使用Libevent進行快速可移植非阻塞網絡編程
傳送門
https://github.com/libevent/libevent
https://libevent.org/
學習libevent
第1章:關於本文檔
這些文檔是Nick Mathewson的(c)2009-2012版權所有,並根據知識共享署名-非商業性共享方式許可版本3.0提供。將來的版本可能會在限制較少的許可下提供。
此外,這些文檔中的源代碼示例還根據所謂的“ 3-Clause”或“ Modified” BSD許可進行了許可。有關完整條款,請參閱與這些文檔一起分發的license_bsd文件。
有關本文檔的最新版本,請參見 http://www.wangafu.net/~nickm/libevent-book/TOC.html
要獲取本文檔最新版本的源代碼,請安裝git並運行“git clone git://github.com/nmathewson/libevent-book.git”
關於本文件
本文檔將教您如何使用Libevent 2.0(及更高版本)以C語言編寫快速可移植的異步網絡IO程序。我們假設:
你已經知道C.
您已經知道基本的C網絡調用(socket(),connect()等)。
範例說明
本文檔中的示例應在Linux,FreeBSD,OpenBSD,NetBSD,Mac OS X,Solaris和Android上正常運行。有些示例可能無法在Windows上編譯。
第2章:異步IO的簡要介紹
大多數入門程序員都從阻塞IO調用開始。IO調用是同步的,如果在調用IO調用之前,它直到操作完成或經過足夠的時間以致網絡堆棧放棄後才返回。例如,當您在TCP連接上調用“ connect()”時,您的操作系統會將SYN數據包排隊到TCP連接另一端的主機。直到它從對等主機接收到SYN ACK數據包,或者經過了足夠的時間決定放棄後,它纔將控制權交還給您的應用程序。
這是一個使用阻止網絡調用的非常簡單的客戶端的示例。它將打開與www.google.com的連接,向其發送一個簡單的HTTP請求,然後將響應輸出到stdout。
示例:一個簡單的阻止HTTP客戶端
/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
/* For gethostbyname */
#include <netdb.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
int main(int c, char **v)
{
const char query[] =
"GET / HTTP/1.0\r\n"
"Host: www.google.com\r\n"
"\r\n";
const char hostname[] = "www.google.com";
struct sockaddr_in sin;
struct hostent *h;
const char *cp;
int fd;
ssize_t n_written, remaining;
char buf[1024];
/* Look up the IP address for the hostname. Watch out; this isn't
threadsafe on most platforms. */
h = gethostbyname(hostname);
if (!h) {
fprintf(stderr, "Couldn't lookup %s: %s", hostname, hstrerror(h_errno));
return 1;
}
if (h->h_addrtype != AF_INET) {
fprintf(stderr, "No ipv6 support, sorry.");
return 1;
}
/* Allocate a new socket */
fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0) {
perror("socket");
return 1;
}
/* Connect to the remote host. */
sin.sin_family = AF_INET;
sin.sin_port = htons(80);
sin.sin_addr = *(struct in_addr*)h->h_addr;
if (connect(fd, (struct sockaddr*) &sin, sizeof(sin))) {
perror("connect");
close(fd);
return 1;
}
/* Write the query. */
/* XXX Can send succeed partially? */
cp = query;
remaining = strlen(query);
while (remaining) {
n_written = send(fd, cp, remaining, 0);
if (n_written <= 0) {
perror("send");
return 1;
}
remaining -= n_written;
cp += n_written;
}
/* Get an answer back. */
while (1) {
ssize_t result = recv(fd, buf, sizeof(buf), 0);
if (result == 0) {
break;
} else if (result < 0) {
perror("recv");
close(fd);
return 1;
}
fwrite(buf, 1, result, stdout);
}
close(fd);
return 0;
}
上面代碼中的所有網絡調用均被阻止:gethostbyname在成功解析www.google.com之前或失敗之前不會返回;連接直到連接才返回;在收到數據或關閉之前,recv調用不會返回;並且send調用至少在將其輸出刷新到內核的寫緩衝區後才返回。
現在,阻止IO不一定是邪惡的。如果您希望程序在此期間沒有其他操作,則阻塞IO將對您來說很好。但是,假設您需要編寫一個程序來一次處理多個連接。爲了使我們的示例更具體:假設您想從兩個連接中讀取輸入,並且您不知道哪個連接將首先獲得輸入。你不能說
不好的例子
/* This won't work. */
char buf[1024];
int i, n;
while (i_still_want_to_read()) {
for (i=0; i<n_sockets; ++i) {
n = recv(fd[i], buf, sizeof(buf), 0);
if (n==0)
handle_close(fd[i]);
else if (n<0)
handle_error(fd[i], errno);
else
handle_input(fd[i], buf, n);
}
}
因爲如果數據首先到達fd [2],則您的程序甚至不會嘗試從fd [2]進行讀取,直到從fd [0]和fd [1]進行的讀取得到一些數據並完成爲止。
有時人們使用多線程或多進程服務器解決此問題。執行多線程的最簡單方法之一是使用單獨的進程(或線程)來處理每個連接。由於每個連接都有其自己的進程,因此等待一個連接的阻塞IO調用不會使其他任何連接的進程都阻塞。
這是另一個示例程序。這是一個普通的服務器,它偵聽端口40713上的TCP連接,一次從其輸入的一行中讀取數據,並在到達時寫出每行的ROT13模糊處理。它使用Unix fork()調用爲每個傳入連接創建一個新進程。
