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libevent源码分析:http-server例子

时间:03-02来源:作者:点击数:63

http-server例子是libevent提供的一个简单web服务器,实现了对静态网页的处理功能。

  • /*
  • * gcc -g -o http-server http-server.c -levent
  • */
  • #include <stdio.h>
  • #include <stdlib.h>
  • #include <string.h>
  • #include <sys/types.h>
  • #include <sys/stat.h>
  • #include <sys/socket.h>
  • #include <signal.h>
  • #include <fcntl.h>
  • #include <unistd.h>
  • #include <dirent.h>
  • #include <errno.h>
  • #include <event2/event.h>
  • #include <event2/http.h>
  • #include <event2/buffer.h>
  • #include <event2/util.h>
  • #include <event2/keyvalq_struct.h>
  • #include <netinet/in.h>
  • #include <arpa/inet.h>
  • char uri_root[512];
  • static const struct table_entry {
  • const char *extension;
  • const char *content_type;
  • } content_type_table[] = {
  • { "txt", "text/plain" },
  • { "c", "text/plain" },
  • { "h", "text/plain" },
  • { "html", "text/html" },
  • { "htm", "text/html" },
  • { "css", "text/css" },
  • { "gif", "image/gif" },
  • { "jpg", "image/jpg" },
  • { "jpeg", "image/jpeg" },
  • { "png", "image/png" },
  • { "pdf", "application/pdf" },
  • { "ps", "application/postscript" },
  • { NULL, NULL },
  • };
  • /* Try to guess a good content-type for 'path' */
  • const char* guess_content_type(const char *path)
  • {
  • const char *last_period, *extension;
  • const struct table_entry *ent;
  • last_period = strrchr(path, '.');
  • if (!last_period || strchr(last_period, '/'))
  • {
  • goto not_found;
  • }
  • extension = last_period + 1;
  • for (ent = &content_type_table[0]; ent->extension; ++ent)
  • {
  • if (!evutil_ascii_strcasecmp(ent->extension, extension))
  • {
  • return ent->content_type;
  • }
  • }
  • not_found:
  • return "application/misc";
  • }
  • /* Callbase used for the /dump URI, and for every non-get request:
  • ** dumps all information to stdout and gives base a trivial 200 ok */
  • void dump_request_cb(struct evhttp_request *req, void *arg)
  • {
  • const char *cmdtype;
  • struct evkeyvalq *headers;
  • struct evkeyval *header;
  • struct evbuffer *buf;
  • switch (evhttp_request_get_command(req))
  • {
  • case EVHTTP_REQ_GET:
  • cmdtype = "GET";
  • break;
  • case EVHTTP_REQ_POST:
  • cmdtype = "POST";
  • break;
  • case EVHTTP_REQ_HEAD:
  • cmdtype = "HEAD";
  • break;
  • case EVHTTP_REQ_PUT:
  • cmdtype = "PUT";
  • break;
  • case EVHTTP_REQ_DELETE:
  • cmdtype = "DELETE";
  • break;
  • case EVHTTP_REQ_OPTIONS:
  • cmdtype = "OPTIONS";
  • break;
  • case EVHTTP_REQ_TRACE:
  • cmdtype = "TRACE";
  • break;
  • case EVHTTP_REQ_CONNECT:
  • break;
  • case EVHTTP_REQ_PATCH:
  • cmdtype = "PATCH";
  • break;
  • default:
  • cmdtype = "unknown";
  • break;
  • }
  • printf("Received a %s request for %s\nHeader:\n", cmdtype, evhttp_request_get_uri(req));
  • headers = evhttp_request_get_input_headers(req);
  • for (header = headers->tqh_first; header; header = header->next.tqe_next)
  • {
  • printf(" %s: %s\n", header->key, header->value);
  • }
  • buf = evhttp_request_get_input_buffer(req);
  • puts("Input data: <<<<");
  • while (evbuffer_get_length(buf))
  • {
  • int n;
  • char cbuf[128];
  • n = evbuffer_remove(buf, cbuf, sizeof(cbuf));
  • if (n > 0)
  • {
  • (void)fwrite(cbuf, 1, n, stdout);
  • }
  • }
  • puts(">>>");
  • evhttp_send_reply(req, 200, "ok", NULL);
  • }
  • /* This callback gets invoked when we get and http request than doesn't match
