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UNIX Sockets

UNIX Sockets. Outline Homework #1 posted by end of day Project #1 posted now UNIX sockets (Applications to continue on Thursday) . Project #1 Logistics. First of three programming assignments for the class Due 10/16 at 11:59:59 Late solutions not accepted Two person teams

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UNIX Sockets

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  1. UNIX Sockets Outline Homework #1 posted by end of day Project #1 posted now UNIX sockets (Applications to continue on Thursday) CS 640

  2. Project #1 Logistics • First of three programming assignments for the class • Due 10/16 at 11:59:59 • Late solutions not accepted • Two person teams • Program will be turned in electronically • Directions to be posted • Programs must be written in C or C++ • Use the Linux/TUX lab for your work • Everyone in class should have an account CS 640

  3. Project #1 Overview • This assignment requires you to write two programs • blaster (server) • sends data • blastee (client) • receives data • makefile • The goal of this project is to introduce you to UNIX network programming • UNIX tools • Editor, compiler, debugger • Sockets CS 640

  4. 8 bit Packet Type 32 bit Sequence Variable Length Payload Project #1 Details • blaster • Sends UDP packets of variable sizes to specified host • Packet format: • Packet types: • ‘D’ = DATA • ‘E’ = END • Sequence number • Unsigned and in network byte order • Reflects number of payload bytes sent • Can start at an arbitrary value • Data payload can be anything CS 640

  5. Project #1 Details contd. • blaster accepts the following command line parameters • Host and port of blastee • Rate at which packets are sent (packets/second) • Total number of packets which will be sent and/or duration of test (in seconds) • Initial sequence number • Size of payload portion of packets • A test consists of blaster sending packets to blastee CS 640

  6. Project #1 Details contd. • blastee must allow user to specify listen port • For each DATA packet received, print to screen and/or file a text line with: • Blaster’s IP (dot notation) and port number • Packet size (bytes) • Packet sequence number • Time (milliseconds) packet was received • After END packet received print to screen and/or file a text line with summary info: • Total packets received • Total bytes received • Average packets/sec and bytes/sec • Duration of test (seconds) CS 640

  7. Grading • Grades given by demo only • 20 points: code compiling cleanly • 30 points: send any data and print that data is received • 10 points: blastee decodes packets and prints details • 10 points: number of packets/duration of test • 10 points: rate of test test and payload size • 10 points: sequence numbers • 10 points: generate/send END and prints summary CS 640

  8. Berkeley Sockets • Networking protocols are implemented as part of the OS • The networking API exported by most OS’s is the socket interface • Originally provided by BSD 4.1c ~1982. • The principal abstraction is a socket • Point at which an application attaches to the network • Defines operations for creating connections, attaching to network, sending/receiving data, closing. CS 640

  9. Connection-oriented example (TCP) Server Socket() Bind() Client Listen() Socket() Accept() Connection Establishmt. Connect() Block until connect Data (request) Send() Recv() Process request Data (reply) Send() Recv() CS 640

  10. Connectionless example (UDP) Server Socket() Client Bind() Socket() Recvfrom() Bind() Block until Data from client Sendto() Data (request) Process request Data (reply) Sendto() Recvfrom() CS 640

  11. Socket call • Means by which an application attached to the network • int socket(int family, int type, int protocol) • Family: address family (protocol family) • AF_UNIX, AF_INET, AF_NS, AF_IMPLINK • Type: semantics of communication • SOCK_STREAM, SOCK_DGRAM, SOCK_RAW • Not all combinations of family and type are valid • Protocol: Usually set to 0 but can be set to specific value. • Family and type usually imply the protocol • Return value is a handle for new socket CS 640

  12. Bind call • Binds a newly created socket to the specified address • Int bind(int socket, struct sockaddr *address, int addr_len) • Socket: newly created socket handle • Address: data structure of address of local system • IP address and port number (demux keys) • Same operation for both connection-oriented and connectionless servers • Can use well known port or unique port CS 640

  13. Listen call • Used by connection-oriented servers to indicate an application is willing to receive connections • Int(int socket, int backlog) • Socket: handle of newly creates socket • Backlog: number of connection requests that can be queued by the system while waiting for server to execute accept call. CS 640

  14. Accept call • After executing listen, the accept call carries out a passive open (server prepared to accept connects). • Int accept(int socket, struct sockaddr *address, int addr_len) • It blocks until a remote client carries out a connection request. • When it does return, it returns with a new socket that corresponds with new connection and the address contains the clients address CS 640

  15. Connect call • Client executes an active open of a connection • Int connect(int socket, struct sockaddr *address, int addr_len) • Call does not return until the three-way handshake (TCP) is complete • Address field contains remote system’s address • Client OS usually selects random, unused port CS 640

  16. Send(to), Recv(from) • After connection has been made, application uses send/recv to data • Int send(int socket, char *message, int msg_len, int flags) • Send specified message using specified socket • Int recv(int scoket, char *buffer, int buf_len, int flags) • Receive message from specified socket into specified buffer CS 640

  17. Socket Implimentation • Protocol implementation • Process per protocol • Use a separate process to implement each protocol • Messages are passes between processes • Process per message • Use one process to handle each message/communication • Generally more efficient • Buffer use • Applications use buffers as do protocols • Copies are VERY expensive • Message abstraction enables pointers to be used and minimal copies CS 640

  18. Practical issues – using sockets • You have to be very careful when using these calls • Specific data structures and formats • Ports cannot be less than 1024 • You can use other tools to see if things are working • Tcpdump • /proc • netstat • Client and server can be on same system • Think about error handling methods • Refer to Stevens • Baby steps!! CS 640

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