Socket Programming

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۱۱ esisas rs il Ox Or ac OF Client.c a structure to contain an internet addre: [0 defined in the include file <netinet/in.h #include <sys/types.h> CAEN G a eS aes ‏اكناباء وتاعم> عفبااء مزع‎ eae esc Ne in_addr ero[8]; /* not used, must * should be AF_INET void error(char *msg){ _perror(msg); _exit(0);} fae ‏ی‎ Uae VOLE naar eee Aaa 1 ‏]عناتاو‎ 506۵00۲16 56۳۷۵00۲: Bea eae tesa ‏تین توت‎ { )3 و 2 ل 00 ‎exit(0);‏ 1 0 0 LCL ۱۱3 ‏یت‎ opening socket 

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۱۱ esisas rs il Ox Or ac OF Client.c Socket System Call - create an end point for #include <stdio.h> Easel ee [of ae #include <sys/socket.h> #include <netinet/in.h> ‏ل ان‎ teo Mabe void error(char *msg){ _perror(msg); fae ‏ی‎ Uae VOLE eee Aaa ۱ ‏:لكر‎ e.g. IPPROTO_UDP, IP Pea ee tec ‏تین توت‎ fies a parti if (arge < 3) { رت ا ‎aca‏ ت۱9 

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۱۱ esisas rs il Ox Or ac OF Client.c 0 if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); ‏:(3000_نمع ف ۱ :(0ه‎ 0 ۱ 1 ۱۲۳ 0000 ea ent Fra Ccon teeters CRN Colac ek )) Peete PaO eek aaa ta e Connect System Call -jnitiat ۱۳ iCuy eee D) 0 icra eat a KO ‎error("ERROR writing to soc!‏ ل ‏(6۲,256)انا0)اعقط ‎۱ ‎if(n <0) ‎۱ ‎۱ ‎Cesena ‏یت‎ ‎ ‎ 

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۱۱ esisas rs il Ox Or ac OF Client.c 0 if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); :(3000_نمع ف )امع 2د ,/300_معدة (4 رهط ) )مع 2ط 1 0 ۱ 1 ۱۲۳ serv_addr.sin_port = htons(portno); لي ل ‎(oR‏ تست و۱ :0۳06609 6۲۲۵۲)۱2۳6۵۵ تک یب تسس ‎Mgt eser-te‏ ععغمع عدمعام")لاماءم ات ‎eis‏ یت n= sendisockfd,buffer,strien(buffer),0); | Emam بصن را )0 < ‎if(n‏ 00 ات نا int ۳۵ 0۱ if(n <0) ‏ل كي‎ lh Pr kas Gm cto descriptor that 7 Cereal ree لكت 

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۱۱ esisas rs il Ox Or ac OF Client.c 0 if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); :(3000_نمع ف )امع 2د ,/300_معدة (4 رهط ) )مع 2ط 1 0 ۱ 1 ۱۲۳ serv_addr.sin_port = htons(portno); لي ل ‎(oR‏ تست و۱ :0۳06609 6۲۲۵۲)۱2۳6۵۵ Ga Rt om Mea Recy System Call ۱ ۰ ۱۳ erence nice : inctu inclu :(8,255,0]أناط, 500110 if(n <0) ‏سس سس تست‎ || Returns number of bytes te PIG LL La descriptor that m Cereal یت لكت 

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۱۱ esisas rs il Ox Or ac OF Client.c ere ureter a Ie) 08 a ted OO Melle el ‏ا لك‎ 1 bzero((char*) &serv_addr, sizeof(serv_addr)); Per et aed eee DCP Cr aes |e eC Rg ۱۳ serv_addr.sin_port = htons(portno); Frater ta te ORS A pete QT) A) error("ERROR connecting" PG eR me Ree ‏:ل"‎ Slose System Call ‏ت۱۳‎ sere ame a Clg aan 0 HD include <unistd h: if(n <0) aaa 00 nt close( int 5); 2 < ۲۵6۷ )50060, rae) ctiptor to be cl eee ‏ل ا‎ cay \n", buffer); Rah ‏تس‎ ‎۲6 0: لكت 

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۱ و <.5/5/500۲6> 06/۵06[ ‎eat tae as‏ رز void error(char *msg){ perror(msg); _exit(0);} 4([]بوعة* ی عوة غمأ)متهد غم ‎nel i‏ ا و ‎ee‏ ا ‎Berita sore‏ 10 ‎if (argc < 2) { fprintf(stderr,"ERROR, no port provided\n"); exit(1); }‏ رت ‎ieee Rage ae ater 1‏ ‎bzero((char *) &serv_addr, sizeof(serv_addr));‏ ‎Pease cle e0)H‏ ‎eC > ۸۴ ۱۴۲:‏ ‎oe Oa‏ ۱۳ ‎Pe Ces reac ea‏ 

