[R-pkg-devel] socketConnection, delay when reading from

[Tomas Kalibera]

On 11/27/21 5:24 PM, Ben Engbers wrote:
> Op 27-11-2021 om 17:03 schreef Jeff Newmiller:
>> This is a null-terminated message protocol [1]. It has to be 
>> processed one byte at a time.
>>
>> [1] https://docs.basex.org/wiki/Server_Protocol
>>
> The message may contain embedded 0x00's. To distinguish these embedded 
> 0x00's (and 0xFF's) from a terminating 0x00, embedded 0x00's and 
> 0xFFare prefixed with a 0xFF byte. This means that when you process 
> one byte at a time you have to perform a check on every byte. This 
> results in totally unacceptable response times (My first version of 
> this client was based on this approach)
>
> The only alternative solution I can think off is to use C++ to create 
> a socket and a function that reads from the socket. But since I have 
> hardly any experience with C++ programming nor using the rcpp package....


I think you could use non-blocking read. Read what is available in 
chunks (e.g. up to 1024 bytes long). And based on what is read already, 
figure out whether it is all data or not. Something along the lines as 
the demo below. The demo, though, is polling too much (re-running 
readBin to only find out no data is available yet). It should be 
possible to improve with socketSelect().

Best
Tomas

# the client

con2 <- socketConnection("localhost", port = 6011, open = "rb")
cat("Connected...\n")
total <- 0

done <- function(n) {
   n >= 1e8
}

while(!done(total)) {
    r <- readBin(con2, "raw", 1024)
    total <- total + length(r)
    cat("Read", length(r), "bytes (total ", total, ").\n")
}
close(con2)

# the server

n <- 1e8
w <- as.raw(runif(n, 0, 255))
con1 <- socketConnection(port = 6011, blocking = TRUE, server = TRUE, 
open="a+b")
cat("Connected...\n")
writeBin(w, con1)
cat("Data sent to client...\n")
close(con1)

>
> Ben
>
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