lookup.java

DNS Java 是java实现的DNS

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 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();
		Name newname = null;
		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() > 1)
			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;
	StringBuffer sb = new StringBuffer("Lookup of " + name + " ");
	if (dclass != DClass.IN)
		sb.append(DClass.string(dclass) + " ");
	sb.append(Type.string(type) + " 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");
}

}