Ch5 Linux Network Programming

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Ch5 Linux Network Programming

• Jianjian SONG
• Software Institute, Nanjing University
• Nov. 2004

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Content

1. TCP/IP Review
2. Berkeley Socket Basics
3. System Calls and Routines
4. Network information
5. Multi-client
6. Using inetd/xinetd
7. Remote Procedure Call (RPC)

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1. TCP/IP Review

• ??????
• 1969?,ARPA????????
• 1972?,ARPAnet,????????,??NCP??(Network Control
  Program)
• 1973?,TCP?????
• 1980?,TCP/IP??UNIX??(BSD4.1)
• 1982?,TCP/IP??NCP?ARPAnet??
• 1983?,?????????(DNS)
• 1991?,WWW???

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TCP/IP OSI Model
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2. Berkeley Socket Basics

• TCP/IP in UNIX
• BSD4.1
• socket
• connection
• lt??????????????????????gt
• socket
• lt????????????gt
• socket????

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??????

• ???????
• ??????????????
• ?????(????)
• ?????????????

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Three Types of Sockets

• ????(SOCK_STREAM)
• ????????????
• ??TCP??
• ??????(SOCK_DGRAM)
• ?????
• ??UDP??
• ?????(SOCK_RAW)
• ????????IP?ICMP????

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???????
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Server?????

• ?????
• ???????????
• ??Client????????socket??
• ?Client?????????
• ??Client??socket????????,?????????????,?BBS
  Server
• ??socket???Client????,?Time Server
• ????????Client???

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Client?????

• ?????
• ?????Server?,??socket??
• ?Server?????????
• ??Server??socket????????,??????
• ??socket???Server??????
• ????????Client???

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??????
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UDP???????

• ???????????,???UDP
• ?????
• ??????????
• ????Client
• ???????????
• ???????,?????????
• ??ICQ?????

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????????

• socket()?????
• UDP Server?????listen?accept
• UDP?????sendto/recvfrom??
• TCP?????connect/accept???UDP?sendto/recvfrom????
  ?????????
• UDPshutdown????

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Byte order

• ??????(NBO,Network Byte Order)
• ?????????,???????
• ??????(HBO,Host Byte Order)
• ?????HBO???,?CPU????
• Motorola 68k??,HBO?NBO??
• Intel x86??,HBO?NBO??

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Byte Ordering Routines

• Convert values between host and network byte
  order
• include ltnetinet/in.hgt
• uint32_t htonl(uint32_t hostlong)
• uint16_t htons(uint16_t hostshort)
• uint32_t ntohl(uint32_t hostlong)
• uint16_t ntohs(uint16_t hostshort)

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3. System Calls Routines
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socket system call

• header file
• include ltsys/types.hgt
• include ltsys/socket.hgt
• socket creates an endpoint for communication and
  returns a descriptor.
• int socket(int domain, int type, int protocol)

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socket system call (contd)

• domain parameter
• Specifies a communication domain, that is,
  selects a protocol family, such as
  PF_UNIX(PF_LOCAL), PF_INET, PF_IPX ...
• type parameter
• Specifies the communication semantics. Three main
  types are SOCK_STREAM, SOCK_DGRAM, SOCK_RAW
• protocol parameter
• usually 0 (default).

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bind system call

• bind binds a name to a socket
• int bind(int sockfd, struct sockaddr my_addr,
  socklen_t addrlen)
• struct sockaddr ?
• struct sockaddr
• sa_family_t sa_family
• char sa_data14
• -gtstruct sockaddr_un
• -gtstruct sockaddr_in

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bind system call (contd)

• struct sockaddr_un
• struct sockaddr_un
• sa_family_t sun_family / AF_UNIX /
• char sun_path108 /pathname /

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bind system call (contd)

• struct sockaddr_in
• struct sockaddr_in
• sa_family_t sin_family
• unsigned short int sin_port
• struct in_addr sin_addr
• unsigned char sin_zero8
• struct in_addr
• __u32 s_addr

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inet_aton inet_ntoa

• Internet address manipulation routines
• int inet_aton(const char cp, struct in_addr
  inp)
• char inet_ntoa (struct in_addr in)
• inet_ntoa???32??????IP??????????IP?????
• inet_addr An obsolete interface to inet_aton
• inet_addr_t inet_addr (const char cp)

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const INADDR_ANY

• An unsigned long int value.
• When INADDR_ANY is specified in the bind call the
  socket will be bound to all local interfaces.

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listen system call

• listen listen for connections on a socket
• int listen(int s, int backlog)
• ?????socket
• ???????bind()??,??????????????
• ????
• ????Client??????????????,??Server????accept???????
  ?
• backlog???????????,??Server????accept?????????????
  ?,???????????

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accept system call

• accept()?????????,????
• int accept(int sockfd,struct sockaddr addr,int
  addrlen)
• accept???????,?????????
• sockfd ??(??)?socket???
• ????,??????socket???(connected socket
  descriptor)?????????????????Client????
• addr???????????????????,????IP?????

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connect system call

• connect initiate a connection on a socket
  (connect to a server).
• int connect(int sockfd, struct sockaddr
  servaddr, int addrlen)
• ???socket
• servaddr?????????,Server?IP??????????????

