DNS
Class DNS

java.lang.Object
  simnet.Resolver
      DNS.DNS

public class DNS

extends Resolver

A simple DNS resolver. Assuming that all domain names are lower case (or, treat domain names as case sensitive). No support for retransmissions of requests or wildcards. No support for multiple addresses for one host.

Nested Class Summary

(package private) class	DNS.CacheCleaner TimerTask to remove stale items from the cache.
(package private) class	DNS.PendingRequest An object for doRemoteQuery to wait for, and to contain the response packet.
(package private) class	DNS.Processor Thread that handles the processing of all requests/responses.
(package private) class	DNS.RecursiveRequestProcessor A thread that processes a recursive request and returns a response to the sender.

Field Summary

(package private) java.util.Hashtable	cache Cache of RRGroups returned by queries to remote name servers, indexed by RRGroup name.
protected int	CACHE_TTL Global Parameter -- how long RRs may be cached before they are considered invalid.
protected java.util.Timer	cacheCleaner Thread to remove expired items from our cache.
protected boolean	client Whether or not this resolver is a stub (client) or local (!client) resolver
protected int	nameserver If we are a client, then this is our nameserver
protected java.util.Hashtable	pending Used to keep track of pending requests.
protected DNS.Processor	processor Our primary thread to handle requests/responses.
protected java.util.Random	random Used to generate request id's, so they (probably) will be unique.
protected java.lang.String	resolverName the name of our resolver (not DNS, but node, mostly used in DNSSEC)
protected int	ROOT Global Parameter -- ip address of root node.
(package private) RRGroup	rootARRG Address of the ROOT name server.
protected java.lang.String	ROOTNAME Global Parameter -- name of root node.
(package private) RRGroup	rootNSRRG Information for ROOT name server.
protected int	RR_DURATION Global Parameter -- how long RRs may last until they are considered invalid.
protected DatagramSocket	sock Used to communicate DNS requests/responses
protected int	TIMEOUT Global Parameter -- amount of time that should pass before we consider a request failed.
(package private) java.util.Hashtable	zones Holds information about our zone(s) -- for servers only.

Fields inherited from class simnet.Resolver

node, sim

Constructor Summary

DNS()

Method Summary

boolean	authoritativeFor(java.lang.String name) Check if we are authoritative for a certain name.
protected void	cache(RRGroup rrg) Put an RRGroup in the cache.
protected RRGroup	checkCache(java.lang.String name, java.lang.String type) Check the cache for an RRGroup that matches this name and type.
java.lang.String	chop(java.lang.String name) Utility method to remove the first part of a period-delimited name.
protected void	clientPreProcessRequest(DNSRequest req) Method where stub resolver can do any processing that it needs to before sending a request.
protected void	createRootRRGs() Fill out our pointers to the ROOT of the DNS
void	customInit(java.lang.String[] config) Loads information for this resolver.
void	dds() Wrapper method to display the DNS state of a resolver.
java.util.LinkedList	doIterativeQuery(java.lang.String name, java.lang.String type) Method that checks our zones database and the cache for information pertaining to to the specified name.
java.util.LinkedList	doRecursiveQuery(java.lang.String name, java.lang.String type) Method to recursively search for the answer to a query.
protected java.util.LinkedList	doRemoteQuery(java.lang.String name, java.lang.String type, int server, boolean recurse) Query a remote name server, get the results and cache and return them.
void	dump_dns_state() Prints the state (zone database, cache and pending requests).
protected java.util.LinkedList	getBestNS(java.lang.String name, boolean includeCache) Method to search all name servers (in our zones and cache) to get the one that is 'most' authoratative for the specified name.
int	getHostByName(java.lang.String name) Performs a lookup of the specified name.
protected java.util.LinkedList	getNameServers(boolean includeCache) Method that finds all Name servers that we know about.
java.lang.String	getNSByName(java.lang.String name)
protected RRGroup	getRRGroup(java.lang.String name, java.lang.String type) Method to search all of our zones for an RRGroup holding an RR for a certain name/type.
boolean	hasFinalAnswer(java.util.LinkedList rrgs, java.lang.String name, java.lang.String type) Check to see if the first item in the linked list is the answer we are looking for -- an NX or A record that has the correct name.
protected boolean	loadRR(java.lang.String zone, java.lang.String[] tokens) Loads the tokenized record for the specified zone into the database.
void	nslookup(java.lang.String name) Method that can be called from the UI to lookup an ip address.
protected void	preProcessRequest(DNSRequest req, int ip) Method where local resolver can do any processing that it needs to on receiving a request.
protected void	preProcessResponse(DNSResponse resp, int ip) Method where local resolver can do any processing that it needs to on receiving a response.
protected boolean	verify(DNSResponse resp)
protected boolean	verify(RRGroup rrg) Determine whether this RRGroup can be used.
boolean	zoneEndsWith(java.lang.String name, java.lang.String zoneName)