Example: Forking ROT13 server
/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define MAX_LINE 16384
char rot13_char(char c)
{
/* We don't want to use isalpha here; setting the locale would change
* which characters are considered alphabetical. */
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;
}
void child(int fd)
{
char outbuf[MAX_LINE+1];
size_t outbuf_used = 0;
ssize_t result;
while (1) {
char ch;
result = recv(fd, &ch, 1, 0);
if (result == 0) {
break;
} else if (result == -1) {
perror("read");
break;
}
/* We do this test to keep the user from overflowing the buffer. */
if (outbuf_used < sizeof(outbuf)) {
outbuf[outbuf_used++] = rot13_char(ch);
}
if (ch == '\n') {
send(fd, outbuf, outbuf_used, 0);
outbuf_used = 0;
continue;
}
}
}
void run(void)
{
int listener;
struct sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = 0;
sin.sin_port = htons(40713);
listener = socket(AF_INET, SOCK_STREAM, 0);
#ifndef WIN32
{
int one = 1;
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
}
#endif
if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
perror("bind");
return;
}
if (listen(listener, 16)<0) {
perror("listen");
return;
}
while (1) {
struct sockaddr_storage ss;
socklen_t slen = sizeof(ss);
int fd = accept(listener, (struct sockaddr*)&ss, &slen);
if (fd < 0) {
perror("accept");
} else {
if (fork() == 0) {
child(fd);
exit(0);
}
}
}
}
int main(int c, char **v)
{
run();
return 0;
}
那麼,我們是否具有完美的解決方案來一次處理多個連接?我現在可以停止寫這本書了,繼續從事其他工作嗎?不完全的。首先,在某些平臺上,進程創建(甚至線程創建)的成本可能很高。在現實生活中,您想使用線程池而不是創建新進程。但是從根本上講,線程不會像您期望的那樣擴展。如果您的程序需要一次處理成千上萬個連接,則處理成千上萬個線程的效率將不如每個CPU僅擁有幾個線程的效率。
但是,如果線程化不是擁有多個連接的答案,那是什麼?在Unix範式中,使套接字成爲非阻塞的。對此的Unix調用是:
fcntl(fd,F_SETFL,O_NONBLOCK);
其中fd是套接字的文件描述符。
[文件描述符是內核在打開套接字時分配給它的編號。您可以使用該數字進行指向套接字的Unix調用。]
一旦使fd(套接字)成爲非阻塞狀態,此後,每當對fd進行網絡調用時,該調用將立即完成操作或返回特殊錯誤代碼,指示“我現在無法取得任何進展,請重試。” 因此,我們的兩路示例可能天真地寫成:
Bad Example: busy-polling all sockets
* This will work, but the performance will be unforgivably bad. */
int i, n;
char buf[1024];
for (i=0; i < n_sockets; ++i)
fcntl(fd[i], F_SETFL, O_NONBLOCK);
while (i_still_want_to_read()) {
for (i=0; i < n_sockets; ++i) {
n = recv(fd[i], buf, sizeof(buf), 0);
if (n == 0) {
handle_close(fd[i]);
} else if (n < 0) {
if (errno == EAGAIN)
; /* The kernel didn't have any data for us to read. */
else
handle_error(fd[i], errno);
} else {
handle_input(fd[i], buf, n);
}
}
}
既然我們正在使用無阻塞套接字,那麼上面的代碼將可以 工作 ……但僅勉強可用。表現將很糟糕,原因有二。首先,當在任何一個連接上都沒有數據可讀取時,循環將無限期旋轉,從而耗盡所有CPU週期。其次,如果您嘗試使用這種方法處理一個或兩個以上的連接,則將對每個連接進行內核調用,無論該連接是否具有任何數據。因此,我們需要一種告訴內核“等到這些套接字之一準備好給我一些數據,然後告訴我哪些已經準備好”的方法。
人們仍然使用的最古老的解決方案是select()。select()調用採用三組fds(以位數組的形式實現):一組用於讀取,一組用於寫入,以及一組用於“ exceptions”。它等待直到其中一個套件中的一個插槽準備就緒,然後將這些套件更改爲僅包含可供使用的插槽。
這是我們再次使用select的示例:
Example: Using select
/* If you only have a couple dozen fds, this version won't be awful */
fd_set readset;
int i, n;
char buf[1024];
while (i_still_want_to_read()) {
int maxfd = -1;
FD_ZERO(&readset);
/* Add all of the interesting fds to readset */
for (i=0; i < n_sockets; ++i) {
if (fd[i]>maxfd) maxfd = fd[i];
FD_SET(fd[i], &readset);
}
/* Wait until one or more fds are ready to read */
select(maxfd+1, &readset, NULL, NULL, NULL);
/* Process all of the fds that are still set in readset */
for (i=0; i < n_sockets; ++i) {
