[jira] [Commented] (THRIFT-1948) Add a stream type

["Carl Yeksigian (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-1948?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13646045#comment-13646045 ] 

Carl Yeksigian commented on THRIFT-1948:
----------------------------------------

Precisely.

I think there are a couple of benefits to the stream approach versus having many calls.

# Client to know how many times to call back to the server
# State does not need to be sent, or regenerated for each call

I also think the use case isn't very well defined in the ticket. I'll put together something a little better defined for the use of this new construct.

                
> Add a stream type
> -----------------
>
>                 Key: THRIFT-1948
>                 URL: https://issues.apache.org/jira/browse/THRIFT-1948
>             Project: Thrift
>          Issue Type: New Feature
>          Components: AS3 - Compiler, AS3 - Library, C glib - Compiler, C glib - Library, C# - Compiler, C# - Library, C++ - Compiler, C++ - Library, Cocoa - Compiler, Cocoa - Library, Compiler (General), D - Compiler, D - Library, Delphi - Compiler, Delphi - Library, Erlang - Compiler, Erlang - Library, Go - Compiler, Go - Library, Haskell - Compiler, Haskell - Library, Java - Compiler, Java - Library, JavaME - Compiler, JavaME - Library, JavaScript - Compiler, JavaScript - Library, Node.js - Compiler, Node.js - Library, OCaml - Compiler, OCaml - Library, Perl - Compiler, Perl - Library, PHP - Compiler, PHP - Library, Python - Compiler, Python - Library, Ruby - Compiler, Ruby - Library, Smalltalk - Compiler, Smalltalk - Library
>            Reporter: Carl Yeksigian
>            Assignee: Carl Yeksigian
>
> This is a proposal for an addition to the Thrift IDL, which allows for sending chunks of data between the server and the client without having the whole message in memory at the start of the communication.
> The new keyword, "stream<T>", would indicate that there is a series of values typed T which would be communicated between client and server. Stream would have three primitives:
> {code}
> next(T)
> error(TException)
> end()
> {code}
> Protocols would be enhanced with the following methods:
> {code}
> writeStreamBegin(etype, streamid)
> writeStreamNext(streamid, streamMessageType)
> writeStreamNextEnd()
> writeStreamErrorEnd()
> etype, streamid = readStreamBegin()
> streamid, streamMessageType = readStreamNext()
> readStreamNextEnd()
> readStreamErrorEnd()
> {code}
> streamMessageType is one of the following:
> # next
>   This means that the message will be of the element type.
> # error
>   An exception was thrown during materialization of the stream.
>   The stream is now closed.
> # end
>   This means that the stream is finished.
>   The stream is now closed.
> Once all streams are closed, readMessageEnd should be called. Before the first writeStreamNext() could be called, the message should otherwise be complete. Otherwise, an exception should be raised.
> It is possible that an exception will be thrown while the stream is being materialized; however, this can only occur inside of a service. In this case, error() will be called; the exception should be one of the exceptions that the service call would have thrown. The values that were generated before the exception will generally be valid, but may only have meaning if the stream is ended. All streams which are currently open may get the same exception.
> If the following service was defined:
> {code}
> stream<i64> random_numbers(stream<i64> max)
> {code}
> A sample session from client to server would be:
> {code}
> writeMessageBegin()
> writeStreamBegin(I64, 0)
> writeStreamNext(0, next)
> writeI64(10)
> writeStreamNextEnd()
> writeStreamNext(0, end)
> writeMessageEnd()
> {code}
> A sample session from server to client would be:
> {code}
> writeMessageBegin()
> writeStreamBegin(i64, 0)
> writeStreamNext(0, next)
> writeI64(3)
> writeStreamNextEnd()
> writeStreamNext(0, end)
> writeMessageEnd()
> {code}
> This change would not be compatible with previous versions of Thrift. Also, for languages which do not support this type of streaming, it could be translated into a list.

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