// Copyright (c) 2002-2004 Brian Wellington (bwelling@xbill.org)
package io.milton.dns.record;
import io.milton.dns.Name;
import io.milton.dns.TextParseException;
import java.util.*;
import java.io.*;
import java.net.*;
/**
* The Lookup object issues queries to caching DNS servers. The input consists
* of a name, an optional type, and an optional class. Caching is enabled
* by default and used when possible to reduce the number of DNS requests.
* A Resolver, which defaults to an ExtendedResolver initialized with the
* resolvers located by the ResolverConfig class, performs the queries. A
* search path of domain suffixes is used to resolve relative names, and is
* also determined by the ResolverConfig class.
*
* A Lookup object may be reused, but should not be used by multiple threads.
*
* @see Cache
* @see Resolver
* @see ResolverConfig
*
* @author Brian Wellington
*/
public final class Lookup {
private static Resolver defaultResolver;
private static Name [] defaultSearchPath;
private static Map defaultCaches;
private static int defaultNdots;
private Resolver resolver;
private Name [] searchPath;
private Cache cache;
private boolean temporary_cache;
private int credibility;
private Name name;
private int type;
private int dclass;
private boolean verbose;
private int iterations;
private boolean foundAlias;
private boolean done;
private boolean doneCurrent;
private List aliases;
private Record [] answers;
private int result;
private String error;
private boolean nxdomain;
private boolean badresponse;
private String badresponse_error;
private boolean networkerror;
private boolean timedout;
private boolean nametoolong;
private boolean referral;
private static final Name [] noAliases = new Name[0];
/** The lookup was successful. */
public static final int SUCCESSFUL = 0;
/**
* The lookup failed due to a data or server error. Repeating the lookup
* would not be helpful.
*/
public static final int UNRECOVERABLE = 1;
/**
* The lookup failed due to a network error. Repeating the lookup may be
* helpful.
*/
public static final int TRY_AGAIN = 2;
/** The host does not exist. */
public static final int HOST_NOT_FOUND = 3;
/** The host exists, but has no records associated with the queried type. */
public static final int TYPE_NOT_FOUND = 4;
public static synchronized void
refreshDefault() {
try {
defaultResolver = new ExtendedResolver();
}
catch (UnknownHostException e) {
throw new RuntimeException("Failed to initialize resolver");
}
defaultSearchPath = ResolverConfig.getCurrentConfig().searchPath();
defaultCaches = new HashMap();
defaultNdots = ResolverConfig.getCurrentConfig().ndots();
}
static {
refreshDefault();
}
/**
* Gets the Resolver that will be used as the default by future Lookups.
* @return The default resolver.
*/
public static synchronized Resolver
getDefaultResolver() {
return defaultResolver;
}
/**
* Sets the default Resolver to be used as the default by future Lookups.
* @param resolver The default resolver.
*/
public static synchronized void
setDefaultResolver(Resolver resolver) {
defaultResolver = resolver;
}
/**
* Gets the Cache that will be used as the default for the specified
* class by future Lookups.
* @param dclass The class whose cache is being retrieved.
* @return The default cache for the specified class.
*/
public static synchronized Cache
getDefaultCache(int dclass) {
DClass.check(dclass);
Cache c = (Cache) defaultCaches.get(Mnemonic.toInteger(dclass));
if (c == null) {
c = new Cache(dclass);
defaultCaches.put(Mnemonic.toInteger(dclass), c);
}
return c;
}
/**
* Sets the Cache to be used as the default for the specified class by future
* Lookups.
* @param cache The default cache for the specified class.
* @param dclass The class whose cache is being set.
*/
public static synchronized void
setDefaultCache(Cache cache, int dclass) {
DClass.check(dclass);
defaultCaches.put(Mnemonic.toInteger(dclass), cache);
}
/**
* Gets the search path that will be used as the default by future Lookups.
* @return The default search path.
*/
public static synchronized Name []
getDefaultSearchPath() {
return defaultSearchPath;
}
/**
* Sets the search path to be used as the default by future Lookups.
