From simon.urbanek at r-project.org  Thu Jun 27 00:58:37 2013
From: simon.urbanek at r-project.org (Simon Urbanek)
Date: Wed, 26 Jun 2013 18:58:37 -0400
Subject: [Rd] How can C++ read the R object written into socket with
	saveRDS or save
In-Reply-To: <OF396F33FA.8A573204-ON48257B95.0055E30F-48257B95.00573B1B@cn.ibm.com>
References: <OF396F33FA.8A573204-ON48257B95.0055E30F-48257B95.00573B1B@cn.ibm.com>
Message-ID: <8EA205C5-7C93-44DD-B6C2-D776B061E14E@r-project.org>

On Jun 25, 2013, at 11:52 AM, Rong lI Li wrote:

> 
> Hi, all,
> 
> Recently, I met one issue when using socket between R & C++ to transmit R
> object. Would you pls help give me some suggestions? Many thanks!
> 
> [Background]:
> I create a socket connection between R & C++ binary first, and then, want
> to use saveRDS() or save() in R to save the object into connection
> directly. So that the C++ binary can read the object, and send it to
> another remote R.
> 
> [What I did so far]:
> 1. I used socketConnection in R and listen/accept in C++, to establish one
> blocking socket.
> 2. I used saveRDS to save the R object into socket directly
> 3. I want to use "recv()" in C++ to receive the R object.
> 
> [Issues I met]:
> I found actually, the saveRDS writes the R object with XDR format. I could
> not know how many bytes are sent into socket, when calling saveRDS to save
> R object. So in the C++ binary, I could not know exactly how many bytes I
> should receive from the socket. It is not safe for me, to always use a
> pre-defined buffer size to read from the socket.
> 
> Any suggestions for this? Are there safe way for me to read the R object
> from the socket?

There is nothing preventing you from adding a frame with the size of the serialization - that is what Rserve does (mentioned earlier by Dirk - it even has a C++ client ...): it uses a fixed-size header that specifies the kind of payload and its length, then the serialization follows in the payload. That way you only need to read a fixed header.

Cheers,
Simon


> I do not do any conversion with the received data, and only need to
> transfer them into a remote R to do the function execution.
> 
> =====================
> 
> Rong "Jessica", Li (????)
> Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
> Tel:86-10-82451010  Email:ronglli at cn.ibm.com
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel



[Rd] How can C++ read the R object written into socket with saveRDS or save
Simon Urbanek