httpd-0.1.0源码分析

httpd-0.1.0介绍

TinyHTTPd是一个轻量级的http server。可以作为初级学习Linux网络编程或者C/C++入门小程序学习。此程序为开源项目。

前期准备

我个人理解的B/S架构是： 1.server先在相应的机器上运行起来，之后server程序检测端口是否有请求。 2.浏览器这时就可以通过网络访问已经运行起来的server。我们通过浏览器访问一个网站（URL可以经过一系列的解析过程变成IP地址），会发送http请求给http 服务器，如果请求的是一个静态的页面或图片，服务器会直接返回结果给浏览器。但如果要完成一个动态的请求，比如需要查询数据库这样的操作，服务器会运行一个单独的程序来执行，这个程序处理完成后会把结果转化为服务器(或者浏览器)可以识别的格式输出。

客户端

不管是C/S还是B/S要想实现功能，server必须先运行起来。

#include <stdio.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> int main(int argc, char *argv[]) { int sockfd; int len; struct sockaddr_in address; int result; char ch = 'A'; sockfd = socket(AF_INET, SOCK_STREAM, 0); /*AF_INET（又称 PF_INET）是 IPv4 网络协议的套接字类型， AF_INET6 则是 IPv6 的；而 AF_UNIX 则是 Unix 系统本地通信。 SOCK_STREAM提供面向连接的稳定数据传输，即TCP协议。 SOCK_STREAM应用在C语言socket编程中， 在进行网络连接前，需要用socket函数向系统申请一个通信端口。 SOCK_STREAM 是数据流,一般是tcp/ip协议的编程, SOCK_DGRAM分是数据包,是udp协议网络编程。 */ address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr("127.0.0.1"); address.sin_port = htons(9734); /* struct sockaddr_in { short sin_family; //Address family一般来说AF_INET（地址族）PF_INET（协议族） unsigned short sin_port; //Port number(必须要采用网络数据格式,普通数字可以用htons()函数转换成网络数据格式的数字) struct in_addr sin_addr; // IP address in network byte order（Internet address） unsigned char sin_zero[8]; // Same size as struct sockaddr没有实际意义,只是为了　跟SOCKADDR结构在内存中对齐 }; */ len = sizeof(address); result = connect(sockfd, (struct sockaddr *)&address, len); //client if (result == -1) { perror("oops: client1"); exit(1); } write(sockfd, &ch, 1); read(sockfd, &ch, 1); printf("char from server = %c\n", ch); close(sockfd); exit(0); }

客户端程序非常简单，就是基本的流程，先创建socket，之后调用connect函数与server建立TCP连接。write和read是Linux提供的I/O函数。用来向socket输入输出数据。

