[Fiware-middleware] DFKI Thrift-based IDL Proposal

[Thomas Michael Bohnert]

Dimitry,

Thanks - just one question. Is this starting from the OMG IDL as 
foundation?

I assume so since this was the task to complete.

Best - Thomas

On 10/21/2014 02:13 PM, Dmitri Rubinstein wrote:
> Hi all,
>
> as discussed in the last meeting I put here information about our IDL
> proposal. When final document appears online I will copy this text to it.
>
> 1. KIARA/DFKI IDL is based on Apache Thrift IDL, with the grammar
> available here:
>
> https://thrift.apache.org/docs/idl
>
> Our grammar is available here:
>
> https://forge.fi-ware.org/plugins/mediawiki/wiki/fi-ware-private/index.php/Middleware_-_KIARA_-_User_and_Programmers_Guide#KIARA_Interface_definition_language
>
> Note: our goal was not to keep a full backwards compatibility with
> Thrift, but to modify a grammar only when necessary. Still technically
> we can be backwards compatible (we can parse already *existing* Thrift
> IDL files), since we avoided to remove any functionality from Thrift
> (only 'oneway' keyword was removed, see below). However, this was not
> tested yet.
>
> 2. We did following modifications:
>
> 2.1 Base types
>
> 2.1.1 Added unsigned types missing in Thrift: u8, u16, u32, u64
>
> 2.1.2 Renamed bool to boolean, byte to i8 (signed byte).
>
> 'boolean' is used more frequently than 'bool' in other IDLs. We can
> switch back to 'bool' if desired.
>
> 'byte' as a signed integer is not consistent with names of other signed
> integers (i16, i32, i64). We can switch back to 'byte' as signed 8-bit
> integer and use 'ubyte' as unsigned 8-bit integer if desired.
>
> A comparison table for basic types for DFKI/KIARA, CORBA, Thrift, etc.
> is here:
>
> https://forge.fi-ware.org/plugins/mediawiki/wiki/fi-ware-private/index.php/Middleware_-_KIARA_-_User_and_Programmers_Guide#Primitive_types
>
> 2.2 Annotations
>
> The official Thirft grammar available on the web (see link above) *does
> not* contain flexible annotation syntax. There is an annotation support
> available in the latest Thrift version:
>
> https://github.com/apache/thrift/blob/master/test/AnnotationTest.thrift
>
> However, annotations are limited to key-value pairs and even more
> important: seems that function arguments and return types can't be
> annotated, there are at least no examples.
>
> Instead of using Thrift annotations we decided to introduce a different
> syntax inspired by WebIDL:
> http://www.w3.org/TR/WebIDL/#idl-extended-attributes.
>
> 2.2.1 Added syntax for defining custom annotations, similar to structs
> and exceptions:
>
> annotation HTTPPort {
>     i32 port = 80
> }
>
> 2.2.2 Added ability to annotate following entities: services, service
> functions, return types of service functions, arguments of service
> functions. We need this especially for security-related features. For
> example:
>
> namespace * enc
>
> // HTTPPort annotates the 'enc' service with argument 8080
> [HTTPPort(8080)]
> service enc {
>
>       // Function ping is annotated with Oneway and Encrypted annotations
>       // without parameters
>       [Oneway, Encrypted]
>       void ping()
>
>       // In function saveString Argument s of type string
>       // is annotated with annotation OptionallyEncrypted without
>       // parameters
>       void saveString(string fileName, [OptionallyEncrypted] string s)
>
>       // Return type of function loadString is annotated with
>       // annotation OptionallyEncrypted without parameters
>       string [OptionallyEncrypted] loadString(string fileName)
> }
>
> Also see our documentation:
> https://forge.fi-ware.org/plugins/mediawiki/wiki/fi-ware-private/index.php/Middleware_-_KIARA_-_User_and_Programmers_Guide#Functions_2
>
> 2.3 Generic types
>
> Original Thrift IDL supports following predefined container types:
> list<T>, map<T1,T2>, and set<T>. We decided to extend this syntax to
> arbitrary generic types: GenericType<T1, T2, ..., Tn> where Ti can be
> either type or constant. In this way we can support types like bounded
> arrays but still keep backwards compatibility with the original syntax:
>
> array< i32, 2> // bounded array of size 2
> array< i32, array< i32, 4> > // two-dimensional array
>
> 2.4 Removed Thrift features
>
> We removed 'oneway' keyword from Thrift because we can use annotation
> Oneway:
>
> Original Thrift:
>
> service Test {
>     oneway void zip()
> }
>
> Our grammar:
>
> service Test {
>     [Oneway] void ping()
> }
>
> If backwards-compatibility to Thrift is desired we can try to support
> both styles.
>
> 2.5 Unused Thrift features
>
> We currently parse but ignore following Thrift features that are missing
> in OMG IDL:
>
> Struct fields can have optional integer identifier.
> Struct fields can be 'required' or 'optional'.
>
> 2.6 Planned extensions
>
> Thrift does not provide entity like CORBA's 'module'. The namespace
> keyword used by Thrift only allow to specify namespace in the generated
> code. We plan to add module NAME { ... } entity in order to provide
> support for nested IDL namespaces as well as annotations per module.
>
> Best,
>
> Dmitri
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