org.jlab.coda.cMsg.cMsgDomain.client

Class cMsg

java.lang.Object

org.jlab.coda.cMsg.common.cMsgDomainAdapter

org.jlab.coda.cMsg.cMsgDomain.client.cMsg

All Implemented Interfaces:

cMsgDomainInterface

Direct Known Subclasses:

cMsgServerClient

public class cMsg
extends cMsgDomainAdapter

This class implements a cMsg client in the cMsg domain.

Version:

1.0

Author:

Carl Timmer

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
(package private) class	cMsg.KeepAlive Class that checks the health of the domain server by reading monitoring information.
(package private) class	cMsg.Multicaster This class defines a thread to multicast a UDP packet to the cMsg name server every second.
(package private) class	cMsg.ParsedUDL This class simply holds information obtained from parsing a UDL or information about an available cMsg server in a server cloud.
(package private) class	cMsg.UdpReceiver This class gets any response to our UDP multicast.
(package private) class	cMsg.UpdateServer Class that periodically sends statistical info to the domain server.

Field Summary

Fields

Modifier and Type	Field and Description
(package private) java.util.ArrayList<java.lang.String>	broadList Domain server's broadcast/subnet addresses.
(package private) java.util.concurrent.locks.Lock	connectLock Lock for calling connect() or disconnect().
(package private) cMsg.ParsedUDL	currentParsedUDL The parsed form of the single UDL the client is currently connected to.
(package private) java.io.DataOutputStream	domainOut Socket output stream associated with domainOutChannel - sends info to server.
(package private) java.net.Socket	domainOutSocket Channel for talking to domain server.
(package private) java.lang.String	domainServerHost Domain server's host.
(package private) int	domainServerPort Domain server's TCP port.
(package private) boolean	hasSend The subdomain server object or client handler implements send(org.jlab.coda.cMsg.cMsgMessage).
(package private) boolean	hasSendAndGet The subdomain server object or client handler implements sendAndGet(org.jlab.coda.cMsg.cMsgMessage, int).
(package private) boolean	hasShutdown The subdomain server object or client handler implements shutdownClients(String, boolean).
(package private) boolean	hasSubscribe The subdomain server object or client handler implements subscribe(String, String, org.jlab.coda.cMsg.cMsgCallbackInterface, Object).
(package private) boolean	hasSubscribeAndGet The subdomain server object or client handler implements subscribeAndGet(String, String, int).
(package private) boolean	hasSyncSend The subdomain server object or client handler implements syncSend(org.jlab.coda.cMsg.cMsgMessage, int).
(package private) boolean	hasUnsubscribe The subdomain server object or client handler implements unsubscribe(org.jlab.coda.cMsg.cMsgSubscriptionHandle).
(package private) java.util.ArrayList<java.lang.String>	ipList Domain server's IP addresses.
(package private) java.net.Socket	keepAliveSocket Socket for checking to see that the domain server is still alive.
(package private) cMsg.KeepAlive	keepAliveThread Thread for sending keep alive commands to domain server to check its health.
(package private) cMsgClientListeningThread	listeningThread Thread listening for messages and responding to domain server commands.
java.lang.String	monitorXML String containing monitor data received from a cMsg server as a keep alive response.
(package private) java.util.concurrent.locks.Lock	notConnectLock Lock for calling methods other than connect() or disconnect().
(package private) java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgGetHelper>	sendAndGets Collection of all of this client's sendAndGet(org.jlab.coda.cMsg.cMsgMessage, int) calls currently in execution.
(package private) java.util.concurrent.locks.Lock	socketLock Lock to ensure that methods using the socket, write in sequence.
(package private) java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgSubscription>	subscribeAndGets Collection of all of this client's subscribeAndGet(String, String, int) calls currently in execution.
(package private) java.util.concurrent.locks.Lock	subscribeLock Lock to ensure subscribe(String, String, org.jlab.coda.cMsg.cMsgCallbackInterface, Object) and unsubscribe(org.jlab.coda.cMsg.cMsgSubscriptionHandle) calls are sequential.
java.util.concurrent.ConcurrentHashMap<cMsgSubscription,java.lang.String>	subscriptions Collection of all of this client's message subscriptions which are cMsgSubscription objects (value of map is dummy so we can use concurrent hashmap).
(package private) java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgGetHelper>	syncSends Collection of all of this client's syncSend(org.jlab.coda.cMsg.cMsgMessage, int) calls currently in execution.
(package private) int	uniqueClientKey Unique id sent by server to use in our responses.
(package private) java.util.concurrent.atomic.AtomicInteger	uniqueId Used to create unique id numbers associated with a specific message subject/type pair.
(package private) cMsg.UpdateServer	updateServerThread Thread for sending periodic monitoring info to domain server to check this client's health.
(package private) boolean	useFailovers If more than one viable failover UDL is given or failover to a cloud is indicated, then this is true, meaning if any request to the server is interrupted, that method will wait a short while for the failover to complete before throwing an exception or continuing on.