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۱) TOP Gerver ta O Server.c if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) ‏ری یت یت‎ ien 0 ی :(6۲,256)/ناط)۵:ععه ۱۳ if (n < 0) error("ERROR reading Pr ae caer eee ata 0 eet تک ی ۱۱ »أل رت ‎#include‏ ۳ ‎aren‏ } int bind i 

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Socket Programming connecting processes Jignesh Patel Palanivel Rathinam Overview • Introduction to Sockets • A generic Client-Server application • Programming Client-Server in C • Programming Client-Server in Java • References Introduction to Sockets Introduction to Sockets • Why Sockets? – Used for Interprocess communication. • The Client-Server model – Most interprocess communication uses client-server model – Client & Server are two processes that wants to communicate with each • other – The Client process connects to the Server process, to make a request for information/services own by the Server. – Once the connection is established between Client process and Server process, they can start sending / receiving information. What are Sockets? – End-point of interprocess communication. – An interface through which processes can send / receive information Socket Introduction to Sockets • What exactly creates a Socket? – <IP address, Port #> tuple • What makes a connection? – {Source<IP address, Port #> , Destination <IP address, Port #>} i.e. source socket – destination socket pair uniquely identifies a connection. • Example 134 3 Server Client 192.168. 0.2 80 134 3 Client 192.168. 0.3 192.168. 0.1 54 88 Client 192.168. 0.2 Introduction to Sockets • Socket Types – STREAM – uses TCP which is reliable, stream oriented protocol – DATAGRAM – uses UDP which is unreliable, message oriented protocol – RAW – provides RAW data transfer directly over IP protocol (no transport layer) • Sockets can use – “unicast” ( for a particular IP address destination) – “multicast” ( a set of destinations – 224.x.x.x) – “broadcast” (direct and limited) – “Loopback” address i.e. 127.x.x.x A generic Client-Server application A generic TCP application • algorithm for TCP client – Find the IP address and port number of server – Create a TCP socket – Connect the socket to server (Server must be up and listening for new requests) – Send/ receive data with server using the socket – Close the connection • algorithm for TCP server – Find the IP address and port number of server – Create a TCP server socket – Bind the server socket to server IP and Port number (this is the port to which clients will connect) – Accept a new connection from client • returns a client socket that represents the client which is connected – Send/ receive data with client using the client socket – Close the connection with client A generic UDP application • • algorithm for UDP client – Find the IP address and port number of server – Create a UDP socket – Send/ receive data with server using the socket – Close the connection algorithm for UDP server – Find the IP address and port number of server – Create a UDP server socket – Bind the server socket to server IP and Port number (this is the port to which clients will send) – Send/ receive data with client using the client socket – Close the connection with client Programming Client-Server in C Programming Client-Server in C • • The steps involved in establishing a socket on the client side are as follows: – Create a socket with the socket() system call – Connect the socket to the address of the server using the connect() system call – Send and receive data using send() and recv() system calls. The steps involved in establishing a socket on the server side are as follows: – Create a socket with the socket() system call – Bind the socket to an address using the bind() system call. For a server socket on the Internet, an address consists of a port number on the host machine. – Listen for connections with the listen() system call – Accept a connection with the accept() system call. This call typically blocks until a client connects with the server. – Send and receive data Programming TCP Client in C Client.c #include #include #include #include #include /* a structure to contain an internet address <stdio.h> <sys/types.h> <sys/socket.h> <netinet/in.h> <netdb.h> void error(char *msg){ perror(msg); int main(int argc, char *argv[]){ int sockfd, portno, n; struct sockaddr_in serv_addr; struct hostent *server; char buffer[256]; exit(0);} defined in the include file <netinet/in.h> */ struct sockaddr_in { short sin_family; /* should be AF_INET */ u_short sin_port; struct in_addr sin_addr; char sin_zero[8]; /* not used, must be zero */ }; struct in_addr { unsigned long s_addr; }; if (argc < 3) { fprintf(stderr,"usage %s hostname port\n", argv[0]); exit(0); } portno = atoi(argv[2]); sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); if (sockfd < 0) error("ERROR opening socket"); Programming TCP Client in C Client.c #include #include #include #include #include Socket System Call – create an end point for communication <stdio.h> <sys/types.h> <sys/socket.h> <netinet/in.h> <netdb.h> void