VILLASnode/documentation/clients/File.md

File

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

Configuration

Every file node supports the following special settings:

in (string: filesystem path)

Specifies the path to a file which contains data for replaying. See below for a description of the file format.

out (string: filesystem path)

Specifies the path to a file where samples will be written to. This setting allows to add special paceholders for time and date values. See strftime(3) for a list of supported placeholder.

Example:

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

will create a file called: path_of_working_directory/logs/measurements_2015-08-09_22-20-50.log

See below for a description of the file format.

file_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 ("now"|"relative"|"absolute")

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.

• epoch_mode = now: The first value is read at now + epoch seconds.
• epoch_mode = relative: The first value is read at start + epoch seconds.
• epoch_mode = absolute: The first value is read at epoch seconds after 1970-01-01 00:00:00.

send_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

file_node = {
	type	= "file",
	
### The following settings are specific to the file node-type!! ###
	mode	= "w+",		# The mode in which files should be opened (see open(2))
						# You might want to use "a+" to append to a file
	
	in	= "logs/file_input.log",	# These options specify the path prefix where the the files are stored
	out	= "logs/file_output_%F_%T.log"	# The output path accepts all format tokens of (see strftime(3))

	epoch_mode = "now"			# One of:
						#  now 		(default)
						#  relative
						#  absolute

	epoch = 10			# The interpretation of this value depends on epoch_mode (default is 0):
						#  - epoch_mode = now:      The first value is read at: _now_ + epoch seconds.
						#  - epoch_mode = relative: The first value is read at _start_ + `epoch` seconds.
						#  - epoch_mode = absolute: The first value is read at epoch seconds after 1970-01-01 00:00:00.
	
	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.
}

File Format

This node-type uses a simple human-readable format to save samples: 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:

1. Seconds in floating point format since 1970-01-01 00:00:00 (aka Unix epoch timestamp: date +%s).
2. Sequence number
3. Up to 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