linux网络编程十二：简单模拟HTTP请求的读取和分析

最近在看《linux高性能服务器编程》，在此做个日记，以激励自己，同时分享于有需要的朋友。

1. 我们简单模拟HTTP请求的读取和分析

判断HTTP头部结束的依据是遇到一个空行，该空行仅包含一对回车换行符<CR><LF> 。如果一次读操作没有读入HTTP请求的整个头部， 即没有遇到空行， 那么我们必须等待客户继续写数据并再次读入。

因此，我们每完成一次读操作，就要分析新读入的数据中是否有空行。在寻找空行的过程中，我们可以同时完成对整个HTTP请求头部的分析，以提高效率。

2. 客户端用telnet测试

请求如下：

GET / HTTP/1.1
Host: www.xxx.com
other...

3. 代码

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <errno.h>#include <fcntl.h>#include <assert.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#define BUFFER_SIZE 4096//主状态机enum CHECK_STATE{CHECK_STATE_REQUESTLINE = 0, //当前正在分析请求行CHECK_STATE_HEADER,//当前正在分析头部字段CHECK_STATE_CONTENT};//从状态机，行的读取状态enum LINE_STATUS{LINE_OK = 0,//读到完整行LINE_BAD,//行出错LINE_OPEN//行数据不完整};//HTTP请求结果enum HTTP_CODE{NO_REQUEST,//请求不完整， 需要继续读取客户端数据GET_REQUEST,//获得了完整的客户请求BAD_REQUEST,//客户请求有语法错误FORBIDDEN_REQUEST,//客户对资源没有足够的访问权限INTERNAL_ERROR,//服务器内部错误CLOSED_CONNECTION//客户端已关闭连接};//发给客户端的应答报文（简化版）static const char *szret[] = {"I get a correct result\n", "Something wrong\n"};LINE_STATUS parse_line(char *buffer, int &checked_index, int &read_index);HTTP_CODE parse_requestline(char *szTemp, CHECK_STATE &checkstate);HTTP_CODE parse_headers(char *szTemp);HTTP_CODE parse_content(char *buffer, int &checked_index, CHECK_STATE &checkstate, int &read_index, int &start_index);int main(int argc, char **argv){if (argc != 3) {fprintf(stderr, "Usage: %s ip port\n", basename(argv[0]));return 1;}const char *ip = argv[1];int port = atoi(argv[2]);struct sockaddr_in address;bzero(&address, sizeof(address));address.sin_family = AF_INET;address.sin_port = htons(port);inet_pton(AF_INET, ip, &address.sin_addr);int listenfd = socket(PF_INET, SOCK_STREAM, 0);assert(listenfd >= 0);int reuse = 1;setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));int ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address));assert(ret != -1);ret = listen(listenfd, 5);assert(ret != -1);struct sockaddr_in client_address;socklen_t client_addrlength = sizeof(client_addrlength);int fd = accept(listenfd, (struct sockaddr*)&client_address, &client_addrlength);if (fd < 0) {printf("errno is: %d\n", errno);}else {char buffer[BUFFER_SIZE];//读缓冲区memset(buffer, '\0', BUFFER_SIZE);int data_read = 0;int read_index = 0;//当前已读取的字节数int checked_index = 0;//当前已分析完的字节数int start_line = 0;//buffer中一行的起始位置//主状态机的初始状态CHECK_STATE checkstate = CHECK_STATE_REQUESTLINE;//循环读取客户端数据并分析while (1) {data_read = recv(fd, buffer+read_index, BUFFER_SIZE-read_index, 0);if (data_read == -1) {printf("reading failed\n");break;}else if (data_read == 0) {printf("remote client has closed the connection\n");break;}read_index += data_read;//分析已读取的数据HTTP_CODE result = parse_content(buffer, checked_index, checkstate, read_index, start_line);if (result == NO_REQUEST) {//不完整请求continue;}else if (result == GET_REQUEST) {//完整请求send(fd, szret[0], strlen(szret[0]), 0);break;}else {//其它情况表示发生错误send(fd, szret[1], strlen(szret[1]), 0);break;}}close(fd);}close(listenfd);return 0;}//解析一行内容LINE_STATUS parse_line(char *buffer, int &checked_index, int &read_index){char temp;for (; checked_index < read_index; ++checked_index) {temp = buffer[checked_index];if (temp == '\r') {if ((checked_index + 1) == read_index) {return LINE_OPEN;}else if (buffer[checked_index+1] == '\n') {buffer[checked_index++] = '\0';buffer[checked_index++] = '\0';return LINE_OK;}return LINE_BAD;}else if (temp == '\n') {if (checked_index > 1 && buffer[checked_index-1] == '\r') {buffer[checked_index-1] = '\0';buffer[checked_index++] = '\0';return LINE_OK;}return LINE_BAD;}}return LINE_OPEN;}/*分析请求行 * 模拟如下： * GET / HTTP/1.1 * Host: www.baidu.com *  */HTTP_CODE parse_requestline(char *szTemp, CHECK_STATE &checkstate){char *szURL = strpbrk(szTemp, " \t");if (!szURL)return BAD_REQUEST;*szURL++ = '\0';char *szMethod = szTemp;//获取方法if (strcasecmp(szMethod, "GET") == 0)printf("The request method is GET\n");elsereturn BAD_REQUEST;szURL += strspn(szURL, " \t");char *szVersion = strpbrk(szURL, " \t");if (!szVersion)return BAD_REQUEST;*szVersion++ = '\0';szVersion += strspn(szVersion, " \t");//获取版本if (strcasecmp(szVersion, "HTTP/1.1") != 0)return BAD_REQUEST;if (strncasecmp(szURL, "http://", 7) == 0) {//获取URLszURL += 7;szURL = strchr(szURL, '/');}if (!szURL || szURL[0] != '/')return BAD_REQUEST;printf("The request URL is: %s\n", szURL);checkstate = CHECK_STATE_HEADER;return NO_REQUEST;}//分析头部字段HTTP_CODE parse_headers(char *szTemp){if (szTemp[0] == '\0') {return GET_REQUEST;//遇到空行，表示我们得到一个正确的HTTP请求}else if (strncasecmp(szTemp, "Host:", 5) == 0) {szTemp += 5;szTemp += strspn(szTemp, " \t");printf("the request host is: %s\n", szTemp);}else {//其它头部字段不处理printf("I can not handle this header\n");}return NO_REQUEST;}//分析HTTP请求HTTP_CODE parse_content(char *buffer, int &checked_index, CHECK_STATE &checkstate, int &read_index, int &start_index){LINE_STATUS linestatus = LINE_OK;//记录当前行的读取状态HTTP_CODE retcode = NO_REQUEST;//记录HTTP请求的处理结果//从buffer中取出完整行while ((linestatus = parse_line(buffer, checked_index, read_index)) == LINE_OK) {char *szTemp = buffer + start_index;//start_line是行的起始位置start_index = checked_index;//记录下一行的起始位置switch(checkstate) {case CHECK_STATE_REQUESTLINE://分析请求行{retcode = parse_requestline(szTemp, checkstate);if (retcode == BAD_REQUEST)return BAD_REQUEST;break;}case CHECK_STATE_HEADER://分析头部字段{retcode = parse_headers(szTemp);if (retcode == BAD_REQUEST) {return BAD_REQUEST;}else if(retcode == GET_REQUEST) {return GET_REQUEST;}break;}default:{return INTERNAL_ERROR;}}}if (linestatus == LINE_OPEN)//不完整行，要继续读取客户端数据才能进一步分析return NO_REQUEST;elsereturn BAD_REQUEST;return BAD_REQUEST;}