深入解析TCP协议源码：揭秘网络通信的底层奥秘

随着互联网的飞速发展，TCP协议作为网络通信的核心协议之一，扮演着至关重要的角色。TCP协议的全称是传输控制协议，它是一种面向连接的、可靠的、基于字节流的传输层通信协议。本文将深入解析TCP协议的源码，带您领略网络通信的底层奥秘。

一、TCP协议概述

TCP协议主要提供以下功能：

1.面向连接：TCP协议在数据传输前需要建立一个连接，确保数据传输的可靠性。 2.可靠传输：TCP协议通过校验和、重传、序号等方式保证数据的正确传输。 3.流量控制：TCP协议通过滑动窗口机制实现流量控制，避免发送方发送过快导致接收方来不及处理。 4.拥塞控制：TCP协议通过慢启动、拥塞避免、快速重传和快速恢复等机制，控制网络拥塞，提高传输效率。

二、TCP协议源码分析

1.TCP协议源码结构

TCP协议的源码主要分为以下几个部分：

（1）头文件：定义了TCP协议的各种数据结构、宏定义和函数声明。 （2）实现文件：实现了TCP协议的核心功能，包括连接建立、数据传输、连接关闭等。 （3）辅助函数：提供了各种辅助函数，如计算校验和、处理IP头等。

2.TCP连接建立

TCP连接建立的过程称为三次握手。以下是三次握手的源码分析：

（1）客户端发送SYN包，表示请求建立连接。

`c tcpsynsend(struct sock *sk, struct skbuff *skb) { ... skb->sk = sk; skb->protocol = htons(ETHPIP); skb->ipsummed = CHECKSUMPARTIAL; skb->ipheader = ipheader(skb); ipheader(skb)->protocol = IPPROTOTCP; tcpheader(skb)->source = inethtons(__skstreamlocalport(sk)); tcpheader(skb)->dest = inethtons(__skstreamremoteport(sk)); tcpheader(skb)->seq = tcpnewseq(skb); tcpheader(skb)->ackseq = 0; tcpheader(skb)->doff = 0; tcpheader(skb)->fin = 0; tcpheader(skb)->syn = 1; tcpheader(skb)->rst = 0; tcpheader(skb)->urg = 0; tcpheader(skb)->window = 0; tcpheader(skb)->check = 0; skb->ipsummed = CHECKSUMNONE; ipheader(skb)->check = csumipv4magic(skb->ipheader, 0, skb->len, 0); skb->ipheader->check = csumipv4magic(skb->ipheader, skb->len, 0, 0); skb->ipheader->daddr = inetaddr(net->ipdefaultrouter); skb->ipheader->saddr = inetaddr(net->iplocaladdr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr); skb->ipheader->dst = inetaddr(net->ipremoteaddr); skb->ipheader->tos = 0; skb->ipheader->ttl = 255; skb->ipheader->totlen = htons(skb->len); skb->ipheader->id = htons(net->ipid); skb->ipheader->df = 0; skb->ipheader->fragoff = 0; skb->ipheader->version = 4; skb->ipheader->ihl = 5; skb->ipheader->protocol = IPPROTOTCP; skb->ipheader->src = inetaddr(net->iplocaladdr