= gpsfake(1)
:author: Eric S. Raymond
:date: 22 January 2021
:email: <esr@thyrsus.com.>
:keywords: gps, gpsd, gpssfake
:manmanual: GPSD Documentation
:mansource: GPSD, Version {gpsdver}
:robots: index,follow
:sectlinks:
:toc: macro
:type: manpage

include::../www/inc-menu.adoc[]

== NAME

gpsfake - test harness for gpsd, simulating a GNSS receiver

== SYNOPSIS

*gpsfake* [OPTIONS] infile

*gpsfake* -h

*gpsfake* -V


== DESCRIPTION

*gpsfake* is a test harness for *gpsd* and its clients. It opens a pty
(pseudo-TTY), launches a *gpsd* instance that thinks the slave side of
the pty is its GNSS device, and repeatedly feeds the contents of one
or more test logfiles through the master side to the GNSS receiver. If
there are multiple logfiles, sentences from them are interleaved in the
order the files are specified.

*gpsfake* does not require root privileges, but will run fine as root.
It can be run concurrently with a production *gpsd* instance without
causing problems, as long as you use the *-P* option.  Running under sudo
will cause minor loss of functionality.

The logfiles may contain packets in any supported format, including in
particular NMEA, SiRF, TSIP, or Zodiac. Leading lines beginning with #
will be treated as comments and ignored, except in the following special
cases.

These are interpreted directly by *gpsfake*:

* a comment of the form *#Serial: [0-9] [78][NOE][12]* may be used to set
serial parameters for the log - baud rate, word length, stop bits.
* a comment of the form *#Transport: UDP* may be used to fake a UDP source
rather than the normal pty.
* a comment of the form *#Transport: TCP* may be used to fake a TCP source
rather than the normal pty.

These are interpreted directly by *gpsd*:

* a comment of the form *# Date: yyyy-mm-dd* (ISO8601 date format) may be
used to set the initial date for the log.

The *gpsd* instance is run in foreground. The thread sending fake GNSS data
to the daemon is run in background.

== OPTIONS

*-?*, *-h*, *--help*::
  Print a usage message and exit.
*-1*, *--singleshot*::
  The logfile is interpreted once only rather than repeatedly. This
  option is intended to facilitate regression testing.
*-b*, *--baton*::
  Enable a twirling-baton progress indicator on standard error. At
  termination, it reports elapsed time.
*-c COUNT*, *--cycle COUNT*::
  Sets the delay between sentences in seconds. Fractional values of
  seconds are legal. The default is zero (no delay).
*-d LVL*, *--debug LVL*::
  Pass a *-D* option to the daemon: thus *-D
  4* is shorthand for *-o="-D 4"*.
*-g*, *-G*, *--gdb*, *--lldb*::
  Use the monitor facility to run the *gpsd* instance within *gpsfake* under
  control of *gdb* or *lldb*, respectively. They also disable the timeout on
  daemon inactivity, to allow for breakpointing. If necessary, the
  timeout can be reenabled by a subsequent *-W* or *--wait* . If
  *xterm* and $DISPLAY are available, these options launch the debugger in
  a separate *xterm* window, to separate the debugger dialog from the
  program output, but otherwise run it directly. In the *gdb* case,
  *-tui* is used with *xterm* but not otherwise, since curses and
  program output don't play nicely together. Although *lldb* lacks an
  equivalent option, some versions have a 'gui' command.
*-i*, *--promptme*::
  Single-step through logfiles. It dumps the line or packet number (and
  the sentence if the protocol is textual) followed by "? ". Only when
  the user keys Enter is the line actually fed to *gpsd*.
*-l*, *--linedump*::
  Print a line or packet number just before each sentence is fed to the
  daemon. If the sentence is textual (e.g. NMEA), the text is printed as
  well. If not, the packet will be printed in hexadecimal (except for
  RTCM packets, which aren't dumped at all). This option is useful for
  checking that *gpsfake* is getting packet boundaries right.
*-m PROG*, *--monitor PROG*::
  Specify a monitor program (PROG) inside which the daemon should be
  run. This option is intended to be used with *valgrind*(1) , *gdb*(1) and
  similar programs.
*-n*, *--nowait*::
  Pass *-n* to the daemon to start the daemon reading the GNSS receiver
  without waiting for a client (equivalent to *-o="-n"*).
*-o="OPTS"*, *--option="OPTS"*::
  Specify options to pass to the daemon. The equal sign (=) and quotes
  are required so that *gpsd* options are not confused with *gpsfake*
  options. To start the daemon reading the GNSS receiver without waiting
  for a client use *-o="-n"* (equivalent to the *-n*) which passes *-n*
  to the *gpsd* daemon. The option *-o="-D 4"* passes a *-D 4* to the
  daemon, equivalent to the using *-D 4*.

