error_object

object error_object

Errors can be organized into lists. To achieve this, a Lua table representing an error object has .prev field and e:set_prev(err) method.

error_object.prev

Return a previous error, if any.

error_object:set_prev(error object)

Set an error as the previous error. Accepts an error object or nil.

Example:

tarantool> e1 = box.error.new({code = 111, reason = 'some cause'})
---
...
tarantool> e2 = box.error.new({code = 111, reason = 'cause of cause'})
---
...
tarantool> e1:set_prev(e2)
---
...
tarantool> e1.prev
---
- cause of cause
...

Cycles are not allowed for error lists:

tarantool> e2:set_prev(e1)
---
- error: 'builtin/error.lua:147: Cycles are not allowed'
...

Setting the previous error does not erase its own previous members:

-- e1 -> e2 -> e3 -> e4
e1:set_prev(e2)
e2:set_prev(e3)
e3:set_prev(e4)
e2:set_prev(e5)
-- Now there are two lists: e1->e2->e5 and e3->e4

The iProto protocol also supports stacked diagnostics. See details in MessagePack extensions – The ERROR type.