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S Guide to Network Programming. Using Internet Sockets Brian "Beej Jorgensen" Hall beej@beej.us Version 3.0.15 July 3, 2012 Copyright © 2012 Brian "Beej Jorgensen" Hall Contents 1. 1.1. 1.2. 1.3. 1.4. 1.5. 1.6. 1.7. 1.8. 1.9. 2. 2.1. 2.2. 3. 3.1. 3.2. 3.3. s 3.4. 4. 5.1. getaddrinfo()—Prepare to launch!

s Guide to Network Programming

5.2. socket()—Get the File Descriptor! 5.3. bind()—What port am I on? 5.4. connect()—Hey, you! 5.5. listen()—Will somebody please call me? 5.6. accept()—"Thank you for calling port 3490. " 5.7. send() and recv()—Talk to me, baby! 5.8. sendto() and recvfrom()—Talk to me, DGRAM-style 5.9. close() and shutdown()—Get outta my face! 5.10. getpeername()—Who are you? 5.11. gethostname()—Who am I? 6. 6.1. 6.2. 6.3. 7. 7.1. 7.2. select()—Synchronous I/O Multiplexing 7.3. 7.4. 7.5. 7.6. 8. 9.1. accept() 9.2. bind() 9.3. connect() 9.4. close() 9.5. getaddrinfo(), freeaddrinfo(), gai_strerror() 9.6. gethostname() 9.7. gethostbyname(), gethostbyaddr() 9.8. getnameinfo() 9.9. getpeername() 9.10. errno 9.11. fcntl() 9.12. htons(), htonl(), ntohs(), ntohl() 10. S Guide to Network Programming.

Using Internet Sockets Brian "Beej Jorgensen" Hall beej@beej.us Version 3.0.15 July 3, 2012 Copyright © 2012 Brian "Beej Jorgensen" Hall Contents 1. 1.1. 1.2. 1.3. 1.4. 1.5. 1.6. 1.7. 1.8. 1.9. 2. 2.1. 2.2. 3. 3.1. 3.2. 3.3. s 3.4. 4. 5.1. getaddrinfo()—Prepare to launch!

s Guide to Network Programming

5.2. socket()—Get the File Descriptor! 5.3. bind()—What port am I on? 5.4. connect()—Hey, you! 5.5. listen()—Will somebody please call me? 5.6. accept()—"Thank you for calling port 3490. " 5.7. send() and recv()—Talk to me, baby! 5.8. sendto() and recvfrom()—Talk to me, DGRAM-style 5.9. close() and shutdown()—Get outta my face! 5.10. getpeername()—Who are you? 5.11. gethostname()—Who am I? 6. 6.1. 6.2. 6.3. 7. 7.1. 7.2. select()—Synchronous I/O Multiplexing 7.3. 7.4. 7.5. 7.6. 8. 9.1. accept() 9.2. bind() 9.3. connect() 9.4. close() 9.5. getaddrinfo(), freeaddrinfo(), gai_strerror() 9.6. gethostname() 9.7. gethostbyname(), gethostbyaddr() 9.8. getnameinfo() 9.9. getpeername() 9.10. errno 9.11. fcntl() 9.12. htons(), htonl(), ntohs(), ntohl() 10.

Handle multiple socket connections with fd_set and select on Linux. #include <stdio.h> #include <string.h> //strlen #include <stdlib.h> #include <errno.h> #include <unistd.h> //close #include <arpa/inet.h> //close #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <sys/time.h> //FD_SET, FD_ISSET, FD_ZERO macros #define TRUE 1 #define FALSE 0 #define PORT 8888 int main(int argc , char *argv[]) int opt = TRUE; int master_socket , addrlen , new_socket , client_socket[30] , max_clients = 30 , activity, i , valread , sd; int max_sd; struct sockaddr_in address; char buffer[1025]; fd_set readfds; char *message = "ECHO Daemon v1.0 \r\n"; for (i = 0; i < max_clients; i++) client_socket[i] = 0; if( (master_socket = socket(AF_INET , SOCK_STREAM , 0)) == 0) perror("socket failed"); exit(EXIT_FAILURE); if( setsockopt(master_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0 ) perror("setsockopt"); address.sin_family = AF_INET; address.sin_addr.s_addr = INADDR_ANY; address.sin_port = htons( PORT ); perror("bind failed"); if (listen(master_socket, 3) < 0)

Handle multiple socket connections with fd_set and select on Linux

The World of select() So just why am I so hyped on select()?

