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In some case, we need to read a first part of a website page or a file (eg a big file). How to limit read size?
We can use CURLOPT_WRITEFUNCTION:
Example 1:

<?php
set_time_limit(0);
$size = 1440;

$ch = curl_init();
$content = '';
$callback = function ($ch, $str) {
    global $content,$size;
    $content.=$str;
    if(curl_getinfo($ch, CURLINFO_SIZE_DOWNLOAD)>$size) return 0;
    return strlen($str);
};
curl_setopt($ch, CURLOPT_URL, 'https://cs508406.userapi.com/4/u330693590/videos/92b2dc68ca.240.mp4?extra=4Gcx1QRbTb9L-KnybR62GHqd-yXkkermpNo9FXlTXyzjAmIy4riNKfKvI6_CNu3_nqAYCj8Tzlk5bj0bZBh5LsvI8tDi4hqaKDbTcCjJWDlpwa7kDw3NGOZzTsco9IathZzQ-Ds5Z-GI');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10000);
curl_setopt($ch, CURLOPT_WRITEFUNCTION, $callback);
curl_exec($ch);
curl_close($ch);
var_dump($content);

Example 2: get header and more information

<?php
set_time_limit(0);
$size = 1440;
$headers = array();
$ch = curl_init();

$content = '';
$callback = function ($ch, $str) {
    global $content,$size;
    $content.=$str;
    if(curl_getinfo($ch, CURLINFO_SIZE_DOWNLOAD)>$size) return 0;
    return strlen($str);
};
curl_setopt($ch, CURLOPT_URL, 'https://cs508406.userapi.com/4/u330693590/videos/92b2dc68ca.240.mp4?extra=4Gcx1QRbTb9L-KnybR62GHqd-yXkkermpNo9FXlTXyzjAmIy4riNKfKvI6_CNu3_nqAYCj8Tzlk5bj0bZBh5LsvI8tDi4hqaKDbTcCjJWDlpwa7kDw3NGOZzTsco9IathZzQ-Ds5Z-GI');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10000);
curl_setopt($ch, CURLOPT_HEADERFUNCTION,'header_callback');
curl_setopt($ch, CURLINFO_HEADER_OUT, true);
curl_setopt($ch, CURLOPT_WRITEFUNCTION, $callback);
curl_exec($ch);
$info = curl_getinfo($ch);
curl_close($ch);
function header_callback($ch, $header_line)
{ 
    global $headers;
    $headers[] = $header_line;
    return strlen($header_line);
}
var_dump($headers,strlen(implode("",$headers)));
var_dump($info);

Result:

array(12) {
  [0]=>
  string(17) "HTTP/1.1 200 OK
"
  [1]=>
  string(16) "Server: Apache
"
  [2]=>
  string(37) "Date: Thu, 11 May 2017 00:13:43 GMT
"
  [3]=>
  string(25) "Content-Type: video/mp4
"
  [4]=>
  string(26) "Content-Length: 77416932
"
  [5]=>
  string(46) "Last-Modified: Sat, 07 Nov 2015 07:18:55 GMT
"
  [6]=>
  string(24) "Connection: keep-alive
"
  [7]=>
  string(26) "ETag: "563da5df-49d49e4"
"
  [8]=>
  string(40) "Expires: Sun, 28 May 2017 00:13:43 GMT
"
  [9]=>
  string(32) "Cache-Control: max-age=1468800
"
  [10]=>
  string(22) "Accept-Ranges: bytes
"
  [11]=>
  string(2) "
"
}
int(313)
array(27) {
  ["url"]=>
  string(214) "https://cs508406.userapi.com/4/u330693590/videos/92b2dc68ca.240.mp4?extra=4Gcx1QRbTb9L-KnybR62GHqd-yXkkermpNo9FXlTXyzjAmIy4riNKfKvI6_CNu3_nqAYCj8Tzlk5bj0bZBh5LsvI8tDi4hqaKDbTcCjJWDlpwa7kDw3NGOZzTsco9IathZzQ-Ds5Z-GI"
  ["content_type"]=>
  string(9) "video/mp4"
  ["http_code"]=>
  int(200)
  ["header_size"]=>
  int(313)
  ["request_size"]=>
  int(244)
  ["filetime"]=>
  int(-1)
  ["ssl_verify_result"]=>
  int(19)
  ["redirect_count"]=>
  int(0)
  ["total_time"]=>
  float(1.654)
  ["namelookup_time"]=>
  float(0)
  ["connect_time"]=>
  float(0.328)
  ["pretransfer_time"]=>
  float(0.983)
  ["size_upload"]=>
  float(0)
  ["size_download"]=>
  float(16071)
  ["speed_download"]=>
  float(9716)
  ["speed_upload"]=>
  float(0)
  ["download_content_length"]=>
  float(77416932)
  ["upload_content_length"]=>
  float(0)
  ["starttransfer_time"]=>
  float(1.654)
  ["redirect_time"]=>
  float(0)
  ["redirect_url"]=>
  string(0) ""
  ["primary_ip"]=>
  string(13) "87.240.163.60"
  ["certinfo"]=>
  array(0) {
  }
  ["primary_port"]=>
  int(443)
  ["local_ip"]=>
  string(11) "192.168.1.4"
  ["local_port"]=>
  int(51182)
  ["request_header"]=>
  string(244) "GET /4/u330693590/videos/92b2dc68ca.240.mp4?extra=4Gcx1QRbTb9L-KnybR62GHqd-yXkkermpNo9FXlTXyzjAmIy4riNKfKvI6_CNu3_nqAYCj8Tzlk5bj0bZBh5LsvI8tDi4hqaKDbTcCjJWDlpwa7kDw3NGOZzTsco9IathZzQ-Ds5Z-GI HTTP/1.1
Host: cs508406.userapi.com
Accept: */*

"
}