Requestor cannot accept a WantToComputeTask message with price set to 0

[shadeofblue]

• add an integration test that reproduces this issue
• addresss the issue

When receiving the WantToComputeTask message, the processing crashes when the price specified by the provider is set to 0

[etam]

2019-03-05 13:18:57 CRITICAL twisted                             Unhandled Error                                                                                                                                                                                               
Traceback (most recent call last):                                                                                                                                                                                                                                             
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/python/log.py", line 103, in callWithLogger                                                                                                                      
    return callWithContext({"system": lp}, func, *args, **kw)                                                                                                                                                                                                                  
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/python/log.py", line 86, in callWithContext                                                                                                                      
    return context.call({ILogContext: newCtx}, func, *args, **kw)                                                                                                                                                                                                              
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/python/context.py", line 122, in callWithContext                                                                                                                 
    return self.currentContext().callWithContext(ctx, func, *args, **kw)                                                                                                                                                                                                       
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/python/context.py", line 85, in callWithContext                                                                                                                  
    return func(*args,**kw)                                                                                                                                                                                                                                                    
--- <exception caught here> ---                                                                                                                                                                                                                                                
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/internet/posixbase.py", line 614, in _doReadOrWrite                                                                                                              
    why = selectable.doRead()                                                                                                                                                                                                                                                  
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/internet/tcp.py", line 205, in doRead                                                                                                                            
    return self._dataReceived(data)                                                                                                                                                                                                                                            
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/venv/lib/python3.6/site-packages/twisted/internet/tcp.py", line 211, in _dataReceived                                                                                                                     
    rval = self.protocol.dataReceived(data)                                                                                                                                                                                                                                    
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/golem/network/transport/tcpnetwork.py", line 335, in dataReceived                                                                                                                                         
    self._interpret(data)                                                                                                                                                                                                                                                      
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/golem/network/transport/tcpnetwork.py", line 361, in _interpret                                                                                                                                           
    self.session.interpret(m)                                                                                                                                                                                                                                                  
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/golem/task/tasksession.py", line 163, in interpret                                                                                                                                                        
    BasicSafeSession.interpret(self, msg)                                                                                                                                                                                                                                      
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/golem/network/transport/session.py", line 75, in interpret                                                                                                                                                
    action(msg)                                                                                                                                                                                                                                                                
  File "/home/etam/code/github/golemfactory/golem/fix_free_providers/golem/task/tasksession.py", line 626, in _react_to_want_to_compute_task                                                                                                                                   
    scaled_price=task.header.max_price / msg.price,                                                                                                                                                                                                                            
builtins.ZeroDivisionError: division by zero                                                                                                                                                                                                                                   

[etam]

@Krigpl In comment to #3453 you wrote

Using scaled_price which is price / max_price

but in #3479 you implemented

scaled_price=task.header.max_price / msg.price

Which one is correct?

[Wiezzel]

@etam I'm not expert in marketplace but price / max_price looks much more reasonable than max_price / price.

[etam]

merged

[etam]

follow up: #3976

[ZmijaWA]

Works fine.
Task started from json file with price 0, provider min price set to 0. Task finished and rendered.