--- Yancat ---

General purpose network/file[descriptor] unidirectional cat utility.

:::: intro

So why another implementation of such a tool ?

- I needed something with certain features that are either hard to find or
  almost nonexistent - to name a few: reblocking, checksumming, mp and/or mt
  support, .... It's not that there're no tools around that cannot do those,
  but kinda hard to find one that does /all/ what I needed (and without
  nasty data-eating bugs - one of the popular tools had those).
- I also needed something natively and cleanly compiling under MinGW, even if in
  slightly limited form when compared to its unix brethrens.

Either way, the end effect is - functionally - a sort of small crossbreed
between mbuffer and socat, but still supporting certain features that neither
those two support or not at the same time.

:::: features available at runtime:

- buffer & block sizes (obviously ...)
- reblocking (separate block sizes on input and output side)
- strict reblocking writes (last block is padded with 0s if necessary)
- resume points for reading (buffer fill level must drop to X after overrun before
  reading is resumed)
- resume points for writing (buffer fill level must rise to X after underrun before
  writing is resumed)
- threading / forking / single process mode (denoted as mt / mp / sp)
- cpu affinity settings
- in sp mode - preferred counts of blocks to read and write (separate values)
  per iteration
- byte (aka "line") mode (reading/writing as soon as there is any space/data
  available, but no more than one block at the time)
- optional fsync after transfer
- input and output crc checksumming (cksum compatible)
- supports preopened file descriptors, regular files, sockets
- TCP and UDP (the latter assuming you /really know/ what you're doing, keep
  checksumming options in mind as well - on both sides of the transfer)
- small subset of useful socket options
- huge pages - (linux only, through hugetlbfs mount (autodetected))
- "hardware" mmap-/shmat- wrapped circular buffer used, if possible
- builtin looping using the same options (until error, or user's interruption);
  this essentially saves you one shell loop when both ends are persistent
  (think socket on one side, and tape device on the other)

:::: features selected during compilation:

 through config.h:

- posix named/unnamed or SysV semaphores
- posix or SysV shared memory, or just malloc (forces sp mode)
- mutexes - (also available in mp mode)

 through make arguments (just peek into Makefile for more details):

- profiling generation (PROFILE=1) / use (PROFILE=2)
- debug build (DEBUG=1|2) (produces some debug messages)
- installation directory (PREFIX=....), defaults to /usr/local
- Makefile.devel as an optional include

 autoselected / directly editable:

- availability of mt, affinity, lfs

:::: limitations / extensions / info:

 win32:

- you need MingW + MSYS to compile it (with banal Makefile adjustments you can
  ignore MSYS)
- only sp mode is allowed; tbh, it's still pretty sufficient :)
- as a result - no features related to mp / mt functionality are enabled and/or
  compiled in (and non-posix api doesn't make them particulary appealing)
- feel free to experiment, though non-unix environment doesn't make it too
  enjoyable ;)

 bsd:

- not much experience besides old openbsd systems; freebsd has almost the same
  features enabled as linux by default (you might want to adjust those, I have
  no freebsd based test machine); the rest of bsd systems - mt is disallowed,
  and sems & shm default to classic SysV api

 linux:

- hugetlbfs mount is detected and used if requested through options
- affinity settings by default enabled
- SysV huge pages - don't forget about /proc/sys/vm/hugetlb_shm_group (and
  other ones related)

 generic:

- the code is by default compiled at very aggresive settings - both in terms of
  enabled warnings and enabled optimization options. Some seemingly pointless
  casts in code reflect that; consider Makefile.devel.example include for
  further proofing if you plan to hack with the code a bit

random tips / info:

- 7-zip (inc. windows) can produce tars /and/ pipe them through stdin|out /and/
  with largefile support /and/ is blocking agnostic; gloria 7-zip ! Really,
  this is probably your best friend if you need native tar handling in windows
  environemnt. Since 9.30 it stores files using utf-8 in tar archives
- keep in mind [bsd]tar's blocking options - they will close pipe in your face
  when they are content with the transfer (it's racy too, you might be faster
  with whatever you have for transfer ;); this may happen with different block
  sizes - for example when you pipe to bsdtar at smaller block size than you
  receive from the other source

compilation:

- see "features selected during compilation" above
- check config.h and Makefile
- or ... just type: make && make install PREFIX=<directory> (for less
  technically inclined folks)

Use -h option to get overview of arguments and available socket options on your
host. The return value is 0 if it's assured that transfer completed fine, otherwise
it's 255.

If you find any problems with the program, don't hesitate to ask. Preferably
use [yancat] tag in subject mail in such case.

Enjoy :)

Michal Soltys <soltys@ziu.info>