服务器端

#include <stdio.h> #include <sys/socket.h> #include <sys/types.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <ctype.h> #include <strings.h> #include <string.h> #include <sys/stat.h> #include <pthread.h> #include <sys/wait.h> #include <stdlib.h> #define ISspace(x) isspace((int)(x)) #define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n" void accept_request(int); void bad_request(int); void cat(int, FILE *); void cannot_execute(int); void error_die(const char *); void execute_cgi(int, const char *, const char *, const char *); int get_line(int, char *, int); void headers(int, const char *); void not_found(int); void serve_file(int, const char *); int startup(u_short *); void unimplemented(int); /**********************************************************************/ /* A request has caused a call to accept() on the server port to * return. Process the request appropriately. * Parameters: the socket connected to the client */ /**********************************************************************/ /* TCP连接建立成功后，服务器启动一个新的线程来处理 客户端的其他请求。 服务器启动一个新的线程来处理客户端的请求(accept_request)， 处理完成后，重新等待新的客户端请求。 */ void accept_request(int client) { char buf[1024]; int numchars; char method[255]; char url[255]; char path[512]; size_t i, j; struct stat st; int cgi = 0; /* becomes true if server decides this is a CGI * program */ char *query_string = NULL; numchars = get_line(client, buf, sizeof(buf)); //从线程中获取数据 i = 0; j = 0; while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) { method[i] = buf[j]; i++; j++; } method[i] = '\0'; /* 一个HTTP请求报文由 请求行（requestline）、请求头部（header）、 空行和请求数据4个部分组成， 请求行由请求方法字段(get或post)、URL字段 和HTTP协议版本字段3个字段组成，它们用空格分隔。 例如，GET /index.html HTTP/1.1。 上面这段代码就是解析请求行， 把方法字段保存在method变量中。 */ if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) //忽略大小写比较字符串 { unimplemented(client); //将一个网页发给客户端 return; } if (strcasecmp(method, "POST") == 0) cgi = 1; i = 0; while (ISspace(buf[j]) && (j < sizeof(buf))) //判断字符是否为空格字符 j++; while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) { //不是空格 i没有到url末尾时 url[i] = buf[j]; i++; j++; } url[i] = '\0'; /* 如果是get方法，请求参数和对应的值附加在URL后面, 利用一个问号（"?"）代表URL的结尾与请求参数的开始， 传递参数长度受限制。例如，/index.jsp?10023 其中10023就是要传递的参数。 这段代码把参数保存在query_string中。 */ if (strcasecmp(method, "GET") == 0) { query_string = url; while ((*query_string != '?') && (*query_string != '\0')) query_string++; if (*query_string == '?') { cgi = 1; *query_string = '\0'; query_string++; } } /* 这段代码保存有效的url地址并加上请求地址的主页索引。 默认的根目录是在htdocs下。 */ sprintf(path, "htdocs%s", url); if (path[strlen(path) - 1] == '/') strcat(path, "index.html"); if (stat(path, &st) == -1) { while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ numchars = get_line(client, buf, sizeof(buf)); not_found(client); } else { if ((st.st_mode & S_IFMT) == S_IFDIR) strcat(path, "/index.html"); if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH) ) cgi = 1; if (!cgi) serve_file(client, path); else execute_cgi(client, path, method, query_string); } close(client); } /**********************************************************************/ /* Inform the client that a request it has made has a problem. * Parameters: client socket */ /**********************************************************************/ void bad_request(int client) { char buf[1024]; sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n"); send(client, buf, sizeof(buf), 0); sprintf(buf, "Content-type: text/html\r\n"); send(client, buf, sizeof(buf), 0); sprintf(buf, "\r\n"); send(client, buf, sizeof(buf), 0); sprintf(buf, "<P>Your browser sent a bad request, "); send(client, buf, sizeof(buf), 0); sprintf(buf, "such as a POST without a Content-Length.\r\n"); send(client, buf, sizeof(buf), 0); } /**********************************************************************/ /* Put the entire contents of a file out on a socket. This function * is named after the UNIX "cat" command, because it might have been * easier just to do something like pipe, fork, and exec("cat"). * Parameters: the client socket descriptor * FILE pointer for the file to cat */ /**********************************************************************/ void cat(int client, FILE *resource) { char buf[1024]; fgets(buf, sizeof(buf), resource); while (!feof(resource)) { send(client, buf, strlen(buf), 0); fgets(buf, sizeof(buf), resource); } } /**********************************************************************/ /* Inform the client that a CGI script could not be executed. * Parameter: the client socket descriptor. */ /**********************************************************************/ void cannot_execute(int client) { char buf[1024]; sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "Content-type: text/html\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "<P>Error prohibited CGI execution.