VILLASnode/doc/nodes/File.md

File

The file node-type can be used to log or replay samples to / from disk.

Configuration

Every file node can be configured to only read or write or to do both at the same time. The node configuration is divided into two sub-groups: in and out.

uri (string: libcurl URI)

Specifies the URI to a file from which is written to or read from depending in which group (inor out) is used.

See below for a description of the file format. This setting allows to add special paceholders for time and date values. See strftime(3) for a list of supported placeholder.

Example:

uri = "logs/measurements_%Y-%m-%d_%H-%M-%S.log"

will create a file called:

./logs/measurements_2015-08-09_22-20-50.log

See below for a description of the file format.

mode (string)

Specifies the mode which should be used to open the output file. See open(2) for an explanation of allowed values. The default value is w+ which will start writing at the beginning of the file and create it in case it does not exist yet.

epoch_mode ("direct" | "wait" | "relative" | "absolute")

The epoch describes the point in time when the first message will be read from the file. This setting allows to select the behaviour of the following epoch setting. It can be used to adjust the point in time when the first value should be read.

The behaviour of epoch is depending on the value of epoch_mode.

To facilitate the following description of supported epoch_mode's, we will introduce some intermediate variables (timestamps). Those variables will also been displayed during the startup phase of the server to simplify debugging.

• epoch is the value of the epoch setting.
• first is the timestamp of the first message / line in the input file.
• offset will be added to the timestamps in the file to obtain the real time when the message will be sent.
• start is the point in time when the first message will be sent (first + offset).
• eta the time to wait until the first message will be send (start - now)

The supported values for epoch_mode:

epoch_mode	offset	start = first + offset
direct	now - first + epoch	now + epoch
wait	now + epoch	now + first
relative	epoch	first + epoch
absolute	epoch - first	epoch
original	0	immeadiatly

rate (float)

By default send_rate has the value 0 which means that the time between consecutive samples is the same as in the in file based on the timestamps in the first column.

If this setting has a non-zero value, the default behaviour is overwritten with a fixed rate.

Example

nodes = {
	file_node = {
		type	= "file",
	
	### The following settings are specific to the file node-type!! ###

		in = {
			uri = "logs/input.log",	# These options specify the URI where the the files are stored
			mode = "w+",			# The mode in which files should be opened (see open(2))
						
			epoch_mode = "direct"		# One of: direct (default), wait, relative, absolute
			epoch = 10			# The interpretation of this value depends on epoch_mode (default is 0).
							# Consult the documentation of a full explanation

			rate = 2.0			# A constant rate at which the lines of the input files should be read
							# A missing or zero value will use the timestamp in the first column
							# of the file to determine the pause between consecutive lines.
		},
		out = {
			uri = "logs/output_%F_%T.log"	# The output URI accepts all format tokens of (see strftime(3))
			mode = "a+"			# You might want to use "a+" to append to a file
		}
	}
}

File Format

This node-type uses a simple human-readable format to save samples to disk: The format is similiar to a conventional CSV (comma seperated values) file. Every line in a file correspondents to a message / sample of simulation data. The columns of a line are seperated by whitespaces (tabs or spaces). The columns are defined as follows:

seconds.nanoseconds+offset(sequenceno)	value0 value1 ... valueN

1. The first column contains a timestamp which is composed of up to 4 parts:

   • Number of seconds after 1970-01-01 00:00:00 UTC
   • A dot: '.'
   • Number of nano seconds of the current second (optional)
   • An offset between the point in time when a message was sent and received (optional)
   • The sequence number of the message (optional)

   A valid timestamp can be generated by the following Unix command: date +%s.%N. Important: The second field is not the fractional part of the second!!!

2. Maximum MSG_VALUES floating point values per sample. The values are seperated by whitespaces as well.

Example

This example shows a dump with three values per sample:

1438959964.162102394(6)	3.489760	-1.882725	0.860070
1438959964.261677582(7)	2.375948	-2.204084	0.907518
1438959964.361622787(8)	3.620115	-1.359236	-0.622333
1438959964.461907066(9)	5.844254	-0.966527	-0.628751
1438959964.561499526(10)	6.317059	-1.716363	0.351925
1438959964.661578339(11)	6.471288	-0.159862	0.123948
1438959964.761956859(12)	7.365932	-1.488268	-0.780568