par_socket_server: Get or set parameters specific to SciViews socket clients

Description

This function manage to persistently store sensible parameters for configuring communication between the server and the client, as well as, any other persistent data you may need. Parameters remain set even if the client disconnects and then reconnects to R, as long R was not restarted.

Usage

par_socket_server(client, server_port = 8888, client_socket = client, ...)
parSocket(client, server_port = 8888, client_socket = client, ...)

Arguments

client

the client identification. By default, it is the socket identifier as it appears in get_socket_clients(). Since no attempt is made to check if the client really exists and is connected, you can create fake ones, outside of the socket server, to test your code for instance.

server_port

the port on which the server is running, 8888 by default. Not important for fake socket client configurations.

client_socket

the Tcl name of the socket where the client is connected. By default, it is the same as client name, but in case it was modified, do provide a correct client_socket string if you want to be able to activate a redirection to it (see socket_client_connection()).

...

the parameters you want to change as named arguments. Non named arguments are ignored with a warning. If you specify arg = NULL, the corresponding variable is deleted from the environment.

Value

Returns the environment where parameters and data for the client are stored. To access those data, see examples below.

Details

You can assign the environment to a variable, and then, access its content like if it was a list (e$var or e$var <- "new value"). To get a list of the content, use ls(par_socket_server(client, port)), or ls(par_socket_server(client, port), all.names = TRUE), but not names(par_socket_server(client, port)). As long as you keep a variable pointing on that environment alive, you have access to last values (i.e., changes done elsewhere are taken into account). If you want a frozen snapshot of the parameters, you should use myvar <- as.list(par_socket_server(client, port).

There is a convenient placeholder for code send by the client to insert automatically the right socket and server_port in par_socket_server(): <<<s>>>. Hence, code that the client send to access or change its environment is just par_socket_server(<<<s>>>, bare = FALSE) or par_socket_server(<<<s>>>)$bare to set or get one parameter. Note that you can set or change many parameters at once.

Currently, parameters are:

bare = TRUE|FALSE for "bare" mode (no prompt, no echo, no multiline; by default, bare = TRUE),
multiline = TRUE|FALSE: does the server accept code spread on multiple lines and send in several steps (by default, yes, but works only if bare = FALSE.
echo = TRUE|FALSE is the command echoed to the regular R console (by default echo = FALSE).
last = "" string to append to each output (for instance to indicate that processing is done),
prompt = "> ", the prompt to use (if not in bare mode) and
continue = "+ " the continuation prompt to use, when multiline mode is active. You can only cancel a multiline mode by completing the R code you are sending to the server, but you can break it too by sending <<<esc>>> before the next instruction. You can indicate <<<q>>> or <<<Q>>> at the very beginning of an instruction to tell R to disconnect the connection after the command is processed and result is returned (with <<<q>>>), or when the instructions are received but before they are processed (with <<<Q>>>). This is useful for "one shot" clients (clients that connect, send code and want to disconnect immediately after that). The code send by the server to the client to tell him to disconnect gracefully (and do some housekeeping) is \\f send at the beginning of one line. So, clients should detect this and perform the necessary actions to gracefully disconnect from the server as soon as possible, and he cannot send further instructions from this moment on.

For clients that repeatedly connect and disconnect, but want persistent data, the default client identifier (the socket name) cannot be used, because that socket name would change from connection to connection. The client must then provide its own identifier. This is done by sending <<<id=myID>>> at the very beginning of a command. This must be done for all commands! myID must use only characters or digits. This code could be followed by <<<e>>>, <<<h>>> or <<<H>>>. These commands are intended for R editors/IDE. The first code <<<e>>> sets the server into a mode that is suitable to evaluate R code (including in a multi-line way). The other code temporarily configure the server to run the command (in single line mode only) in a hidden way. They can be used to execute R code without displaying it in the console (for instance, to start context help, to get a calltip, or a completion list, etc.). The differences between <<<h>>> and <<<H>>> is that the former waits for command completion and returns results of the command to the client before disconnecting, while the latter disconnects from the client before executing the command.

There is a simple client (written in Tcl) available in the /etc subdirectory of this package installation. Please, read the 'ReadMe.txt' file in the same directory to learn how to use it. You can use this simple client to experiment with the communication using these sockets, but it does not provide advanced command line edition, no command history, and avoid pasting more than one line of code into it.

Examples

Run this code

# NOT RUN {
# We use a fake socket client configuration environment
e <- par_socket_server("fake")
# Look at what it contains
ls(e)
# Get one data
e$bare
# ... or
par_socket_server("fake")$bare

# Change it
par_socket_server("fake", bare = FALSE)$bare
# Note it is changed too for e
e$bare

# You can change it too with
e$bare <- TRUE
e$bare
par_socket_server("fake")$bare

# Create a new entry
e$foo <- "test"
ls(e)
par_socket_server("fake")$foo
# Now delete it
par_socket_server("fake", foo = NULL)
ls(e)

# Our fake socket config is in SciViews:TempEnv environment
s <- search()
l <- length(s)
pos <- (1:l)[s == "SciViews:TempEnv"]
ls(pos = pos)  # It is named 'socket_client_fake'
# Delete it
rm(socket_client_fake, pos = pos)
# Do some house keeping
rm(list = c("s", "l", "pos"))
# }

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