Copyright (C) 1999-2001 Internet Software Consortium.

See COPYRIGHT in the source root or http://isc.org/copyright.html for terms.

$Id: omapi,v 1.7 2001/01/09 21:46:48 bwelling Exp $

This file documents the protocol that the ISC DHCP server and ISC

Object Management clients (clients that use the ISC Object Management

API) speak between one another.

Protocol:

All multi-byte numbers are represented in network byte order.

On startup, each side sends a status message indicating what version

of the protocol they are speaking. The status message looks like

this:

+---------+---------+

| version | hlength |

+---------+---------+

version - a 32-bit fixed-point number with the decimal point between

the third and second decimal digits from the left,

representing the version of the protocol. The current

protocol version is 1.00. If the field were considered as

a 32-bit integer, this would correspond to a value of 100

decimal, or 0x64.

hlength - a 32-bit integer representing the length of the fixed-length

header in subsequent messages. This is normally 56, but

can be changed to a value larger than 56 by either side

without upgrading the revision number.

The startup message is not authenticated. Either side may reject the

other side's startup message as invalid by simply closing the

connection. The only fixed part of the startup message is the

version number - future versions may delete hlength, or add further

startup information.

Following the startup message, all messages have the same format.

Currently, the format includes a fixed-length header (the length in

hlength, above)

+--------+----+--------+----+-----+---------+------------+------------+-----+

| authid | op | handle | id | rid | authlen | msg values | obj values | sig |

+--------+----+--------+----+-----+---------+------------+------------+-----+

The fixed-length header consists of:

authid = a 32-bit authenticator handle.

For an original message (one not in response to some other

message), this will be chosen by the originator. For a

message in response to another message, the authenticator for

that message is used, except if the response is an error

message indicating that the authenticator used was unknown,

in which case the null authenticator is used. Messages that

are generated as the result of a notify registration use the

authenticator used in the original notify registration.

The authenticator itself is generated by having one side of

the connection send an object of type "authenticator" to the

other side with values that indicate what kind of

authentication mechanism to use and what key to use. The two

most likely things here are a Kerberos V principal name or the

name of a shared secret that can be used to calculate an MD5

hash. The mechanism for doing this has yet to be finalized.

If authid is zero, the message is not authenticated.

[[

This is not consistent with what the code does (as originally written),

which is read a header that has, in order:

authid, authlen, op, handle, id, rid

]]

op = 32-bit opcode, one of:

open = 1

refresh = 2

update = 3

notify = 4

error = 5

delete = 6

handle = 32-bit object handle

A handle on the object being opened, created, refreshed or

updated. If no handle is yet available (e.g., with open and

new), then the value zero is sent.

id = 32-bit transaction id of the message - a monotonically increasing

number that starts with some randomly chosen number at the

beginning of the life of the connection. The value should never

be zero.

rid = 32-bit transaction ID of the message to which this message is a

response, or zero if this message is not in response to a

message from the other side.

authlen = a 32-bit number representing the length of the authenticator

msg values = a series of name+value pairs, specific to this message.

Each name+value pair starts with a 16-bit name length,

followed by that many bytes of name, followed by a 32-bit

value length, followed by that many bytes of value. If the

length is zero, this is a value of the blank string. If the

length is all ones (2^32-1), then there is no value - for an

update, this means the value for this name and the name

itself should be deleted from the object, which may or may

not be possible. The list of name/value pairs ends with a

zero-length name, which is not followed by a value

length/value pair.

obj values = a series of name+value pairs, as above, specific to the

object being created, updated or refreshed.

signature = authlen bytes of data signing the message. The signature

algorithm is a property of the authenticator handle.

Message types:

1: open

relevant input values:

object-type = the name of the type of object

open:create = boolean - create the object if it doesn't yet exist

open:exclusive = boolean - don't open the object if it does exist

open:update = boolean - update the object with included values

if it matches.

the handle should always be the null handle

The input value must also contain key information for the type of

object being searched that uniquely identifies an object, or search

information that matches only one object. Each object has a key

specification (a key is something that uniquely identifies an

object), so see the key specification for that object to see

what to send here. An open message with the create flag set must

specify a key, and not merely matching criteria. Some objects may

allow more than one key, and it may be that the union of those keys

is required to uniquely identify the object, or it may be that any

one such key will uniquely identify the object. The documentation

for the type of object will specify this.

An open message will result in an immediate response message whose

opcode will either be "error" or "update". The error message may

include an error:reason value containing a text string explaining

the error, and will always include an error:code value which will

be the numeric error code for what went wrong. Possible error

codes are:

not found - no such object exists

already exists - object already exists, and exclusive flag was

set.

not unique - more than one object matching the specification

exists.

permission denied - the authenticator ID specified does not

have authorization to access this object,

or if the update flag was specified, to

update the object.

If the response is an update message, the update message will

include the object handle and all of the name/value pairs

associated with that object.

