A better way to validate URL in C# than try-catch?

Question

I\'m building an application to retrieve an image from internet. Even though it works fine, it is slow (on wrong given URL) when using try-catch statements in the applicatio

Answer 1

I ran into a very similar case so I wrote a static class which can be easily used along with xUnit tests to verify the logic passed several cases.

Usage (returns ValidationModel):

var message = UrlValidator.Validate(input).ValidationMessage;

or

var result = UrlValidator.Validate(input).IsValid;

ValidationModel.cs

    public class ValidationModel
    {
        public const string InvalidScheme = "Invalid URI scheme.";
        public const string EmptyInputValue = "Empty input value.";
        public const string InvalidUriFormat = "Invalid URI format.";
        public const string PassedValidation = "Passed validation";
        public const string HttpScheme = "http://";
        public const string HttpsScheme = "https://";

        public bool IsValid { get; set; }
        public string ValidationMessage { get; set; }
        
    }

UrlValidator.cs

    public static class UrlValidator
    {
        public static ValidationModel Validate(string input)
        {
            var validation = new ValidationModel();

            if (input == string.Empty)
            {
                validation.IsValid = false;
                validation.ValidationMessage = ValidationModel.EmptyInputValue;
                return validation;
            }

            try
            {
                var uri = new Uri(input);
                var leftPart = uri.GetLeftPart(UriPartial.Scheme);

                if (leftPart.Equals(ValidationModel.HttpScheme) || leftPart.Equals(ValidationModel.HttpsScheme))
                {
                    validation.IsValid = true;
                    validation.ValidationMessage = ValidationModel.PassedValidation;
                    return validation;
                }
                
                validation.IsValid = false;
                validation.ValidationMessage = ValidationModel.InvalidScheme;
            }
            catch (UriFormatException)
            {
                validation.IsValid = false;
                validation.ValidationMessage = ValidationModel.InvalidUriFormat;
            }
            
            return validation;
        }
    }

UrlValidatorTests.cs

    public class UrlValidatorTests
    {
        [Theory]
        [InlineData("http://intel.com", true, ValidationModel.PassedValidation)]
        [InlineData("https://intel.com", true, ValidationModel.PassedValidation)]
        [InlineData("https://intel.com/index.html", true, ValidationModel.PassedValidation)]
        [InlineData("", false, ValidationModel.EmptyInputValue)]
        [InlineData("http://", false, ValidationModel.InvalidUriFormat)]
        [InlineData("//intel.com", false, ValidationModel.InvalidScheme)]
        [InlineData("://intel.com", false, ValidationModel.InvalidUriFormat)]
        [InlineData("f://intel.com", false, ValidationModel.InvalidScheme)]
        [InlineData("htttp://intel.com", false, ValidationModel.InvalidScheme)]
        [InlineData("intel.com", false, ValidationModel.InvalidUriFormat)]
        [InlineData("ftp://intel.com", false, ValidationModel.InvalidScheme)]
        [InlineData("http:intel.com", false, ValidationModel.InvalidUriFormat)]
        public void Validate_Input_ExpectedResult(string input, bool expectedResult, string expectedInvalidMessage)
        {
            //Act
            var result = UrlValidator.Validate(input);

            //Assert
            Assert.Equal(expectedResult, result.IsValid);
            Assert.Equal(expectedInvalidMessage, result.ValidationMessage);
        }
    }

TEST RESULTS:

Answer 2

Or this source code good image valid optimization:

 public static string ValidateImage(string absoluteUrl,string defaultUrl)
        { 
           Uri myUri=null; 
           if (Uri.TryCreate(absoluteUrl, UriKind.Absolute, out myUri))
            {
                using (WebClient client = new WebClient())
                {
                    try
                    {
                        using (Stream stream = client.OpenRead(myUri))
                        {
                            Image image = Image.FromStream(stream);
                            return (image != null) ? absoluteUrl : defaultUrl;
                        }
                    }
                    catch (ArgumentException)
                    {
                        return defaultUrl;
                    }
                    catch (WebException)
                    {
                        return defaultUrl;
                    }
                }
            }
            else
            {
                return defaultUrl;
            }
        }

Sou and demo asp.net mvc source image created:

<img src="@ValidateImage("http://example.com/demo.jpg","nophoto.png")"/>

Answer 3

Hi you validate https http,ftp,sftp,ftps,any thing starting with www.

string regular = @"^(ht|f|sf)tp(s?)\:\/\/[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&%\$#_]*)?$";
string regular123 = @"^(www.)[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&%\$#_]*)?$";

string myString = textBox1.Text.Trim();
if (Regex.IsMatch(myString, regular))
{
    MessageBox.Show("It is valide url  " + myString);
}
else if (Regex.IsMatch(myString, regular123))
{
    MessageBox.Show("Valide url with www. " + myString);
}
else 
{
    MessageBox.Show("InValide URL  " + myString);
}

Answer 4

Some examples when using Uri to test a valid URL fails

Uri myUri = null;
if (Uri.TryCreate("Host: www.stackoverflow.com", UriKind.Absolute, out myUri))
{
}

  myUri = null;
if (Uri.TryCreate("Accept: application/json, text/javascript, */*; q=0.01", UriKind.Absolute, out myUri))
{
}

  myUri = null;
if (Uri.TryCreate("User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0", UriKind.Absolute, out myUri))
{
}

  myUri = null;
if (Uri.TryCreate("DNT: 1", UriKind.Absolute, out myUri))
{
}

I Was surprised to have all this nonsense appear in my listview after validating with the above. But it all passes the validation test.

Now I add the following after the above validation

url = url.ToLower();
if (url.StartsWith("http://") || url.StartsWith("https://")) return true;