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From "Nikolay Rapotkin (Jira)" <j...@apache.org>
Subject [jira] [Created] (THRIFT-5104) Forwarding callContext into methods of handler as very last parameter
Date Wed, 19 Feb 2020 13:52:00 GMT
Nikolay Rapotkin created THRIFT-5104:
----------------------------------------

             Summary: Forwarding callContext into methods of handler as very last parameter
                 Key: THRIFT-5104
                 URL: https://issues.apache.org/jira/browse/THRIFT-5104
             Project: Thrift
          Issue Type: Improvement
          Components: C++ - Compiler, C++ - Library
            Reporter: Nikolay Rapotkin


I faced with common issue: I want be able to check if sender is a authorized user and to know
who she/he is. I Decided to provide some heads to every single call by Injecting authorization
token. For this purpose i made a ProtocolWrapper that do stuff like the following:
{code:java}
uint32_t ProtocolWrapper ::writeMessageBegin_virt(const std::string& name, const MessageType
type, const int32_t seqid)
{
  auto size = TProtocolDecorator::writeMessageBegin_virt(name, type, seqid);
  if (type == MessageType::T_CALL || type == MessageType::T_ONEWAY)
    size += TProtocolDecorator::writeString(token);
  
  return size;
}
{code}
 

Then It's needed to process request , take out this authorization token, change it on user
information and provide access to it inside methods of a heandler.


Taking out authorization token from data stream is pretty easy to do. For instance TMultiplexProcessor
does the same stuff. Or there is even a better way - providing a ProcessorEventHandler which
operates callContext which can do this work.


But the accessing taken data inside methods of a handler appeared a very difficult thing because
callContext CAN NOT really influence on a method call or method arguments!


So, the idea is to generate a handler interface which can take callContext of Processor for
it's direct access.

 

For example from this thrift service definition

 
{code:java}
service SomeService {
  void someMethod(),
  void anotherMethod(
   1: int value,
  ),
}
{code}
would generate the following code:

 

 
{code:java}
class SomeServiceIf {
public:
  virtual ~SomeServiceIf() {}

  virtual void someMethod() = 0;             // usual
  virtual void anotherMethod(int value) = 0; // methods

  // virtual methods but
  // with default implementation
  // for backward compatibility
  virtual void someMethod(void* ctx) {
    someMethod();
  }
  virtual void anotherMethod(int value, void* ctx) {
     anotherMethod(value);
  }
}
{code}
 

 

This requires small change in a SomeServiceProcessor. It should call method with context.


But this change wont break an existing code because of forwarding calls to non-context methods
by default.


Does it make any sense or there is a better way to do what I want?

 

you can look at prototype of this change in [my fork|https://github.com/Rapotkinnik/thrift/tree/feature/cpp/callcontext-forwarding-to-handler]



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