*-p*, *--pipe*::
  Sets watcher mode and dump the NMEA and GPSD notifications generated
  by the log to standard output. This is useful for regression testing.
*-P PORT*, *--port PORT*::
  Sets the daemon's listening port to PORT.
*-q*, *--quiet*::
  Tell *gpsfake* to suppress normal progress output and thus act in a
  quiet manner.
*-r STR*, *--clientinit STR*::
  Specify an initialization command to use in pipe mode. The default is
  *?WATCH={"enable":true,"json":true}*.
*-s SPEED*, *--speed SPEED*::
  Sets the baud rate for the slave tty. The default is 4800.
*-S*, *--slow*::
  Tells *gpsfake* to insert realistic delays in the test input rather than
  trying to stuff it through the daemon as fast as possible. This will
  make the test(s) run much slower, but avoids flaky failures due to
  machine load and possible race conditions in the pty layer.
*-t*, *--tcp*::
  Forces the test framework to use TCP rather than pty devices. Besides
  being a test of TCP source handling, this may be useful for testing
  from within chroot jails where access to pty devices is locked out.
*-T*, *--sysinfo*::
  Makes *gpsfake* print some system information and then exit.
*-u*, *--udp*::
  Forces the test framework to use UDP rather than pty devices. Besides
  being a test of UDP source handling, this may be useful for testing
  from within chroot jails where access to pty devices is locked out.
*-v*, *--verbose*::
  Enable verbose progress reports to stderr. Use multiple times to
  increase verbosity. It is mainly useful for debugging *gpsfake* itself.
*-w SEC*, *--wait SEC*::
  Set the timeout on daemon inactivity, in seconds. The default timeout
  is 60 seconds, and a value of 0 suppresses the timeout altogether.
  Note that the actual timeout is longer due to internal delays,
  typically by about 20 seconds.
*-x*, *--predump*::
  Dump packets as *gpsfake* gathers them. It is mainly useful for
  debugging *gpsfake* itself.

The last argument(s) must be the name of a file or files containing the
data to be cycled at the device. *gpsfake* will print a notification each
time it cycles.

Normally, *gpsfake* creates a pty for each logfile and passes the slave
side of the device to the daemon. If the header comment in the logfile
contains the string "UDP", packets are instead shipped via UDP port 5000
to the address 192.168.0.1.255. You can monitor the packet with *tcpdump*
this way:

----
tcpdump -s0 -n -A -i lo udp and port 5000
----

== MAGIC COMMENTS

Certain magic comments in test load headers can change the conditions of
the test. These are:

*Serial*::
  May contain a serial-port setting such as 4800 7N2 - baud rate
  followed by 7 or 8 for byte length, N or O or E for parity and 1 or 2
  for stop bits. The test is run with those settings on the slave port
  that the daemon sees.
*Transport*::
  Values 'TCP' and 'UDP' force the use of TCP and UDP feeds respectively
  (the default is a pty).
*Delay-Cookie*::
  Must be followed by two whitespace-separated fields, a delimiter
  character and a numeric delay in seconds. Instead of being broken up
  by packet boundaries, the test load is split on the delimiters. The
  delay is performed after each feed. Can be useful for imposing write
  boundaries in the middle of packets.

== CUSTOM TESTS

*gpsfake* is a trivial wrapper around a Python module, also named *gpsfake*,
that can be used to fully script sessions involving a *gpsd* instance, any
number of client sessions, and any number of fake GPSes feeding the
daemon instance with data from specified sentence logs.

Source and embedded documentation for this module is shipped with the
*gpsd* development tools. You can use it to torture test either *gpsd*
itself or any *gpsd*-aware client application.

Logfiles for the use with *gpsfake* can be retrieved using *gpspipe*,
*gpscat*, or *cgps* from the *gpsd* distribution, or any other application
which is able to create a compatible output.

== ENVIRONMENT

=== WRITE_PAD

For unknown reasons *gpsfake* may sometimes time out and fail. Set the
WRITE_PAD environment value to a larger value to avoid this issue. A
starting point might be "WRITE_PAD = 0.005". Values as large os 0.200
may be required.

=== GPSD_HOME

If *gpsfake* exits with "Cannot execute gpsd: executable not found." the
environment variable GPSD_HOME can be set to the path where *gpsd* can be
found. (instead of adding that folder to the PATH environment variable

== RETURN VALUES

*0*:: on success.
*1*:: on failure

== SEE ALSO

*gpsd*(8), *gps*(1), *gpspipe*(1), *gpscat*(1), *cgps*(1), *tcpdump*(1),
*gdb*(1), *lldb*(1), *valgrind*(1)

== RESOURCES

*Project web site:* {gpsdweb}

== COPYING

This file is Copyright 2013 by the GPSD project +
SPDX-License-Identifier: BSD-2-clause