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send/recv

• send/recv connection-oriented
• int send(int s, const void msg, size_t len, int
  flag)
• int recv(int s, void buf, size_t len, int flag)
• ?write/read??
• ssize_t write(int fd, const void buf, size_t
  count)
• ssize_t read(int fd, void buf, size_t count)
• flag
• send MSG_OOB, MSG_DONTROUTE, MSG_DONTWAIT,
  MSG_NOSIGNAL, ...
• recv MSG_OOB, MSG_PEEK, MSG_WAITALL,
  MSG_NOSIGNAL, ...

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sendto/recvfrom

• sendto/recvfrom
• int sendto(int s, const void msg, size_t len,
  int flags, const struct sockaddr to, socketlen_t
  tolen)
• int recvfrom(int s, void buf, size_t len, int
  flags, struct sockaddr from, socklen_t fromlen)

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close shutdown

• close
• int close(int sockfd)
• shutdown
• int shutdown(int sockfd, int how)
• how SHUT_RD, SHUT_WR, SHUT_RDWR
• shutdown???TCP??????,close????????????

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4. Examples

• ????socket C/S??
• ???socket C/S??

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5. Network information

• Host name and address conversions
• Service name and port number conversions

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Host name and address conversions

• Domain Name System

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Host name and address conversions (contd)

• Files
• /etc/resolv.conf, /etc/hosts
• Functions
• include ltnetdb.hgt
• struct hostent gethostbyname(const char name)
• struct hostent gethostbyaddr(const char addr,
  size_t len, int type)
• struct hostent
• struct hostent
• char h_name / official name of host /
• char h_aliases / alias list /
• int h_addrtype / host address type /
• int h_length / length of address /
• char h_addrlist / list of addresses /

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Service name and port number conversions

• File
• /etc/services
• Functions
• include ltnetdb.hgt
• struct servent getservbyname(const char name,
  const char proto)
• struct servent getservbyport(int port, const
  char proto)
• struct servent
• struct servent
• char s_name / official service name /
• char s_aliases / alias list /
• int s_port / port number /
• char s_proto / protocol to use /

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Review

• Berkley Socket????
• ??????
• ??/??socket??????
• ????

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??????

• socket
• bind
• connect
• listen
• accept
• recv, recvfrom
• send, sendto
• close, shutdown

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??/??socket??????

• gethostbyaddr, gethostbyname
• getservbyname, getservbyport
• getsockname, getpeername
• getsockopt, setsockopt
• fcntl/ioctl

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????

• IP????
• inet_aton()
• inet_ntoa()
• ??????
• htons()--"Host to Network Short"
• htonl()--"Host to Network Long"
• ntohs()--"Network to Host Short"
• ntohl()--"Network to Host Long"

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6. Multi-client

• Multi-client, n servers?
• Iterative server
• Concurrent server
• Multi-process/multi-thread
• I/O Models
• Block mode
• Non-block mode
• I/O multiplexing
• Signal-driven I/O
• Asynchronous I/O

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Multi-process server
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I/O Models

• Block model
• default
• Non-block model
• I/O multiplexing
• Signal-driven I/O
• Asynchronous I/O

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Non-block mode

• ???????????
• errno - EWOULDBLOCK
• ??????
• int flags
• if ( (flagsfcntl(sock_fd, F_GETFL, 0)) lt 0)
• err_sys()
• flags O_NONBLOCK
• if ( fcntl(sock_fd, F_SETFL, flags) lt 0)
• err_sys()

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Signal-driven I/O

• ????????
• ????
• SIGURG, SIGIO
• ??
• fcntl(conn_fd, F_SETOWN, getpid())
• sigaction

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I/O multiplexing

• ????
• ????????????,????????(?select),???????????????????
  I/O????,??????????????????I/O.

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select

• select synchronous I/O multiplexing.
• include ltsys/select.hgt
• int select(int n, fd_set readfds, fd_set
  writefds, fd_set exceptfds, struct timeval
  timeout)
• FD_ZERO(fd_set set)
• FD_SET(int fd, fd_set set)
• FD_CLR(int fd, fd_set set)
• FD_ISSET(int fd, fd_set set)

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7. Using inetd/xinetd

• The disadvantages of the old model
• inetd/xinetd
• Internet service daemon (also referred as
  super-server).
• /etc/inetd.conf or /etc/xinetd.conf

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xinetd???????

• xinetd?????/etc/xinetd??????(?????/etc/inetd??),??
  ???????????????????????????,???????select()???????
  ??
• ????????bind(),?????????????/etc/xinetd???????????
  ??
• ???TCP????????listen(),??????????UDP???,?????????
  
• ????????,????select()?????????????
• ?select()??TCP???,???accept()??????????UDP,???????
  ??

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xinetd???????(?)

• xinetd??fork()?????,???????????
• ????????????,????????????????????TCP?accept()?????
  ?,??UDP???????????????????dup()??,??????????0?1?2,
  ??????????????????????,??????????
• ?????/etc/xinetd???????,????root??,??????setuid?se
  tgid???ID??ID???????????
• ??TCP???,?????????????????????????????select()??,?
  ???????????
• ??????????????????,????????????????????

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Example

• ?xinetd??????
• hello.c

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8. RPC

• RPC
• Remote Procedure Call
• IPC vs. RPC
• Explicit vs. implicit network programming
• RPC-gtDistributed Object (CORBA, RMI, etc.)

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Review