win7下libevent實現的rot13服務器

// libev_rot13.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <event2/event.h>
#include <assert.h>
#define MAX_LINE 16384

void do_read(evutil_socket_t fd, short events, void *arg);
void do_write(evutil_socket_t fd, short events, void *arg);

char rot13_char(char c)
{
	if ((c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M'))
        return c + 13;
    else if ((c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z'))
        return c - 13;
    else
        return c;
}

struct fd_state {
    char buffer[MAX_LINE];
    size_t buffer_used;

    size_t n_written;
    size_t write_upto;

    struct event *read_event;
    struct event *write_event;
};

struct fd_state * alloc_fd_state(struct event_base *base, evutil_socket_t fd)
{
    struct fd_state *state = (struct fd_state *)malloc(sizeof(struct fd_state));
    if (!state)
        return NULL;
    
	state->read_event = event_new(base, fd, EV_READ|EV_PERSIST, do_read, state);
    if (!state->read_event) {
        free(state);
        return NULL;
    }

	state->write_event = event_new(base, fd, EV_WRITE|EV_PERSIST, do_write, state);
    if (!state->write_event) {
        event_free(state->read_event);
        free(state);
        return NULL;
    }

    state->buffer_used = state->n_written = state->write_upto = 0;

    assert(state->write_event);
    return state;
}

void free_fd_state(struct fd_state *state)
{
    event_free(state->read_event);
    event_free(state->write_event);
    free(state);
}

void do_read(evutil_socket_t fd, short events, void *arg)
{
    struct fd_state *state = (struct fd_state *)arg;
	char buf[1024] = {0};
    int i;
    size_t result = 0;
    while (1) {
        assert(state->write_event);
        result = recv(fd, buf, sizeof(buf), 0);
        if (result == SOCKET_ERROR)
            break;

        for (i=0; i < result; ++i)  {
            if (state->buffer_used < sizeof(state->buffer))
                state->buffer[state->buffer_used++] = rot13_char(buf[i]);
            if (buf[i] == '\n') {
                assert(state->write_event);
                event_add(state->write_event, NULL);
                state->write_upto = state->buffer_used;
            }
        }
    }

    if (result == 0) {
		perror("read error");
        free_fd_state(state);
    } else if (result < 0) {
        if (WSAGetLastError() == WSAEWOULDBLOCK) // XXXX use evutil macro
            return;
        perror("recv");
        free_fd_state(state);
    }
}

void do_write(evutil_socket_t fd, short events, void *arg)
{
    struct fd_state *state = (struct fd_state *)arg;

    while (state->n_written < state->write_upto) {
        int result = send(fd, state->buffer + state->n_written,
                              state->write_upto - state->n_written, 0);
        if (result == SOCKET_ERROR) {
			if (WSAGetLastError() == WSAEWOULDBLOCK) // XXX use evutil macro
                return;
            free_fd_state(state);
            return;
        }
        assert(result != 0);

        state->n_written += result;
    }

    if (state->n_written == state->buffer_used)
        state->n_written = state->write_upto = state->buffer_used = 1;

    event_del(state->write_event);
}

void do_accept(evutil_socket_t listener, short event, void *arg)
{
    struct event_base *base = (struct event_base *)arg;
    struct sockaddr_storage ss;
    int slen = sizeof(ss);
    int fd = accept(listener, (struct sockaddr*)&ss, &slen);
    if (fd == INVALID_SOCKET) {
        perror("accept");
    }  else {
        struct fd_state *state;
        evutil_make_socket_nonblocking(fd);
        state = alloc_fd_state(base, fd);
        assert(state);
        assert(state->write_event);
        event_add(state->read_event, NULL);
    }
}

void run(void)
{
    evutil_socket_t listener;
    struct sockaddr_in sin;
    struct event_base *base;
    struct event *listener_event;

    base = event_base_new();
    if (!base)
        return;

    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(40713);

    listener = socket(AF_INET, SOCK_STREAM, 0);
    evutil_make_socket_nonblocking(listener);

    if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
        perror("bind");
        return;
    }

    if (listen(listener, 16)<0) {
        perror("listen");
        return;
    }

    listener_event = event_new(base, listener, EV_READ|EV_PERSIST, do_accept, (void*)base);
	
    event_add(listener_event, NULL);

    event_base_dispatch(base);
}

int main(int c, char **v)
{
	WORD wVersionRequested;
	WSADATA wsaData;
	int err;

	wVersionRequested = MAKEWORD( 2, 2 );
	err = WSAStartup( wVersionRequested, &wsaData );
	if ( err != 0 ) {
		return -1;
	}

    setvbuf(stdout, NULL, _IONBF, 0);

    run();

	WSACleanup();

    return 0;
}

工作過程

WSAStartup()

event_base_new()   新建一個event loop

創建偵聽socket，並調用evutil_make_socket_nonblocking，設置爲非阻塞。

bind

listen

event_new  創建偵聽socket的事件對象，置EV_READ|EV_PERSIST標誌位表明是感興趣讀事件，並設置listen socket的read callback。當調用到這個callback的時候，說明有外來連接到來。

event_add  將新創建的event事件對象加入到eventloop中。

event_base_dispatch  開始處理請求。

do_accept過程

accept  接收一個連接

evutil_make_socket_nonblocking    設置新socket爲非阻塞。

針對新收到的socket，創建read event和write event，並分配存儲區存儲會話過程中的數據。

event_add   將socket的read event加入到event loop中。 當這個socket收到數據時，會調用到do_read

do_read過程

recv  接收數據

處理數據，直至一段數據end。

event_add 將socket的write event加入到event loop中，開始回送response。

do_write過程

send  發送數據

event_del  發送完成後，將write event從event loop中刪除。