Fields inherited from class org.jlab.coda.cMsg.common.cMsgDomainAdapter

connected, debug, description, domain, host, name, receiving, shutdownHandler, UDL, UDLremainder

Constructor Summary

Constructors

Constructor and Description
cMsg() Constructor which does NOT automatically try to connect to the name server specified.

Method Summary

Modifier and Type	Method and Description
void	connect() Method to connect to the domain server from this client.
protected void	connectWithMulticast() Method to multicast in order to find the domain server from this client.
void	disconnect() Method to close the connection to the domain server.
void	flush(int timeout) This method does nothing.
java.lang.String	getCurrentUDL() Get the UDL the client is currently connected to or null if no connection.
java.lang.String	getInfo(java.lang.String cmd) Get a string of information dependent upon the argument.
java.lang.String	getServerHost() Get the host of the cMsg server that this client is connected to.
int	getServerPort() Get the TCP port of the cMsg server that this client is connected to.
cMsgMessage	monitor(java.lang.String command) This method is a synchronous call to receive a message containing monitoring data which describes the state of the cMsg domain the user is connected to.
(package private) cMsg.ParsedUDL	parseUDL(java.lang.String udl) Method to parse the Universal Domain Locator (UDL) into its various components.
void	send(cMsgMessage message) Method to send a message to the domain for further distribution.
cMsgMessage	sendAndGet(cMsgMessage message, int timeout) The message is sent as it would be in the cMsgDomainInterface.send(org.jlab.coda.cMsg.cMsgMessage) method and a single synchronous response is received.
void	setUDL(java.lang.String UDL) Set the UDL of the client which may be a semicolon separated list of UDLs in this domain.
void	shutdownClients(java.lang.String client, boolean includeMe) Method to shutdown the given client(s).
void	shutdownServers(java.lang.String server, boolean includeMyServer) Method to shutdown the given server(s).
cMsgSubscriptionHandle	subscribe(java.lang.String subject, java.lang.String type, cMsgCallbackInterface cb, java.lang.Object userObj) Method to subscribe to receive messages of a subject and type from the domain.
cMsgMessage	subscribeAndGet(java.lang.String subject, java.lang.String type, int timeout) This method is like a one-time subscribe.
int	syncSend(cMsgMessage message, int timeout) Method to send a message to the domain for further distribution and wait for a response from the subdomain handler that got it.
(package private) void	talkToNameServerFromClient(java.net.Socket socket) This method gets the host and port of the domain server from the name server.
void	unsubscribe(cMsgSubscriptionHandle obj) Method to unsubscribe a previous subscription to receive messages of a subject and type from the domain.

Methods inherited from class org.jlab.coda.cMsg.common.cMsgDomainAdapter

getDebug, getDescription, getDomain, getHost, getName, getShutdownHandler, getUDL, getUDLRemainder, isConnected, isReceiving, setDebug, setDescription, setName, setShutdownHandler, setUDLRemainder, start, stop

Methods inherited from class java.lang.Object

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

Field Detail

currentParsedUDL

cMsg.ParsedUDL currentParsedUDL

The parsed form of the single UDL the client is currently connected to.

useFailovers

volatile boolean useFailovers

If more than one viable failover UDL is given or failover to a cloud is indicated, then this is true, meaning if any request to the server is interrupted, that method will wait a short while for the failover to complete before throwing an exception or continuing on.

ipList

java.util.ArrayList<java.lang.String> ipList

Domain server's IP addresses.

