Socket 基本概念

Socket 是对 TCP/IP 协议族的一种封装，是应用层与TCP/IP协议族通信的中间软件抽象层。从设计模式的角度看来，Socket其实就是一个门面模式，它把复杂的TCP/IP协议族隐藏在Socket接口后面，对用户来说，一组简单的接口就是全部，让Socket去组织数据，以符合指定的协议。

Socket 还可以认为是一种网络间不同计算机上的进程通信的一种方法，利用三元组（ip地址，协议，端口）就可以唯一标识网络中的进程，网络中的进程通信可以利用这个标志与其它进程进行交互。

Socket 起源于 Unix ，Unix/Linux 基本哲学之一就是“一切皆文件”，都可以用“打开(open) –> 读写(write/read) –> 关闭(close)”模式来进行操作。因此 Socket 也被处理为一种特殊的文件。

写一个简易的 WebServer

一个简易的 Server 的流程如下：

1.建立连接，接受一个客户端连接。
2.接受请求，从网络中读取一条 HTTP 请求报文。
3.处理请求，访问资源。
4.构建响应，创建带有 header 的 HTTP 响应报文。
5.发送响应，传给客户端。
省略流程 3，大体的程序与调用的函数逻辑如下：

socket() 创建套接字
bind() 分配套接字地址
listen() 等待连接请求
accept() 允许连接请求
read()/write() 数据交换
close() 关闭连接

代码如下：

#include

#include <unistd.h>

#include <sys/socket.h>

#include <arpa/inet.h>

#include

using namespace std;

const int port = 9090;
const int buffer_size = 1<<20;
const int method_size = 1<<10;
const int filename_size = 1<<10;
const int common_buffer_size = 1<<10;

void handleError(const string &message);
void requestHandling(int sock);
void sendError(int sock);
void sendData(int sock, char filename);
void sendHTML(int sock, char filename);
void sendJPG(int sock, char filename);

int main()
{
int server_sock;
int client_sock;

struct sockaddr_in server_address;
struct sockaddr_in client_address;

socklen_t client_address_size;

server_sock = socket(PF_INET, SOCK_STREAM, 0);

if (server_sock == -1)
{
    handleError("socket error");
}

memset(&server_address,0,sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(port);

if(bind(server_sock,(struct sockaddr*)&server_address, sizeof(server_address)) == -1){
    handleError("bind error");
}

if(listen(server_sock, 5) == -1) {
    handleError("listen error");
}

while(true) {
    client_address_size = sizeof(client_address);
    client_sock = accept(server_sock, (struct sockaddr*) &client_address, &client_address_size);

    if (client_sock == -1) {
        handleError("accept error");
    }
    requestHandling(&client_sock);
}

//system("open http://127.0.0.1:9090/index.html");
close(server_sock);

return 0;

}

void requestHandling(int sock){
int client_sock = sock;
char buffer[buffer_size];
char method[method_size];
char filename[filename_size];

read(client_sock, buffer, sizeof(buffer)-1);

if(!strstr(buffer, "HTTP/")) {
    sendError(sock);
    close(client_sock);
    return;
}

strcpy(method, strtok(buffer," /"));
strcpy(filename, strtok(NULL, " /"));

if(0 != strcmp(method, "GET")) {
    sendError(sock);
    close(client_sock);
    return;
}

sendData(sock, filename);

}

void sendData(int sock, char filename) {
int client_sock = *sock;
char buffer[common_buffer_size];
char type[common_buffer_size];

strcpy(buffer, filename);

strtok(buffer, ".");
strcpy(type, strtok(NULL, "."));

if(0 == strcmp(type, "html")){
    sendHTML(sock, filename);
}else if(0 == strcmp(type, "jpg")){
    sendJPG(sock, filename);
}else{
    sendError(sock);
    close(client_sock);
    return ;
}

}

void sendHTML(int sock, char filename) {
int client_sock = sock;
char buffer[buffer_size];
FILE fp;

char status[] = "HTTP/1.0 200 OK\r\n";
char header[] = "Server: A Simple Web Server\r\nContent-Type: text/html\r\n\r\n";

write(client_sock, status, strlen(status));
write(client_sock, header, strlen(header));

fp = fopen(filename, "r");
if(!fp){
    sendError(sock);
    close(client_sock);
    handleError("failed to open file");
    return ;
}

fgets(buffer,sizeof(buffer), fp);
while(!feof(fp)) {
    write(client_sock, buffer, strlen(buffer));
    fgets(buffer, sizeof(buffer), fp);
}

fclose(fp);
close(client_sock);

}

void sendJPG(int sock, char filename) {
int client_sock = sock;
char buffer[buffer_size];
FILE fp;
FILE *fw;

char status[] = "HTTP/1.0 200 OK\r\n";
char header[] = "Server: A Simple Web Server\r\nContent-Type: image/jpeg\r\n\r\n";

write(client_sock, status, strlen(status));
write(client_sock, header, strlen(header));

fp = fopen(filename, "rb");
if(NULL == fp){
    sendError(sock);
    close(client_sock);
    handleError("failed to open file");
    return ;
}

fw = fdopen(client_sock, "w");
fread(buffer, 1, sizeof(buffer), fp);
while (!feof(fp)){
    fwrite(buffer, 1, sizeof(buffer), fw);
    fread(buffer, 1, sizeof(buffer), fp);
}

fclose(fw);
fclose(fp);
close(client_sock);

}

void handleError(const string &message) {
cout<<message;
exit(1);
}

void sendError(int sock){
int client_sock = sock;

char status[] = "HTTP/1.0 400 Bad Request\r\n";
char header[] = "Server: A Simple Web Server\r\nContent-Type: text/html\r\n\r\n";
char body[] = "<html><head><title>Bad Request</title></head><body><p>400 Bad Request</p></body></html>";

write(client_sock, status, sizeof(status));
write(client_sock, header, sizeof(header));
write(client_sock, body, sizeof(body));

}