如何使所有连接的浏览器由服务器端事件启动重新加载

发布于 2024-08-16 06:52:00 字数 154 浏览 3 评论 0原文

假设有一个包含动态生成内容的网页 - 比如说一个包含当前连接浏览器数量的 div。当服务器上的计数发生变化时，我希望所有连接的浏览器重新加载计数，以便每个人都能看到增量/减量。

实现这一目标的最佳方法是什么？

关键词：ajax、广播、浏览器、div、jquery

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静赏你的温柔 2024-08-23 06:52:00

我认为 COMET 可能就是您正在寻找的。 Web Sockets 是理想的选择，但由于缺乏浏览器的采用，目前还无法实现。

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天冷不及心凉 2024-08-23 06:52:00

HTTP 协议在设计上是无状态的。实现此目的的唯一方法是通过 AJAX 实现客户端轮询。

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云淡风轻 2024-08-23 06:52:00

以下是如何使用 ajax 长轮询进行服务器推送。浏览器发出 ajax 请求，启动服务器端自轮询。 ajax 请求保持打开状态，等待响应，直到文件发生更改，一旦获得响应，它就会发出新的长轮询请求。

这是使用 jQuery 和 php 的效果，实现了在 html 中实时更新 div 的示例，显示了当前连接的客户端：

index.html：

<html>
<head>
<title>Comet Test</title>
  <script type="text/javascript" src="jquery.js"></script>
  <script type="text/javascript" src="longpolling.js"></script>
</head>
<body>
  Number of connected users: <div id="total">0</div>
</body>
</html>

longpolling.js：

$(document).ready(function() { connectToServer(1); });

function connectToServer( incp ) {
  $.get("LongPolling.php",
        { inc: incp },
        function(resp) {
          $('#total').html(resp);
          connectToServer(0);
        }
       );
}

LongPolling.php：

<?php

# (over)write file with contents, locking the file while doing so.
# just barf and die if there's an error.
function update($file, $contents)
{
  $f = fopen($file, 'w');
  if(!$f) { echo "ERROR1"; exit; } # couldn't open file for writing.
  if(!flock($f, LOCK_EX)) { echo "ERROR2"; exit; } # couldn't get lock.
  fwrite($f, $contents);
  fclose($f);  # this also releases the lock.
  return $contents;
}

# fetch the contents of the given file.
# if the file doesn't exist, create it with contents "0"
function fetch($file)
{
  if(file_exists($file)) {
    if(!is_readable($file)) { echo "ERROR3"; exit; }
    $x = file_get_contents($file);
  } else {
    $x = 0;
    update($file, $x);
  }
  return $x;
}

$fc = 'connx.txt';   # file that stores the number of connections.

if ( $_REQUEST['inc'] == 1 ) {  # someone just connected.
  echo update($fc, fetch($fc)+1);
} else {  # someone is reconnecting (also happens immediately after connect).
  $last = filemtime($fc);
  do {  # wait until some other instance causes $fc to change...
    sleep(1);
    clearstatcache(); # otherwise filemtime() results are cached!
  } while(filemtime($fc) == $last);
  echo fetch($fc);
}
?>

注意：这不会跟踪断开连接，因此它更像是实时跟踪页面浏览总数。
请参阅在浏览器关闭时运行服务器端函数有关跟踪浏览器断开连接的信息，即客户端断开连接时的服务器端操作。

Here's how to do server-push using ajax long-polling. The browser makes an ajax request which initiates server-side self-polling. The ajax request remains open, waiting for a response until the file changes, and as soon as it gets a response, it makes a new long-polling request.

Here's what it looks like with jQuery and php, implementing the example of live-updating a div in the html showing the number of clients currently connected:

index.html:

<html>
<head>
<title>Comet Test</title>
  <script type="text/javascript" src="jquery.js"></script>
  <script type="text/javascript" src="longpolling.js"></script>
</head>
<body>
  Number of connected users: <div id="total">0</div>
</body>
</html>

longpolling.js:

$(document).ready(function() { connectToServer(1); });

function connectToServer( incp ) {
  $.get("LongPolling.php",
        { inc: incp },
        function(resp) {
          $('#total').html(resp);
          connectToServer(0);
        }
       );
}

LongPolling.php:

<?php

# (over)write file with contents, locking the file while doing so.
# just barf and die if there's an error.
function update($file, $contents)
{
  $f = fopen($file, 'w');
  if(!$f) { echo "ERROR1"; exit; } # couldn't open file for writing.
  if(!flock($f, LOCK_EX)) { echo "ERROR2"; exit; } # couldn't get lock.
  fwrite($f, $contents);
  fclose($f);  # this also releases the lock.
  return $contents;
}

# fetch the contents of the given file.
# if the file doesn't exist, create it with contents "0"
function fetch($file)
{
  if(file_exists($file)) {
    if(!is_readable($file)) { echo "ERROR3"; exit; }
    $x = file_get_contents($file);
  } else {
    $x = 0;
    update($file, $x);
  }
  return $x;
}

$fc = 'connx.txt';   # file that stores the number of connections.

if ( $_REQUEST['inc'] == 1 ) {  # someone just connected.
  echo update($fc, fetch($fc)+1);
} else {  # someone is reconnecting (also happens immediately after connect).
  $last = filemtime($fc);
  do {  # wait until some other instance causes $fc to change...
    sleep(1);
    clearstatcache(); # otherwise filemtime() results are cached!
  } while(filemtime($fc) == $last);
  echo fetch($fc);
}
?>

NOTE: This does not track disconnects, so it's more like live-tracking the total number of pageviews.
See Running server-side function as browser closes for info on keeping track of browser disconnects, ie, server-side action on client disconnect.

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