1 / 26

Sockets: Network IPC

Sockets: Network IPC. Internet Socket UNIX Domain Socket. Sockets. Allows processes to communicate Process on the same machine Process on different machines connect via a network Sockets are identified by socket descriptors Implemented with file descriptors in UNIX

roland
Download Presentation

Sockets: Network IPC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sockets: Network IPC • Internet Socket • UNIX Domain Socket

  2. Sockets • Allows processes to communicate • Process on the same machine • Process on different machines connect via a network • Sockets are identified by socket descriptors • Implemented with file descriptors in UNIX • Not all functions that work with file descriptors work with sockets. See page 548 for which ones do work

  3. Sockets int socket(int domain, int type, int protocol); • domain defines the address family • AF_INET – IPv4 • AF_INET6 – IPv6 • AF_UNIX – UNIX domain (covered later) • AF_UNSPEC – unspecified

  4. Sockets • type defines the type of socket • SOCK_DGRAM • SOCK_RAW • SOCK_SEQPACKET • SOCK_STREAM • protocol defines which of the available protocols to use for this socket • We usually use 0 for the default protocol • AF_INET + SOCK_STREAM  TCP • AF_INET + SOCK_DGRAM  UDP

  5. Byte Ordering • In order to connect to a remote computer and use a socket, we need to use its address • LINUX is little-endian but TCP/IP uses big-endian byte ordering

  6. Byte Ordering • 4 conversion functions for TCP/IP uint32_t htonl(uint32_t hostlong); uint16_t htons(uint16_t hostshort); uint32_t ntohl(uint32_t netlong); uint16_t ntohs(uint16_t netshort); • h – host • n - network

  7. Binding a Socket • Binds a network address to a socket • Used by server so a remote computer can connect to the socket int bind(int sockfd, const struct sockaddr *my_addr, socklen_t addrlen); • sockfd socket descriptor • addrlen size in bytes of struct pointed to by my_addr

  8. Binding a Socket • my_addr points to a struct that represents an address on the network • Format of struct depends on specified domain. So that we can use a single bind function, it is typecast to the generic struct sockaddr { sa_family_t sa_family; char sa_data[]; … };

  9. Binding a Socket • IPv4 addresses are represented by struct sockaddr_in { sa_family_t sin_family; /*addr family*/ in_port_t sin_port; /* port number */ struct in_addr sin_addr; /*IPv4 addr*/ unsigned char sin_zero[8]; /*LINUX only*/ }; struct in_addr { in_addr_t s_addr; /*IPv4 address*/ };

  10. listen int listen(int sockfd, int backlog); • Causes the server to wait for an incoming connection • sockfd socket descriptor of an open socket • backlog suggested max connection requests to queue

  11. accept int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); • Creates a new socket from those queued by listen function • Returns new socket descriptor on success or -1 on failure • Newly created socket used for send and recv • Old socket that we called listen on still exists waiting for more incoming connections

  12. accept • If we don’t care about the identity of the client, we can pass in NULL for addr and addrlen • Otherwise, addr should point to a buffer and addrlen should be the size of the buffer in bytes • accept function blocks if no pending connect requests unless the socket is created non-blocking

  13. connect • Used by client to connect to a server int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen); • sockfd – socket descriptor of an open socket • sockaddr – address of server we wish to connect to • addrlen – size in bytes of the struct pointed to by sockaddr

  14. Summery of Connecting • Server • socket • bind • listen • accept • Client • socket • connect

  15. send and recv ssize_t send(int s, const void *buf, size_t len, int flags); ssize_t recv(int s, void *buf, size_t len, int flags); • s is the socket descriptor for an open and connected socket • buf is a buffer of information to send or an empty buffer to receive information • len is the size of the buffer in bytes • flags – zero or an OR of MSG_EOR (end of record), MSG_OOB (out-of-band data) See page 565 for full list

  16. sendto and recvfrom • sendto and recvfrom used with connectionless sockets (SOCK_DGRAM) • Server • socket, bind, recvfrom • Client • socket, sendto

  17. shutdown and close • close(sfd); will not deallocate the socket until we close the last descriptor that references it (we may have several) int shutdown(int s, int how); • Use shutdown to force a full or partial closure of a socket • s is a socket descriptor • how can be SHUT_RD, SHUT_WR or SHUT_RDWR

  18. Network Address Functions • inet_addr - converts an IP address in numbers-and-dots notation into an unsigned long (in_addr_t). Note: this function is deprecated! • inet_aton - converts an IP address in numbers-and-dots notation into an in_addr struct int inet_aton(const char *cp, struct in_addr *inp);

  19. Network Address Functions • inet_ntoa - converts an IP address in an in_addr struct into dots-and-numbers notation char *inet_ntoa(struct in_addr in); • inet_ntop - converts a network address into a dots-and-numbers address const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt);

  20. Network Address Functions • inet_pton - converts a network address in numbers-and-dots notion into a network address structure int inet_pton(int af, const char *src, void *dst);

  21. Network Addresses From Host Names • To get an address from a host name we need to obtain it from DNS struct hostent *gethostbyname(const char *name); 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_addr_list; /* list of addresses */ }; #define h_addr h_addr_list[0] /* for backward compatibility */ • This function marked obsolete by POSIX.1 • See page 555 for getaddrinfo function

  22. Peer Name int getpeername(int s, struct sockaddr *name, socklen_t *namelen); • Sets sockaddr with the name of the connect peer. Can be used by hosts after calling accept to get the name of a client

  23. Hostname int gethostname(char *name, size_t len); • Retrieves the hostname of the system running the process

  24. UNIX Domain Sockets • Socket for communicating with another process on the same machine only • Provides an optimization since there is no network overhead

  25. UNIX Domain Sockets • Uses sockaddr_un structure instead of sockaddr_in struct sockaddr_un { sa_family_t sun_family; /* AF_UNIX */ char sun_path[108]; /* pathname */ };

  26. UNIX Domain Sockets • When the socket is bound a new special file (type “s”) corresponding to sun_path is created • This file is NOT automatically deleted, so we should be careful to unlink it • If bind finds the file already exists, it will fail

More Related