The World of select()

One traditional way to write network servers is to have the main server block on accept(), waiting for a connection. Once a connection comes in, the server fork()s, the child process handles the connection and the main server is able to service new incoming requests. With select(), instead of having a process for each request, there is usually only one process that "multi-plexes" all requests, servicing each request as much as it can. So one main advantage of using select() is that your server will only require a single process to handle all requests. Thus, your server will not need shared memory or synchronization primitives for different 'tasks' to communicate. One major disadvantage of using select(), is that your server cannot act like there's only one client, like with a fork()'ing solution.

Okay, so how do you use select()? Select() works by blocking until something happens on a file descriptor (aka a socket). Repeat this process forever. Introduction to non-blocking I/O. Programs that use non-blocking I/O tend to follow the rule that every function has to return immediately, i.e. all the functions in such programs are nonblocking.

Introduction to non-blocking I/O

Thus control passes very quickly from one routine to the next. You have to understand the overall picture to some extent before any one piece makes sense. (This makes it harder to get your mind around than the same program written with blocking calls, but the benefits mentioned elsewhere in this document make up for this trouble, so don't be discouraged.) Many objects need to wait for time to pass or for an external event to occur, but because their methods must return immediately, they can't do the obvious or natural thing. Instead, they use the "state machine" technique. To illustrate this, let's consider a simple networking class that lets you send a file to a remote machine, assuming the connection is all set up. See also: Copyright Dan Kegel 1999.

IEEE 802.11. IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6, 5 and 60 GHz frequency bands.

IEEE 802.11

They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version of the standard was released in 1997 and has had subsequent amendments. The standard and amendments provide the basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when it is incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products. As a result, in the market place, each revision tends to become its own standard. The LinksysWRT54G contains a router with an 802.11b/g radio and two antennae General description[edit] History[edit] 802.11 technology has its origins in a 1985 ruling by the U.S.

Protocol[edit] 802.11b[edit] DHCP. Time to live. IP packets[edit] DNS records[edit] TTLs also occur in the Domain Name System (DNS), where they are set by an authoritative name server for a particular resource record.

Time to live

When a caching (recursive) nameserver queries the authoritative nameserver for a resource record, it will cache that record for the time (in seconds) specified by the TTL. If a stub resolver queries the caching nameserver for the same record before the TTL has expired, the caching server will simply reply with the already cached resource record rather than retrieve it from the authoritative nameserver again. Nameservers may also have a TTL set for NXDOMAIN (acknowledgment that a domain does not exist); but they are generally short in duration (three hours at most).

The units used are seconds. Newer DNS methods that are part of a DR (Disaster Recovery) system may have some records deliberately set extremely low on TTL. HTTP[edit] Time to live may also be expressed as a date and time on which a record expires. See also[edit] Network interface controller. A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter, and by similar terms) is a computer hardware component that connects a computer to a computer network.[1] Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus; the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

Network interface controller

Purpose[edit] The network controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Wi-Fi or Token Ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP. Although other network technologies exist (e.g. token ring), Ethernet has achieved near-ubiquity since the mid-1990s. Implementation[edit] NAT. NAT. IPv6. IPv4. Internet Protocol version 4 (IPv4) is the fourth version in the development of the Internet Protocol (IP) Internet, and routes most traffic on the Internet.[1] However, a successor protocol, IPv6, has been defined and is in various stages of production deployment.

IPv4

IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980). IPv4 is a connectionless protocol for use on packet-switched networks. It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol, such as the Transmission Control Protocol (TCP). Addressing [edit] Decomposition of the quad-dotted IPv4 address representation to its binary value IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4294967296 (232) addresses.

Address representations[edit] Allocation[edit] Port (computer networking) In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system.

Port (computer networking)

The purpose of ports is to uniquely identify different applications or processes running on a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet. In the context of the Internet Protocol, a port is associated with an IP address of the host, as well as the type of protocol used for communication. The protocols that primarily use ports are the Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number. The port number, added to a computer's IP address, completes the destination address for a communications session. Examples include: Jump up ^ Postel, John.