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src="/touchsocket/img/TouchSocketlogo.png" alt="TouchSocket Logo" class="themedImage_ToTc themedImage--dark_i4oU"><b>TouchSocket</b></a><nav aria-label="Docs sidebar" class="menu thin-scrollbar menu_SIkG"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/touchsocket/docs/">01、说明（使用前必要阅读）</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/touchsocket/docs/upgrade">02、历史更新</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/donate">03、支持作者及商业运营</a></div></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/touchsocket/docs/startguide">04、入门指南</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/bytepool">05、Core</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="/touchsocket/docs/tcpintroduction">06、Tcp组件</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/touchsocket/docs/tcpintroduction">6.1 Tcp入门基础</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/touchsocket/docs/createtcpservice">6.2 创建TcpService</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/touchsocket/docs/createtcpclient">6.3 创建TcpClient</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/touchsocket/docs/waitingclient">6.4 同步请求</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/touchsocket/docs/natservice">6.5 Tcp端口转发</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/touchsocket/docs/resetid">6.6 服务器重置ID</a></li><li class="theme-doc-sidebar-item-link 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href="/touchsocket/docs/createudpsession">07、Udp组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/adapterdescription">08、数据处理适配器</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/createhttpservice">09、Http组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/websocketdescription">10、WebSocket组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/generateproxydescription">11、Rpc代理生成</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/touchrpcdescription">12、TouchRpc组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/webapidescription">13、WebApi组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/jsonrpcdescription">14、JsonRpc组件</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/touchsocket/docs/xmlrpcdescription">15、XmlRpc组件件</a></div></li></ul></nav><button type="button" title="Collapse sidebar" aria-label="Collapse sidebar" class="button button--secondary button--outline collapseSidebarButton_PEFL"><svg width="20" height="20" aria-hidden="true" class="collapseSidebarButtonIcon_kv0_"><g fill="#7a7a7a"><path 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class="breadcrumbs__link" href="/touchsocket/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">06、Tcp组件</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">6.1 Tcp入门基础</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Tcp入门基础</h1></header><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="一说明">一、说明<a href="#一说明" class="hash-link" aria-label="Direct link to 一、说明" title="Direct link to 一、说明"></a></h2><p>传输控制协议（TCP，Transmission Control Protocol）是一种面向连接的、可靠的、基于字节流的<code>传输层</code>通信协议。</p><p><strong>特点：</strong></p><ol><li>基于流的方式；</li><li>面向连接；</li><li>可靠通信方式；</li><li>在网络状况不佳的时候尽量降低系统由于重传带来的带宽开销；</li><li>通信连接维护是面向通信的两个端点的，而不考虑中间网段和节点。</li></ol><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="二建立连接">二、建立连接<a href="#二建立连接" class="hash-link" aria-label="Direct link to 二、建立连接" title="Direct link to 二、建立连接"></a></h2><p><strong>TCP三次握手的过程如下：</strong></p><ol><li>客户端发送SYN（SEQ=x）报文给服务器端，进入SYN_SEND状态。</li><li>服务器端收到SYN报文，回应一个SYN （SEQ=y）ACK（ACK=x+1）报文，进入SYN_RECV状态。</li><li>客户端收到服务器端的SYN报文，回应一个ACK（ACK=y+1）报文，进入Established状态。</li></ol><p>三次握手完成，TCP客户端和服务器端成功地建立连接，可以开始传输数据了。</p><img loading="lazy" src="/touchsocket/assets/images/tcpintroduction-1-6c44f6ba3c610fb21ff8bf22695be71d.gif" width="500" class="img_ev3q"><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="三断开连接">三、断开连接<a href="#三断开连接" class="hash-link" aria-label="Direct link to 三、断开连接" title="Direct link to 三、断开连接"></a></h2><p>建立一个连接需要三次握手，而终止一个连接要经过四次握手，这是由TCP的半关闭（half-close）造成的。