* @param domains The default search path.
*/
public static synchronized void
setDefaultSearchPath(Name [] domains) {
defaultSearchPath = domains;
}
/**
* Sets the search path that will be used as the default by future Lookups.
* @param domains The default search path.
* @throws TextParseException A name in the array is not a valid DNS name.
*/
public static synchronized void
setDefaultSearchPath(String [] domains) throws TextParseException {
if (domains == null) {
defaultSearchPath = null;
return;
}
Name [] newdomains = new Name[domains.length];
for (int i = 0; i < domains.length; i++)
newdomains[i] = Name.fromString(domains[i], Name.root);
defaultSearchPath = newdomains;
}
private final void
reset() {
iterations = 0;
foundAlias = false;
done = false;
doneCurrent = false;
aliases = null;
answers = null;
result = -1;
error = null;
nxdomain = false;
badresponse = false;
badresponse_error = null;
networkerror = false;
timedout = false;
nametoolong = false;
referral = false;
if (temporary_cache)
cache.clearCache();
}
/**
* Create a Lookup object that will find records of the given name, type,
* and class. The lookup will use the default cache, resolver, and search
* path, and look for records that are reasonably credible.
* @param name The name of the desired records
* @param type The type of the desired records
* @param dclass The class of the desired records
* @throws IllegalArgumentException The type is a meta type other than ANY.
* @see Cache
* @see Resolver
* @see Credibility
* @see Name
* @see Type
* @see DClass
*/
public
Lookup(Name name, int type, int dclass) {
Type.check(type);
DClass.check(dclass);
if (!Type.isRR(type) && type != Type.ANY)
throw new IllegalArgumentException("Cannot query for " +
"meta-types other than ANY");
this.name = name;
this.type = type;
this.dclass = dclass;
synchronized (Lookup.class) {
this.resolver = getDefaultResolver();
this.searchPath = getDefaultSearchPath();
this.cache = getDefaultCache(dclass);
}
this.credibility = Credibility.NORMAL;
this.verbose = Options.check("verbose");
this.result = -1;
}
/**
* Create a Lookup object that will find records of the given name and type
* in the IN class.
* @param name The name of the desired records
* @param type The type of the desired records
* @throws IllegalArgumentException The type is a meta type other than ANY.
* @see #Lookup(Name,int,int)
*/
public
Lookup(Name name, int type) {
this(name, type, DClass.IN);
}
/**
* Create a Lookup object that will find records of type A at the given name
* in the IN class.
* @param name The name of the desired records
* @see #Lookup(Name,int,int)
*/
public
Lookup(Name name) {
this(name, Type.A, DClass.IN);
}
/**
* Create a Lookup object that will find records of the given name, type,
* and class.
* @param name The name of the desired records
* @param type The type of the desired records
* @param dclass The class of the desired records
* @throws TextParseException The name is not a valid DNS name
* @throws IllegalArgumentException The type is a meta type other than ANY.
* @see #Lookup(Name,int,int)
*/
public
Lookup(String name, int type, int dclass) throws TextParseException {
this(Name.fromString(name), type, dclass);
}
/**
* Create a Lookup object that will find records of the given name and type
* in the IN class.
* @param name The name of the desired records
* @param type The type of the desired records
* @throws TextParseException The name is not a valid DNS name
* @throws IllegalArgumentException The type is a meta type other than ANY.
* @see #Lookup(Name,int,int)
*/
public
Lookup(String name, int type) throws TextParseException {
this(Name.fromString(name), type, DClass.IN);
}
/**
* Create a Lookup object that will find records of type A at the given name
* in the IN class.
* @param name The name of the desired records
* @throws TextParseException The name is not a valid DNS name
* @see #Lookup(Name,int,int)
*/
public
Lookup(String name) throws TextParseException {
this(Name.fromString(name), Type.A, DClass.IN);
}
/**
* Sets the resolver to use when performing this lookup. This overrides the
* default value.
* @param resolver The resolver to use.
*/
public void
setResolver(Resolver resolver) {
this.resolver = resolver;
}
/**
* Sets the search path to use when performing this lookup. This overrides the
* default value.