broadList

java.util.ArrayList<java.lang.String> broadList

Domain server's broadcast/subnet addresses.

domainServerHost

java.lang.String domainServerHost

Domain server's host.

domainServerPort

int domainServerPort

Domain server's TCP port.

domainOutSocket

java.net.Socket domainOutSocket

Channel for talking to domain server.

domainOut

java.io.DataOutputStream domainOut

Socket output stream associated with domainOutChannel - sends info to server.

keepAliveSocket

java.net.Socket keepAliveSocket

Socket for checking to see that the domain server is still alive.

monitorXML

public java.lang.String monitorXML

String containing monitor data received from a cMsg server as a keep alive response.

listeningThread

cMsgClientListeningThread listeningThread

Thread listening for messages and responding to domain server commands.

keepAliveThread

cMsg.KeepAlive keepAliveThread

Thread for sending keep alive commands to domain server to check its health.

updateServerThread

cMsg.UpdateServer updateServerThread

Thread for sending periodic monitoring info to domain server to check this client's health.

subscriptions

public java.util.concurrent.ConcurrentHashMap<cMsgSubscription,java.lang.String> subscriptions

Collection of all of this client's message subscriptions which are cMsgSubscription objects (value of map is dummy so we can use concurrent hashmap). A concurrent map is needed so that:

• Client listening thread will not need to grab a mutex while iterating through this set to send messages to callbacks. If the callback cue fills up, then all changes to subscriptions would be impossible.
• UpdateServer thread will not need to grab a mutex while iterating thru this set. Nothing must be able to stop the update thread or the server will think this client is dead.

A client is either a regular client or a bridge but not both. That means it does not matter that a bridge client will add namespace data to the stored subscription but a regular client will not.

subscribeAndGets

java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgSubscription> subscribeAndGets

Collection of all of this client's subscribeAndGet(String, String, int) calls currently in execution. SubscribeAndGets are very similar to subscriptions and can be thought of as one-shot subscriptions. Key is receiverSubscribeId object, value is cMsgSubscription object.

sendAndGets

java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgGetHelper> sendAndGets

Collection of all of this client's sendAndGet(org.jlab.coda.cMsg.cMsgMessage, int) calls currently in execution. Key is senderToken object, value is cMsgGetHelper object.

syncSends

java.util.concurrent.ConcurrentHashMap<java.lang.Integer,cMsgGetHelper> syncSends

Collection of all of this client's syncSend(org.jlab.coda.cMsg.cMsgMessage, int) calls currently in execution. Key is senderToken object, value is cMsgGetHelper object.

connectLock

java.util.concurrent.locks.Lock connectLock

Lock for calling connect() or disconnect().

notConnectLock

java.util.concurrent.locks.Lock notConnectLock

Lock for calling methods other than connect() or disconnect().

subscribeLock

java.util.concurrent.locks.Lock subscribeLock

Lock to ensure subscribe(String, String, org.jlab.coda.cMsg.cMsgCallbackInterface, Object) and unsubscribe(org.jlab.coda.cMsg.cMsgSubscriptionHandle) calls are sequential.

socketLock

java.util.concurrent.locks.Lock socketLock

Lock to ensure that methods using the socket, write in sequence.

uniqueId

java.util.concurrent.atomic.AtomicInteger uniqueId

Used to create unique id numbers associated with a specific message subject/type pair.

uniqueClientKey

int uniqueClientKey

Unique id sent by server to use in our responses.

hasSend

boolean hasSend

The subdomain server object or client handler implements send(org.jlab.coda.cMsg.cMsgMessage).

hasSyncSend

boolean hasSyncSend

The subdomain server object or client handler implements syncSend(org.jlab.coda.cMsg.cMsgMessage, int).

hasSubscribeAndGet

boolean hasSubscribeAndGet

The subdomain server object or client handler implements subscribeAndGet(String, String, int).

hasSendAndGet

boolean hasSendAndGet

The subdomain server object or client handler implements sendAndGet(org.jlab.coda.cMsg.cMsgMessage, int).

hasSubscribe

boolean hasSubscribe

The subdomain server object or client handler implements subscribe(String, String, org.jlab.coda.cMsg.cMsgCallbackInterface, Object).

hasUnsubscribe

boolean hasUnsubscribe

The subdomain server object or client handler implements unsubscribe(org.jlab.coda.cMsg.cMsgSubscriptionHandle).

hasShutdown

boolean hasShutdown

The subdomain server object or client handler implements shutdownClients(String, boolean).

