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% File src/library/tools/man/startDynamicHelp.Rd
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% Part of the R package, https://www.R-project.org
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% Copyright 2009-2015 R Core Team
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% Distributed under GPL 2 or later
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\name{startDynamicHelp}
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\alias{startDynamicHelp}
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\alias{help.ports}
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\alias{R_DISABLE_HTTPD}
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\title{Start the Dynamic HTML Help System}
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\description{
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  This function starts the internal help server, so that HTML help pages
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  are rendered when requested.
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}
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\usage{
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startDynamicHelp(start = TRUE)
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}
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\arguments{
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  \item{start}{logical: whether to start or shut down the dynamic help
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    system.  If \code{NA}, the server is started if not already running.}
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}
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\details{
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  This function starts the internal HTTP server, which runs on the
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  loopback interface (\code{127.0.0.1}).  If \code{options("help.ports")}
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  is set to a vector of non-zero integer values, \code{startDynamicHelp} will try
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  those ports in order; otherwise, it tries up to 10 random ports to
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  find one not in use.  It can be disabled by setting the environment
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  variable \env{R_DISABLE_HTTPD} to a non-empty value or \code{options("help.ports")}
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  to \code{0}.
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  \code{startDynamicHelp} is called by functions that need to use the
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  server, so would rarely be called directly by a user.
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  Note that \code{options(help_type = "html")} must be set to actually
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  make use of HTML help, although it might be the default for an \R
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  installation.
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  If the server cannot be started or is disabled,
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  \code{\link{help.start}} will be unavailable and requests for HTML
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  help will give text help (with a warning).
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  The browser in use does need to be able to connect to the loopback
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  interface: occasionally it is set to use a proxy for HTTP on all
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  interfaces, which will not work -- the solution is to add an exception
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  for \code{127.0.0.1}.
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}
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\value{
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  The chosen port number is returned invisibly (which will be \code{0}
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  if the server has been stopped).
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}
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\seealso{
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  \code{\link{help.start}} and \code{\link{help}(help_type = "html")}
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  will attempt to start the HTTP server if required
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  \code{\link{Rd2HTML}} is used to render the package help pages.
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}
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\keyword{ documentation }