* @param domains An array of names containing the search path.
*/
public void
setSearchPath(Name [] domains) {
this.searchPath = domains;
}
/**
* Sets the search path to use when performing this lookup. This overrides the
* default value.
* @param domains An array of names containing the search path.
* @throws TextParseException A name in the array is not a valid DNS name.
*/
public void
setSearchPath(String [] domains) throws TextParseException {
if (domains == null) {
this.searchPath = null;
return;
}
Name [] newdomains = new Name[domains.length];
for (int i = 0; i < domains.length; i++)
newdomains[i] = Name.fromString(domains[i], Name.root);
this.searchPath = newdomains;
}
/**
* Sets the cache to use when performing this lookup. This overrides the
* default value. If the results of this lookup should not be permanently
* cached, null can be provided here.
* @param cache The cache to use.
*/
public void
setCache(Cache cache) {
if (cache == null) {
this.cache = new Cache(dclass);
this.temporary_cache = true;
} else {
this.cache = cache;
this.temporary_cache = false;
}
}
/**
* Sets ndots to use when performing this lookup, overriding the default value.
* Specifically, this refers to the number of "dots" which, if present in a
* name, indicate that a lookup for the absolute name should be attempted
* before appending any search path elements.
* @param ndots The ndots value to use, which must be greater than or equal to
* 0.
*/
public void
setNdots(int ndots) {
if (ndots < 0)
throw new IllegalArgumentException("Illegal ndots value: " +
ndots);
defaultNdots = ndots;
}
/**
* Sets the minimum credibility level that will be accepted when performing
* the lookup. This defaults to Credibility.NORMAL.
* @param credibility The minimum credibility level.
*/
public void
setCredibility(int credibility) {
this.credibility = credibility;
}
private void
follow(Name name, Name oldname) {
foundAlias = true;
badresponse = false;
networkerror = false;
timedout = false;
nxdomain = false;
referral = false;
iterations++;
if (iterations >= 6 || name.equals(oldname)) {
result = UNRECOVERABLE;
error = "CNAME loop";
done = true;
return;
}
if (aliases == null)
aliases = new ArrayList();
aliases.add(oldname);
lookup(name);
}
private void
processResponse(Name name, SetResponse response) {
if (response.isSuccessful()) {
RRset [] rrsets = response.answers();
List l = new ArrayList();
Iterator it;
int i;
for (i = 0; i < rrsets.length; i++) {
it = rrsets[i].rrs();
while (it.hasNext())
l.add(it.next());
}
result = SUCCESSFUL;
answers = (Record []) l.toArray(new Record[l.size()]);
done = true;
} else if (response.isNXDOMAIN()) {
nxdomain = true;
doneCurrent = true;
if (iterations > 0) {
result = HOST_NOT_FOUND;
done = true;
}
} else if (response.isNXRRSET()) {
result = TYPE_NOT_FOUND;
answers = null;
done = true;
} else if (response.isCNAME()) {
CNAMERecord cname = response.getCNAME();
follow(cname.getTarget(), name);
} else if (response.isDNAME()) {
DNAMERecord dname = response.getDNAME();
try {
follow(name.fromDNAME(dname), name);
} catch (NameTooLongException e) {
result = UNRECOVERABLE;
error = "Invalid DNAME target";
done = true;
}
} else if (response.isDelegation()) {
// We shouldn't get a referral. Ignore it.
referral = true;
}
}
private void
lookup(Name current) {
SetResponse sr = cache.lookupRecords(current, type, credibility);
if (verbose) {
System.err.println("lookup " + current + " " +
Type.string(type));
System.err.println(sr);
}
processResponse(current, sr);
if (done || doneCurrent)
return;
Record question = Record.newRecord(current, type, dclass);
Message query = Message.newQuery(question);
Message response = null;
try {
response = resolver.send(query);
}
catch (IOException e) {
// A network error occurred. Press on.
if (e instanceof InterruptedIOException)
timedout = true;
else
networkerror = true;
return;
}
int rcode = response.getHeader().getRcode();
if (rcode != Rcode.NOERROR && rcode != Rcode.NXDOMAIN) {
// The server we contacted is broken or otherwise unhelpful.
