httpd.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <pthread.h>
#include <unistd.h>
#include <stdint.h>
#include <arpa/inet.h>

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"

void accept_request(void*);
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);

int main(void) {
    int       listenfd, connfd;
    u_short   port = 4000;
    pthread_t newthread;

    listenfd = startup(&port);
    printf("httpd running on port %d\n", port);

    while (1) {
        connfd = accept(listenfd, NULL, NULL);
        if (connfd == -1)
            error_die("accept");
        else
            printf("accept success\n");
        if (pthread_create(&newthread, NULL, (void*)accept_request,
                           (void*)(intptr_t)connfd)
            != 0)
            perror("pthread_create");
    }

    close(listenfd);

    return (0);
}

// 获取一个bind成功的listenfd
int startup(u_short* port) {
    int                httpd;
    int                on = 1;
    struct sockaddr_in name;

    httpd = socket(AF_INET, SOCK_STREAM, 0);
    if (httpd == -1) error_die("socket");

    memset(&name, 0, sizeof(name));
    name.sin_family      = AF_INET;
    name.sin_port        = htons(*port);
    name.sin_addr.s_addr = htonl(INADDR_ANY);    // INADDR_ANY: 通配地址

    if ((setsockopt(httpd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))) < 0)
        error_die("setsockopt failed");

    if (bind(httpd, (struct sockaddr*)&name, sizeof(name)) < 0)
        error_die("bind");

    // 如果传入的端口号是0，程序会随机分配一个监听端口，并用port指向该值
    if (*port == 0) {
        int namelen = sizeof(name);
        if (getsockname(httpd, (struct sockaddr*)&name, (socklen_t*)&namelen)
            == -1)
            error_die("getsockname");
        *port = ntohs(name.sin_port);
    }

    if (listen(httpd, 5) == -1) error_die("listen");

    return (httpd);
}

// 线程主函数
void accept_request(void* arg) {
    int         client = (intptr_t)arg;
    char        buf[1024];
    size_t      numchars;
    char        method[255];
    char        url[255];
    char        path[512];
    size_t      i = 0, j = 0;
    struct stat st;
    int         cgi = 0;

    char* query_string = NULL;

    // 一个HTTP请求报文：请求行、请求头部、空行、请求数据
    // 请求行：请求方法字段(get/post)、URL字段、HTTP协议版本字段，如：GET /index.html HTTP/1.1
    numchars =
            get_line(client, buf,
                     sizeof(buf));    // 从与客户端连接的套接字中读一行到buf中

    // 将方法字段保存到method中
    while (!isspace(buf[i]) && (i < sizeof(method) - 1)) {
        method[i] = buf[i];
        i++;
    }
    j         = i;
    method[i] = '\0';

    // 请求方法不支持
    if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {
        unimplemented(client);
        return;
    }

    //
    if (strcasecmp(method, "POST") == 0) cgi = 1;

    // 解析URL字段，保存在url[]中
    i = 0;
    while (isspace(buf[j]) && (j < numchars)) j++;
    while (!isspace(buf[j]) && (i < sizeof(url) - 1) && (j < numchars)) {
        url[i] = buf[j];
        i++;
        j++;
    }
    url[i] = '\0';

    // 如果是GET方法，解析URL结尾 ? 后的的参数值，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++;
        }
    }

    // 将url地址加上请求地址的主页索引，保存在path[]中
    sprintf(path, "htdocs%s", url);
    if (path[strlen(path) - 1] == '/') strcat(path, "index.html");

    // 如果路径不存在，
    if (stat(path, &st) == -1) {
        while ((numchars > 0) && strcmp("\n", buf))    // 忽略请求头部
            numchars = get_line(client, buf, sizeof(buf));
        not_found(client);
    }
    //如果路径存在，提供文件或调用CGI程序处理
    else {
        if ((st.st_mode & S_IFMT)
            == S_IFDIR)    // 文件类型为目录时末尾添加/index.html
            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);
}

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))
        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);
}

void headers(int client, const char* filename) {
    char buf[1024];
    (void)filename;

    strcpy(buf, "HTTP/1.0 200 OK\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);
}

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);
    }
}

void execute_cgi(int client, const char* path, const char* method,
                 const char* query_string) {
    char  buf[1025];
    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))
            numchars = get_line(client, buf, sizeof(buf));
    else if (strcasecmp(method, "POST") == 0) {
        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;
        }
    } else {
    }

    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;
    }

    sprintf(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);
    if (pid == 0) {
        char meth_env[255];
        char query_env[255];
        char length_env[255];

        dup2(cgi_output[1], STDOUT_FILENO);
        dup2(cgi_input[0], STDIN_FILENO);
        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 {
            sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
            putenv(length_env);
        }
        execl(path, "", NULL);
        exit(0);
    } else {
        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);
    }
}

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);
}

int get_line(int sock, char* buf, int size) {
    int  i = 0;
    char c = '\0';
    int  n;

    while ((i < size - 1) && (c != '\n')) {
        n = recv(sock, &c, 1, 0);
        if (n > 0) {
            if (c == '\r') {
                n = recv(sock, &c, 1, MSG_PEEK);
                if ((n > 0) && (c == '\n'))
                    recv(sock, &c, 1, 0);
                else
                    c = '\n';
            }
            buf[i] = c;
            i++;
        } else
            c = '\0';
    }
    buf[i] = '\0';

    return (i);
}

void cannot_execute(int client) {
    char buf[1024];

    sprintf(buf, "HTTP/1.0 500 Internal Server Error\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>Error prohibited CGI execution.\r\n");
    send(client, buf, sizeof(buf), 0);
}

void unimplemented(int client) {
    char buf[1024];

    sprintf(buf, "HTTP/1.0 501 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><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);
}

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);
}

void error_die(const char* sc) {
    perror(sc);
    exit(1);
}