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

[Simon Urbanek]

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 (ÀîÈÙ)
> Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
> Tel:86-10-82451010  Email:ronglli at cn.ibm.com
> 	[[alternative HTML version deleted]]
> 
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