  • * any other callback. Like any evhttp server callback, it has a simple job:
  • * it must eventually call evhttp_send_error() or evhttp_send_reply().
  • */
  • void send_document_cb(struct evhttp_request *req, void *arg)
  • {
  • struct evbuffer *evb = NULL;
  • const char *docroot = arg;
  • const char *uri = evhttp_request_get_uri(req);
  • struct evhttp_uri *decoded = NULL;
  • const char *path;
  • char *decoded_path;
  • char *whole_path = NULL;
  • size_t len;
  • int fd = -1;
  • struct stat st;
  • if (evhttp_request_get_command(req) != EVHTTP_REQ_GET)
  • {
  • dump_request_cb(req, arg);
  • return;
  • }
  • printf("Got a GET request for <%s>\n", uri);
  • /* Decode the URI */
  • decoded = evhttp_uri_parse(uri);
  • if (!decoded)
  • {
  • printf("It's not a good URI, Sneding BADREQUEST\n");
  • evhttp_send_error(req, HTTP_BADREQUEST, 0);
  • return;
  • }
  • /* Let's see what path the user asked for. */
  • path = evhttp_uri_get_path(decoded);
  • if (!path)
  • {
  • path = "/";
  • }
  • /* We need to decode it, to see what path the user really wanted */
  • decoded_path = evhttp_uridecode(path, 0, NULL);
  • if (decoded_path == NULL)
  • {
  • goto err;
  • }
  • /* Don't allow any ".."'s in the path, to avoid exposing stuff outside
  • * of the docroot. This test is both overzealous and underzealous:
  • * it forbids aceptable paths like "/this/one..here", but it doesn't
  • * do anything to prevent symlink following. */
  • if (strstr(decoded_path, ".."))
  • {
  • goto err;
  • }
  • len = strlen(decoded_path) + strlen(docroot) + 2;
  • if (!(whole_path = malloc(len)))
  • {
  • perror("malloc");
  • goto err;
  • }
  • evutil_snprintf(whole_path, len, "%s/%s", docroot, decoded_path);
  • if (stat(whole_path, &st) < 0)
  • {
  • goto err;
  • }
  • /* This holds the content we're sending */
  • evb = evbuffer_new();
  • if (S_ISDIR(st.st_mode))
  • {
  • /* If it's a directory, read the comments and make a little index page */
  • DIR *d;
  • struct dirent *ent;
  • const char *trailing_slash = "";
  • if (!strlen(path) || path[strlen(path) - 1] != '/')
  • {
  • trailing_slash = "/";
  • }
  • if (!(d = opendir(whole_path)))
  • {
  • goto err;
  • }
  • evbuffer_add_printf(evb,
  • "<!DOCTYPE html>\n"
  • "<html>\n "
  • " <head>\n"
  • " <meta charset='utf-8'>\n"
  • " <title>%s</title>\n"
  • " <base href='%s%s'>\n"
  • " </head>\n"
  • " <body>\n"
  • " <h1>%s</h1>\n"
  • " <ul>\n",
  • decoded_path, /* xxx html-escape this. */
  • path, /* xxx html-escape this? */
  • trailing_slash,
  • decoded_path /* xx html-escape this */
  • );
  • while ((ent = readdir(d)))
  • {
  • const char *name = ent->d_name;
  • evbuffer_add_printf(evb,
  • " <li><a href=\"%s\">%s</a>\n", name, name);
  • }
  • evbuffer_add_printf(evb, "</ul></body></html>\n");
  • closedir(d);
  • evhttp_add_header(evhttp_request_get_output_headers(req),
  • "Content-Type", "text/html");
  • }
  • else
  • {
  • /* Otherwise it's a file; and it to the buffer to get send via sendfile */
  • const char *type = guess_content_type(decoded_path);
  • if ((fd = open(whole_path, O_RDONLY)) < 0)
  • {
  • perror("open");
  • goto err;
  • }
  • if (fstat(fd, &st) < 0)
  • {
  • /* Make sure the length still matches, now that we opened the file :/ */
  • perror("fstat");
  • goto err;
  • }
  • evhttp_add_header(evhttp_request_get_output_headers(req),
  • "Content-Type", type);
  • evbuffer_add_file(evb, fd, 0, st.st_size);
  • }
  • evhttp_send_reply(req, 200, "OK", evb);
  • goto done;
