JSONP 是否对响应施加了一些大小限制？

Question

我已经实现了一个简单的 PHP 脚本来为一组我希望通过跨域请求访问的 JSON 文件提供 JSONP 支持。

这里是：

<?php
$jsonFile = $_GET['resource'] . ".json";
$fh = fopen($jsonFile, 'r');
$jsonData = fread($fh, filesize($jsonFile));
fclose($fh);

$jsonData = trim($jsonData);
header("Content-type: application/json");  
echo $_GET['callback'] . '(' . $jsonData . ');'; 
?>

当我手动输入网址时，这非常有用。 如果我的网址类似于： http://mywebserverdotcom/jsonp/data.php?resource=jsondata&callback=processJsonData

我看到以下形式的响应：

processJsonData([{"record_id":"317", ...}]);

我的数据是完整的，一切看起来都很好。

但是，当我在我的 HTML/JS 中使用以下方法尝试此操作时：

1) 我在 HTML 文件的底部添加了一个

2) 实现了一个带有回调函数的JS文件

我得到一个错误。我使用Web Inspector查看错误，它在回调中显示错误，并且看起来回调在响应中大约200个字符左右（我没有计算）字符被切断，所以响应是现在：

processJsonData([{"record_id":"317", ...

数据被截断，所以JSON格式乱了，没有关闭）；在函数调用结束时，这会产生错误。错误是：找不到 processJsonData 变量。

所以...要么我只是做错了，要么通过脚本元素使用 JSONP 回调允许的响应大小有一些大小限制，或者我没有想到的其他东西....

非常感谢任何帮助！

谢谢

Answer 1

确保您的 JSONP 响应脚本包含在 包含回调函数的脚本之后。错误消息似乎表明您的脚本标签乱序。您的脚本标签应按如下顺序排列：

<script type="text/javascript" src="myscript.js" />
<script type="text/javascript" src="jsonprequest.php?callback=processJsonData&arg=1" />

脚本标签的 JavaScript 直到所有之前的脚本都执行完毕后才会执行。当您的 JSONP 请求脚本执行时，它期望处理程序已经存在。但是如果在 JSONP 脚本之后才包含包含处理程序的脚本，那就太迟了。

Answer 2

以下是数据样本。我已经在前面的回调中离开了。这只是数据的一部分，所以结尾 ]);不包括在内。是公开数据。我知道它是有效的 JSON，因为我使用 exact 相同的文件，使用 Ajax 而不是 JSONP 从我的本地计算机加载它，它工作正常。只有当从远程服务器通过此 JSONP/PHP 脚本访问时，它才会因错误而失败。确切的错误信息是：

ReferenceError: Can't find variable: callback

错误的位置是 data.php:1，这是我的远程 PHP 脚本。

callback([{"record_id":"317","artist":"Vern Luce","title":"Untitled","date":"1983","medium":"Painted steel","discipline":"sculpture","dimensions":"a: 93 \" x 40 \" x 64 \", b: 76.5 \" x 31 \" x 29 \", c: 48.5 \" x 85 \" x 20 \"","funding_source":"CETA","location":"MacLeay Park","street":"NW 29th Ave and Upshur St","city":"Portland","state":"OR","zipcode":"","lat":"45.535999799999999","lng":"-122.7110045","description":"Three geometric abstract steel sculptures are placed in a raised landscaped area in and located directly south of the Thurman Street Bridge.  In siting the work, the artist wanted the sculptures to respond both to the surrounding greenspace (thus, the bright red color) and to the broad horizontal expanse of the Thurman Street bridge (thus, the vertical nature of the sculptures).  At the time the pieces were installed, Vern Luce lived near Lower MacLeay Park and selected the site both for its visual beauty and its proximity to his home.\n\nProject History\nThe Comprehensive Education Training Act of the early 70's provided grants to a number of Portland artists that enabled them to create artwork.  As a result, over 500 works by 52 artists became part of the City of Portland's collection, providing a rich and diverse history of art in Portland.  Aside from Lower MacLeay Park, two other Portland parks feature permanent sculptures acquired through this program: a sculpture by Bruce West in Lair Hill Park and a piece by Jerry Allen in Peninsula Park.","image_url":"http:\/\/data.racc.org\/pa_inventory\/0240\/0240thumb.jpg","detail_url":"http:\/\/racc.org\/public-art\/search\/?recid=317.192","date_modified":"2010-07-19 00:00:00"},{"record_id":"359","artist":"Bruce West","title":"BW1","date":"1978","medium":"Cor-ten steel","discipline":"sculpture","dimensions":"6' x 30' x 20'","funding_source":"CETA 1976-77","location":"Lair Hill Park","street":"3000 SW Barbur Blvd","city":"Portland","state":"OR","zipcode":"97201","lat":"45.501570100000002","lng":"-122.68130650000001","description":"","image_url":"http:\/\/data.racc.org\/pa_inventory\/0098\/0098thumb.jpg","detail_url":"http:\/\/racc.org\/public-art\/search\/?recid=359.185","date_modified":"2010-12-29 00:00:00"},{"record_id":"362","artist":"Jerry  Allen","title":"Disc #4","date":"1979","medium":"Cast silicon bronze","discipline":"sculpture","dimensions":"diameter: 4 1\/2'","funding_source":"CETA 1977-78","location":"Peninsula Park","street":"6222 N. Albina  Avenue","city":"Portland","state":"OR","zipcode":"97217","lat":"45.568221899999998","lng":"-122.6748716","description":"","image_url":"http:\/\/data.racc.org\/pa_inventory\/0102\/0102thumb.jpg","detail_url":"http:\/\/racc.org\/public-art\/search\/?recid=360.55","date_modified":"2010-03-12 00:00:00"},

Answer 3

不，使用 JSONP 不会限制响应的大小。就 HTTP 传输层而言，您只是将一些文本数据从服务器发送到客户端；它并不关心文本数据是什么或内部结构如何。

问题可能出在服务器端代码的某个地方。你能把你正在使用的PHP贴出来吗？