2: refresh

no input values except the handle need be specified. The null

handle may not be specified. If the handle is valid, and the

authenticator ID specified has permission to examine the object,

then an update message will be sent for that object. Otherwise,

one of the following errors will be sent:

invalid handle - the handle does not refer to a known object

permisson denied - the handle refers to an object that the

requestor does not have permission to

examine.

3: update

Requests that the contents of the specified object be updated with

the values included. Values that are not specified are not

updated. The response will be either an error message or an

update-ok message. If rid is nonzero, no response will be

generated, even if there was an error. Possible errors include:

invalid handle - no such object was found

permission denied - the handle refers to an object that the

requestor does not have permission to

modify.

not confirmed - the update could not be committed due to some

kind of resource problem, for example

insufficient memory or a disk failure.

4: notify

Requests that whenever the object with the specified handle is

modified, an update be sent. If there is something wrong with the

request, an error message will be returned immediately.

Otherwise, whenever a change is made to the object, an update

message will be sent containing whatever changes were made (or

possibly all the values associated with the object, depending on

the implementation). Possible errors:

invalid handle

permission denied - the handle refers to an object that the

requestor does not have permission to

examine.

not supported - the object implementation does not support

notifications

5: status

Sends a status code in response to a message. Always sent in

response to a message sent by the other side. There should never

be a response to this message.

6: delete

Deletes the specified object. Response will be either request-ok,

or error. Possible errors include:

invalid handle - no such object was found

permission denied - the handle refers to an object that the

requestor does not have permission to

modify.

not confirmed - the deletion could not be committed due to

some kind of resource problem, for example

insufficient memory or a disk failure.

7: notify-cancel

Like notify, but requests that an existing notification be cancelled.

8: notify-cancelled

Indicates that because of a local change, a notification that had

been registered can no longer be performed. This could be as a

result of the permissions on a object changing, or an object being

deleted. There should never be a response to this message.

internals:

Both client and server use same protocol and infrastructure. There

are many object types, each of which is stored in a registry.

Objects whose type is not recognized can either be handled by the

generic object type, which is registered with the type "*". If no

generic object type is registered, then objects with unknown types are

simply not supported. On the client, there are probably no special

object handlers (although this is by no means forbidden). On the

server, probably everything is a special object.

Each object type has the following methods:

dhcpctl_status dhcpctl_connect (dhcpctl_handle *connection,

char *server_name, int port,

dhcpctl_handle *authinfo)

synchronous

returns nonzero status code if it didn't connect, zero otherwise

stores connection handle through connection, which can be used

for subsequent access to the specified server.

server_name is the name of the server, and port is the TCP

port on which it is listening.

authinfo is the handle to an object containing authentication

information.

dhcpctl_status dhcpctl_open_object (dhcpctl_handle h,

dhcpctl_handle connection,

int flags)

asynchronous - just queues the request

returns nonzero status code if open couldn't be queued

returns zero if open was queued

h is a handle to an object created by dhcpctl_new_object

connection is a connection to a DHCP server

flags include:

DHCPCTL_CREATE - if the object doesn't exist, create it

DHCPCTL_UPDATE - update the object on the server using the

attached parameters

DHCPCTL_EXCL - error if the object exists and DHCPCTL_CREATE

was also specified

dhcpctl_status dhcpctl_new_object (dhcpctl_handle *h,

dhcpctl_handle connection,

char *object_type)

synchronous - creates a local handle for a host entry.

returns nonzero status code if the local host entry couldn't

be created

stores handle to host through h if successful, and returns zero.

object_type is a pointer to a NUL-terminated string containing

the ascii name of the type of object being accessed - e.g., "host"

dhcpctl_status dhcpctl_set_callback (dhcpctl_handle h, void *data,

void (*callback) (dhcpctl_handle,

dhcpctl_status, void *))

synchronous, with asynchronous aftereffect

handle is some object upon which some kind of process has been

started - e.g., an open, an update or a refresh.

data is an anonymous pointer containing some information that

the callback will use to figure out what event completed.

return value of 0 means callback was successfully set, a nonzero

status code is returned otherwise.

Upon completion of whatever task is in process, the callback

will be passed the handle to the object, a status code

indicating what happened, and the anonymous pointer passed to

dhcpctl_status dhcpctl_wait_for_completion (dhcpctl_handle h,

dhcpctl_status *s)

synchronous

returns zero if the callback completes, a nonzero status if

there was some problem relating to the wait operation. The

status of the queued request will be stored through s, and

will also be either zero for success or nonzero for some kind

of failure. Never returns until completion or until the

connection to the server is lost. This performs the same

function as dhcpctl_set_callback and the subsequent callback,

for programs that want to do inline execution instead of using

callbacks.

dhcpctl_status dhcpctl_get_value (data_string *result,

dhcpctl_handle h, char *value_name)

synchronous

returns zero if the call succeeded, a nonzero status code if

it didn't.

result is the address of an empty data string (initialized

with bzero or cleared with data_string_forget). On

successful completion, the addressed data string will contain

the value that was fetched.

dhcpctl_handle refers to some dhcpctl item

value_name refers to some value related to that item - e.g.,

for a handle associated with a completed host lookup, value

could be one of "hardware-address", "dhcp-client-identifier",

"known" or "client-hostname".

dhcpctl_status dhcpctl_get_boolean (int *result,

dhcpctl_handle h, char *value_name)

like dhcpctl_get_value, but more convenient for boolean

values, since no data_string needs to be dealt with.

dhcpctl_status dhcpctl_set_value (dhcpctl_handle h, data_string value,

char *value_name)

Sets a value on an object referred to by a dhcpctl_handle.

