Best Way to Check If a Url Is Valid

Best way to check if a URL is valid

You can use a native Filter Validator

filter_var($url, FILTER_VALIDATE_URL);

Validates value as URL (according to » http://www.faqs.org/rfcs/rfc2396), optionally with required components. Beware a valid URL may not specify the HTTP protocol http:// so further validation may be required to determine the URL uses an expected protocol, e.g. ssh:// or mailto:. Note that the function will only find ASCII URLs to be valid; internationalized domain names (containing non-ASCII characters) will fail.

Example:

if (filter_var($url, FILTER_VALIDATE_URL) === FALSE) {
    die('Not a valid URL');
}

Check if a JavaScript string is a URL

A related question with an answer

Or this Regexp from Devshed:

function validURL(str) {
  var pattern = new RegExp('^(https?:\\/\\/)?'+ // protocol
    '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
    '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
    '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
    '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
    '(\\#[-a-z\\d_]*)?$','i'); // fragment locator
  return !!pattern.test(str);
}

What is the best way to check if a URL exists in PHP?

You can use get_headers($url)

Example 2 from Manual:

<?php
// By default get_headers uses a GET request to fetch the headers. If you
// want to send a HEAD request instead, you can do so using a stream context:
stream_context_set_default(
    array(
        'http' => array(
            'method' => 'HEAD'
        )
    )
);
print_r(get_headers('http://example.com'));

// gives
Array
(
    [0] => HTTP/1.1 200 OK 
    [Date] => Sat, 29 May 2004 12:28:14 GMT
    [Server] => Apache/1.3.27 (Unix)  (Red-Hat/Linux)
    [Last-Modified] => Wed, 08 Jan 2003 23:11:55 GMT
    [ETag] => "3f80f-1b6-3e1cb03b"
    [Accept-Ranges] => bytes
    [Content-Length] => 438
    [Connection] => close
    [Content-Type] => text/html
)

The first array element will contain the HTTP Response Status code. You have to parse that.

Note that the get_headers function in the example will issue an HTTP HEAD request, which means it will not fetch the body of the URL. This is more efficient than using a GET request which will also return the body.

Also note that by setting a default context, any subsequent calls using an http stream context, will now issue HEAD requests. So make sure to reset the default context to use GET again when done.

PHP also provides the variable $http_response_header

The $http_response_header array is similar to the get_headers() function. When using the HTTP wrapper, $http_response_header will be populated with the HTTP response headers. $http_response_header will be created in the local scope.

If you want to download the content of a remote resource, you don't want to do two requests (one to see if the resource exists and one to fetch it), but just one. In that case, use something like file_get_contents to fetch the content and then inspect the headers from the variable.

How to check for a valid URL in Java?

Consider using the Apache Commons UrlValidator class

UrlValidator urlValidator = new UrlValidator();
urlValidator.isValid("http://my favorite site!");

There are several properties that you can set to control how this class behaves, by default http, https, and ftp are accepted.

How to check whether a string is a valid HTTP URL?

Try this to validate HTTP URLs (uriName is the URI you want to test):

Uri uriResult;
bool result = Uri.TryCreate(uriName, UriKind.Absolute, out uriResult) 
    && uriResult.Scheme == Uri.UriSchemeHttp;

Or, if you want to accept both HTTP and HTTPS URLs as valid (per J0e3gan's comment):

Uri uriResult;
bool result = Uri.TryCreate(uriName, UriKind.Absolute, out uriResult) 
    && (uriResult.Scheme == Uri.UriSchemeHttp || uriResult.Scheme == Uri.UriSchemeHttps);

C# How can I check if a URL exists/is valid?

You could issue a "HEAD" request rather than a "GET"?
So to test a URL without the cost of downloading the content:

// using MyClient from linked post
using(var client = new MyClient()) {
    client.HeadOnly = true;
    // fine, no content downloaded
    string s1 = client.DownloadString("http://google.com");
    // throws 404
    string s2 = client.DownloadString("http://google.com/silly");
}

You would try/catch around the DownloadString to check for errors; no error? It exists...

---

With C# 2.0 (VS2005):

private bool headOnly;
public bool HeadOnly {
    get {return headOnly;}
    set {headOnly = value;}
}

and

using(WebClient client = new MyClient())
{
    // code as before
}

What is the best way to check a url is valid every second (or less), with Task await or ContinueWith in a C# Window Forms Application (.NET)

This answer will focus on the Task timer loop to answer the specific part of your question "check a url is valid every second". There are lots of answers about how to perform the actual Ping (like How do you check if a website is online in C#) and here's the Microsoft documentation for Ping if you choose to go that route.

Since it's not uncommon to set a timeout value of 120 seconds for a ping request, it calls into question whether it would have any value to do this on a steady tick of one second. My suggestion is that it would make more sense to:

1. Make a background thread
2. Perform a synchronous ping (wait for the result) on the background thread.
3. Marshal the ping result onto the UI thread to perform the other tasks you have laid out.
4. Synchronously wait a Task.Delay on the background thread before performing the next ping.

Here is how I personally go about doing that in my own production code:

void execPing()
{
    Task.Run(() => 
    {
        while (!DisposePing.IsCancellationRequested)
        {
            var pingSender = new Ping();
            var pingOptions = new PingOptions
            {
                DontFragment = true,
            };
            // https://learn.microsoft.com/en-us/dotnet/api/system.net.networkinformation.ping?view=net-6.0#examples
            // Create a buffer of 32 bytes of data to be transmitted.
            string data = "Best Way to Check If a Url Is ValidBest Way to Check If a Url Is ValidBest Way to Check If a Url Is ValidBest Way to Check If a Url Is Valid";
            byte[] buffer = Encoding.ASCII.GetBytes(data);
            int timeout = 120;
            try
            {
                // https://stackoverflow.com/a/25654227/5438626
                if (Uri.TryCreate(textBoxUri.Text, UriKind.Absolute, out Uri? uri)
                    && (uri.Scheme == Uri.UriSchemeHttp || 
                    uri.Scheme == Uri.UriSchemeHttps))
                {
                    PingReply reply = pingSender.Send(
                        uri.Host, 
                        timeout, buffer, 
                        pingOptions);
                    switch (reply.Status)
                    {
                        case IPStatus.Success:
                            Invoke(() => onPingSuccess());
                            break;
                        default:
                            Invoke(() => onPingFailed(reply.Status));
                            break;
                    }
                }
                else
                {
                    Invoke(() => labelStatus.Text = 
                        $"{DateTime.Now}: Invalid URI: try 'http://");
                }
            }
            catch (Exception ex)
            {
                // https://stackoverflow.com/a/60827505/5438626
                if (ex.InnerException == null)
                {
                    Invoke(() => labelStatus.Text = ex.Message);
                }
                else
                {
                    Invoke(() => labelStatus.Text = ex.InnerException.Message);
                }
            }
            Task.Delay(1000).Wait();
        }
    });
}

What works for me is initializing it when the main window handle is created:

protected override void OnHandleCreated(EventArgs e)
{
    base.OnHandleCreated(e);
    if (!(DesignMode || _isHandleInitialized))
    {
        _isHandleInitialized = true;
        execPing();
    }
}
bool _isHandleInitialized = false;

Where:

private void onPingSuccess()
{
    labelStatus.Text = $"{DateTime.Now}: {IPStatus.Success}";
    // Up to you what you do here
}

private void onPingFailed(IPStatus status)
{
    labelStatus.Text = $"{DateTime.Now}: {status}";
    // Up to you what you do here
}

public CancellationTokenSource DisposePing { get; } = new CancellationTokenSource();

Example 404:

---

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