c# - How to build a Url?

Question

Are there any helper classes available in .NET to allow me to build a Url?

For example, if a user enters a string:

stackoverflow.com

and i try to pass that to an HttpWebRequest:

WebRequest.CreateHttp(url);

It will fail, because it is not a valid url (it has no prefix).

What i want is to be able to parse the partial url the user entered:

Uri uri = new Uri(url);

and then fix the missing pieces:

if (uri.Port == 0)
   uri.Port = 3333;
if (uri.Scheme == "")
   uri.Scheme = "https";

Does .NET have any classes that can be used to parse and manipulate Uri's?

The UriBuilder class can't do the job

The value that the user entered (e.g. stackoverflow.com:3333) is valid; i just need a class to pick it apart. i tried using the UriBuilder class:

UriBuilder uriBuilder = new UriBuilder("stackoverflow.com:3333");

unfortunately, the UriBuilder class is unable to handle URIs:

• uriBuilder.Path = 3333
• uriBuilder.Port = -1
• uriBuidler.Scheme = stackoverflow.com

So i need a class that can understand host:port, which especially becomes important when it's not particularly http, but could be.

Bonus Chatter

Console application.

From the other question

Some examples of URL's that require parsing:

• server:8088
• server:8088/func1
• server:8088/func1/SubFunc1
• http://server
• http://server/func1
• http://server/func/SubFunc1
• http://server:8088
• http://server:8088/func1
• http://server:8088/func1/SubFunc1
• magnet://server
• magnet://server/func1
• magnet://server/func/SubFunc1
• magnet://server:8088
• magnet://server:8088/func1
• magnet://server:8088/func1/SubFunc1
• http://[2001:db8::1]
• http://[2001:db8::1]:80

The format of a Url is:

  foo://example.com:8042/over/there?name=ferret#nose
  \_/   \_________/ \__/\_________/\__________/ \__/
   |         |        |     |           |        |
scheme      host    port   path       query   fragment

Bonus Chatter

Just to point out again that UriBuilder does not work:

• https://dotnetfiddle.net/s66kdZ

Answer 1

If you need to ensure that some string coming as user input is valid url you could use the Uri.TryCreate method:

Uri uri;
string someUrl = ...
if (!Uri.TryCreate(someUrl, UriKind.Absolute, out uri))
{
    // the someUrl string did not contain a valid url 
    // inform your users about that
}
else
{
    var request = WebRequest.Create(uri);
    // ... safely proceed with executing the request
}

Now if on the other hand you want to be building urls in .NET there's the UriBuilder class specifically designed for that purpose. Let's take an example. Suppose you wanted to build the following url: http://example.com/path?foo=bar&baz=bazinga#some_fragment where the bar and bazinga values are coming from the user:

string foo = ... coming from user input
string baz = ... coming from user input

var uriBuilder = new UriBuilder("http://example.com/path");
var parameters = HttpUtility.ParseQueryString(string.Empty);
parameters["foo"] = foo;
parameters["baz"] = baz;
uriBuilder.Query = parameters.ToString();
uriBuilder.Fragment = "some_fragment";

Uri finalUrl = uriBuilder.Uri;
var request = WebRequest.Create(finalUrl);
... safely proceed with executing the request