of method "' .. v ..'". Some queue'
+                     .. ' functionality may not work properly.')
+        end
+    end
+end
+
+-- Cache of already verified drivers.
+local checked_drivers = {}
+
 local function make_self(driver, space, tube_name, tube_type, tube_id, opts)
     opts = opts or {}
     local self
@@ -362,6 +407,12 @@ local function make_self(driver, space, tube_name, tube_type, tube_id, opts)
     }, {
         __index = tube
     })
+
+    if checked_drivers[tube_type] == nil then
+        check_driver_api(self.raw, tube_type)
+        checked_drivers[tube_type] = true
+    end
+
     self:on_task_change(opts.on_task_change)
     queue.tube[tube_name] = self