基於Libevent的HTTP Server
阿新 • • 發佈：2019-01-30
簡單的Http Server
使用Libevent內建的http相關介面，可以很容易的構建一個Http Server，一個簡單的Http Server如下：
#include <event2/event.h> #include <event2/buffer.h> #include <event2/http.h> #include <Winsock2.h> #include <stdlib.h> #include <stdio.h> int init_win_socket() { WSADATA wsaData;if(WSAStartup(MAKEWORD(2,2) , &wsaData) != 0) { return -1; } return 0; } void generic_handler(struct evhttp_request *req, void *arg) { struct evbuffer *buf = evbuffer_new(); if(!buf) { puts("failed to create response buffer \n"); return; } evbuffer_add_printf(buf,"Server Responsed. Requested: %s\n", evhttp_request_get_uri(req)); evhttp_send_reply(req, HTTP_OK, "OK", buf); evbuffer_free(buf); } int main(int argc, char* argv[]) { #ifdef WIN32 init_win_socket(); #endif short http_port = 8081; char *http_addr = "127.0.0.1";struct event_base * base = event_base_new(); struct evhttp * http_server = evhttp_new(base); if(!http_server) { return -1; } int ret = evhttp_bind_socket(http_server,http_addr,http_port); if(ret!=0) { return -1; } evhttp_set_gencb(http_server, generic_handler, NULL); printf("http server start OK! \n"); event_base_dispatch(base); evhttp_free(http_server); WSACleanup(); return 0; }
通過Libevent的介面構建一個Http Server的過程如下：
（1）初始化：在event_base上新建一個evhttp，將這個evhttp繫結到監聽的IP和埠號。
（2）設定Http回撥函式：使用evhttp_set_gencb設定Http Server的處理請求的回撥函式。
（3）啟動Http Server：等待請求進入事件迴圈。
在Http Server中使用定時器提供更新服務
#include <event2/event.h> #include <event2/buffer.h> #include <event2/http.h> #include <sys/stat.h> #include <Winsock2.h> #include <assert.h> #include <string.h> #include <stdlib.h> #include <stdio.h> #define DEFAULT_FILE "F:\\Libevent\\LibeventTest\\Debug\\sample.txt" char *filedata; time_t lasttime = 0; char filename[80]; int counter = 0; struct event *loadfile_event; struct timeval tv; void read_file() { unsigned long size = 0; char *data; struct stat buf; if(stat(filename,&buf)<0) { printf("Read file error! \n"); return; } if (buf.st_mtime > lasttime) { if (counter++) fprintf(stderr,"Reloading file: %s",filename); else fprintf(stderr,"Loading file: %s",filename); FILE *f = fopen(filename, "rb"); if (f == NULL) { fprintf(stderr,"Couldn't open file\n"); return; } size = buf.st_size; filedata = (char *)malloc(size+1); memset(filedata,0,size+1); fread(filedata, sizeof(char), size, f); fclose(f); fprintf(stderr," (%d bytes)\n",size); lasttime = buf.st_mtime; } } void read_file_timer_cb(evutil_socket_t listener, short event, void *arg) { if (!evtimer_pending(loadfile_event, NULL)) { event_del(loadfile_event); evtimer_add(loadfile_event, &tv); } read_file(); } void load_file(struct event_base * base) { tv.tv_sec = 5; tv.tv_usec = 0; //loadfile_event = malloc(sizeof(struct event)); loadfile_event = evtimer_new(base,read_file_timer_cb,NULL); //evtimer_set(loadfile_event,load_file,loadfile_event); evtimer_add(loadfile_event,&tv); } void generic_handler(struct evhttp_request *req, void *arg) { struct evbuffer *buf = evbuffer_new(); if(!buf) { puts("failed to create response buffer \n"); return; } evbuffer_add_printf(buf,"%s",filedata); evhttp_send_reply(req, HTTP_OK, "OK", buf); evbuffer_free(buf); } int init_win_socket() { WSADATA wsaData; if(WSAStartup(MAKEWORD(2,2) , &wsaData) != 0) { return -1; } return 0; } int main(int argc, char* argv[]) { #ifdef WIN32 init_win_socket(); #endif short http_port = 8081; char *http_addr = "127.0.0.1"; if (argc > 1) { strcpy(filename,argv[1]); printf("Using %s\n",filename); } else { strcpy(filename,DEFAULT_FILE); } struct event_base * base = event_base_new(); struct evhttp * http_server = evhttp_new(base); if(!http_server) { return -1; } int ret = evhttp_bind_socket(http_server,http_addr,http_port); if(ret!