PLUMB(6) PLUMB(6)
NAME
plumb - format of plumb messages and rules
SYNOPSIS
#include <plumb.h>
DESCRIPTION
Message format
The messages formed by the plumb(2) library are formatted
for transmission between processes into textual form, using
newlines to separate the fields. Only the data field may
contain embedded newlines. The fields occur in a specified
order, and each has a name, corresponding to the elements of
the Plumbmsg structure, that is used in the plumbing rules.
The fields, in order, are:
src application/service generating message
dst destination `port' for message
wdir working directory (used if data is a file name)
type form of the data, e.g. text
attr attributes of the message, in name=value pairs
separated by white space (the value must follow
the usual quoting convention if it contains
white space or quote characters or equal signs;
it cannot contain a newline)
ndata number of bytes of data
data the data itself
At the moment, only textual data (type=text) is supported.
All fields are optional, but type should usually be set
since it describes the form of the data, and ndata must be
an accurate count (possibly zero) of the number of bytes of
data. A missing field is represented by an empty line.
Plumbing rules
The plumber (see plumb(2)) receives messages on its send
port (applications send messages there), interprets and
reformats them, and (typically) emits them from a destina-
tion port. Its behavior is determined by a plumbing rules
file, default /usr/$user/lib/plumbing, which defines a set
of pattern/action rules with which to analyze, rewrite, and
dispatch received messages.
The file is a sequence of rule sets, each of which is a set
of one-line rules called patterns and actions. There must
be at least one pattern and one action in each rule set.
(The only exception is that a rule set may contain nothing
but plumb to rules; such a rule set declares the named ports
but has no other effect.) A blank line terminates a rule
set. Lines beginning with a # character are commentary and
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are regarded as blank lines.
A line of the form
include file
substitutes the contents of file for the line, much as in a
C #include statement. Unlike in C, the file name is not
quoted. If file is not an absolute path name, or one begin-
ning ./ or ../, file is looked for first in the directory in
which the plumber is executing, and then in /sys/lib/plumb.
When a message is received by the plumber, the rule sets are
examined in order. For each rule set, if the message
matches all the patterns in the rule set, the actions asso-
ciated with the rule set are triggered to dispose of the
message. If a rule set is triggered, the rest are ignored
for this message. If none is triggered, the message is dis-
carded (giving a write error to the sender) unless it has a
dst field that specifies an existing port, in which case the
message is emitted, unchanged, from there.
Patterns and actions all consist of three components: an
object, a verb, and arguments. These are separated by white
space on the line. The arguments may contain quoted strings
and variable substitutions, described below, and in some
cases contain multiple words. The object and verb are sin-
gle words from a pre-defined set.
The object in a pattern is the name of an element of the
message, such as src or data, or the special case arg, which
refers to the argument component of the current rule. The
object in an action is always the word plumb.
The verbs in the pattern rules describe how the objects and
arguments are to be interpreted. Within a rule set, the
patterns are evaluated in sequence; if one fails, the rule
set fails. Some verbs are predicates that check properties
of the message; others rewrite components of the message and
implicitly always succeed. Such rewritings are permanent,
so rules that specify them should be placed after all
pattern-matching rules in the rule set.
add The object must be attr. Append the argument,
which must be a sequence of name=value pairs,
to the list of attributes of the message.
delete The object must be attr. If the message has an
attribute whose name is the argument, delete it
from the list of attributes of the message.
(Even if the message does not, the rule matches
the message.)
is If the text of the object is identical to the
text of the argument, the rule matches.
isdir If the text of the object is the name of an
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existing directory, the rule matches and sets
the variable $dir to that directory name.
isfile If the text of the object is the name of an
existing file (not a directory), the rule
matches and sets the variable $file to that
file name.
matches If the entire text of the object matches the
regular expression specified in the argument,
the rule matches. This verb is described in
more detail below.
set The value of the object is set to the value of
the argument.
The matches verb has special properties that enable the
rules to select which portion of the data is to be sent to
the destination. By default, a data matches rule requires
that the entire text matches the regular expression. If,
however, the message has an attribute named click, that
reports that the message was produced by a mouse click
within the text and that the regular expressions in the rule
set should be used to identify what portion of the data the
user intended. Typically, a program such as an editor will
send a white-space delimited block of text containing the
mouse click, using the value of the click attribute (a num-
ber starting from 0) to indicate where in the textual data
the user pointed.
