A simple http proxy that deploy in clent end.

CLIENT --- (1)http request ---> PROXY --- (2)http request ---> SERVER
CLIENT <-- (4)http response --- PROXY <-- (3)http response --- SERVER

+--------+                            +-------+                           +--------+
|        | -- (1)TCP connection ----> |       |                           |        |
|        | -- (2)http request ------> |       | --- (3)TCP connection --> |        |
|        |                            |       | --- (4)http request ----> |        |
| CLIENT |                            | PROXY |                           | SERVER |
|        | <- (6)http response ------ |       | <-- (5)http response ---  |        |
|        |         ...                |       |          ...              |        |
|        |                            |       |                           |        |
|        | <- (n+1)close connection - |       | <-- (n)close 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)

EAGAIN or EWOULDBLOCK: The file descriptor fd refers to a socket and has been marked 
                       nonblocking (O_NONBLOCK), and the read would block.
EBADF: fd is not a valid file descriptor or is not open for reading.

EAGAIN or EWOULDBLOCK: The file descriptor fd refers to a socket and has been marked
                       nonblocking (O_NONBLOCK), and the write would block.
EBADF: fd is not a valid file descriptor or is not open for writing.
EPIPE: fd is connected to a pipe or socket whose reading end is closed.