时间：2021-07-01 10:21:17 帮助过：22人阅读
HTTP协议的作用原理
连接：Web浏览器与Web服务器建立连接，打开一个称为socket（套接字）的虚拟文件，此文件的建立标志着连接建立成功。应答：Web浏览器提交请求后，通过HTTP协议传送给Web服务器。Web服务器接到后，进行事务处理，处理结果又通过HTTP传回给Web浏览器，从而在Web浏览器上显示出所请求的页面。
然后返回 网页内容到客户端，客户端更具 Conntent-Type 来解析
其实Web服务器也就是一个一般的Socket的服务器，只不过它遵守HTTP协议来实现的罢了
//// server.c//// David J. Malan// malan@harvard.edu//// feature test macro requirements#define _GNU_SOURCE#define _XOPEN_SOURCE 700#define _XOPEN_SOURCE_EXTENDED// limits on an HTTP request's size, based on Apache's// http://httpd.apache.org/docs/2.2/mod/core.html#define LimitRequestFields 50#define LimitRequestFieldSize 4094#define LimitRequestLine 8190// number of octets for buffered reads#define OCTETS 512// header files#include#include #include #include #include #include #include #include #include #include #include // typestypedef char octet;// prototypesbool connected(void);bool error(unsigned short code);void handler(int signal);ssize_t load(void);const char* lookup(const char* extension);ssize_t parse(void);void reset(void);void start(short port, const char* path);void stop(void);// server's rootchar* root = NULL;// file descriptor for socketsint cfd = -1, sfd = -1;// buffer for requestoctet* request = NULL;// FILE pointer for filesFILE* file = NULL;// buffer for response-bodyoctet* body = NULL;int main(int argc, char* argv[]){ // a global variable defined in errno.h that's "set by system // calls and some library functions [to a nonzero value] // in the event of an error to indicate what went wrong" errno = 0; // default to a random port int port = 0; // usage const char* usage = "Usage: server [-p port] /path/to/root"; // parse command-line arguments int opt; while ((opt = getopt(argc, argv, "hp:")) != -1) { switch (opt) { // -h case 'h': printf("%s\n", usage); return 0; // -p port case 'p': port = atoi(optarg); break; } } // ensure port is a non-negative short and path to server's root is specified if (port < 0 || port > SHRT_MAX || argv[optind] == NULL || strlen(argv[optind]) == 0) { // announce usage printf("%s\n", usage); // return 2 just like bash's builtins return 2; } // start server start(port, argv[optind]); // listen for SIGINT (aka control-c) signal(SIGINT, handler); // accept connections one at a time while (true) { // reset server's state reset(); // wait until client is connected if (connected()) { // parse client's HTTP request ssize_t octets = parse(); if (octets == -1) { continue; } // extract request's request-line // http://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html const char* haystack = request; char* needle = strstr(haystack, "\r\n"); if (needle == NULL) { error(400); continue; } else if (needle - haystack + 2 > LimitRequestLine) { error(414); continue; } char line[needle - haystack + 2 + 1]; strncpy(line, haystack, needle - haystack + 2); line[needle - haystack + 2] = '\0'; // log request-line printf("\n%s", line); // TODO: validate request-line char* method = line; char* request_target; char* version; char* absolute_path; char* s1; s1 = strstr (line," "); if (s1 == NULL || (version = strstr(s1 + 1, " ")) == NULL || strncmp(line + sizeof(line) - 2, "\r\n", 2) == 0) { error(400); continue; } request_target = strdup(s1 + 1); request_target[version - s1 - 1] = '\0'; //printf("request_target is %s, version is %s", request_target, version); if (strncmp(method,"GET",3) != 0) { error(405); continue; } if (strncmp(request_target, "/", 1) != 0) { error(501); continue; } if (strchr(request_target, '\"') != NULL) { error(400); continue; } if (strncmp (version + 1,"HTTP/1.1",8) != 0) { error(505); continue; } if (strchr(request_target, '.') == NULL) { error(501); continue; } // TODO: extract query from request-target char *query = strchr(request_target, '?'); if (query == NULL) query = ""; else query = query + 1; //printf("query is %s\n", query); // TODO: concatenate root and absolute-path absolute_path = strdup(request_target);// printf("%s. %d\n", absolute_path, query-request_target); if (strcmp(query, "") != 0) absolute_path[query - request_target - 1] = '\0'; //printf("absolute path is %s\n", absolute_path); char *path = (char*)malloc(1000); strcpy(path, root);// strcat(path, "/"); strcat(path, absolute_path); //printf("path is %s\n", path); // TODO: ensure path exists if (access(path, F_OK) == -1) { error(404); continue; } // TODO: ensure path is readable if (access(path, R_OK) == -1) { error(403); continue; } // TODO: extract path's extension char* extension; if ((extension = strrchr(absolute_path, '.')) == NULL) { error(501); continue; } extension = extension + 1; //printf("extension is %s\n", extension); // dynamic content if (strcasecmp("php", extension) == 0) { // open pipe to PHP interpreter char* format = "QUERY_STRING=\"%s\" REDIRECT_STATUS=200 SCRIPT_FILENAME=\"%s\" php-cgi"; char command[strlen(format) + (strlen(path) - 2) + (strlen(query) - 2) + 1]; sprintf(command, format, query, path); file = popen(command, "r"); if (file == NULL) { error(500); continue; } // load file ssize_t size = load(); if (size == -1) { error(500); continue; } // subtract php-cgi's headers from body's size to get content's length haystack = body; needle = memmem(haystack, size, "\r\n\r\n", 4); if (needle == NULL) { error(500); continue; } size_t length = size - (needle - haystack + 4); // respond to client if (dprintf(cfd, "HTTP/1.1 200 OK\r\n") < 0) { continue; } if (dprintf(cfd, "Connection: close\r\n") < 0) { continue; } if (dprintf(cfd, "Content-Length: %i\r\n", length) < 0) { continue; } if (write(cfd, body, size) == -1) { continue; } } // static content else { // look up file's MIME type const char* type = lookup(extension); if (type == NULL) { error(501); continue; } // open file file = fopen(path, "r"); if (file == NULL) { error(500); continue; } // load file ssize_t length = load(); if (length == -1) { error(500); continue; } // TODO: respond to client // respond with Status-Line dprintf(cfd, "HTTP/1.1 200 OK\r\n"); // respond with Connection header dprintf(cfd, "Connection: close\r\n"); // respond with Content-Length header dprintf(cfd, "Content-Length: %i\r\n", length); // respond with Content-Type header dprintf(cfd, "Content-Type: text/html\r\n"); // respond with CRLF dprintf(cfd, "\r\n"); write(cfd, body, length); } // announce OK printf("\033[32m"); printf("HTTP/1.1 200 OK"); printf("\033[39m\n"); } }}/** * Accepts a connection from a client, blocking (i.e., waiting) until one is heard. * Upon success, returns true; upon failure, returns false. */bool connected(void){ struct sockaddr_in cli_addr; memset(&cli_addr, 0, sizeof(cli_addr)); socklen_t cli_len = sizeof(cli_addr); cfd = accept(sfd, (struct sockaddr*) &cli_addr, &cli_len); if (cfd == -1) { return false; } return true;}/** * Handles client errors (4xx) and server errors (5xx). */bool error(unsigned short code){ // ensure client's socket is open if (cfd == -1) { return false; } // ensure code is within range if (code < 400 || code > 599) { return false; } // determine Status-Line's phrase // http://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html#sec6.1 const char* phrase = NULL; switch (code) { case 400: phrase = "Bad Request"; break; case 403: phrase = "Forbidden"; break; case 404: phrase = "Not Found"; break; case 405: phrase = "Method Not Allowed"; break; case 413: phrase = "Request Entity Too Large"; break; case 414: phrase = "Request-URI Too Long"; break; case 418: phrase = "I'm a teapot"; break; case 500: phrase = "Internal Server Error"; break; case 501: phrase = "Not Implemented"; break; case 505: phrase = "HTTP Version Not Supported"; break; } if (phrase == NULL) { return false; } // template char* template = " %i %s %i %s
"; char content[strlen(template) + 2 * ((int) log10(code) + 1 - 2) + 2 * (strlen(phrase) - 2) + 1]; int length = sprintf(content, template, code, phrase, code, phrase); // respond with Status-Line if (dprintf(cfd, "HTTP/1.1 %i %s\r\n", code, phrase) < 0) { return false; } // respond with Connection header if (dprintf(cfd, "Connection: close\r\n") < 0) { return false; } // respond with Content-Length header if (dprintf(cfd, "Content-Length: %i\r\n", length) < 0) { return false; } // respond with Content-Type header if (dprintf(cfd, "Content-Type: text/html\r\n") < 0) { return false; } // respond with CRLF if (dprintf(cfd, "\r\n") < 0) { return false; } // respond with message-body if (write(cfd, content, length) == -1) { return false; } // announce Response-Line printf("\033[31m"); printf("HTTP/1.1 %i %s", code, phrase); printf("\033[39m\n"); return true;}/** * Loads file into message-body. */ssize_t load(void){ // ensure file is open if (file == NULL) { return -1; } // ensure body isn't already loaded if (body != NULL) { return -1; } // buffer for octets octet buffer[OCTETS]; // read file ssize_t size = 0; while (true) { // try to read a buffer's worth of octets ssize_t octets = fread(buffer, sizeof(octet), OCTETS, file); // check for error if (ferror(file) != 0) { if (body != NULL) { free(body); body = NULL; } return -1; } // if octets were