administrivia

hw 3 due tomorrow

ex15 due Friday

designated initializers in C

struct addrinfo {
  int ai_flags;             /* input flags */
  int ai_family;            /* protocol family for socket */
  int ai_socktype;          /* socket type */
  ...
};

/* designated initializer: C only */
struct addrinfo hints = {
  .ai_family = AF_UNSPEC,
  .ai_socktype = SOCK_STREAM
};

/* C/C++ */
struct addrinfo hints = {0};
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;

today’s plan

review client sockets

server sockets

send a file over network

client: read file from disk & write data to socket (ex15)

layering

applications don’t worry about packet reordering/loss using TCP

caching

client-side write ensures data reaches server?

server-side write ensures data reaches disk?

client sockets recap

DNS: getaddrinfo/freeaddrinfo

socket, connect, close

read (or recv), write (or send)

server sockets

imagine a Q&A session with a group of people

step 1: find a place to stand (so people can see you)

step 2: say you’re ready to go

step 3: take a question from the audience

/* bind a name to a socket */
int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
/* listen for connections */
int listen(int sockfd, int backlog);
/* accept a connection */
int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

server sockets overview

echo server

example: echosrv.c

bind

int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);

port < 1024 requires root (linux CAP_NET_BIND_SERVICE)

SO_REUSEADDR

listen

int listen(int sockfd, int backlog);

backlog: hint for the number of pending connections

accept

int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

addr, addrlen: client address

pass NULL if you don’t need them

server architectures

our echo server: one connection at a time

how to talk to multiple clients at the same time?

zero copy

send a file over network & bypass userspace

write with mmap

sendfile

ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count);

more on HTTP

how to decide the length of request/response: close the connection, Content-Length field, or chunked transfer encoding

one HTTP request outstanding per TCP connection

server push

see HTTP/2