error(char *msg){ #include <sys/types.h> #include <sys/socket.h> int socket(int domain, int type, int protocol); perror(msg); int main(int argc, char *argv[]){ int sockfd, portno, n; struct sockaddr_in serv_addr; struct hostent *server; char buffer[256]; exit(0);} Returns a descriptor domain: selects protocol family e.g. PF_IPX, PF_X25, PF_APPLETALK type: specifies communication semantics e.g. SOCK_DGRAM, SOCK_RAW protocol: specifies a particular protocol to be used e.g. IPPROTO_UDP, IPPROTO_ICMP if (argc < 3) { fprintf(stderr,"usage %s hostname port\n", argv[0]); exit(0); } portno = atoi(argv[2]); sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); if (sockfd < 0) error("ERROR opening socket"); Programming TCP Client in C Client.c exit(0); server = gethostbyname(argv[1]); if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); } bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr , server->h_length); serv_addr.sin_port = htons(portno); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); Connect System Call – initiates a printf("Please enter the message: "); connection on a socket bzero(buffer,256); fgets(buffer,255,stdin); n = send(sockfd,buffer,strlen(buffer),0); #include <sys/types.h> #include <sys/socket.h> if (n < 0) error("ERROR writing to socket"); bzero(buffer,256); int connect( int sockfd, n = recv(sockfd,buffer,255,0); const struct sockaddr *serv_addr, if (n < 0) socklen_t addrlen); error("ERROR reading from socket"); Returns 0 on success printf("%s\n",buffer); sockfd: descriptor that must refer to a socket close(sockfd); serv_addr: address to which we want to return 0; } connect addrlen: length of serv_addr Programming TCP Client in C Client.c exit(0); server = gethostbyname(argv[1]); if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); } bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr , server->h_length); serv_addr.sin_port = htons(portno); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); Send System Call – send a message to a printf("Please enter the message: "); socket bzero(buffer,256); fgets(buffer,255,stdin); #include <sys/types.h> n = send(sockfd,buffer,strlen(buffer),0); #include <sys/socket.h> if (n < 0) error("ERROR writing to socket"); bzero(buffer,256); int send( int s, const void *msg, size_t len, n = recv(sockfd,buffer,255,0); int flags); if (n < 0) error("ERROR reading from socket"); Returns number of characters sent on success s: descriptor that must refer to a socket in printf("%s\n",buffer); connected state close(sockfd); msg: data that we want to send return 0; len: length of data } flags: use default 0. MSG_OOB, MSG_DONTWAIT Programming TCP Client in C Client.c exit(0); server = gethostbyname(argv[1]); if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); } bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr , server->h_length); serv_addr.sin_port = htons(portno); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); Recv System Call – receive a message from a printf("Please enter the message: "); socket bzero(buffer,256); fgets(buffer,255,stdin); #include <sys/types.h> n = send(sockfd,buffer,strlen(buffer),0); #include <sys/socket.h> if (n < 0) error("ERROR writing to socket"); bzero(buffer,256); int recv( int s, const void *buff, size_t len, n = recv(sockfd,buffer,255,0); int flags); if (n < 0) error("ERROR reading from socket"); Returns number of bytes received on success s: descriptor that must refer to a socket in printf("%s\n",buffer); connected state close(sockfd); buff: data that we want to receive return 0; len: length of data } flags: use default 0. MSG_OOB, MSG_DONTWAIT Programming TCP Client in C Client.c exit(0); server = gethostbyname(argv[1]); if (server == NULL) { fprintf(stderr,"ERROR, no such host\n"); } bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr , server->h_length); serv_addr.sin_port = htons(portno); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); Close System Call – close a socket printf("Please enter the message: "); descriptor bzero(buffer,256); fgets(buffer,255,stdin); n = send(sockfd,buffer,strlen(buffer),0); #include <unistd.h> if (n < 0) error("ERROR writing to socket"); int close( int s); bzero(buffer,256); n = recv(sockfd,buffer,255,0); Returns 0 on success if (n < 0) s: descriptor to be closed error("ERROR reading from socket"); printf("%s\n",buffer); close(sockfd); return 0; } Programming TCP Server in C Server.c #include #include #include #include <stdio.h> <sys/types.h> <sys/socket.h> <netinet/in.h> void error(char *msg){ perror(msg); exit(0);} int main(int argc, char *argv[]){ int sockfd, newsockfd, portno, clilen; char buffer[256]; struct sockaddr_in serv_addr, cli_addr; int n; if (argc < 2) { fprintf(stderr,"ERROR, no port provided\n"); exit(1); } sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd < 0) error("ERROR opening socket"); bzero((char *) &serv_addr, sizeof(serv_addr)); portno = atoi(argv[1]); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(portno); Programming TCP Server in C Server.c 