Commit 5b097c33 authored by Tomek Mrugalski's avatar Tomek Mrugalski 🛰
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[2994] Added missing v4 hooks description

parent 049d11fa
// Copyright (C) 2013 Internet Systems Consortium, Inc. ("ISC")
//
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/**
@page dhcpv4Hooks The Hooks API for the DHCPv4 Server
@section dhcpv4HooksIntroduction Introduction
BIND10 features an API (the "Hooks" API) that allows user-written code to
be integrated into BIND 10 and called at specific points in its processing.
An overview of the API and a tutorial for writing such code can be found in
the @ref hooksDevelopersGuide. Information for BIND 10 maintainers can be
found in the @ref hooksComponentDeveloperGuide.
This manual is more specialised and is aimed at developers of hook
code for the DHCPv4 server. It describes each hook point, what the callouts
attached to the hook are able to do, and the arguments passed to the
callouts. Each entry in this manual has the following information:
- Name of the hook point.
- Arguments for the callout. As well as the argument name and data type, the
information includes the direction, which can be one of:
- @b in - the server passes values to the callout but ignored any data
returned.
- @b out - the callout is expected to set this value.
- <b>in/out</b> - the server passes a value to the callout and uses whatever
value the callout sends back. Note that the callout may choose not to
do any modification, in which case the server will use whatever value
it sent to the callout.
- Description of the hook. This explains where in the processing the hook
is located, the possible actions a callout attached to this hook could take,
and a description of the data passed to the callouts.
- Skip flag action: the action taken by the server if a callout chooses to set
the "skip" flag.
@section dhcpv4HooksHookPoints Hooks in the DHCPv4 Server
The following list is ordered by appearance of specific hook points during
packet processing. Hook points that are not specific to packet processing
(e.g. lease expiration) will be added to the end of this list.
@subsection dhcpv4HooksPkt4Receive pkt4_receive
- @b Arguments:
- name: @b query4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
- @b Description: this callout is executed when an incoming DHCPv4
packet is received and its content is parsed. The sole argument -
query4 - contains a pointer to an isc::dhcp::Pkt4 object that contains
all information regarding incoming packet, including its source and
destination addresses, interface over which it was received, a list
of all options present within and relay information. All fields of
the Pkt4 object can be modified at this time, except data_. (data_
contains the incoming packet as raw buffer. By the time this hook is
reached, that information has already parsed and is available though
other fields in the Pkt4 object. For this reason, it doesn't make
sense to modify it.)
- <b>Skip flag action</b>: If any callout sets the skip flag, the server will
drop the packet and start processing the next one. The reason for the drop
will be logged if logging is set to the appropriate debug level.
@subsection dhcpv4HooksSubnet4Select subnet4_select
- @b Arguments:
- name: @b query4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
- name: @b subnet4, type: isc::dhcp::Subnet4Ptr, direction: <b>in/out</b>
- name: @b subnet4collection, type: const isc::dhcp::Subnet4Collection *, direction: <b>in</b>
- @b Description: this callout is executed when a subnet is being
selected for the incoming packet. All parameters, addresses and
prefixes will be assigned from that subnet. A callout can select a
different subnet if it wishes so, the list of all subnets currently
configured being provided as 'subnet4collection'. The list itself must
not be modified.
- <b>Skip flag action</b>: If any callout installed on 'subnet4_select'
sets the skip flag, the server will not select any subnet. Packet processing
will continue, but will be severely limited (i.e. only global options
will be assigned).
@subsection dhcpv4HooksLeaseSelect lease4_select
- @b Arguments:
- name: @b subnet4, type: isc::dhcp::Subnet4Ptr, direction: <b>in</b>
- name: @b fake_allocation, type: bool, direction: <b>in</b>
- name: @b lease4, type: isc::dhcp::Lease4Ptr, direction: <b>in/out</b>
- @b Description: this callout is executed after the server engine
has selected a lease for client's request but before the lease
has been inserted into the database. Any modifications made to the
isc::dhcp::Lease4 object will be stored in the lease's record in the
database. The callout should make sure that any modifications are
sanity checked as the server will use that data as is with no further
checking.\n\n The server processes lease requests for DISCOVER and
REQUEST in a very similar way. The only major difference is that
for DISCOVER the lease is just selected, but not inserted into
the database. It is possible to distinguish between DISCOVER and
REQUEST by checking value of the fake_allocation flag: a value of true
means that the lease won't be inserted into the database (DISCOVER),
a value of false means that it will (REQUEST).
- <b>Skip flag action</b>: If any callout installed on 'lease4_select'
sets the skip flag, the server will not assign any lease. Packet
processing will continue, but client will not get an address.
@subsection dhcpv4HooksPkt4Send pkt4_send
- @b Arguments:
- name: @b response4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
- @b Description: this callout is executed when server's response
is about to be send back to the client. The sole argument - response4 -
contains a pointer to an isc::dhcp::Pkt4 object that contains the
packet, with set source and destination addresses, interface over which
it will be send, list of all options and relay information. All fields
of the Pkt4 object can be modified at this time, except bufferOut_.
(This is scratch space used for constructing the packet after all
pkt4_send callouts are complete, so any changes to that field will
be overwritten.)
- <b>Skip flag action</b>: if any callout sets the skip flag, the server
will drop this response packet. However, the original request packet
from a client was processed, so server's state was most likely changed
(e.g. lease was allocated). Setting this flag merely stops the change
being communicated to the client.
*/
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