if (FD_ISSET(fd[i], &readset)) {
n = recv(fd[i], buf, sizeof(buf), 0);
if (n == 0) {
handle_close(fd[i]);
} else if (n < 0) {
if (errno == EAGAIN)
; /* The kernel didn't have any data for us to read. */
else
handle_error(fd[i], errno);
} else {
handle_input(fd[i], buf, n);
}
}
}
}
這是我們ROT13服務器的重新實現,這次使用select()。
Example: select()-based ROT13 server
/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
/* For fcntl */
#include <fcntl.h>
/* for select */
#include <sys/select.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#define MAX_LINE 16384
char rot13_char(char c)
{
/* We don't want to use isalpha here; setting the locale would change
* which characters are considered alphabetical. */
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;
int writing;
size_t n_written;
size_t write_upto;
};
struct fd_state * alloc_fd_state(void)
{
struct fd_state *state = malloc(sizeof(struct fd_state));
if (!state)
return NULL;
state->buffer_used = state->n_written = state->writing =
state->write_upto = 0;
return state;
}
void free_fd_state(struct fd_state *state)
{
free(state);
}
void make_nonblocking(int fd)
{
fcntl(fd, F_SETFL, O_NONBLOCK);
}
int do_read(int fd, struct fd_state *state)
{
char buf[1024];
int i;
ssize_t result;
while (1) {
result = recv(fd, buf, sizeof(buf), 0);
if (result <= 0)
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') {
state->writing = 1;
state->write_upto = state->buffer_used;
}
}
}
if (result == 0) {
return 1;
} else if (result < 0) {
if (errno == EAGAIN)
return 0;
return -1;
}
return 0;
}
int do_write(int fd, struct fd_state *state)
{
while (state->n_written < state->write_upto) {
ssize_t result = send(fd, state->buffer + state->n_written,
state->write_upto - state->n_written, 0);
if (result < 0) {
if (errno == EAGAIN)
return 0;
return -1;
}
assert(result != 0);
state->n_written += result;
}
if (state->n_written == state->buffer_used)
state->n_written = state->write_upto = state->buffer_used = 0;
state->writing = 0;
return 0;
}
void run(void)
{
int listener;
struct fd_state *state[FD_SETSIZE];
struct sockaddr_in sin;
int i, maxfd;
fd_set readset, writeset, exset;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = 0;
sin.sin_port = htons(40713);
for (i = 0; i < FD_SETSIZE; ++i)
state[i] = NULL;
listener = socket(AF_INET, SOCK_STREAM, 0);
make_nonblocking(listener);
#ifndef WIN32
{
int one = 1;
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
}
#endif
if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
perror("bind");
return;
}
if (listen(listener, 16)<0) {
perror("listen");
return;
}
FD_ZERO(&readset);
FD_ZERO(&writeset);
FD_ZERO(&exset);
while (1) {
maxfd = listener;
FD_ZERO(&readset);
FD_ZERO(&writeset);
FD_ZERO(&exset);
FD_SET(listener, &readset);
for (i=0; i < FD_SETSIZE; ++i) {
if (state[i]) {
if (i > maxfd)
maxfd = i;
FD_SET(i, &readset);
if (state[i]->writing) {
FD_SET(i, &writeset);
}
}
}
if (select(maxfd+1, &readset, &writeset, &exset, NULL) < 0) {
perror("select");
return;
}
if (FD_ISSET(listener, &readset)) {
struct sockaddr_storage ss;
socklen_t slen = sizeof(ss);
int fd = accept(listener, (struct sockaddr*)&ss, &slen);
if (fd < 0) {
perror("accept");
} else if (fd > FD_SETSIZE) {
close(fd);
} else {
make_nonblocking(fd);