0) } if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < error("ERROR on binding"); listen(sockfd,5); clilen = sizeof(cli_addr); newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen); if (newsockfd < 0) error("ERROR on accept"); bzero(buffer,256); n = recv(newsockfd,buffer,255,0); if (n < 0) error("ERROR reading from socket"); printf("Here is the message: %s\n",buffer); n = send(newsockfd,"I got your message",18,0); if (n < 0) error("ERROR writing to socket"); Bind System Call – bind a name to a socket close(newsockfd); #include <sys/types.h> close(sockfd); #include <sys/socket.h> return 0; int bind( int sockfd, const struct sockaddr * serv_addr, socklen_t addrlen); Returns 0 on success sockfd: descriptor that must refer to a socket serv_addr: address to which we want to connect addrlen: length of serv_addr Programming TCP Server in C Server.c 0) } if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < error("ERROR on binding"); listen(sockfd,5); clilen = sizeof(cli_addr); newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen); if (newsockfd < 0) error("ERROR on accept"); bzero(buffer,256); n = recv(newsockfd,buffer,255,0); if (n < 0) error("ERROR reading from socket"); printf("Here is the message: %s\n",buffer); n = send(newsockfd,"I got your message",18,0); if (n < 0) error("ERROR writing to socket"); Listen System Call – listen for connections on a socket close(newsockfd); close(sockfd); #include <sys/types.h> return 0; #include <sys/socket.h> int listen( int s, int backlog); Returns 0 on success s: descriptor that must refer to a socket backlog: maximum length the queue for completely established sockets waiting to be accepted addrlen: length of serv_addr Programming TCP Server in C Server.c 0) } if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < error("ERROR on binding"); listen(sockfd,5); clilen = sizeof(cli_addr); newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen); if (newsockfd < 0) error("ERROR on accept"); bzero(buffer,256); n = recv(newsockfd,buffer,255,0); if (n < 0) error("ERROR reading from socket"); printf("Here is the message: %s\n",buffer); n = send(newsockfd,"I got your message",18,0); if (n < 0) error("ERROR writing to socket"); Accept System Call – accepts a connection on a socket close(newsockfd); close(sockfd); #include <sys/types.h> #include <sys/socket.h> return 0; int accept( int sockfd, const struct sockaddr * addr, socklen_t addrlen); Returns a non-negative descriptor on success sockfd: descriptor that must refer to a socket addr: filled with address of connecting entity addrlen: length of addr Programming UDP Client in C • The client code for a datagram socket client is the same as that for a stream socket with the following differences. – the socket system call has SOCK_DGRAM instead of SOCK_STREAM as its second argument & IPPROTO_UDP instead of IPPROTO_TCP as its third argument. – there is no connect() system call – instead of send() and recv(), the client uses sendto() and recvfrom() sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); len = sizeof(struct sockaddr_in); while (1) { /* write */ n = sendto(sock,“Got your message\n",17, 0,(struct sockaddr *) &server, len); f (n < 0) error("sendto"); /* read */ n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from, len); if (n < 0) error("recvfrom"); } Programming UDP Server in C • Server code with a datagram socket is similar to the stream socket code with following differences. – Servers using datagram sockets do not use the listen() or the accept() system calls. – After a socket has been bound to an address, the program calls recvfrom() to read a message or sendto() to send a message. sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); len = sizeof(struct sockaddr_in); while (1) { /* read */ n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from, len); if (n < 0) error("recvfrom"); /* write */ n = sendto(sock,"Got your message\n",17, 0,(struct sockaddr *)&from, len); f (n < 0) error("sendto"); } Programming Client-Server in C • In case of Windows Everything in the code is same as described previously except the following differences – You have to tell your compiler to link in the Winsock library, usually called wsock32.lib or winsock32.lib – On Visual C++, this can be done through the Project menu, under Settings.... Click the Link tab, and look for the box titled "Object/library modules". Add "wsock32.lib" to that list. – On Visual Studio .NET, add “wsock32.lib” under Project menu, Properties -> Linker -> Input -> Additional Dependencies #include <winsock.h> ….. void main(int argc,char *argv[]){ WSADATA wsda; // if this doesn’t work // WSAData wsda; // then try this WSAStartup(0x0101,&wsda); ….. WSACleanup(); closesocket(sockfd); } Programming Client-Server in Java Programming TCP Client-Server in Java • • • All the classes related to sockets are in the java.net package, so make sure to import that package when you program sockets. All the input/output stream classes are in the java.io package, include this also How to open a socket? – If you are programming a client, then you would