Linux下Socket写http协议下载文件代码以及说明

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转载最新推荐文章于 2026-07-28 18:47:56 发布 3.8k 阅读 AI 写同款· GEO 优化 ›

手写Socket Web服务器：深入HTTP协议底层原理 HTTP协议是Web通信的基石，其本质是一套严格定义的文本格式与状态交互规范。理解它需回归传输层——TCP连接建立、请求响应格式（如状态行、头/体分隔符\r\n\r\n）、字符编码与字节长度一致性等核心原理。这些知识直接决定CORS拦截、中文乱码、Content-Length错误等高频问题的排查效率。在现代框架封装日益厚重的今天，亲手用Socket实现一个可被Chrome识别的极简Web服务器，成为掌握Web运行机制最有效的实践路径。本文即以DebugLZQ经典案例为蓝本，还原从URI解析、DNS查询、So 阅读详情

看代码：

#include <string>

#include <iostream>
#include <stdio.h>
#include <winsock.h>
#include <conio.h>
using namespace std;
#pragma comment("ws2_32.lib")
string host2ip(const string& strdomain);
void save2file(char *buffer,const string& filename);
int getlength(const string& sheader);
bool getstatus(const string& sheader);
int getleftlength(const string& sheader);
void sethttphead(const string& file,const string& server);
int port = 80;
int error=0;
string serveraddr;
int i = 0;
const int BUFFER_SIZE = 1024;
char buffer[BUFFER_SIZE] = {0};
char msg[BUFFER_SIZE];
FILE *f;
const string file = "/BT/200801/3/117906.torrent";
const string url = "www.supbt.com";
const string filename = "117906.torrent";
int main(void)
{
int r;
WSADATA wsa;
SOCKET sock;
struct sockaddr_in sin;
f = fopen(filename.c_str(),"ab");
sethttphead(file,url);
if(WSAStartup(MAKEWORD(2,2),&wsa))
{
printf("WSAStartup Error: %d/n",WSAGetLastError());
getche();
return -1;
}
if((sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==INVALID_SOCKET)
{
printf("Socket Error: %d/n",WSAGetLastError());
getche();
return -1;
}
sin.sin_family=AF_INET;
sin.sin_port=htons(port);
serveraddr = host2ip(url);
cout << serveraddr << endl;
sin.sin_addr.s_addr=inet_addr(serveraddr.c_str());
if(connect(sock,(struct sockaddr *)&sin,sizeof(sin))==SOCKET_ERROR)
{
printf("Connect Error: %d/n",WSAGetLastError());
printf("请检测网络连接！/n");
getche();
return -1;
}
if((r=send(sock,msg,sizeof(msg),0))==SOCKET_ERROR)
{
printf("Send Error: %d/n",WSAGetLastError());
getche();
return -1;
}
memset(buffer,0,BUFFER_SIZE);
if((r=recv(sock,buffer,BUFFER_SIZE,0))==SOCKET_ERROR)
{
printf("Recv Error: %d/n",WSAGetLastError());
closesocket(sock);
return -1;
}
string header = string(buffer);
int ilength = getlength(header);
int leftlength = ilength;
int icount;
if(getstatus(header)){
//current is r
char *q = buffer;
char *p = strstr(buffer, "/r/n/r/n");
p += 4;
//注意这里得 r - (p-q) 非常关键得问题
fwrite(p,r - (p - q),1,f);
leftlength -= r - (p - q);
int i=0;
icount = r - (p - q);
while(true)
{
memset(buffer, 0, BUFFER_SIZE);
r = recv(sock, buffer, BUFFER_SIZE, 0);
if (r < 0) {
closesocket(sock);
return 2;
}
if (r == 0) {
break;
}
int tmp;
tmp = leftlength; //209 100 100 92
leftlength -= r;
if(leftlength > 0){
fwrite(buffer,r,1,f);
icount += r;
}
else if(leftlength == 0){
//
break;
}
else{
icount += tmp;
fwrite(buffer,tmp,1,f);
break;
}
cout << i++ << " r is "<< r << endl;
}
}else{
cout << "http protocal error" << endl;
}
cout << icount << endl;
fclose(f);
closesocket(sock);
WSACleanup();
getche();
return 0;
}
/*
构造HTTP头
*/
void sethttphead(const string& file,const string& server)
{
strcat(msg,"GET ");
strcat(msg,file.c_str());
strcat(msg," HTTP/1.1");
strcat(msg,"/r/n");
strcat(msg,"Accept:*/*");
strcat(msg,"/r/n");
//strcat(msg,"Accept-Language: zh-cn");
//strcat(msg,"/r/n");
//strcat(msg,"Accept-Encoding: gzip, deflate");
//strcat(msg,"/r/n");
strcat(msg,"User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)");
strcat(msg,"/r/n");
strcat(msg,"Host:");
strcat(msg,server.c_str());
strcat(msg,"/r/n");
strcat(msg,"Connection: Keep-Alive");
strcat(msg,"/r/n");
strcat(msg,"/r/n");
}
//---------------------------------------------------------------------------
/*
将domain 转换为IP地址
*/
string host2ip(const string& strdomain)
{
SOCKADDR_IN saddr;
WORD wVersionRequested;
WSADATA wsaData;
hostent *pHostIp;
int nErrorNum;
wVersionRequested = MAKEWORD(2, 2);
nErrorNum = WSAStartup(wVersionRequested, &wsaData);
if(nErrorNum != 0)
{
return "";
}
saddr.sin_family = AF_INET;
pHostIp = gethostbyname(strdomain.c_str());
if(pHostIp == NULL)
{
return "0.0.0.0";
}
WSACleanup();
return (string)inet_ntoa(*(LPIN_ADDR)*(pHostIp->h_addr_list));
}
/*
该方法为测试用法，并为应用到项目中
*/
void save2file(char *buffer,const string& filename)
{
FILE *f;
f = fopen(filename.c_str(),"a+");
fwrite(buffer,strlen(buffer),1,f);
fclose(f);
}
/*
该方法获取待下载文件大小
*/
int getlength(const string& sheader){
char * cont_len_pos;
unsigned long cont_length;
const char* header = sheader.c_str();
cont_len_pos =(char *)strstr(header,"Content-Length:");
cont_len_pos = (char *)strchr(cont_len_pos,' ');
cont_len_pos++;
sscanf(cont_len_pos, "%ld", &cont_length);
return cont_length;
}
/*
该方法判断是否Get成功，不成功就取消下载文件
*/
bool getstatus(const string& sheader){
string start = "HTTP/1.1 200 OK";
if(sheader.find(start,0) != string::npos){
return true;
}
else{
return false;
}
}
/*
该方法并没有用到，开始考虑多了
*/
int getleftlength(const string& sheader){
int nreturnl = 0;
int ilength = sheader.length();
string _send = "/r/n/r/n";
int istart = sheader.find_last_of(_send);
if(istart != string::npos){
nreturnl = ilength - istart -_send.length();
}
return nreturnl;
}

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用TCP/IP进行网际互连

Linux/Unix Shell

标签

#socket #linux #buffer #header #string

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Linux下Socket写http协议下载文件代码以及说明

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