state[fd] = alloc_fd_state();
assert(state[fd]);/*XXX*/
}
}
for (i=0; i < maxfd+1; ++i) {
int r = 0;
if (i == listener)
continue;
if (FD_ISSET(i, &readset)) {
r = do_read(i, state[i]);
}
if (r == 0 && FD_ISSET(i, &writeset)) {
r = do_write(i, state[i]);
}
if (r) {
free_fd_state(state[i]);
state[i] = NULL;
close(i);
}
}
}
}
int main(int c, char **v)
{
setvbuf(stdout, NULL, _IONBF, 0);
run();
return 0;
}
但是我們還沒有完成。由於生成和讀取select()位數組所花費的時間與您爲select()提供的最大fd成正比,因此,當套接字數很高時,select()調用會成比例地擴展。
[在用戶空間方面,生成和讀取位數組可以花費與您爲select()提供的fds數量成比例的時間。但是在內核方面,讀取位數組所花費的時間與位數組中的最大fd成正比,而該fd往往在整個程序中使用的fds總數附近,而不管向其中的集合添加了多少fds選擇()。]
不同的操作系統提供了不同的替換功能供選擇。這些包括poll(),epoll(),kqueue(),evports和/ dev / poll。所有這些都提供比select()更好的性能,除poll()之外,所有這些都爲O(1)提供了添加套接字,移除套接字以及通知套接字已準備好進行IO的性能。
不幸的是,沒有一個有效的接口是普遍存在的標準。Linux有epoll(),BSD(包括Darwin)有kqueue(),Solaris有evports和/ dev / poll… ,而這些操作系統都沒有其他操作系統。因此,如果要編寫一個可移植的高性能異步應用程序,則需要一個包裝所有這些接口的抽象,並提供其中任何一個最有效。
這就是Libevent API最低級別的功能。它使用運行它的計算機上可用的最高效的版本,爲各種select()替換提供一致的接口。
這是異步ROT13服務器的另一個版本。這次,它使用Libevent 2而不是select()。請注意,fd_sets現在不見了:相反,我們將事件與struct event_base關聯和取消關聯,可以通過select(),poll(),epoll(),kqueue()等實現。
Example: A low-level ROT13 server with Libevent
/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
/* For fcntl */
#include <fcntl.h>
#include <event2/event.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.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)
{
/* We don't want to use isalpha here; setting the locale would change
* which characters are considered alphabetical. */
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 = 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 = arg;
char buf[1024];
int i;
ssize_t result;
while (1) {
assert(state->write_event);
result = recv(fd, buf, sizeof(buf), 0);
if (result <= 0)
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) {
free_fd_state(state);
} else if (result < 0) {
if (errno == EAGAIN) // 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 = arg;
while (state->n_written < state->write_upto) {
ssize_t result = send(fd, state->buffer + state->n_written,
state->write_upto - state->n_written, 0);
if (result < 0) {
if (errno == EAGAIN) // 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 = arg;
struct sockaddr_storage ss;
socklen_t slen = sizeof(ss);
int fd = accept(listener, (struct sockaddr*)&ss, &slen);
if (fd < 0) { // XXXX eagain??
perror("accept");
} else if (fd > FD_SETSIZE) {
close(fd); // XXX replace all closes with EVUTIL_CLOSESOCKET */
} else {
struct fd_state *state;
evutil_make_socket_nonblocking(fd);
state = alloc_fd_state(base, fd);
assert(state); /*XXX err*/
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; /*XXXerr*/
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);
#ifndef WIN32
{
int one = 1;
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
}
#endif
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);
/*XXX check it */
event_add(listener_event, NULL);
event_base_dispatch(base);
}
int main(int c, char **v)
{
setvbuf(stdout, NULL, _IONBF, 0);
run();
return 0;
}
(代碼中需要注意的其他事項:我們不是使用evutil_socket_t類型來輸入套接字,而是使用evutil_socket_t類型。不是調用fcntl(O_NONBLOCK)來使套接字成爲非阻塞狀態,而是調用evutil_make_socket_nonblocking。這些更改使我們代碼與Win32網絡API的不同部分兼容。)
What about convenience? (and what about Windows?)