create an object of Socket class – Machine name is the machine you are trying to open a connection to, – PortNumber is the port (a number) on which the server you are trying to connect to is running. select one that is greater than 1,023! Why?? Socket MyClient; try { MyClient = new Socket("Machine name", PortNumber); } catch (IOException e) { System.out.println(e); } Programming TCP Client-Server in Java • If you are programming a server, then this is how you open a socket: ServerSocket MyService; try { MyServerice = new ServerSocket(PortNumber); } catch (IOException e) { System.out.println(e); } • When implementing a server you also need to create a socket object from the ServerSocket in order to listen for and accept connections from clients. Socket clientSocket = null; try { clientSocket = MyService.accept(); } catch (IOException e) { System.out.println(e); } Programming TCP Client-Server in Java • How to create an input stream? – On the client side, you can use the DataInputStream class to create an input stream to receive response from the server: DataInputStream input; try { input = new DataInputStream(MyClient.getInputStream()); } catch (IOException e) { System.out.println(e); } – The class DataInputStream allows you to read lines of text and Java primitive data types in a portable way. It has methods such as read, readChar, readInt, readDouble, and readLine,. DataInputStream input; – On the server side, tryyou { can use DataInputStream to receive input from input = new the client: DataInputStream(clientSocket.getInputStream()); } catch (IOException e) { System.out.println(e); } Programming TCP Client-Server in Java • How to create an output stream? – On the client side, you can create an output stream to send information to the server socket using the class PrintStream or DataOutputStream of java.io: PrintStream output; try { output = new PrintStream(MyClient.getOutputStream()); } catch (IOException e) { System.out.println(e); has } methods for displaying textual representation – The class PrintStream of Java primitive data types. Its write and println methods are important. Also, you may want to use the DataOutputStream: DataOutputStream output; try { output = new DataOutputStream(MyClient.getOutputStream()); } catch (IOException e) { write aSystem.out.println(e); single Java primitive type to the output stream. } – Many of its methods The method writeBytes is a useful one. Programming TCP Client-Server in Java • On the server side – you can use the class PrintStream to send information to the client. PrintStream output; try { output = new PrintStream(clientSocket.getOutputStream()); } catch (IOException e) { System.out.println(e); } • Note: You can use the class DataOutputStream as mentioned previously. Programming TCP Client-Server in Java • How to close sockets? – You should always close the output and input stream before you close the socket. – On the client side: try { output.close(); input.close(); MyClient.close(); } catch (IOException e) { System.out.println(e); } – On the server try { side:output.close(); input.close(); clientSocket.close(); MyService.close(); } catch (IOException e) { System.out.println(e); } Programming UDP Client-Server in Java • How to open a datagram socket? – If you are programming a client, then you would create an object of DatagramSocket class try { DatagramSocket socket = new DatagramSocket(); } catch (IOException e) { System.out.println(e); } • If you are programming a server, then this is how you open a socket: DatagramSocket socket = null; try { socket = new DatagramSocket(4445); } catch (IOException e) { System.out.println(e); } Programming UDP Client-Server in Java • How to send/receive on Datagram sockets? – On the client side, you can use the DatagramPacket class – To send data byte[] buf = new byte[256]; InetAddress address = InetAddress.getByName(args[0]); DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445); socket.send(packet); – To receive data packet = new DatagramPacket(buf, buf.length); socket.receive(packet); String received = new String(packet.getData()); System.out.println(“Received from server: " + received); Programming UDP Client-Server in Java • How to send/receive on Datagram sockets? – On the Server side, you can use the DatagramPacket class – To receive data byte[] buf = new byte[256]; DatagramPacket packet = new DatagramPacket(buf, buf.length); socket.receive(packet); • To send data InetAddress address = packet.getAddress(); int port = packet.getPort(); packet = new DatagramPacket(buf, buf.length, address, port); socket.send(packet); socket.close(); • How to close a Datagram socket? References • • • • • Man pages in Linux Accesssible through following command – man 2 <system_call_name> – E.g. man 2 socket “Unix network programming” by Richard Stevens Beej’s guide to Network Programming http://beej.us/guide/bgnet/ The Java Tutorial – Custom Networking http://java.sun.com/docs/books/tutorial/networking/ Lecture notes of cs423 from Dr. Bob Cotter http://www.sce.umkc.edu/~cotterr/cs423_fs05/cs423_fs05_lectures.html