buffchan (8) - Linux Manuals

buffchan: Buffered file-writing backend for INN


buffchan - Buffered file-writing backend for INN


buffchan [-bru] [-c lines] [-C seconds] [-d directory] [-f num-fields] [-l lines] [-L seconds] [-m map] [-p pid-file] [-s format]


buffchan reads lines from standard input and copies the initial fields in each line to the files named by the remaining fields on the line. buffchan is intended to be called by innd as an exploder feed.

The input is interpreted as a sequence of lines. Each line contains a fixed number of initial fields, followed by a variable number of filename fields. All fields in a line are separated by whitespace and do not contain any whitespace. The default number of initial fields is one.

For each line of input, buffchan writes the initial fields, separated by a space and followed by a newline, to each of the files named in the filename fields. The output files are kept open and are only flushed or closed based on the schedule given by the -c, -C, -l, and -L options.

As an exploder feed (see newsfeeds(5) for an explanation), buffchan interprets lines beginning with an exclamation point as commands. Besides "!begin" (which only marks the start of the feed), there are three supported commands:

!flush [site]
The flush command closes and reopens all open files. An optional site can be specified, in which case buffchan flushes only that file. This command is analogous to the "ctlinnd flush" command. This command can be sent via innd using "ctlinnd send buffchan-site 'flush site'".

Applications can tell that flush has completed by renaming the file before issuing the command. When the original file name has reappeared, the flush is complete. If fchmod(3) is available, buffchan also changes the file to read-only while it's actively writing to it and changes it back to read/write once it has been closed. It will change the mode back to read-only only if it reopens the same file.

!drop [site]
The drop command is similar to the flush command, except that no files are reopened. If given an argument, only the specified site is dropped; otherwise, all sites are dropped. (Note that a site will be restarted if the input stream mentions the site again.)

When a "ctlinnd drop site" command is sent, innd will automatically forward the command to buffchan if the site is listed as a funnel feeding into the buffchan exploder. To drop all sites, use "ctlinnd send buffchan-site drop".

The map file specified with the -m option, if given, will be reloaded.

Once buffchan opens a file, it keeps it open (in the absence of a drop command). The input must therefore never specify more files than the maximum number of files a process may open.


Force the output to be buffered. (This is generally the default, but it may depend on the operating system.) If -b is given, a buffer size of BUFSIZ (a constant of the system standard I/O library) is used.
-c lines
If the -c flag is given, buffchan will close and reopen a file after every lines lines are written to the file.
-C seconds
If the -C flag is given, buffchan will close and reopen a file if it has been open for more than seconds seconds.
-d directory
This flag may be used to specify a directory the program should change to before starting. If this flag is used, the default for the -s flag (see below) is changed to be a simple %s (in other words, output files are considered to be relative to directory).
-f num-fields
By default, each line is expected to contain one fixed field followed by some number of filename fields. If this flag is given, num-fields will be used as the number of initial fixed fields.
-l lines
If the -l flag is given, buffchan will flush the output after every lines lines are written to a file.
-L seconds
If the -L flag is given, buffchan will flush each output file every seconds seconds.
-m map
Map files translate the names in the filename fields on each line into filenames that should be used instead. It's used primarily when short names are used in newsfeeds, but the output files should use the full domain names of remote peers.

In the map file, blank lines and lines starting with a number sign ("#") are ignored. All other lines should have two host names separated by a colon. The first field is the name that may appear in the input stream; the second field names the file to be used when the name in the first field appears. For example:

    # This is a comment
-p pid-file
If the -p option is given, buffchan will write a line containing its process ID (in text) to the specified file when it starts.
By default, buffchan sends its error messages to pathlog/errlog. To suppress this redirection and send error messages to standard error, use the -r flag.
The -s flag may be used to specify a format that maps a filename from the filename fields at the end of each line to an actual filename. This is a sprintf(3) format string that should contain a single instance of %s, which will be replaced with the value of the filename field (possibly after mapping with the map file from -m). The default value is pathoutgoing/%s.
If the -u flag is used, the output will be unbuffered.


If buffchan is invoked with "-f 2" and given the following input:

    news/software/b/132 <1643 [at] munnari.oz.au> foo uunet
    news/software/b/133 <102060 [at] litchi.foo.com> uunet munnari
    comp/sources/unix/2002 <999 [at] news.foo.com> foo uunet munnari

Then the file foo will have these lines:

    news/software/b/132 <1643 [at] munnari.oz.au>
    comp/sources/unix/2002 <999 [at] news.foo.com>

the file munnari will have these lines:

    news/software/b/133 <102060 [at] litchi.foo.com>
    comp/sources/unix/2002 <999 [at] news.foo.com>

and the file uunet will have these lines:

    news/software/b/132 <1643 [at] munnari.oz.au>
    news/software/b/133 <102060 [at] litchi.foo.com>
    comp/sources/unix/2002 <999 [at] news.foo.com>


Written by Rich $alz <rsalz [at] uunet.uu.net> for InterNetNews. Converted to POD by Russ Allbery <eagle [at] eyrie.org>.

$Id: buffchan.pod 9768 2014-12-07 21:22:57Z iulius $


ctlinnd(8), filechan(8), inn.conf(5), innd(8), newsfeeds(5).