Constructor Detail

cMsg

public cMsg()
     throws cMsgException

Constructor which does NOT automatically try to connect to the name server specified. That's because the UDL, UDLremainder, name, description, and debug are passed in later throught the setter methods. This object is constructed generically through class names found by parsing the UDL at the top level.

Throws:

cMsgException - if local host name cannot be found

Method Detail

setUDL

public void setUDL(java.lang.String UDL)
            throws cMsgException

Set the UDL of the client which may be a semicolon separated list of UDLs in this domain.

Specified by:

setUDL in interface cMsgDomainInterface

Overrides:

setUDL in class cMsgDomainAdapter

Parameters:

UDL - UDL of client

Throws:

cMsgException - if UDL is null, no beginning cmsg://, no host given, unknown host

getCurrentUDL

public java.lang.String getCurrentUDL()

Get the UDL the client is currently connected to or null if no connection.

Specified by:

getCurrentUDL in interface cMsgDomainInterface

Overrides:

getCurrentUDL in class cMsgDomainAdapter

Returns:

UDL the client is currently connected to or null if no connection

getServerHost

public java.lang.String getServerHost()

Get the host of the cMsg server that this client is connected to.

Specified by:

getServerHost in interface cMsgDomainInterface

Overrides:

getServerHost in class cMsgDomainAdapter

Returns:

cMsg server's host; null if unknown

getServerPort

public int getServerPort()

Get the TCP port of the cMsg server that this client is connected to.

Specified by:

getServerPort in interface cMsgDomainInterface

Overrides:

getServerPort in class cMsgDomainAdapter

Returns:

cMsg server's port; 0 if unknown

getInfo

public java.lang.String getInfo(java.lang.String cmd)

Get a string of information dependent upon the argument. In this domain, a cmd arg of "serverName" returns the name of the cMsg name server this client is connected to in the form "IPaddress:port".

Specified by:

getInfo in interface cMsgDomainInterface

Overrides:

getInfo in class cMsgDomainAdapter

Parameters:

cmd - input string

Returns:

string dependent on argument's value; may be null

connect

public void connect()
             throws cMsgException

Method to connect to the domain server from this client. This method handles multiple UDLs, but passes off the real work to connectDirect(java.util.List<java.lang.String>).

Specified by:

connect in interface cMsgDomainInterface

Overrides:

connect in class cMsgDomainAdapter

Throws:

cMsgException - if there are problems parsing the UDL or communication problems with the server(s)

connectWithMulticast

protected void connectWithMulticast()
                             throws cMsgException

Method to multicast in order to find the domain server from this client. Once the server is found and returns its host and port, a direct connection can be made. Only called when connectLock is held.

Throws:

cMsgException - if there are problems parsing the UDL or communication problems with the server.

flush

public void flush(int timeout)

This method does nothing.

Specified by:

flush in interface cMsgDomainInterface

Overrides:

flush in class cMsgDomainAdapter

Parameters:

timeout - ignored

disconnect

public void disconnect()

Method to close the connection to the domain server. This method results in this object becoming functionally useless.

Specified by:

disconnect in interface cMsgDomainInterface

Overrides:

disconnect in class cMsgDomainAdapter

send

public void send(cMsgMessage message)
          throws cMsgException

Method to send a message to the domain for further distribution.

Specified by:

send in interface cMsgDomainInterface

Overrides:

send in class cMsgDomainAdapter

Parameters:

message - message to send

Throws:

cMsgException - if there are communication problems with the server; subject and/or type is null; message is too big for UDP packet size if doing UDP send

syncSend

public int syncSend(cMsgMessage message,
                    int timeout)
             throws cMsgException

Method to send a message to the domain for further distribution and wait for a response from the subdomain handler that got it.

