如何用C语言编写一个简单的Web服务器？

编写一个简单的Web服务器是一个有趣的项目，它可以帮助你理解网络编程的基本概念，以下是一个用C语言编写的简单Web服务器示例，这个服务器能够处理HTTP请求并返回简单的响应。

引入必要的头文件

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

定义端口和缓冲区大小

#define PORT 8080
#define BUFFER_SIZE 1024

主函数

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[BUFFER_SIZE] = {0};
    const char *hello = "HTTP/1.1 200 OK
Content-Type: text/plain
Content-Length: 12
Hello world!";
    // 创建套接字文件描述符
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
    // 绑定套接字到端口8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }
    // 读取客户端发送的数据
    read(new_socket, buffer, BUFFER_SIZE);
    printf("Request received:
%s
", buffer);
    // 发送响应给客户端
    send(new_socket, hello, strlen(hello), 0);
    printf("Hello message sent
");
    // 关闭套接字
    close(new_socket);
    close(server_fd);
    return 0;
}

编译和运行

将上述代码保存为simple_web_server.c，然后使用以下命令进行编译和运行：

gcc -o simple_web_server simple_web_server.c
./simple_web_server

测试服务器

打开浏览器，访问http://localhost:8080，你应该会看到"Hello world!"的消息。

相关问题与解答

问题1：如何修改服务器以处理多个并发连接？

解答：要处理多个并发连接，可以使用多线程或多进程，以下是使用多线程的示例：

#include <pthread.h>
void *handle_client(void *socket_desc) {
    int sock = *(int*)socket_desc;
    char buffer[BUFFER_SIZE] = {0};
    const char *hello = "HTTP/1.1 200 OK
Content-Type: text/plain
Content-Length: 12
Hello world!";
    // 读取客户端发送的数据
    read(sock, buffer, BUFFER_SIZE);
    printf("Request received:
%s
", buffer);
    // 发送响应给客户端
    send(sock, hello, strlen(hello), 0);
    printf("Hello message sent
");
    // 关闭套接字
    close(sock);
    free(socket_desc);
    return NULL;
}
int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    pthread_t thread_id;
    // 创建套接字文件描述符
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
    // 绑定套接字到端口8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    while((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))) {
        printf("Connection established
");
        int *new_sock = malloc(sizeof(int));
        *new_sock = new_socket;
        if(pthread_create(&thread_id, NULL, handle_client, (void*) new_sock) < 0) {
            perror("could not create thread");
            return 1;
        }
        printf("Handler assigned
");
    }
    if (new_socket < 0) {
        perror("accept failed");
        exit(EXIT_FAILURE);
    }
    return 0;
}

问题2：如何让服务器支持静态文件服务？

解答：要让服务器支持静态文件服务，你需要解析HTTP请求中的文件路径，并根据路径读取相应的文件内容返回给客户端，以下是一个简单的示例：

#include <fcntl.h>
#include <sys/stat.h>
#include <dirent.h>
#include <stdbool.h>
#include <errno.h>
const char *get_mime_type(const char *filename) {
    if (strstr(filename, ".html")) return "text/html";
    if (strstr(filename, ".jpg") || strstr(filename, ".jpeg")) return "image/jpeg";
    if (strstr(filename, ".png")) return "image/png";
    if (strstr(filename, ".css")) return "text/css";
    if (strstr(filename, ".js")) return "application/javascript";
    return "application/octet-stream"; // default mime type
}
void handle_client(int client_socket) {
    char buffer[BUFFER_SIZE] = {0};
    read(client_socket, buffer, BUFFER_SIZE);
    printf("Request received:
%s
", buffer);
    char method[10], path[100], protocol[10];
    sscanf(buffer, "%s %s %s", method, path, protocol);
    printf("Method: %s, Path: %s, Protocol: %s
", method, path, protocol);
    if (strcmp(method, "GET") != 0) {
        char *response = "HTTP/1.1 405 Method Not Allowed\r
\r
";
        send(client_socket, response, strlen(response), 0);
        close(client_socket);
        return;
    }
    if (path[0] != '/') { // relative path to absolute path conversion
        char abs_path[128];
        sprintf(abs_path, ".%s", path); // assuming the current directory is the root directory for simplicity
        strcpy(path, abs_path);
    }
    FILE *file = fopen(path + 1, "rb"); // skip the first character which is '/' in path
    if (!file) {
        char *response = "HTTP/1.1 404 Not Found\r
\r
";
        send(client_socket, response, strlen(response), 0);
        close(client_socket);
        return;
    }
    fseek(file, 0, SEEK_END);
    long file_size = ftell(file);
    rewind(file);
    char *content_type = get_mime_type(path + 1); // skip the first character which is '/' in path for mime type detection as well
    char *header = "HTTP/1.1 200 OK\r
";
    char content_length[50];
    sprintf(content_length, "Content-Length: %ld\r
", file_size);
    char *response = malloc(file_size + strlen(header) + strlen(content_length) + strlen("\r
\r
") + 1);
    strcpy(response, header);
    strcat(response, "Content-Type: ");
    strcat(response, content_type);
    strcat(response, "\r
");
    strcat(response, content_length);
    strcat(response, "\r
\r
");
    send(client_socket, response, strlen(response), 0); // send header first
    free(response); // free header memory after sending it out
    char data[BUFFER_SIZE]; // buffer to store file chunks to send them one by one to avoid large memory allocation at once for big files.
    while (!feof(file)) { // reading and sending file in chunks of this way can be useful when dealing with larger files to avoid high memory usage.
        int bytesRead = fread(data, 1, BUFFER_SIZE, file); // read a chunk of data from the file into 'data' buffer.
        send(client_socket, data, bytesRead, 0); // send the chunk of data to the client.
    } // end of while loop. The loop will continue until the entire file has been read and sent to the client. It ensures that even large files are handled efficiently without consuming too much memory at once. This approach is beneficial for handling large files or when dealing with limited system resources. By reading and sending the file in manageable chunks, it helps prevent high memory usage issues and ensures smoother operation even under constrained conditions.

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