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How Facebook link preview happens?

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小鲜肉
小鲜肉 2021-02-01 17:47

When you type a URL into facebook, it automatically comes up with the \"post a link\" feature. With most websites, it automatically loads a selection of images it pulls from som

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  • 醉酒成梦
    醉酒成梦 (楼主)
    2021-02-01 18:23

    I think following steps are involved

    • Using Javascript find the links in the written text
    • From the found links get the last link in the text (FB shows only for last link)
    • Using AJAX send this link detail to a server side page (PHP/ASP/JSP etc.)
    • The server side page gets the required data (from Meta tags) including
      • Title (Preferably Open graph og:title if missing from </code></li> <li>Description (Preferably Open graph <code>og:description</code> if missing from <code><meta name="description" ....</code></li> <li>Images (Preferably Open graph <code>og:image</code> if missing from <code><img src=....</code></li> </ul></li> <li>In PHP you can get these datas either using <code>curl</code> or <code>file_get_contents</code> and parse for required data detailed above. Not sure about other Language.</li> <li>Show the result thus found in the AJAX request.</li> </ul> <p>Additionally I think FB stores the data, once found, in database and 1st queries there. This helps them to get faster result and hence same article shared and liked generate the image and details from the stored data.</p> <p>You will need Javascript to show this preview in runtime (while you write in the textarea). However if you only need it after posting of data it can be done with pure server side language (you can avoid javascript) and following above steps just remove AJAX call. </p> </p> <div class="appendcontent"> </div> </div> <div class="jieda-reply"> <span class="jieda-zan button_agree" type="zan" data-id='2007197'> <i class="iconfont icon-zan"></i> <em>0</em> </span> <span type="reply" class="showpinglun" data-id="2007197"> <i class="iconfont icon-svgmoban53"></i> 讨论(0) </span> <div class="jieda-admin"> </div> <div class="noreplaytext bb"> <center><div> <a href="https://www.e-learn.cn/qa/q-979133.html"> 查看其它4个回答 </a> </div></center> </div> </div> <div class="comments-mod " style="display: none; float:none;padding-top:10px;" id="comment_2007197"> <div class="areabox clearfix"> <form class="layui-form" action=""> <div class="layui-form-item"> <label class="layui-form-label" style="padding-left:0px;width:60px;">发布评论:</label> <div class="layui-input-block" style="margin-left:90px;"> <input type="text" placeholder="不少于5个字" AUTOCOMPLETE="off" class="comment-input layui-input" name="content" /> <input type='hidden' value='0' name='replyauthor' /> </div> <div class="mar-t10"><span class="fr layui-btn layui-btn-sm addhuidapinglun" data-id="2007197">提交评论 </span></div> </div> </form> </div> <hr> <ul class="my-comments-list nav"> <li class="loading"> <img src='https://www.e-learn.cn/qa/static/css/default/loading.gif' align='absmiddle' />  加载中... </li> </ul> </div> </li> </ul> <div class="layui-form layui-form-pane"> <form id="huidaform" name="answerForm" method="post"> <div class="layui-form-item layui-form-text"> <a name="comment"></a> <div class="layui-input-block"> <script type="text/javascript" src="https://www.e-learn.cn/qa/static/js/neweditor/ueditor.config.js"></script> <script type="text/javascript" src="https://www.e-learn.cn/qa/static/js/neweditor/ueditor.all.js"></script> <script type="text/plain" id="editor" name="content" style="width:100%;height:200px;"></script> <script type="text/javascript"> var isueditor=1; var editor = UE.getEditor('editor',{ //这里可以选择自己需要的工具按钮名称,此处仅选择如下五个 toolbars:[['source','fullscreen', '|', 'undo', 'redo', '|', 'bold', 'italic', 'underline', 'fontborder', 'strikethrough', 'removeformat', 'formatmatch', 'autotypeset', 'blockquote', 'pasteplain', '|', 'forecolor', 'backcolor', 'insertorderedlist', 'insertunorderedlist', 'selectall', 'cleardoc', '|', 'rowspacingtop', 'rowspacingbottom', 'lineheight', '|', 'customstyle', 'paragraph', 'fontfamily', 'fontsize', '|', 'indent', '|', 'justifyleft', 'justifycenter', 'justifyright', 'justifyjustify', '|', 'link', 'unlink', 'anchor', '|', 'simpleupload', 'insertimage', 'scrawl', 'insertvideo', 'attachment', 'map', 'insertcode', '|', 'horizontal', '|', 'preview', 'searchreplace', 'drafts']], initialContent:'', //关闭字数统计 wordCount:false, zIndex:2, //关闭elementPath elementPathEnabled:false, //默认的编辑区域高度 initialFrameHeight:250 //更多其他参数，请参考ueditor.config.js中的配置项 //更多其他参数，请参考ueditor.config.js中的配置项 }); editor.ready(function() { editor.setDisabled(); }); $("#editor").find("*").css("max-width","362px"); </script> </div> </div> <div class="layui-form-item"> <label for="L_vercode" class="layui-form-label">验证码</label> <div class="layui-input-inline"> <input type="text" id="code" name="code" value="" required lay-verify="required" placeholder="图片验证码" autocomplete="off" class="layui-input"> </div> <div class="layui-form-mid"> <span style="color: #c00;"><img class="hand" src="https://www.e-learn.cn/qa/user/code.html" onclick="javascript:updatecode();" id="verifycode"><a class="changecode" href="javascript:updatecode();"> 看不清?</a></span> </div> </div> <div class="layui-form-item"> <input type="hidden" value="979133" id="ans_qid" name="qid"> <input type="hidden" id="tokenkey" name="tokenkey" value=''/> <input type="hidden" value="How Facebook link preview happens?" id="ans_title" name="title"> <div class="layui-btn layui-btn-disabled" id="ajaxsubmitasnwer" >提交回复</div> </div> </form> </div> </div> <input type="hidden" value="979133" id="adopt_qid" name="qid" /> <input type="hidden" id="adopt_answer" value="0" name="aid" /> </div> <div class="layui-col-md4"> <!-- 热门讨论问题 --> <dl class="fly-panel fly-list-one"> <dt class="fly-panel-title">热议问题</dt> <!-- 本周热门讨论问题显示10条-->