read, append to body if (octets > 0) { body = realloc(body, size + octets); if (body == NULL) { return -1; } memcpy(body + size, buffer, octets); size += octets; } // check for EOF if (feof(file) != 0) { break; } } return size;}/** * Handles signals. */void handler(int signal){ // control-c if (signal == SIGINT) { // ensure this isn't considered an error // (as might otherwise happen after a recent 404) errno = 0; // announce stop printf("\033[33m"); printf("Stopping server\n"); printf("\033[39m"); // stop server stop(); }}/** * Returns MIME type for supported extensions, else NULL. */const char* lookup(const char* extension){ // TODO if (strcasecmp(extension, "css")) return "text/css"; if (strcasecmp(extension, "html")) return "text/html"; if (strcasecmp(extension, "gif")) return "image/gif"; if (strcasecmp(extension, "ico")) return "image/x-icon"; if (strcasecmp(extension, "jpg")) return "image/jpeg"; if (strcasecmp(extension, "js")) return "text/javascript"; if (strcasecmp(extension, "png")) return "image/png"; return NULL;}/** * Parses an HTTP request. */ssize_t parse(void){ // ensure client's socket is open if (cfd == -1) { return -1; } // ensure request isn't already parsed if (request != NULL) { return -1; } // buffer for octets octet buffer[OCTETS]; // parse request ssize_t length = 0; while (true) { // read from socket ssize_t octets = read(cfd, buffer, sizeof(octet) * OCTETS); if (octets == -1) { error(500); return -1; } // if octets have been read, remember new length if (octets > 0) { request = realloc(request, length + octets); if (request == NULL) { return -1; } memcpy(request + length, buffer, octets); length += octets; } // else if nothing's been read, socket's been closed else { return -1; } // search for CRLF CRLF int offset = (length - octets < 3) ? length - octets : 3; char* haystack = request + length - octets - offset; char* needle = memmem(haystack, request + length - haystack, "\r\n\r\n", 4); if (needle != NULL) { // trim to one CRLF and null-terminate length = needle - request + 2 + 1; request = realloc(request, length); if (request == NULL) { return -1; } request[length - 1] = '\0'; break; } // if buffer's full and we still haven't found CRLF CRLF, // then request is too large if (length - 1 >= LimitRequestLine + LimitRequestFields * LimitRequestFieldSize) { error(413); return -1; } } return length;}/** * Resets server's state, deallocating any resources. */void reset(void){ // free response's body if (body != NULL) { free(body); body = NULL; } // close file if (file != NULL) { fclose(file); file = NULL; } // free request if (request != NULL) { free(request); request = NULL; } // close client's socket if (cfd != -1) { close(cfd); cfd = -1; }}/** * Starts server. */void start(short port, const char* path){ // path to server's root root = realpath(path, NULL); if (root == NULL) { stop(); } // ensure root exists if (access(root, F_OK) == -1) { stop(); } // ensure root is executable if (access(root, X_OK) == -1) { stop(); } // announce root printf("\033[33m"); printf("Using %s for server's root, size is %ld", root, sizeof(root)); printf("\033[39m\n"); // create a socket sfd = socket(AF_INET, SOCK_STREAM, 0); if (sfd == -1) { stop(); } // allow reuse of address (to avoid "Address already in use") int optval = 1; setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)); // assign name to socket struct sockaddr_in serv_addr; memset(&serv_addr, 0, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_port = htons(port); serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); if (bind(sfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1) { stop(); } // listen for connections if (listen(sfd, SOMAXCONN) == -1) { stop(); } // announce port in use struct sockaddr_in addr; socklen_t addrlen = sizeof(addr); if (getsockname(sfd, (struct sockaddr*) &addr, &addrlen) == -1) { stop(); } printf("\033[33m"); printf("Listening on port %i", ntohs(addr.sin_port)); printf("\033[39m\n");}/** * Stop server, deallocating any resources. */void stop(void){ // preserve errno across this function's library calls int errsv = errno; // reset server's state reset(); // free root, which was allocated by realpath if (root != NULL) { free(root); } // close server socket if (sfd != -1) { close(sfd); } // terminate process if (errsv == 0) { // success exit(0); } else { // announce error printf("\033[33m"); printf("%s", strerror(errsv)); printf("\033[39m\n"); // failure exit(1); }}
运行方法
./server -p 8080 public
其中public目录是存放html和php文件的