The opposite of dhcpctl_get_value. Does not update the

server - just sets the value on the handle.

dhcpctl_status dhcpctl_set_string_value (dhcpctl_handle h, char *value,

char *value_name)

Sets a NUL-terminated ASCII value on an object referred to by

a dhcpctl_handle. like dhcpctl_set_value, but saves the

trouble of creating a data_string for a NUL-terminated string.

Does not update the server - just sets the value on the handle.

dhcpctl_status dhcpctl_set_boolean (dhcpctl_handle h, int value,

char *value_name)

Sets a boolean value on an object - like dhcpctl_set_value,

only more convenient for booleans.

dhcpctl_status dhcpctl_object_update (dhcpctl_handle h)

Queues an update on the object referenced by the handle (there

can't be any other work in progress on the handle). An

update means local parameters will be sent to the server.

dhcpctl_status dhcpctl_object_refresh (dhcpctl_handle h)

Queues an update on the object referenced by the handle (there

can't be any other work in progress on the handle). An

update means local parameters will be sent to the server.

dhcpctl_status dhcpctl_object_delete (dhcpctl_handle h)

Queues a delete of the object referenced by the handle (there

can't be any other work in progress on the handle). A

delete means that the object will be permanently deleted on

the remote end, assuming the remote end supports object

persistence.

So a sample program that would update a host declaration would look

something like this:

/* Create a local object into which to store authentication

information. */

if ((status = dhcpctl_new_object (&auth, dhcpctl_null_handle,

"authentication-information")))

dhcpctl_error ("Can't create authentication information: %m");

/* Set up the authenticator with an algorithm type, user name and

password. */

if ((status = dhcpctl_set_string_value (&auth, "mellon", "username")))

dhcpctl_error ("Can't set username: %m", status);

if ((status = dhcpctl_set_string_value (&auth, "three blind mice",

"password")))

dhcpctl_error ("Can't set password: %m", status);

if ((status = dhcpctl_set_string_value (&auth, "md5-hash",

"algorithm")))

dhcpctl_error ("Can't set authentication algorithm: %m.",

status);

/* Connect to the server. */

if ((status = dhcpctl_connect (&c, "dhcp.server.com", 612, &auth)))

dhcpctl_error ("Can't connect to dhcp.server.com: %m",

status);

/* Create a host object. */

if ((status = dhcpctl_new_object (&hp, c, "host")))

dhcpctl_error ("Host create failed: %m", status);

/* Create a data_string to contain the host's client

identifier, and set it. */

if ((status =

data_string_create_from_hex (&client_id,

"1:08:00:2b:34:1a:c3")))

dhcpctl_error ("Can't create client identifier: %m");

if ((status = dhcpctl_set_value (hp, client_id,

"dhcp-client-identifier")))

dhcpctl_error ("Host client identifier set failed.");

/* Set the known flag to 1. */

if ((status = dhcpctl_set_boolean (hp, 1, "known")))

dhcpctl_error ("Host known set failed.");

/* Open an existing host object that matches the client identifier,

and update it from the local context, or if no host entry

yet exists matching the identifier, create one and

initialize it. */

if ((status = dhcpctl_open_object (&hp, c,

DHCPCTL_CREATE | DHCPCTL_UPDATE)))

dhcpctl_error ("Can't open host: %m", status);

/* Wait for the process to complete, check status. */

if ((status = dhcpctl_wait_for_completion (hp, &wait_status)))

dhcpctl_error ("Host create/lookup wait failed: %m", status);

if (waitstatus)

dhcpctl_error ("Host create/lookup failed: %m", status);

The API is a bit complicated, for a couple of reasons. I want to

make it general, so that there aren't a bazillion functions to call,

one for each data type. I want it to be thread-safe, which is why

each function returns a status and the error printer requires a status

code for input. I want it to be possible to make it asynchronous, so

that it can work in tandem with, for example, an X toolkit. If

you're just writing a simple update cgi program, you probably won't

want to bother to use the asynchronous callbacks, and indeed the above

example doesn't.

I glossed over data strings above - basically, they're objects with a

pointer to a reference-counted buffer structure, an offset into that

buffer, and a length. These are used within the DHCP server, so you

can get an idea of how they work - basically, they're a convenient and

efficient way to store a string with a length such that substrings can

easily be taken and such that more than one user at a time can have a

pointer to the string.

I will also probably add locking primitives, so that you can get the

value of something and be sure that some other updator process won't

modify it while you have the lock.