具体过程如下图所示。</p><ol><li>某个应用进程首先调用close，称该端执行“主动关闭”（active close）。该端的TCP于是发送一个FIN分节，表示数据发送完毕。</li><li>接收到这个FIN的对端执行 “被动关闭”（passive close），这个FIN由TCP确认。</li><li>一段时间后，接收到这个文件结束符的应用进程将调用close关闭它的套接字。这导致它的TCP也发送一个FIN。</li><li>接收这个最终FIN的原发送端TCP（即执行主动关闭的那一端）确认这个FIN。</li></ol><div class="theme-admonition theme-admonition-info alert alert--info admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 14 16"><path fill-rule="evenodd" d="M7 2.3c3.14 0 5.7 2.56 5.7 5.7s-2.56 5.7-5.7 5.7A5.71 5.71 0 0 1 1.3 8c0-3.14 2.56-5.7 5.7-5.7zM7 1C3.14 1 0 4.14 0 8s3.14 7 7 7 7-3.14 7-7-3.14-7-7-7zm1 3H6v5h2V4zm0 6H6v2h2v-2z"></path></svg></span>注意</div><div class="admonitionContent_S0QG"><p>FIN的接收也作为一个文件结束符（end-of-file）传递给接收端应用进程，放在已排队等候该应用进程接收的任何其他数据之后，因为，FIN的接收意味着接收端应用进程在相应连接上再无额外数据可接收。</p></div></div><p>既然每个方向都需要一个FIN和一个ACK，因此通常需要4个分节。</p><div class="theme-admonition theme-admonition-caution alert alert--warning admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 16 16"><path fill-rule="evenodd" d="M8.893 1.5c-.183-.31-.52-.5-.887-.5s-.703.19-.886.5L.138 13.499a.98.98 0 0 0 0 1.001c.193.31.53.501.886.501h13.964c.367 0 .704-.19.877-.5a1.03 1.03 0 0 0 .01-1.002L8.893 1.5zm.133 11.497H6.987v-2.003h2.039v2.003zm0-3.004H6.987V5.987h2.039v4.006z"></path></svg></span>注意</div><div class="admonitionContent_S0QG"><ol><li>“通常”是指，某些情况下，步骤1的FIN随数据一起发送，另外，步骤2和步骤3发送的分节都出自执行被动关闭那一端，有可能被合并成一个分节。</li><li>在步骤2与步骤3之间，从执行被动关闭一端到执行主动关闭一端流动数据是可能的，这称为“半关闭”（half-close）。</li><li>当一个Unix进程无论自愿地（调用exit或从main函数返回）还是非自愿地（收到一个终止本进程的信号）终止时，所有打开的描述符都被关闭，这也导致仍然打开的任何TCP连接上也发出一个FIN。</li></ol><p>无论是客户还是服务器，任何一端都可以执行主动关闭。通常情况是，客户执行主动关闭。</p></div></div><img loading="lazy" src="/touchsocket/assets/images/tcpintroduction-2-6e5c8e256f20ef5d40baa6ed7919bc12.gif" width="500" class="img_ev3q"><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="四发送">四、发送<a href="#四发送" class="hash-link" aria-label="Direct link to 四、发送" title="Direct link to 四、发送"></a></h2><p>当调用Send函数时，实际上在Socket内部会做以下事项：</p><ol><li>检查Send数据的有效性。例如是否为null，长度是否为0等。</li><li>检查发送缓存区是否有空闲，如果有，将需要发送的数据<code>复制</code>到缓存区，并且返回已复制的字节数。如果没有空闲，则会一直等待。</li></ol><p>通过上述两个步骤，我们会明白，Send函数的返回，仅仅是保证数据被复制到了发送缓存区，而不是已被接收方收到。</p><div class="theme-admonition theme-admonition-tip alert alert--success admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 12 16"><path fill-rule="evenodd" d="M6.5 0C3.48 0 1 2.19 1 5c0 .92.55 2.25 1 3 1.34 2.25 1.78 2.78 2 4v1h5v-1c.22-1.22.66-1.75 2-4 .45-.75 1-2.08 1-3 0-2.81-2.48-5-5.5-5zm3.64 7.48c-.25.44-.47.8-.67 1.11-.86 1.41-1.25 2.06-1.45 3.23-.02.05-.02.11-.02.17H5c0-.06 0-.13-.02-.17-.2-1.17-.59-1.83-1.45-3.23-.2-.31-.42-.67-.67-1.11C2.44 6.78 2 5.65 2 5c0-2.2 2.02-4 4.5-4 1.22 0 2.36.42 3.22 1.19C10.55 2.94 11 3.94 11 5c0 .66-.44 1.78-.86 2.48zM4 14h5c-.23 1.14-1.3 2-2.5 2s-2.27-.86-2.5-2z"></path></svg></span>提示</div><div class="admonitionContent_S0QG"><p>由于Tcp协议的可靠性设计，如果成功将数据复制到缓存区，且在<code>没有断开</code>的情况下，数据就一定会被成功发送。</p></div></div><div class="theme-admonition theme-admonition-tip alert alert--success admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 12 16"><path fill-rule="evenodd" d="M6.5 0C3.48 0 1 2.19 1 5c0 .92.55 2.25 1 3 1.34 2.25 1.78 2.78 2 4v1h5v-1c.22-1.22.66-1.75 2-4 .45-.75 1-2.08 1-3 0-2.81-2.48-5-5.5-5zm3.64 7.48c-.25.44-.47.8-.67 1.11-.86 1.41-1.25 2.06-1.45 3.23-.02.05-.02.11-.02.17H5c0-.06 0-.13-.02-.17-.2-1.17-.59-1.83-1.45-3.23-.2-.31-.42-.67-.67-1.11C2.44 6.78 2 5.65 2 5c0-2.2 2.02-4 4.5-4 1.22 0 2.36.42 3.22 1.19C10.55 2.94 11 3.94 11 5c0 .66-.44 1.78-.86 2.48zM4 14h5c-.23 1.14-1.3 2-2.5 2s-2.27-.86-2.5-2z"></path></svg></span>提示</div><div class="admonitionContent_S0QG"><p>调用完Send后，返回的字节数可能会小于需要发送的字节数，所以一般需要循环发送。但是在TouchSocket中，已经做了封装，所有调用Send的字节，都是完整数据发送。</p></div></div></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://gitee.com/rrqm_home/touchsocket/tree/master/handbook/docs/tcpintroduction.mdx" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 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