PLUMBER(4)

NAME
plumber - file system for interprocess messaging

SYNOPSIS
plumber [ -p plumbing ]

DESCRIPTION
The plumber is a user-level file server that receives, examines, rewrites, and dispatches plumb(7) messages between programs. Its behavior is programmed by a plumbing file (default $HOME/lib/plumbing) in the format of plumb(7).

Its services are posted via 9pserve(4) as plumb. and consist of two pre-defined files, plumb/send and plumb/rules, and a set of output ports for dispatching messages to applications.

Programs use fswrite (see 9pclient(3)) to deliver messages to the send file, and fsread to receive them from the corresponding port. For example, sam(1)'s plumb menu item or the B command cause a message to be sent to plumb/send; sam in turn reads from, by convention, plumb/edit to receive messages about files to open.

A copy of each message is sent to each client that has the corresponding port open. If none has it open, and the rule has a plumb client or plumb start rule, that rule is applied. A plumb client rule causes the specified command to be run and the message to be held for delivery when the port is opened. A plumb start rule runs the command but discards the message. If neither start or client is specified and the port is not open, the message is discarded and a write error is returned to the sender.

The set of output ports is determined dynamically by the specification in the plumbing rules file: a port is created for each unique destination of a plumb to rule.

The set of rules currently active may be examined by reading the file plumb/rules; appending to this file adds new rules to the set, while creating it (opening it with OTRUNC) clears the rule set. Thus the rule set may be edited dynamically with a traditional text editor. However, ports are never deleted dynamically; if a new set of rules does not include a port that was defined in earlier rules, that port will still exist (although no new messages will be delivered there).

FILES

$HOME/lib/plumbing
    default rules file

/usr/local/plan9/plumb
    directory to search for files in include statements

plumb
    mount name for plumber(4).

SOURCE
/usr/local/plan9/src/cmd/plumb

SEE ALSO
plumb(1), plumb(3), plumb(7)