Test if socket is empty (was: Reading data from a raw socket) - r

Question

At the start, I thought that the bad performance of my driver was caused by the way in which I read data from a socket.
This was the original function I used:
socket_char_reader = function(in_sock) {
string_read <- raw(0)
while((rd <- readBin(in_sock, what = "raw", n=1)) > 0) {
string_read <- c(string_read, rd)
}
return(string_read %>% strip_CR_NUL() %>% rawToChar())
}
The results from 3 consecutive calls to this function give the expected result. It takes 0.004 seconds to read 29 bytes in total.
My second try reads the socket until it is empty. Another function splits the resulting raw array in 3 separate parts.
get_response = function() {
in_sock <- self$get_socket()
BUF_SIZE <- 8
chars_read <- raw(0)
while (length(rd <- readBin(in_sock, what = "raw", n=BUF_SIZE)) > 0) {
chars_read <- c(chars_read, rd)
}
return(chars_read)
},
Reading from the socket now takes 2.049 seconds!
Can somebody explain to me what could be the cause for this difference (or what is the best method for reading the socket until it is empty)?
In the meantime I'll return to my original solution and continue looking for the cause of the bad performance.
Ben
I believe, I found the cause (but not the solution).
While debuging, I noticed that the delay is caused by the last call to readBin().
In socket_char_reader(), the stop-condition for the while-loop is based on the value of rd; if that value equals 0, the loop stops.
In get_response() the stop-condition is based on the number of bytes in the buffer. Before that number can be determined, readBin() first waits if any other bytes will be send to the socket.
The timeOut-period is set in the socketConnection() call.
private$conn <- socketConnection(host = "localhost", port,
open = "w+b", server = FALSE, blocking = TRUE,
encoding = "UTF-8", timeout = 1)
Timeout has to be give a value > 0, otherwise it will take days before the loop stops.
Is it possible to check if there still are any bytes in the socket without actually reading?
Ben