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

[Gabor Grothendieck]

Does the message start with a length or a command whose argument length is known
depending on the particular command?
If so first read the length or command and from that the length of the
remainder of
the message can be determined.

On Sat, Nov 27, 2021 at 4:09 AM Ben Engbers <Ben.Engbers using be-logical.nl> wrote:
>
>
> Hi,
>
> I have been working on a R-client for the BaseX XML-database and version
> 0.9.2 is nearly finished (submitting version 0.9.0 was rejected by CRAN).
> Version 0.3 of RBaseX can be found here
> (https://cran.microsoft.com/web/packages/RBaseX/index.html).
>
> The client-server protocol specifies that the communication between the
> client and the database is based on a socket. The code (below) shows how
> I create that socket.
>
> Writing to the socket works perfect. Reading from the sockets (see
> second codeblock) also produces correct results. The problem however is
> that the timeout, as specified when initializing the socket, causes a 1
> second delay for every read-operation.
> I have experimented a lot with different settings and have been
> searching a lot on internet, but I can't find any method to get rid of
> that delay. (In C or C++ that should be easier but I have never before
> had any need to use those languages).
> The very first version of my client used a block-size of 1 when reading.
> That gave acceptable response times for small query-results but reading
> large responses from the database took very long time.
>
> Do you have any suggestions on how to cope with this problem?
>
> Ben Engbers
>
> -----------------------------
>      CreateSocket = function(host, port = 1984L, username, password) {
>        tryCatch(
>          {conn <- private$conn <- socketConnection(
>            host = "localhost", port,
>            open = "w+b", server = FALSE, blocking = TRUE, encoding =
> "UTF-8", timeout = 1)
>          }, error = function(e) {
>            stop("Cannot open the connection")
>          }
>        )
>
> -----------------------------
>
> readBin_ <- function(conn) {
>    chars_read <- raw(0)
>    rd <- readBin(conn, what = "raw", 1024)
>    while(length(rd) == 1024) {
>      chars_read <- c(chars_read, rd)
>      rd <- readBin(conn, "raw", 1024)
>      }
>    if (length(rd) > 0) chars_read <- c(chars_read, rd)
>    return(chars_read)
> }
>
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