=0) { return -1; } evhttp_set_gencb(http_server, generic_handler, NULL); read_file(); load_file(base); printf("http server start OK! \n"); event_base_dispatch(base); evhttp_free(http_server); WSACleanup(); return 0; }
在這個Http Server中提供了一個每5秒觸發一次的定時器，讀取一個檔案，如果這個檔案被更新過，則讀取更新後的內容。
當訪問這個Http Server時，提供這個檔案中最新的內容。
多執行緒的Http Server
在上面的Http Server中，處理Http請求的回撥函式generic_handler和定時器讀取檔案的回撥函式read_file_timer_cb都在同一個event_base的dispatch中，並且都在同一個程序中，使用多執行緒可以改善程式的效能，下面是一個來自網路的多執行緒Http Server：
#include <event.h> #include <evhttp.h> #include <pthread.h> #include <errno.h> #include <string.h> #include <fcntl.h> #include <sys/socket.h> #include <sys/types.h> #include <netinet/in.h> int httpserver_bindsocket(int port, int backlog); int httpserver_start(int port, int nthreads, int backlog); void* httpserver_Dispatch(void *arg); void httpserver_GenericHandler(struct evhttp_request *req, void *arg); void httpserver_ProcessRequest(struct evhttp_request *req); int httpserver_bindsocket(int port, int backlog) { int r; int nfd; nfd = socket(AF_INET, SOCK_STREAM, 0); if (nfd < 0) return -1; int one = 1; r = setsockopt(nfd, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(int)); struct sockaddr_in addr; memset(&addr, 0, sizeof(addr)); addr.sin_family = AF_INET; addr.sin_addr.s_addr = INADDR_ANY; addr.sin_port = htons(port); r = bind(nfd, (struct sockaddr*)&addr, sizeof(addr)); if (r < 0) return -1; r = listen(nfd, backlog); if (r < 0) return -1; int flags; if ((flags = fcntl(nfd, F_GETFL, 0)) < 0 || fcntl(nfd, F_SETFL, flags | O_NONBLOCK) < 0) return -1; return nfd; } int httpserver_start(int port, int nthreads, int backlog) { int r, i; int nfd = httpserver_bindsocket(port, backlog); if (nfd < 0) return -1; pthread_t ths[nthreads]; for (i = 0; i < nthreads; i++) { struct event_base *base = event_init(); if (base == NULL) return -1; struct evhttp *httpd = evhttp_new(base); if (httpd == NULL) return -1; r = evhttp_accept_socket(httpd, nfd); if (r != 0) return -1; evhttp_set_gencb(httpd, httpserver_GenericHandler, NULL); r = pthread_create(&ths[i], NULL, httpserver_Dispatch, base); if (r != 0) return -1; } for (i = 0; i < nthreads; i++) { pthread_join(ths[i], NULL); } } void* httpserver_Dispatch(void *arg) { event_base_dispatch((struct event_base*)arg); return NULL; } void httpserver_GenericHandler(struct evhttp_request *req, void *arg) { httpserver_ProcessRequest(req); } void httpserver_ProcessRequest(struct evhttp_request *req) { struct evbuffer *buf = evbuffer_new(); if (buf == NULL) return; //here comes the magic } int main(void) { httpserver_start(80, 10, 10240); }
上面的程式碼基於Libevent 1.X版本的，不過很容易很看懂：在一個監聽socket上建立了多個event_base例項和evhttp例項，在不同的執行緒中排程不同的event_base，繼而可以在不同的執行緒中處理http請求。
這裡還有一個基於Libevent的多執行緒Http Server：https://sourceforge.net/projects/libevent-thread/，看原始碼處理的過程和上面類似，只是每次在監聽的socket上accept一個連線請求時，將對應的處理放到一個工作佇列裡，在佇列裡由多執行緒處理相應的回撥函式。