您可能已經注意到,隨着我們的代碼變得越來越高效,它也變得越來越複雜。回到分叉時,我們不必爲每個連接管理緩衝區:我們爲每個進程只有一個單獨的堆棧分配緩衝區。我們不需要顯式地跟蹤每個套接字是否正在讀取或寫入:這在代碼中的位置是隱式的。而且,我們不需要一種結構來跟蹤每個操作完成了多少:我們只使用了循環和堆棧變量。
此外,如果您對Windows上的聯網有深刻的經驗,您會意識到Libevent像上面的示例中那樣使用時可能無法獲得最佳性能。在Windows上,執行快速異步IO的方法不是使用類似於select()的接口:而是使用IOCP(IO完成端口)API。與所有快速網絡API不同,當套接字準備好要執行的程序必須執行的操作時,IOCP不會警告您的程序。而是,程序告訴Windows網絡堆棧開始網絡操作,而IOCP告訴程序操作何時完成。
幸運的是,Libevent 2“ bufferevents”接口解決了這兩個問題:它使程序更易於編寫,並提供了一個可以在Windows 和 Unix上有效實現的接口。
這是上一次使用bufferevents API的ROT13服務器。
Example: A simpler ROT13 server with Libevent
/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>
/* For fcntl */
#include <fcntl.h>
#include <event2/event.h>
#include <event2/buffer.h>
#include <event2/bufferevent.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.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)
{
/* We don't want to use isalpha here; setting the locale would change
* which characters are considered alphabetical. */
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;
}
void readcb(struct bufferevent *bev, void *ctx)
{
struct evbuffer *input, *output;
char *line;
size_t n;
int i;
input = bufferevent_get_input(bev);
output = bufferevent_get_output(bev);
while ((line = evbuffer_readln(input, &n, EVBUFFER_EOL_LF))) {
for (i = 0; i < n; ++i)
line[i] = rot13_char(line[i]);
evbuffer_add(output, line, n);
evbuffer_add(output, "\n", 1);
free(line);
}
if (evbuffer_get_length(input) >= MAX_LINE) {
/* Too long; just process what there is and go on so that the buffer
* doesn't grow infinitely long. */
char buf[1024];
while (evbuffer_get_length(input)) {
int n = evbuffer_remove(input, buf, sizeof(buf));
for (i = 0; i < n; ++i)
buf[i] = rot13_char(buf[i]);
evbuffer_add(output, buf, n);
}
evbuffer_add(output, "\n", 1);
}
}
void errorcb(struct bufferevent *bev, short error, void *ctx)
{
if (error & BEV_EVENT_EOF) {
/* connection has been closed, do any clean up here */
/* ... */
} else if (error & BEV_EVENT_ERROR) {
/* check errno to see what error occurred */
/* ... */
} else if (error & BEV_EVENT_TIMEOUT) {
/* must be a timeout event handle, handle it */
/* ... */
}
bufferevent_free(bev);
}
void do_accept(evutil_socket_t listener, short event, void *arg)
{
struct event_base *base = arg;
struct sockaddr_storage ss;
socklen_t slen = sizeof(ss);
int fd = accept(listener, (struct sockaddr*)&ss, &slen);
if (fd < 0) {
perror("accept");
} else if (fd > FD_SETSIZE) {
close(fd);
} else {
struct bufferevent *bev;
evutil_make_socket_nonblocking(fd);
bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, readcb, NULL, errorcb, NULL);
bufferevent_setwatermark(bev, EV_READ, 0, MAX_LINE);
bufferevent_enable(bev, EV_READ|EV_WRITE);
}
}
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; /*XXXerr*/
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);
#ifndef WIN32
{
int one = 1;
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
}
#endif
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);
/*XXX check it */
event_add(listener_event, NULL);
event_base_dispatch(base);
}
int main(int c, char **v)
{
setvbuf(stdout, NULL, _IONBF, 0);
run();
return 0;
}
How efficient is all of this, really?
XXXX write an efficiency section here. The benchmarks on the libevent page are really out of date.