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Merge remote-tracking branch 'origin/topic/dnthayer/langref'

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* origin/topic/dnthayer/langref:
  Minor improvements to script language reference docs
  Add more script language reference documentation
  Split the types and attributes reference doc into two docs

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BIT-1269 #merged
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Robin Sommer 2014-10-07 14:18:08 -07:00
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Attributes
==========
The Bro scripting language supports the following attributes.
+-----------------------------+-----------------------------------------------+
| Name | Description |
+=============================+===============================================+
| :bro:attr:`&redef` |Redefine a global constant or extend a type. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&priority` |Specify priority for event handler or hook. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&log` |Mark a record field as to be written to a log. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&optional` |Allow a record field value to be missing. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&default` |Specify a default value. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&add_func` |Specify a function to call for each "redef +=".|
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&delete_func` |Same as "&add_func", except for "redef -=". |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&expire_func` |Specify a function to call when container |
| |element expires. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&read_expire` |Specify a read timeout interval. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&write_expire` |Specify a write timeout interval. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&create_expire` |Specify a creation timeout interval. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&synchronized` |Synchronize a variable across nodes. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&persistent` |Make a variable persistent (written to disk). |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&rotate_interval`|Rotate a file after specified interval. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&rotate_size` |Rotate a file after specified file size. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&encrypt` |Encrypt a file when writing to disk. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&raw_output` |Open file in raw mode (chars. are not escaped).|
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&mergeable` |Prefer set union for synchronized state. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&group` |Group event handlers to activate/deactivate. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&error_handler` |Used internally for reporter framework events. |
+-----------------------------+-----------------------------------------------+
| :bro:attr:`&type_column` |Used by input framework for "port" type. |
+-----------------------------+-----------------------------------------------+
Here is a more detailed explanation of each attribute:
.. bro:attr:: &redef
Allows for redefinition of initial values of global objects declared as
constant.
In this example, the constant (assuming it is global) can be redefined
with a :bro:keyword:`redef` at some later point::
const clever = T &redef;
.. bro:attr:: &priority
Specifies the execution priority (as a signed integer) of a hook or
event handler. Higher values are executed before lower ones. The
default value is 0. Example::
event bro_init() &priority=10
{
print "high priority";
}
.. bro:attr:: &log
Writes a :bro:type:`record` field to the associated log stream.
.. bro:attr:: &optional
Allows a record field value to be missing (i.e., neither initialized nor
ever assigned a value).
In this example, the record could be instantiated with either
"myrec($a=127.0.0.1)" or "myrec($a=127.0.0.1, $b=80/tcp)"::
type myrec: record { a: addr; b: port &optional; };
The ``?$`` operator can be used to check if a record field has a value or
not (it returns a ``bool`` value of ``T`` if the field has a value,
and ``F`` if not).
.. bro:attr:: &default
Specifies a default value for a record field, container element, or a
function/hook/event parameter.
In this example, the record could be instantiated with either
"myrec($a=5, $c=3.14)" or "myrec($a=5, $b=53/udp, $c=3.14)"::
type myrec: record { a: count; b: port &default=80/tcp; c: double; };
In this example, the table will return the string ``"foo"`` for any
attempted access to a non-existing index::
global mytable: table[count] of string &default="foo";
When used with function/hook/event parameters, all of the parameters
with the "&default" attribute must come after all other parameters.
For example, the following function could be called either as "myfunc(5)"
or as "myfunc(5, 53/udp)"::
function myfunc(a: count, b: port &default=80/tcp)
{
print a, b;
}
.. bro:attr:: &add_func
Can be applied to an identifier with &redef to specify a function to
be called any time a "redef <id> += ..." declaration is parsed. The
function takes two arguments of the same type as the identifier, the first
being the old value of the variable and the second being the new
value given after the "+=" operator in the "redef" declaration. The
return value of the function will be the actual new value of the
variable after the "redef" declaration is parsed.
.. bro:attr:: &delete_func
Same as :bro:attr:`&add_func`, except for :bro:keyword:`redef` declarations
that use the "-=" operator.
.. bro:attr:: &expire_func
Called right before a container element expires. The function's
first parameter is of the same type of the container and the second
parameter the same type of the container's index. The return
value is an :bro:type:`interval` indicating the amount of additional
time to wait before expiring the container element at the given
index (which will trigger another execution of this function).
.. bro:attr:: &read_expire
Specifies a read expiration timeout for container elements. That is,
the element expires after the given amount of time since the last
time it has been read. Note that a write also counts as a read.
.. bro:attr:: &write_expire
Specifies a write expiration timeout for container elements. That
is, the element expires after the given amount of time since the
last time it has been written.
.. bro:attr:: &create_expire
Specifies a creation expiration timeout for container elements. That
is, the element expires after the given amount of time since it has
been inserted into the container, regardless of any reads or writes.
.. bro:attr:: &synchronized
Synchronizes variable accesses across nodes. The value of a
``&synchronized`` variable is automatically propagated to all peers
when it changes.
.. bro:attr:: &persistent
Makes a variable persistent, i.e., its value is written to disk (per
default at shutdown time).
.. bro:attr:: &rotate_interval
Rotates a file after a specified interval.
.. bro:attr:: &rotate_size
Rotates a file after it has reached a given size in bytes.
.. bro:attr:: &encrypt
Encrypts files right before writing them to disk.
.. bro:attr:: &raw_output
Opens a file in raw mode, i.e., non-ASCII characters are not
escaped.
.. bro:attr:: &mergeable
Prefers merging sets on assignment for synchronized state. This
attribute is used in conjunction with :bro:attr:`&synchronized`
container types: when the same container is updated at two peers
with different values, the propagation of the state causes a race
condition, where the last update succeeds. This can cause
inconsistencies and can be avoided by unifying the two sets, rather
than merely overwriting the old value.
.. bro:attr:: &group
Groups event handlers such that those in the same group can be
jointly activated or deactivated.
.. bro:attr:: &error_handler
Internally set on the events that are associated with the reporter
framework: :bro:id:`reporter_info`, :bro:id:`reporter_warning`, and
:bro:id:`reporter_error`. It prevents any handlers of those events
from being able to generate reporter messages that go through any of
those events (i.e., it prevents an infinite event recursion). Instead,
such nested reporter messages are output to stderr.
.. bro:attr:: &type_column
Used by the input framework. It can be used on columns of type
:bro:type:`port` (such a column only contains the port number) and
specifies the name of an additional column in
the input file which specifies the protocol of the port (tcp/udp/icmp).
In the following example, the input file would contain four columns
named "ip", "srcp", "proto", and "msg"::
type Idx: record {
ip: addr;
};
type Val: record {
srcp: port &type_column = "proto";
msg: string;
};