No, according to the specification the minimal number of bytes that is
returned is 2. There is no maximum. (When querying a database you never
know on forehand how many records match the query so by definition you
can't calculate the size of the message).
In some C, C++ or Java-code I found on internet, it was possible to
change the timeout settings so that there would be no delay. Of course
this would have as consequence that in your code you have to deal with
the possibility that the message has not been completely returned.
In R you can set the timeout to 0 but that results in errors (at least
on Windows)
Op 27-11-2021 om 14:57 schreef 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.engb...@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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