How can one check to see if a remote file exists using PHP?

You can instruct curl to use the HTTP HEAD method via CURLOPT_NOBODY.

More or less

$ch = curl_init("http://www.example.com/favicon.ico");curl_setopt($ch, CURLOPT_NOBODY, true);curl_exec($ch);$retcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);// $retcode >= 400 -> not found, $retcode = 200, found.curl_close($ch);

Anyway, you only save the cost of the HTTP transfer, not the TCP connection establishment and closing. And being favicons small, you might not see much improvement.

Caching the result locally seems a good idea if it turns out to be too slow.HEAD checks the time of the file, and returns it in the headers. You can do like browsers and get the CURLINFO_FILETIME of the icon. In your cache you can store the URL => [ favicon, timestamp ]. You can then compare the timestamp and reload the favicon.

As Pies say you can use cURL. You can get cURL to only give you the headers, and not the body, which might make it faster. A bad domain could always take a while because you will be waiting for the request to time-out; you could probably change the timeout length using cURL.

Here is example:

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 $ret;}$exists = remoteFileExists('http://stackoverflow.com/favicon.ico');if ($exists) {    echo 'file exists';} else {    echo 'file does not exist';   }

CoolGoose's solution is good but this is faster for large files (as it only tries to read 1 byte):

if (false === file_get_contents("http://example.com/path/to/image",0,null,0,1)) {    $image = $default_image;}