  • err:
  • evhttp_send_error(req, 404, "Document was not found");
  • if (fd >= 0)
  • {
  • close(fd);
  • }
  • done:
  • if (decoded)
  • {
  • evhttp_uri_free(decoded);
  • }
  • if (decoded_path)
  • {
  • free(decoded_path);
  • }
  • if (whole_path)
  • {
  • free(whole_path);
  • }
  • if (evb)
  • {
  • evbuffer_free(evb);
  • }
  • }
  • void syntax(void)
  • {
  • fprintf(stdout, "Syntax: http-server <docroot>\n");
  • }
  • int main(int argc, char **argv)
  • {
  • struct event_base *base;
  • struct evhttp *http;
  • struct evhttp_bound_socket *handle;
  • int port = 0;
  • if (signal(SIGPIPE, SIG_IGN) == SIG_ERR)
  • {
  • printf("signal error, errno[%d], error[%s]", errno, strerror(errno));
  • return -1;
  • }
  • if (argc < 2)
  • {
  • syntax();
  • return -1;
  • }
  • base = event_base_new();
  • if (!base)
  • {
  • printf("Couldn't create an event_base:exiting\n");
  • return -1;
  • }
  • /* Create a new http oject to handle request */
  • http = evhttp_new(base);
  • if (!http)
  • {
  • printf("Couldn't create evhttp.Exiting\n");
  • return -1;
  • }
  • /* The /dump URI will dump all requests to stdout and say 200 ok */
  • evhttp_set_cb(http, "/dump", dump_request_cb, NULL);
  • /* We want to accept arbitrary requests, so we need to set a "generic" cb
  • * We can also add callbacks for specific paths */
  • evhttp_set_gencb(http, send_document_cb, argv[1]);
  • /* Now we teel the evhttp what port to listen on */
  • handle = evhttp_bind_socket_with_handle(http, "0.0.0.0", port);
  • if (!handle)
  • {
  • printf("Couldn't bind to port[%d], exiting\n", port);
  • return -1;
  • }
  • {
  • /* Extract and display the address we're listening on. */
  • struct sockaddr_storage ss;
  • evutil_socket_t fd;
  • ev_socklen_t socklen = sizeof(ss);
  • char addrbuf[128];
  • void *inaddr;
  • const char *addr;
  • int got_port = -1;
  • fd = evhttp_bound_socket_get_fd(handle);
  • memset(&ss, 0, sizeof(ss));
  • if (getsockname(fd, (struct sockaddr *)&ss, &socklen))
  • {
  • perror("getsockname() failed");
  • return -1;
  • }
  • if (ss.ss_family == AF_INET)
  • {
  • got_port = ntohs(((struct sockaddr_in*)&ss)->sin_port);
  • inaddr = &((struct sockaddr_in*)&ss)->sin_addr;
  • }
  • else if (ss.ss_family == AF_INET6)
  • {
  • got_port = ntohs(((struct sockaddr_in6*)&ss)->sin6_port);
  • inaddr = &((struct sockaddr_in6*)&ss)->sin6_addr;
  • }
  • else
  • {
  • printf("Weird address family\n");
  • return 1;
  • }
  • addr = evutil_inet_ntop(ss.ss_family, inaddr, addrbuf, sizeof(addrbuf));
  • if (addr)
  • {
  • printf("Listening on %s:%d\n", addr, got_port);
  • evutil_snprintf(uri_root, sizeof(uri_root), "http://%s:%d", addr, got_port);
  • }
  • else
  • {
  • printf("evutil_inet_ntop failed\n");
  • return -1;
  • }
  • }
  • event_base_dispatch(base);
  • return 0;
  • }

下面就通过分析这个例子来理解evhttp对象的使用与实现:

1、首先介绍一个这段代码里面的几个函数及其作用:

1)guess_content_type:传入请求的路径,返回文件类型(根据请求资源的后缀名返回响应的MIME类型)

2)dump_requese_cb:这个函数是当uri为/dump时的回调,操作是打印全部的请求信息。

3)send_document_cb:这个函数是通用uri的回调函数,就是将请求的资源发送给客户端(浏览器)。

4)syntax:打印用法的函数

5)main:主函数

2、调用event_base_new函数得到一个event base对象。

3、调用evhttp_new函数得到一个evhttp对象。

4、调用evhttp_set_cb、evthttp_set_gencb设置回调函数和通用回调函数。

5、调用evhttp_bind_socket_with_handle函数设置监听端口。

6、打印监听端口信息。

7、调用event_base_dispatch进入事件循环。

这里使用了一个新的类evhttp,这个也是对基本函数更高层次的封装,方便编写http相关的程序,关于这个类会在后面详细的分析,这里略过。

到这里就分析完http-server了,可以发现使用libevent提供的函数来编写一个http-server服务器是多么的简单。

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