G. Pape
ipsvd

Name

ipsvd-instruct - format of the ipsvd(8) instructions directory

Description

The internet protocol service daemons, ipsvd(7), can be told to read and follow instructions from a directory on incoming connections to the socket they listen on.

For mostly static instructions or for performance reasons, it is possible to compile the instructions from a directory into a constant database (cdb) with ipsvd-cdb(8) for faster lookup, and to tell ipsvd(7) to read the instructions from there.

Matching

On each incoming connection, the ipsvd(7) matches the client's IP address against files in the instructions directory. For example, the IP address a.b.c.d which reverse resolves to eric.burdon.smarden.org is matched against the following files in the instructions directory, in this order, first match wins:
    .
  1. a.b.c.d
  2. .
  3. a.b.c
  4. .
  5. a.b
  6. .
  7. a

If the client's hostname has been successfully looked up in DNS:

    .
  1. eric.burdon.smarden.org
  2. .
  3. burdon.smarden.org
  4. .
  5. smarden.org
  6. .
  7. org

And finally the catchall file ``0'' (zero):

    .
  1. 0

After successfully matching a client's IP address or hostname against the instructions directory, ipsvd(7) examines the file that matched the IP address or hostname, and acts accordingly:

    .
  1. If neither the user's read permission, nor the user's execute permission is set for the file, the connection is closed immediately.
  2. .
  3. If the file has the user's execute permission set, ipsvd(7) reads the contents of the file and runs /bin/sh -c '<contents>' instead of the default program prog given at the command line for this connection.
  4. .
  5. If the file has the user's read permission set, ipsvd(7) reads the contents of the file and interprets each line as an instruction for this connection (see below).

If the client's IP address or hostname doesn't match any file in the instructions directory, the default action is taken (the program prog is run to handle the connection).

Instructions

If ipsvd(7) is given instructions for an incoming connection, it reads the corresponding file and interprets each line as follows. The file may be empty, meaning that there is no special instruction.
+VAR=VALUE
environment. If the line starts with a plus (``+''), and the string following the plus contains a ``='', ipsvd(7) puts the string following the plus into the environment before starting prog to handle the connection. If the string following the plus doesn't contain a ``='', ipsvd(7) makes sure that the environment variable with the name string is not set.
Cnum[:msg]
concurrency. If the line starts with a ``C'', and is followed by a number, the per host concurrency limit for the IP address that initiated the connection is set to this number. If num is followed by ``:msg'', the message msg is written to this client if possible, if the per host concurrency limit is reached.

msg may contain backslash-escaped characters as follows: ``\\'' is converted to a single backslash, ``\n'' is converted to a new line character, and ``\r'' is converted to a carriage return.

Only the first concurrency instruction is considered. Not all ipsvd(7)'s support per host concurrency.

If ipsvd(7) cannot interpret a line, it prints a warning, discards the line, and continues with the next instruction if any.

Example Instructions

+MEMORY=20000
This instruction causes the environment variable ``MEMORY'' with the value ``20000'' to be available to the program prog that handles the connection.
+DEBUG=
This instruction adds the variable ``DEBUG'' with an empty value to the environment.
+LOGNAME
This instructions makes sure that the environment variable ``LOGNAME'' is unset when running prog.
C16
Set the per host concurrency to 16. A connection will be closed silently if there are already 16 active connections from this client's IP address.

See Also

ipsvd(7), ipsvd-cdb(8), tcpsvd(8), udpsvd(8)

http://smarden.org/ipsvd/

Author

Gerrit Pape <pape@smarden.org>


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