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require 'net/ssh/multi/server'
module Net; module SSH; module Multi
# Represents a lazily evaluated collection of servers. This will usually be
# created via Net::SSH::Multi::Session#use(&block), and is useful for creating
# server definitions where the name or address of the servers are not known
# until run-time.
#
# session.use { lookup_ip_address_of_server }
#
# This prevents +lookup_ip_address_of_server+ from being invoked unless the
# server is actually needed, at which point it is invoked and the result
# cached.
#
# The callback should return either +nil+ (in which case no new servers are
# instantiated), a String (representing a connection specification), an
# array of Strings, or an array of Net::SSH::Multi::Server instances.
class DynamicServer
# The Net::SSH::Multi::Session instance that owns this dynamic server record.
attr_reader :master
# The Proc object to call to evaluate the server(s)
attr_reader :callback
# The hash of options that will be used to initialize the server records.
attr_reader :options
# Create a new DynamicServer record, owned by the given Net::SSH::Multi::Session
# +master+, with the given hash of +options+, and using the given Proc +callback+
# to lazily evaluate the actual server instances.
def initialize(master, options, callback)
@master, @options, @callback = master, options, callback
@servers = nil
end
# Returns the value for the given +key+ in the :properties hash of the
# +options+. If no :properties hash exists in +options+, this returns +nil+.
def [](key)
(options[:properties] || {})[key]
end
# Iterates over every instantiated server record in this dynamic server.
# If the servers have not yet been instantiated, this does nothing (e.g.,
# it does _not_ automatically invoke #evaluate!).
def each
(@servers || []).each { |server| yield server }
end
# Evaluates the callback and instantiates the servers, memoizing the result.
# Subsequent calls to #evaluate! will simply return the cached list of
# servers.
def evaluate!
@servers ||= Array(callback[options]).map do |server|
case server
when String then Net::SSH::Multi::Server.new(master, server, options)
else server
end
end
end
alias to_ary evaluate!
end
end; end; end
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