\r\n"); send(client, buf, strlen(buf), 0); } /**********************************************************************/ /* Print out an error message with perror() (for system errors; based * on value of errno, which indicates system call errors) and exit the * program indicating an error. */ /**********************************************************************/ void error_die(const char *sc) { perror(sc); exit(1); } /**********************************************************************/ /* Execute a CGI script. Will need to set environment variables as * appropriate. * Parameters: client socket descriptor * path to the CGI script */ /**********************************************************************/ void execute_cgi(int client, const char *path, const char *method, const char *query_string) { char buf[1024]; int cgi_output[2]; int cgi_input[2]; pid_t pid; int status; int i; char c; int numchars = 1; int content_length = -1; buf[0] = 'A'; buf[1] = '\0'; if (strcasecmp(method, "GET") == 0) while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ numchars = get_line(client, buf, sizeof(buf)); else /* POST */ { numchars = get_line(client, buf, sizeof(buf)); while ((numchars > 0) && strcmp("\n", buf)) { buf[15] = '\0'; if (strcasecmp(buf, "Content-Length:") == 0) content_length = atoi(&(buf[16])); numchars = get_line(client, buf, sizeof(buf)); } if (content_length == -1) { bad_request(client); return; } } sprintf(buf, "HTTP/1.0 200 OK\r\n"); send(client, buf, strlen(buf), 0); if (pipe(cgi_output) < 0) { cannot_execute(client); return; } if (pipe(cgi_input) < 0) { cannot_execute(client); return; } if ( (pid = fork()) < 0 ) { cannot_execute(client); return; } if (pid == 0) /* child: CGI script */ { char meth_env[255]; char query_env[255]; char length_env[255]; dup2(cgi_output[1], 1); dup2(cgi_input[0], 0); close(cgi_output[0]); close(cgi_input[1]); sprintf(meth_env, "REQUEST_METHOD=%s", method); putenv(meth_env); if (strcasecmp(method, "GET") == 0) { sprintf(query_env, "QUERY_STRING=%s", query_string); putenv(query_env); } else { /* POST */ sprintf(length_env, "CONTENT_LENGTH=%d", content_length); putenv(length_env); } execl(path, path, NULL); exit(0); } else { /* parent */ close(cgi_output[1]); close(cgi_input[0]); if (strcasecmp(method, "POST") == 0) for (i = 0; i < content_length; i++) { recv(client, &c, 1, 0); write(cgi_input[1], &c, 1); } while (read(cgi_output[0], &c, 1) > 0) send(client, &c, 1, 0); close(cgi_output[0]); close(cgi_input[1]); waitpid(pid, &status, 0); } } /**********************************************************************/ /* Get a line from a socket, whether the line ends in a newline, * carriage return, or a CRLF combination. Terminates the string read * with a null character. If no newline indicator is found before the * end of the buffer, the string is terminated with a null. If any of * the above three line terminators is read, the last character of the * string will be a linefeed and the string will be terminated with a * null character. * Parameters: the socket descriptor * the buffer to save the data in * the size of the buffer * Returns: the number of bytes stored (excluding null) */ /**********************************************************************/ int get_line(int sock, char *buf, int size) // 1024 { int i = 0; char c = '\0'; int n; while ((i < size - 1) && (c != '\n')) { n = recv(sock, &c, 1, 0); /* DEBUG printf("X\n", c); */ if (n > 0) { if (c == '\r') { n = recv(sock, &c, 1, MSG_PEEK); /* DEBUG printf("X\n", c); */ if ((n > 0) && (c == '\n')) recv(sock, &c, 1, 0); else c = '\n'; } buf[i] = c; i++; } else c = '\n'; } buf[i] = '\0'; return(i); } /**********************************************************************/ /* Return the informational HTTP headers about a file. */ /* Parameters: the socket to print the headers on * the name of the file */ /**********************************************************************/ void headers(int client, const char *filename) { char buf[1024]; (void)filename; /* could use filename to determine file type */ strcpy(buf, "HTTP/1.0 200 OK\r\n"); send(client, buf, strlen(buf), 0); strcpy(buf, SERVER_STRING); send(client, buf, strlen(buf), 0); sprintf(buf, "Content-Type: text/html\r\n"); send(client, buf, strlen(buf), 