Specified by:

syncSend in interface cMsgDomainInterface

Overrides:

syncSend in class cMsgDomainAdapter

Parameters:

message - message to send

timeout - ignored

Returns:

0

Throws:

cMsgException - if there are communication problems with the server; subject and/or type is null

subscribe

public cMsgSubscriptionHandle subscribe(java.lang.String subject,
                                        java.lang.String type,
                                        cMsgCallbackInterface cb,
                                        java.lang.Object userObj)
                                 throws cMsgException

Method to subscribe to receive messages of a subject and type from the domain. Note about the server failing and an IOException being thrown. All existing subscriptions are resubscribed on the new failover server by the keepAlive thread. However, this routine will recover from an IO error during the subscribe itself if the failover is successful.

Specified by:

subscribe in interface cMsgDomainInterface

Overrides:

subscribe in class cMsgDomainAdapter

Parameters:

subject - message subject

type - message type

cb - callback object whose single method is called upon receiving a message of subject and type

userObj - any user-supplied object to be given to the callback method as an argument

Returns:

handle object to be used for unsubscribing

Throws:

cMsgException - if the callback, subject and/or type is null or blank; an identical subscription already exists; there are communication problems with the server

unsubscribe

public void unsubscribe(cMsgSubscriptionHandle obj)
                 throws cMsgException

Method to unsubscribe a previous subscription to receive messages of a subject and type from the domain. Note about the server failing and an IOException being thrown. To have "unsubscribe" make sense on the failover server, we must wait until all existing subscriptions have been successfully resubscribed on the new server.

Specified by:

unsubscribe in interface cMsgDomainInterface

Overrides:

unsubscribe in class cMsgDomainAdapter

Parameters:

obj - the object returned from a subscribe call

Throws:

cMsgException - if there are communication problems with the server; object arg is null

subscribeAndGet

public cMsgMessage subscribeAndGet(java.lang.String subject,
                                   java.lang.String type,
                                   int timeout)
                            throws cMsgException,
                                   java.util.concurrent.TimeoutException

This method is like a one-time subscribe. The domain grabs the first incoming message of the requested subject and type and sends that to the caller. NOTE: Disconnecting when one thread is in the waiting part of a subscribeAndGet may cause that thread to block forever. It is best to always use a timeout with subscribeAndGet so the thread is assured of eventually resuming execution.

Specified by:

subscribeAndGet in interface cMsgDomainInterface

Overrides:

subscribeAndGet in class cMsgDomainAdapter

Parameters:

subject - subject of message desired from server

type - type of message desired from server

timeout - time in milliseconds to wait for a message

Returns:

response message

Throws:

cMsgException - if there are communication problems with the server; server dies; subject and/or type is null or blank

java.util.concurrent.TimeoutException - if timeout occurs

sendAndGet

public cMsgMessage sendAndGet(cMsgMessage message,
                              int timeout)
                       throws cMsgException,
                              java.util.concurrent.TimeoutException

The message is sent as it would be in the cMsgDomainInterface.send(org.jlab.coda.cMsg.cMsgMessage) method and a single synchronous response is received. The domain notes the fact that a response to it is expected, and sends it to all subscribed to its subject and type. When a marked response is received from a client, it sends that first response back to the original sender regardless of its subject or type. The response may be null. NOTE: Disconnecting when one thread is in the waiting part of a sendAndGet may cause that thread to block forever. It is best to always use a timeout with sendAndGet so the thread is assured of eventually resuming execution.

Specified by:

sendAndGet in interface cMsgDomainInterface

Overrides:

sendAndGet in class cMsgDomainAdapter

Parameters:

message - message sent to server

timeout - time in milliseconds to wait for a response message, zero means wait forever.

Returns:

response message

Throws:

cMsgException - if there are communication problems with the server; server died; subject and/or type is null

java.util.concurrent.TimeoutException - if timeout occurs

monitor

public cMsgMessage monitor(java.lang.String command)

This method is a synchronous call to receive a message containing monitoring data which describes the state of the cMsg domain the user is connected to.

Any non-null value of the argument is used as an XML fragment which is appended to the keep alive packet this client sends to the server. A value of "" will remove it (null is just ignored).

