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;
}

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

Should work ;)

A radical solution would be to display the favicons as background images in a div above your default icon. That way, all overhead would be placed on the client while still not displaying broken images (missing background images are ignored in all browsers AFAIK).

You should issue HEAD requests, not GET one, because you don't need the URI contents at all. As Pies said above, you should check for status code (in 200-299 ranges, and you may optionally follow 3xx redirects).

The answers question contain a lot of code examples which may be helpful: PHP / Curl: HEAD Request takes a long time on some sites

If the file is not hosted external you might translate the remote URL to an absolute Path on your webserver. That way you don't have to call CURL or file_get_contents, etc.

function remoteFileExists($url) {

    $root = realpath($_SERVER["DOCUMENT_ROOT"]);
    $urlParts = parse_url( $url );

    if ( !isset( $urlParts['path'] ) )
        return false;

    if ( is_file( $root . $urlParts['path'] ) )
        return true;
    else
        return false;

}

remoteFileExists( 'https://www.yourdomain.com/path/to/remote/image.png' );

Note: Your webserver must populate DOCUMENT_ROOT to use this function

If you're using the Laravel framework or guzzle package, there is also a much simpler way using the guzzle client, it also works when links are redirected:

$client = new \GuzzleHttp\Client(['allow_redirects' => ['track_redirects' => true]]);
try {
    $response = $client->request('GET', 'your/url');
    if ($response->getStatusCode() != 200) {
        // not exists
    }
} catch (\GuzzleHttp\Exception\GuzzleException $e) {
    // not exists
}

More in Document : https://docs.guzzlephp.org/en/latest/faq.html#how-can-i-track-redirected-requests

Don't know if this one is any faster when the file does not exist remotely, is_file(), but you could give it a shot.

$favIcon = 'default FavIcon';
if(is_file($remotePath)) {
   $favIcon = file_get_contents($remotePath);
}

If you're using the Symfony framework, there is also a much simpler way using the HttpClientInterface:

private function remoteFileExists(string $url, HttpClientInterface $client): bool {
    $response = $client->request(
        'GET',
        $url //e.g. http://example.com/file.txt
    );

    return $response->getStatusCode() == 200;
}

The docs for the HttpClient are also very good and maybe worth looking into if you need a more specific approach: https://symfony.com/doc/current/http_client.html

You can use the filesystem: use Symfony\Component\Filesystem\Filesystem; use Symfony\Component\Filesystem\Exception\IOExceptionInterface;

and check $fileSystem = new Filesystem(); if ($fileSystem->exists('path_to_file')==true) {...

Please check this URL. I believe it will help you. They provide two ways to overcome this with a bit of explanation.

Try this one.

// Remote file url
$remoteFile = 'https://www.example.com/files/project.zip';

// Initialize cURL
$ch = curl_init($remoteFile);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_exec($ch);
$responseCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

// Check the response code
if($responseCode == 200){
    echo 'File exists';
}else{
    echo 'File not found';
}

or visit the URL

https://www.codexworld.com/how-to/check-if-remote-file-exists-url-php/#:~:text=The%20file_exists()%20function%20in,a%20remote%20server%20using%20PHP.