A simple http proxy at the clent side.
+--------+
| |
| DNS |
| SERVER |
| |
+--------+
^
|
(3) resolve the host name
|
v
+--------+ +-------+ +--------+
| | -- (1)TCP connection ----> | | | |
| | -- (2)http request ------> | | --- (4)TCP connection ---> | |
| | | | --- (5)http request -----> | |
| CLIENT | | PROXY | | SERVER |
| | <- (7)http response ------ | | <-- (6)http response ----- | |
| | ... | | ... | |
| | | | | |
| | -- (n)close connection --> | | - (n+1)close connection -> | |
+--------+ +-------+ +--------+
-
proxy plays two roles: server and client
-
we need to know how client interacts with server and every possible exceptional state
-
client send TCP SYN to server, pending in SYN queue, waiting for server accept.
-
from the view of programmer, epoll
-
connect() return 0
-
connect() return -1 && errno == EINPROGRESS
-
if the async connect() finish, the sockfd will become writable (POLLOUT is set), check the error with getsockopt(listenfd, SOL_SOCKET, SO_ERROR,...)
-
errno in this phase:
-
ECONNREFUSED: remote port is not open, or server connection reaches maximum [listen(fd, backlog)]
-
ETIMEOUT: connection timed out
-
EINPROGRESS: non-blocking connect request is pended to SYN queue
-
-
the connection is established after server received ACK
-
accept(listenfd, ) return success
-
listenfd become readable (POLLIN is set)
-
errno in this phase:
-
EAGAIN or EWOULDBLOCK (when fd is set to nonblocking): no pending connection
-
EBADF: listenfd is not an open file descriptor
-
-
client send/write data
-
client recv/read data
-
remove the session if the peer close the connection
-
errno in this phase:
-
EAGAIN or EWOULDBLOCK: The file descriptor fd refers to a socket and has been marked nonblocking (O_NONBLOCK), and the write/read would block.
-
EBADF: sockfd is not a valid open file descriptor.
-
ECONNRESET: Connection reset by peer.
-
EPIPE: The local end has been shut down on a connection oriented socket.
-
todo: check http Content-Length or Transfer-Encoding
-
-
client close the connection
-
server close the connection
- call close() after read/write() finish
- read() should return 0 on receipt of a FIN from the peer
- when write() returns EPIPE, it also raises the SIGPIPE signal - you never see the EPIPE error unless you handle or ignore the signal
- how to tell if peer close the connection
close() will prevent any more reads and writes to the socket and free it.
int shutdown(int sockfd, int how);
The shutdown() call causes all or part of a full-duplex connection on the socket associated with sockfd to be shut down. If how is SHUT_RD, further receptions will be disallowed. If how is SHUT_WR, further transmissions will be disallowed. If how is SHUT_RDWR, further receptions and transmissions will be disallowed.
But shutdown() doesn't free a the socket descriptor.
read() is equivalent to recv() with a flags parameter of 0. Other values for the flags parameter change the behaviour of recv(). Similarly, write() is equivalent to send() with flags == 0.
MSG_DONTWAIT (since Linux 2.2)
Enables nonblocking operation; if the operation would block,
the call fails with the error EAGAIN or EWOULDBLOCK.
[reference](http://man7.org/linux/man-pages/man2/recv.2.html)
- http parser: https://github.com/h2o/picohttpparser
- hash table : https://github.com/attractivechaos/klib
- memory pool: https://github.com/silentbicycle/mpool