Methods inherited from class simnet.Resolver

finalize, initialize

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

client

protected boolean client

Whether or not this resolver is a stub (client) or local (!client) resolver

nameserver

protected int nameserver

If we are a client, then this is our nameserver

resolverName

protected java.lang.String resolverName

the name of our resolver (not DNS, but node, mostly used in DNSSEC)

random

protected java.util.Random random

Used to generate request id's, so they (probably) will be unique.

sock

protected DatagramSocket sock

Used to communicate DNS requests/responses

pending

protected java.util.Hashtable pending

Used to keep track of pending requests. Indexed by request ID, holds Objects of type DNS.PendingRequest.

processor

protected DNS.Processor processor

Our primary thread to handle requests/responses.

cacheCleaner

protected java.util.Timer cacheCleaner

Thread to remove expired items from our cache. (Only for local resolvers)

zones

java.util.Hashtable zones

Holds information about our zone(s) -- for servers only. Objects of type ZoneData are indexed by zone name. Each ZoneData object holds RRGroups, which in turn hold RRs. (only used by local resolvers)

cache

java.util.Hashtable cache

Cache of RRGroups returned by queries to remote name servers, indexed by RRGroup name. (only used by local resolvers)

rootNSRRG

RRGroup rootNSRRG

Information for ROOT name server. All name servers may use this as a fall back when they cannot produce any information about a request.

rootARRG

RRGroup rootARRG

Address of the ROOT name server. All name servers may use this as a fall back when they cannot produce any information about a request.

CACHE_TTL

protected int CACHE_TTL

Global Parameter -- how long RRs may be cached before they are considered invalid.

RR_DURATION

protected int RR_DURATION

Global Parameter -- how long RRs may last until they are considered invalid.

ROOT

protected int ROOT

Global Parameter -- ip address of root node.

ROOTNAME

protected java.lang.String ROOTNAME

Global Parameter -- name of root node.

TIMEOUT

protected int TIMEOUT

Global Parameter -- amount of time that should pass before we consider a request failed.

Constructor Detail

DNS

public DNS()

Method Detail

customInit

public void customInit(java.lang.String[] config)
                throws java.lang.Exception

Loads information for this resolver. This is where a resolver can do any resolver-specific initialization it requires.

Specified by:

customInit in class Resolver

Parameters:

config - Parsed array that represents resource records and server information.

Throws:

java.lang.Exception - If an entry of config cannot be processed correctly

loadRR

protected boolean loadRR(java.lang.String zone,
                         java.lang.String[] tokens)
                  throws java.lang.Exception

Loads the tokenized record for the specified zone into the database. Returns if the record was valid.

Parameters:

zone - The zone this record is in

tokens - Parsed string that specifies an RR

Returns:

whether or not the tokens could correspond to a valid RR

Throws:

java.lang.Exception - If the RR isn't defined correctly

createRootRRGs

protected void createRootRRGs()

Fill out our pointers to the ROOT of the DNS

doIterativeQuery

public java.util.LinkedList doIterativeQuery(java.lang.String name,
                                             java.lang.String type)

Method that checks our zones database and the cache for information pertaining to to the specified name.

Parameters:

name - The name of the node we are looking up.

Returns:

A LinkedList containing pertinent RRGroups. If we found an RRGroup containing an A or NX RR, it will be the first RRGroup in the list. If we have an NS record, it will be the first in the list and will be followed by an A record indicating the IP address of the NS.

doRecursiveQuery

public java.util.LinkedList doRecursiveQuery(java.lang.String name,
                                             java.lang.String type)
                                      throws DNSException

Method to recursively search for the answer to a query. Unlike doIterativeQuery(), does not return until it has received an A or NX record.

Parameters:

name - The name of the node to query

Returns:

a LinkedList of pertinant records, starting with the most useful (either an A or NX). The second record is the NS that gave the response, the third is the A for that NS, etc..

