PHP fsockopen() Function

The PHP fsockopen() function opens Internet or Unix domain socket connection.

By default, the socket is opened in blocking mode. It can be switched to non-blocking mode by using stream_set_blocking().

The function stream_socket_client() is similar but provides a richer set of options, including non-blocking connection and the ability to provide a stream context.

Syntax

fsockopen(hostname, port, error_code, error_message, timeout)

Parameters

`hostname`	`Required.` Specify a hostname (like "www.alphacodingskills.com"). If OpenSSL support is installed, the hostname can be prefixed with either ssl:// or tls:// to use an SSL or TLS client connection over TCP/IP to connect to the remote host.
`port`	`Optional.` Specify the port number. This can be omitted and skipped with -1 for transports that do not use ports, like unix://.
`error_code`	`Optional.` Specify the system level error number.
`error_message`	`Optional.` Specify the error message as a string.
`timeout`	`Optional.` Specify the connection timeout, in seconds. When null, the default_socket_timeout of php.ini setting is used.

Return Value

Returns a file pointer which can be used together with the other file functions, such as fgets(), fgetss(), fwrite(), fclose(), and feof(), or false on failure.

Exceptions

Throws E_WARNING if hostname is not a valid domain.

Example: fsockopen() example

The example below shows the usage of fsockopen() function.

<?php
$fp = fsockopen("www.example.com", 80, $errno, $errstr, 20);
if (!$fp) {
  echo "$errstr ($errno)<br>\n";
} else {
  $out = "GET / HTTP/1.1\r\n";
  $out .= "Host: www.example.com\r\n";
  $out .= "Connection: Close\r\n\r\n";
  fwrite($fp, $out);
  while (!feof($fp)) {
    echo fgets($fp, 128);
  }
  fclose($fp);
}
?>

The output of the above code will be similar to:

HTTP/1.1 200 OK
Age: 491454
Cache-Control: max-age=604800
Content-Type: text/html; charset=UTF-8
Date: Sun, 31 Oct 2021 08:32:38 GMT
Etag: "3147526947+ident"
Expires: Sun, 07 Nov 2021 08:32:38 GMT
Last-Modified: Thu, 17 Oct 2019 07:18:26 GMT
Server: ECS (dna/63AA)
Vary: Accept-Encoding
X-Cache: HIT
Content-Length: 1256
Connection: close

<!doctype html>
<html>
<head>
    <title>Example Domain</title>

    <meta charset="utf-8" />
    <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <style type="text/css">
    body {
        background-color: #f0f0f2;
        margin: 0;
        padding: 0;
        font-family: -apple-system, system-ui, BlinkMacSystemFont, "Segoe UI", 
                     "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
        
    }
    div {
        width: 600px;
        margin: 5em auto;
        padding: 2em;
        background-color: #fdfdff;
        border-radius: 0.5em;
        box-shadow: 2px 3px 7px 2px rgba(0,0,0,0.02);
    }
    a:link, a:visited {
        color: #38488f;
        text-decoration: none;
    }
    @media (max-width: 700px) {
        div {
            margin: 0 auto;
            width: auto;
        }
    }
    </style>    
</head>

<body>
<div>
    <h1>Example Domain</h1>
    <p>This domain is for use in illustrative examples in documents. You may use this
    domain in literature without prior coordination or asking for permission.</p>
    <p><a href="https://www.iana.org/domains/example">More information...</a></p>
</div>
</body>
</html>

Example: using UDP connection

In the example below, the fsockopen() function is used with UDP connection.

<?php
$fp = fsockopen("udp://127.0.0.1", 13, $errno, $errstr);
if (!$fp) {
  echo "ERROR: $errno - $errstr<br>\n";
} else {
  fwrite($fp, "\n");
  echo fread($fp, 26);
  fclose($fp);
}
?>

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