Error Handling

Error handling flow

### Error flow 
try
retry 
on succeeded write operation add to rollback/undo log 
catch 
error code swicth case 
send back Error Model: 
  code: 500
  urn: io.kitset.{entity} 
  key: validation.{field}
  name: Title  
  msg: Message
  trace: Error stack (optional) 
client has the same case on error catch 
attempt rollback 
  rollback failed
    retry 
    cloud watch - alert 
      cloud watch alert failed 
        retry
        add to logs 
  rollback succeeded
    send back to client 
      update client toast 
    


eg. Controller.method = req, res, next
  try
    Service.method(attr)
    rollback.prepend('info', Service.oppositeOfMethod)
  catch(err)
    next(err)
    

error types

## compile
Syntax errors: errors due to the fact that the syntax of the language is not respected.
Semantic errors: errors due to an improper use of program statements.
Logical errors: errors due to the fact that the specification is not respected.

## run time errors
dynamic semantic errors, and logical errors, that cannot be detected by the compiler (debugging).
this can be handled with asserts (unit tests) 
wrong type
variable/object doesnt exist 
object doesnt have method
method expected to return type of 
object attributes expected to be of type  

## validation
property type
property not set 
property doesnt exist
property not valid 
json validation - nested object has object has object check 


## database/model
inherits validation
relationship doesnt exist
relationship validation - nested model has model has model through join 

null errors 
- empty set 
- relationship empty - eg. no children for user 

column doesnt exist 
wrong type - trying to write the wrong type 
not unique 
cant delete - proptected 

## http
route doesnt exist
validation of header (exists, type, regex) 
validation of body 
access control/CORS
method not supported 

## request - server to another server 


## authn/authz
not authenticated 
not authorized 
not paid? 
user removed or blocked? 

## platforms
http server not responding
database/cache not responding 


## rollback 
rollback id, name, action 
attempted rollback failed 

## debug/production 
env file missing 
env file malformed
env doesnt have attribute 
env attribute is not valid 
warning: should be in debug mode 

## timeout 
async doesnt return 
too long 
unknown error