When the message has a click attribute, the data matches
rules extract the longest leftmost match to the regular
expression that contains or abuts the textual location iden-
tified by the click. For a sequence of such rules within a
given rule set, each regular expression, evaluated by this
specification, must match the same subset of the data for
the rule set to match the message. For example, here is a
pair of patterns that identify a message whose data contains
the name of an existing file with a conventional ending for
an encoded picture file:
data matches '[a-zA-Z0-9_-./]+'
data matches '([a-zA-Z0-9_-./]+).(jpe?g|gif|bit|ps|pdf)'
The first expression extracts the largest subset of the data
around the click that contains file name characters; the
second sees if it ends with, for example, .jpeg. If only
the second pattern were present, a piece of text horse.gift
could be misinterpreted as an image file named horse.gif.
If a click attribute is specified in a message, it will be
deleted by the plumber before sending the message if the
data matches rules expand the selection.
The action rules all have the object plumb. There are only
three verbs for action rules:
to The argument is the name of the port to which
the message will be sent. If the message has a
destination specified, it must match the to
port of the rule set or the entire rule set
will be skipped. (This is the only rule that
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is evaluated out of order.)
client If no application has the port open, the argu-
ments to a plumb start rule specify a shell
program to run in response to the message. The
message will be held, with the supposition that
the program will eventually open the port to
retrieve it.
start Like client, but the message is discarded.
Only one start or client rule should be speci-
fied in a rule set.
The arguments to all rules may contain quoted strings,
exactly as in rc(1). They may also contain simple string
variables, identified by a leading dollar sign $. Variables
may be set, between rule sets, by assignment statements in
the style of rc. Only one variable assignment may appear on
a line. The plumber also maintains some built-in variables:
$0 The text that matched the entire regular expres-
sion in a previous data matches rule. $1, $2,
etc. refer to text matching the first, second,
etc. parenthesized subexpression.
$attr The textual representation of the attributes of
the message.
$data The contents of the data field of the message.
$dir The directory name resulting from a successful
isdir rule. If no such rule has been applied,
it is the string constructed syntactically by
interpreting data as a file name in wdir.
$dst The contents of the dst field of the message.
$file The file name resulting from a successful isfile
rule. If no such rule has been applied, it is
the string constructed syntactically by inter-
preting data as a file name in wdir.
$type The contents of the type field of the message.
$src The contents of the src field of the message.
$wdir The contents of the wdir field of the message.
EXAMPLE
The following is a modest, representative file of plumbing
rules.
# these are generally in order from most specific to least,
# since first rule that fires wins.
addr=':(#?[0-9]+):?'
protocol='(https?|ftp|file|gopher|mailto|news|nntp|telnet|wais)'
domain='[a-zA-Z0-9_@]+([.:][a-zA-Z0-9_@]+)*/?[a-zA-Z0-9_?,%#~&/\-]+'
file='([:.][a-zA-Z0-9_?,%#~&/\-]+)*'
# image files go to page
type is text
data matches '[a-zA-Z0-9_\-./]+'
data matches '([a-zA-Z0-9_\-./]+).(jpe?g|gif|bit)'
arg isfile $0
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plumb to image
plumb start page -w $file
# URLs go to web browser
type is text
data matches $protocol://$domain$file
plumb to web
plumb start window webbrowser $0
# existing files, possibly tagged by line number, go to edit/sam
type is text
data matches '([.a-zA-Z0-9_/-]+[a-zA-Z0-9_/\-])('$addr')?'
arg isfile $1
data set $file
attr add addr=$3
plumb to edit
plumb start window sam $file
# .h files are looked up in /sys/include and passed to edit/sam
type is text
data matches '([a-zA-Z0-9]+\.h)('$addr')?'
arg isfile /sys/include/$1
data set $file
attr add addr=$3
plumb to edit
plumb start window sam $file
The following simple plumbing rules file is a good beginning
set of rules.
# to update: cp /usr/$user/lib/plumbing /mnt/plumb/rules
editor = acme
# or editor = sam
include basic
FILES
/usr/$user/lib/plumbing default rules file.
/mnt/plumb mount point for plumber(4).
/sys/lib/plumb directory for include files.
/sys/lib/plumb/fileaddr public macro definitions.
/sys/lib/plumb/basic basic rule set.
SEE ALSO
plumb(1), plumb(2), plumber(4), regexp(6)
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