On 2/1/07, Jean-Sebastien Delfino <[EMAIL PROTECTED]> wrote:
Simon Laws wrote: > I notice in implementing the PHP extension (yes - believe it or not I'm > nearly ready to make a patch for the next version ;-) that, given the way > that I have implemented the PHP extension there is insufficient > information > available in the SCA runtime in order to do correct type conversions when > passing messages between components. I imagine this has been raised > before > but I looked at the archive and couldn't find a relevant thread. > > Imagine the scenario: > > C++ Component (ComponentA) ---WireA---> PHP Component (ComponentB) > ---WireB----> C++ Component (ComponentC) > > Currently the build process looks at the header files described in the > component type files and generates wrappers and proxies for the C++ > components. I have currently implemented the PHP Extension to use generic > wrappers and proxies, i.e. it doesn't use those generated based on the > interface descriptions, so they need to dynamically manage the type > conversions for data coming in and going out of a PHP component. > > WireA. > > This is OK because the C++ SCA operation object that appears at > Component B > has a set of data/types based on the generated proxy. The PHP > extension can > look at this and effect the right type conversions. > > WireB > > This is problematic. The dynamic PHP proxy has to generate an operation > object to pass to the the wrapper of ComponentC. The issue is that > there is, > as far as I can tell, no dynamic way of getting at the list of types that > are expected for any particular operation. There is of course a static > C++ > proxy/wrapper combination that has been generated but I can't inspect > it at > runtime. > > I'm not keen on generating PHP specific interface classes. PHP is a > dynamic > environment and it's a whole stack of extra files we could do without > having > to manage particularly if we have to adapt the generator for every > extension > that's constructed. Can we extend the wrapper/proxy mechanism to > encapsulate > a runtime list of required types alongside the static method descriptions > that are already generated? We would need this to work for script to > script > calls as well as for the script/C++ combination so maybe we need > something > that hangs off the interface description part of the model. I'm not that > familiar with how that part of the model is used so a little > investigation > is required. > > Thoughts? > > Simon > Simon, It's an interesting issue. To explore it let's walk through the wiring scenario you describe and assume the following: - ComponentA (C++) -> WireA -> ComponentB (PHP) -> WireB -> ComponentC (C++) - ComponentA (C++) passes a short int to ComponentB (PHP) - ComponentB executes a PHP script which in turn passes a number to ComponentC (C++) - ComponentC expects that number to be given as a long int. Here's what I think should happen in the runtime: 1. At the source of WireA, a generated C++ CPPServiceProxy adds to our Operation object a Parameter of a type decided by the C++ client code: a C++ short int, with type == ParameterType::SHORT. 2. At the end of WireA, a PHPServiceWrapper converts that parameter to what the PHP script expects, for the sake of simplicity now I am going to assume that it needs to convert it to a C++ std::string. 3. The PHP script executes, now passes an std::string containing a number to the PHPServiceProxy at the source of WireB. 4. The PHPServiceProxy does not have much type info about that std::string parameter and can only add it to the Operation object as a std::string with type == ParameterType::STRING. 5. The CPPServiceWrapper at the end of WireB (actually the C++ ServiceWrapper generated for ComponentC) receives the std::string and should convert it to what ComponentC expects: a long int. The general idea is that a ServiceProxy sends what it is given (or picks the most natural type out of the ParameterTypes that we have defined and converts the data to it). A ServiceWrapper converts what it receives to the type expected by the code it wraps. I think that the CPPServiceWrapper code and the generated C++ ServiceWrappers are simply missing the logic to convert data to what the target expects. At the moment this limitation also prevents a C++ method getCustomer(long customerID) to be exposed as a REST service for example, as the generated C++ ServiceWrapper is missing the logic to convert the customerID received in string form from the REST query string to the expected C++ long int. So we just need to add the missing type conversion logic to the C++ ServiceWrappers :) Thoughts? -- Jean-Sebastien --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Hi Jean-Sebastien
It could well be simpler if, as you suggest, the conversion happens in the generated wrapper in this case. So we need such type information, as is required to effect the type conversion, to be generated into the wrapper. However I think we should try and arrange it so that we are not trying to do any more conversions than are necessary so I'm not convinced that the proxy should be guessing what type to produce only for it to be coerced again at the wrapper unless this is a natural effect of the transport/protocol involved, for example, In your REST example. I.e. we want the proxy to have the best information available to it in marshaling the data it has. I also need to address complex types in the PHP extension. Where a remote interface is used you can imagine the WSDL, SMD or whatever being parsed at the client component to construct a proxy capable of suitable type checking and of providing convenience functions such as "giveMeAnSDOWithTheRightModelLoaded()". Looking at the code and samples at the moment it seems that the C++ infrastructure loads available XSDs and provides some handy helper methods for creating SDOs based on the types available. I don't how they are related to particular interfaces though. I expect I'm overlooking something. Regards Simon
