PHP Curl在下载之前检查文件是否存在

Question

I am writing a PHP program that downloads a pdf from a backend and save to a local drive. Now how do I check whether the file exists before downloading?

Currently I am using curl (see code below) to check and download but it still downloads the file which is 1KB in size.

$url = "http://wedsite/test.pdf";
$path = "C:\\test.pdf;"
downloadAndSave($url,$path);

function downloadAndSave($urlS,$pathS)
    {
        $fp = fopen($pathS, 'w');

        $ch = curl_init($urlS);

        curl_setopt($ch, CURLOPT_FILE, $fp);
        $data = curl_exec($ch);

        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        echo $httpCode;
        //If 404 is returned, then file is not found.
        if(strcmp($httpCode,"404") == 1)
        {
            echo $httpCode;
            echo $urlS; 
        }

        fclose($fp);

    }

I want to check whether the file exists before even downloading. Any idea how to do it?

Answer 1

You can do this with a separate curl HEAD request:

curl_setopt($ch, CURLOPT_NOBODY, true);
$data = curl_exec($ch);

$httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

When you actually want to download you can use set NOBODY to false .

Answer 2

Since you are using HTTP to fetch a resource on the internet, what you really want to check is that the return code is a 404.

On some PHP installations, you can just use file_exists($url) out of the box. This does not work in all environments, however. http://www.php.net/manual/en/wrappers.http.php

Here is a function much like file_exists but for URLs, using curl:

<?php function curl_exists()
  $file_headers = @get_headers($url);
  if($file_headers[0] == 'HTTP/1.1 404 Not Found') {
    $exists = false;
  }
  else {
    $exists = true;
  }
} ?>

source: http://www.php.net/manual/en/function.file-exists.php#75064

Sometimes the CURL extension isn't installed with PHP. In that case you can still use the socket library in the PHP core:

<?php function url_exists($url) {
       $a_url = parse_url($url);
       if (!isset($a_url['port'])) $a_url['port'] = 80;
       $errno = 0;
       $errstr = '';
       $timeout = 30;
       if(isset($a_url['host']) && $a_url['host']!=gethostbyname($a_url['host'])){
           $fid = fsockopen($a_url['host'], $a_url['port'], $errno, $errstr, $timeout);
           if (!$fid) return false;
           $page = isset($a_url['path'])  ?$a_url['path']:'';
           $page .= isset($a_url['query'])?'?'.$a_url['query']:'';
           fputs($fid, 'HEAD '.$page.' HTTP/1.0'."\r\n".'Host: '.$a_url['host']."\r\n\r\n");
           $head = fread($fid, 4096);
           $head = substr($head,0,strpos($head, 'Connection: close'));
           fclose($fid);
           if (preg_match('#^HTTP/.*\s+[200|302]+\s#i', $head)) {
            $pos = strpos($head, 'Content-Type');
            return $pos !== false;
           }
       } else {
           return false;
       }
   } ?>

source: http://www.php.net/manual/en/function.file-exists.php#73175

An even faster function can be found here: http://www.php.net/manual/en/function.file-exists.php#76246

Answer 3

Call this before your download function and it's done:

<?php function remoteFileExists($url) {
    $curl = curl_init($url);

    //don't fetch the actual page, you only want to check the connection is ok
    curl_setopt($curl, CURLOPT_NOBODY, true);

    //do request
    $result = curl_exec($curl);

    $ret = false;

    //if request did not fail
    if ($result !== false) {
        //if request was ok, check response code
        $statusCode = curl_getinfo($curl, CURLINFO_HTTP_CODE);  

        if ($statusCode == 200) {
            $ret = true;   
        }
    }

    curl_close($curl);

    return $ret;
}

?>

Answer 4

In the first example above $file_headers[0] may contain more than or something other than 'HTTP/1.1 404 Not Found', eg:

HTTP/1.1 404 Document+%2Fdb%2Fscotbiz%2Freports%2FR20131212%2Exml+not+found

So it's important to use some other test, eg, regex, as '==' is not reliable.