// Press on.
badresponse = true;
badresponse_error = Rcode.string(rcode);
return;
}
if (!query.getQuestion().equals(response.getQuestion())) {
// The answer doesn't match the question. That's not good.
badresponse = true;
badresponse_error = "response does not match query";
return;
}
sr = cache.addMessage(response);
if (sr == null)
sr = cache.lookupRecords(current, type, credibility);
if (verbose) {
System.err.println("queried " + current + " " +
Type.string(type));
System.err.println(sr);
}
processResponse(current, sr);
}
private void
resolve(Name current, Name suffix) {
doneCurrent = false;
Name tname = null;
if (suffix == null)
tname = current;
else {
try {
tname = Name.concatenate(current, suffix);
}
catch (NameTooLongException e) {
nametoolong = true;
return;
}
}
lookup(tname);
}
/**
* Performs the lookup, using the specified Cache, Resolver, and search path.
* @return The answers, or null if none are found.
*/
public Record []
run() {
if (done)
reset();
if (name.isAbsolute())
resolve(name, null);
else if (searchPath == null)
resolve(name, Name.root);
else {
if (name.labels() > defaultNdots)
resolve(name, Name.root);
if (done)
return answers;
for (int i = 0; i < searchPath.length; i++) {
resolve(name, searchPath[i]);
if (done)
return answers;
else if (foundAlias)
break;
}
}
if (!done) {
if (badresponse) {
result = TRY_AGAIN;
error = badresponse_error;
done = true;
} else if (timedout) {
result = TRY_AGAIN;
error = "timed out";
done = true;
} else if (networkerror) {
result = TRY_AGAIN;
error = "network error";
done = true;
} else if (nxdomain) {
result = HOST_NOT_FOUND;
done = true;
} else if (referral) {
result = UNRECOVERABLE;
error = "referral";
done = true;
} else if (nametoolong) {
result = UNRECOVERABLE;
error = "name too long";
done = true;
}
}
return answers;
}
private void
checkDone() {
if (done && result != -1)
return;
StringBuilder sb = new StringBuilder("Lookup of " + name + " ");
if (dclass != DClass.IN)
sb.append(DClass.string(dclass)).append(" ");
sb.append(Type.string(type)).append(" isn't done");
throw new IllegalStateException(sb.toString());
}
/**
* Returns the answers from the lookup.
* @return The answers, or null if none are found.
* @throws IllegalStateException The lookup has not completed.
*/
public Record []
getAnswers() {
checkDone();
return answers;
}
/**
* Returns all known aliases for this name. Whenever a CNAME/DNAME is
* followed, an alias is added to this array. The last element in this
* array will be the owner name for records in the answer, if there are any.
* @return The aliases.
* @throws IllegalStateException The lookup has not completed.
*/
public Name []
getAliases() {
checkDone();
if (aliases == null)
return noAliases;
return (Name []) aliases.toArray(new Name[aliases.size()]);
}
/**
* Returns the result code of the lookup.
* @return The result code, which can be SUCCESSFUL, UNRECOVERABLE, TRY_AGAIN,
* HOST_NOT_FOUND, or TYPE_NOT_FOUND.
* @throws IllegalStateException The lookup has not completed.
*/
public int
getResult() {
checkDone();
return result;
}
/**
* Returns an error string describing the result code of this lookup.
* @return A string, which may either directly correspond the result code
* or be more specific.
* @throws IllegalStateException The lookup has not completed.
*/
public String
getErrorString() {
checkDone();
if (error != null)
return error;
switch (result) {
case SUCCESSFUL: return "successful";
case UNRECOVERABLE: return "unrecoverable error";
case TRY_AGAIN: return "try again";
case HOST_NOT_FOUND: return "host not found";
case TYPE_NOT_FOUND: return "type not found";
}
throw new IllegalStateException("unknown result");
}
}