0); strcpy(buf, "\r\n"); send(client, buf, strlen(buf), 0); } /**********************************************************************/ /* Give a client a 404 not found status message. */ /**********************************************************************/ void not_found(int client) { char buf[1024]; sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, SERVER_STRING); send(client, buf, strlen(buf), 0); sprintf(buf, "Content-Type: text/html\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "<BODY><P>The server could not fulfill\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "your request because the resource specified\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "is unavailable or nonexistent.\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "</BODY></HTML>\r\n"); send(client, buf, strlen(buf), 0); } /**********************************************************************/ /* Send a regular file to the client. Use headers, and report * errors to client if they occur. * Parameters: a pointer to a file structure produced from the socket * file descriptor * the name of the file to serve */ /**********************************************************************/ void serve_file(int client, const char *filename) { FILE *resource = NULL; int numchars = 1; char buf[1024]; buf[0] = 'A'; buf[1] = '\0'; while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ numchars = get_line(client, buf, sizeof(buf)); resource = fopen(filename, "r"); if (resource == NULL) not_found(client); else { headers(client, filename); cat(client, resource); } fclose(resource); } /**********************************************************************/ /* This function starts the process of listening for web connections * on a specified port. If the port is 0, then dynamically allocate a * port and modify the original port variable to reflect the actual * port. * Parameters: pointer to variable containing the port to connect on * Returns: the socket */ /**********************************************************************/ /*程序创建一个服务器socket对象，然后绑写(bind)， 并监听指定的端口(listen)，这些动作都是在startup函数实现的。 这些也是Linux建立TCP连接的基本准备。 有一个细节稍微注意一下，如果传来的端口是0, 程序会随机分配一个监听的端口。 并通过指向port变量的地址返回该值。 */ int startup(u_short *port) { int httpd = 0; struct sockaddr_in name; httpd = socket(PF_INET, SOCK_STREAM, 0); if (httpd == -1) error_die("socket"); memset(&name, 0, sizeof(name)); //内存清空 name.sin_family = AF_INET; //IPv4 name.sin_port = htons(*port); //端口号 name.sin_addr.s_addr = htonl(INADDR_ANY); //INADDR_ANY就是指定地址为0.0.0.0的地址，这个地址事实上表示不确定地址，或“所有地址”、“任意地址”。 一般来说，在各个系统中均定义成为0值。 if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0) error_die("bind"); if (*port == 0) /* if dynamically allocating a port */ { int namelen = sizeof(name); if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1) // 获得套接字名称 error_die("getsockname"); *port = ntohs(name.sin_port); } if (listen(httpd, 5) < 0) error_die("listen"); return(httpd); } /**********************************************************************/ /* Inform the client that the requested web method has not been * implemented. * Parameter: the client socket */ /**********************************************************************/ void unimplemented(int client) { char buf[1024]; sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, SERVER_STRING); send(client, buf, strlen(buf), 0); sprintf(buf, "Content-Type: text/html\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "</TITLE></HEAD>\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n"); send(client, buf, strlen(buf), 0); sprintf(buf, "</BODY></HTML>\r\n"); send(client, buf, strlen(buf), 0); } /**********************************************************************/ int main(void) { int server_sock = -1; u_short port = 0; int client_sock = -1; struct sockaddr_in client_name; int client_name_len = sizeof(client_name); pthread_t newthread; server_sock = startup(&port); //初始化 printf("httpd running on port %d\n", port); while (1) { /*套接字收到客户端连接请求*/ client_sock = accept(server_sock, (struct sockaddr *)&client_name, &client_name_len);//新的socket来完成数据传输的任务， if (client_sock == -1) error_die("accept"); /*派生新线程用accept_request 函数处理新请求*/ /* accept_request(client_sock); */ if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0) // 线程开启 perror("pthread_create"); } close(server_sock); return(0); }

服务器程序也是先创建socket，之后调用startup函数初始化端口，然后服务器会在accpet函数阻塞。 当客户端的TCP连接请求到达时，accpet函数返回一个新的专用于数据传输的socket。此后服务器读写数据都是通过新的socket。 之后服务器程序开启一个线程负责这个TCP连接的数据传输。 accept_request函数会回应客户端的http请求，cat函数将读到的内容作为http响应报文的数据部分发送回客户端。