Specified by:

monitor in interface cMsgDomainInterface

Overrides:

monitor in class cMsgDomainAdapter

Parameters:

command - xml fragment appended to the keep alive packet

Returns:

response message containing monitoring information

shutdownClients

public void shutdownClients(java.lang.String client,
                            boolean includeMe)
                     throws cMsgException

Method to shutdown the given client(s). Wildcards used to match client names with the given string where "*" means any or no characters, "?" means exactly 1 character, and "#" means 1 or no positive integer. No failover done here because you do not want to automatically shutdown clients on the new server. It's better to have this call fail.

Specified by:

shutdownClients in interface cMsgDomainInterface

Overrides:

shutdownClients in class cMsgDomainAdapter

Parameters:

client - client(s) to be shutdown

includeMe - if true, it is permissible to shutdown calling client

Throws:

cMsgException - if there are communication problems with the server

shutdownServers

public void shutdownServers(java.lang.String server,
                            boolean includeMyServer)
                     throws cMsgException

Method to shutdown the given server(s). Wildcards used to match server names with the given string. No failover done here because you do not want to automatically shutdown servers connected to the new server. It's better to have this call fail.

Specified by:

shutdownServers in interface cMsgDomainInterface

Overrides:

shutdownServers in class cMsgDomainAdapter

Parameters:

server - server(s) to be shutdown

includeMyServer - if true, it is permissible to shutdown calling client's cMsg server

Throws:

cMsgException - if server arg is not in the correct form (host:port), the host is unknown, client not connected to server, or IO error.

talkToNameServerFromClient

void talkToNameServerFromClient(java.net.Socket socket)
                         throws java.io.IOException,
                                cMsgException

This method gets the host and port of the domain server from the name server. It also gets information about the subdomain handler object. Note to those who would make changes in the protocol, keep the first three ints the same. That way the server can reliably check for mismatched versions.

Parameters:

socket - socket to server

Throws:

java.io.IOException - if there are communication problems with the name server

cMsgException - if the name server's domain does not match the UDL's domain; the client cannot be registered; the domain server cannot open a listening socket or find a port to listen on; or the name server cannot establish a connection to the client

parseUDL

cMsg.ParsedUDL parseUDL(java.lang.String udl)
                 throws cMsgException

Method to parse the Universal Domain Locator (UDL) into its various components. The general cMsg domain UDL is of the form:

cMsg:cMsg://<host>:<port>/<subdomainType>/<subdomain remainder>?tag=value&tag2=value2 ...

• port is not necessary to specify but is the name server's TCP port if connecting directly or the server's UDP port if multicasting. If not specified, defaults are cMsgNetworkConstants.nameServerTcpPort if connecting directly, else cMsgNetworkConstants.nameServerUdpPort if multicasting

• host can be "localhost" and may also be in dotted form (129.57.35.21), but may not contain a colon. It can also be "multicast"

• if domainType is cMsg, subdomainType is automatically set to cMsg if not given. if subdomainType is not cMsg, it is required

• the domain name is case insensitive as is the subdomainType

• remainder is passed on to the subdomain plug-in

• client's password is in tag=value part of UDL as cmsgpassword=<password>

• domain server port is in tag=value part of UDL as domainPort=<port>

• multicast timeout is in tag=value part of UDL as multicastTO=<time out in seconds>

• subnet is in tag=value part of UDL as subnet=<preferred subnet in dot-decimal>

• failover is in tag=value part of UDL as failover=<cloud, cloudonly, or any>

• cloud is in tag=value part of UDL as failover=<local or any>

• the tag=value part of UDL parsed here as regime=low or regime=high means:

  • low message/data throughput client if regime=low, meaning many clients are serviced by a single server thread and all msgs retain time order

  • high message/data throughput client if regime=high, meaning each client is serviced by multiple threads to maximize throughput. Msgs are NOT guaranteed to be handled in time order

  • if regime is not specified (default), it is assumed to be medium, where a single thread is dedicated to a single client and msgs are guaranteed to be handled in time order

The first "cMsg:" is optional. IN the case of the "cMsg" subdomain, its presence in the udl is also optional. The cMsg subdomain interprets the subdoman remainder as a namespace in which messages live with no crossing of messages into other namespaces.

Parameters:

udl - UDL to parse

Returns:

an object with all the parsed UDL information in it

Throws:

cMsgException - if UDL is null, no beginning cmsg://, no host given, unknown host