Throws:

DNSException - if verification of RRGroups fail. This is only if they are expired for regular DNS

doRemoteQuery

protected java.util.LinkedList doRemoteQuery(java.lang.String name,
                                             java.lang.String type,
                                             int server,
                                             boolean recurse)
                                      throws DNSException

Query a remote name server, get the results and cache and return them.

Parameters:

name - The name to lookup

server - The name server to query

recurse - Whether or not this should be recurive. Clients should set this to true, servers should not.

Returns:

The responses from the remote host

Throws:

DNSException - When verification of results fail.

cache

protected void cache(RRGroup rrg)

Put an RRGroup in the cache.

Parameters:

rrg - The RRGroup to cache.

checkCache

protected RRGroup checkCache(java.lang.String name,
                             java.lang.String type)

Check the cache for an RRGroup that matches this name and type.

Parameters:

name - the name the RRGroup should match

type - the type of the RR that this RRGroup should hold

Returns:

the specific RRGroup, null if there in no match

verify

protected boolean verify(RRGroup rrg)

Determine whether this RRGroup can be used. This method should be over-ridden to verify signatures, right now it just checks that no Resource Record has expired (it never should be).

Parameters:

rrg - The RRGroup to verify

Returns:

whether or not this RRGroup should be trusted

verify

protected boolean verify(DNSResponse resp)

getBestNS

protected java.util.LinkedList getBestNS(java.lang.String name,
                                         boolean includeCache)

Method to search all name servers (in our zones and cache) to get the one that is 'most' authoratative for the specified name.

Parameters:

name - the name we are querying

includeCache - whether or not we should search our cache too

Returns:

a 2-RRGroup linked list holding the NS that we feel is most likely responsible for the queried node and a RRGroup containing an A record for the NS.

zoneEndsWith

public boolean zoneEndsWith(java.lang.String name,
                            java.lang.String zoneName)

getNameServers

protected java.util.LinkedList getNameServers(boolean includeCache)

Method that finds all Name servers that we know about. Checks our zones and our cache.

Parameters:

includeCache - whether or not to check the cache

Returns:

a Linked list of alternating seta of RRGroups, even entries (0,2,4...) are RRGroups that contain NS RRs, odd entries contain A RRs describing the NS

getRRGroup

protected RRGroup getRRGroup(java.lang.String name,
                             java.lang.String type)

Method to search all of our zones for an RRGroup holding an RR for a certain name/type.

Parameters:

name - The name we want to search.

Returns:

the RRGroup holding the corresponding A record, null if we can't find one.

authoritativeFor

public boolean authoritativeFor(java.lang.String name)

Check if we are authoritative for a certain name.

Parameters:

name - The name to check

Returns:

whether or not we are authoratative for this name

nslookup

public void nslookup(java.lang.String name)

Method that can be called from the UI to lookup an ip address.

Parameters:

name - The name we are looking up

getNSByName

public java.lang.String getNSByName(java.lang.String name)

getHostByName

public int getHostByName(java.lang.String name)

Performs a lookup of the specified name.

Specified by:

getHostByName in class Resolver

Parameters:

name - The name we are querying

Returns:

This ip address of the name, -1 if we couldn't find an answer.

hasFinalAnswer

public boolean hasFinalAnswer(java.util.LinkedList rrgs,
                              java.lang.String name,
                              java.lang.String type)

Check to see if the first item in the linked list is the answer we are looking for -- an NX or A record that has the correct name.

Parameters:

rrgs - list or RRGroups that we are checking

name - the name we are looking for

Returns:

whether or not this linked list contains an answer that we can use (A or NX)

preProcessResponse

protected void preProcessResponse(DNSResponse resp,
                                  int ip)

Method where local resolver can do any processing that it needs to on receiving a response.

Parameters:

resp - The response we received.

ip - The ip this response will be sent to.

preProcessRequest

protected void preProcessRequest(DNSRequest req,
                                 int ip)

Method where local resolver can do any processing that it needs to on receiving a request.

Parameters:

req - The request we received.

clientPreProcessRequest

protected void clientPreProcessRequest(DNSRequest req)

Method where stub resolver can do any processing that it needs to before sending a request.

Parameters:

req - The request we will send.

chop

public java.lang.String chop(java.lang.String name)

Utility method to remove the first part of a period-delimited name.

dds

public void dds()

Wrapper method to display the DNS state of a resolver. (got sick of typing "dump_dns_state")

dump_dns_state

public void dump_dns_state()

Prints the state (zone database, cache and pending requests).