Replace host in Uri

Question

What is the nicest way of replacing the host-part of an Uri using .NET?

I.e.:

string ReplaceHost(string original, string newHostName);
//...
string s = ReplaceHost("http://oldhostname/index.html", "newhostname");
Assert.AreEqual("http://newhostname/index.html", s);
//...
string s = ReplaceHost("http://user:pass@oldhostname/index.html", "newhostname");
Assert.AreEqual("http://user:pass@newhostname/index.html", s);
//...
string s = ReplaceHost("ftp://user:pass@oldhostname", "newhostname");
Assert.AreEqual("ftp://user:pass@newhostname", s);
//etc.

System.Uri does not seem to help much.

score 165 · Accepted Answer · edited Nov 23 '20 at 02:43

165

System.UriBuilder is what you are after...

string ReplaceHost(string original, string newHostName) {
    var builder = new UriBuilder(original);
    builder.Host = newHostName;
    return builder.Uri.ToString();
}

edited Nov 23 '20 at 02:43

Pang

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answered Jan 26 '09 at 13:36

Ishmael

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I would have recommended the Uri class, but I would have been wrong. Good answer. – Jonathan C Dickinson Jan 26 '09 at 14:43
Works great, just note that if you read the Query property, it is prepended with a ?, and if you set the Query Property with a string beginning with ?, another ? will be prepended. – Dave Feb 14 '18 at 17:06
You'll have to handle ports, if they are specified in either original or new. – Subjective Reality Apr 05 '18 at 22:00

Drew Noakes · Answer 2 · 2013-06-14T13:38:58.113

44

As @Ishmael says, you can use System.UriBuilder. Here's an example:

// the URI for which you want to change the host name
var oldUri = Request.Url;

// create a new UriBuilder, which copies all fragments of the source URI
var newUriBuilder = new UriBuilder(oldUri);

// set the new host (you can set other properties too)
newUriBuilder.Host = "newhost.com";

// get a Uri instance from the UriBuilder
var newUri = newUriBuilder.Uri;

edited Jun 14 '13 at 13:38

answered Aug 18 '12 at 10:42

Drew Noakes

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I suspect it might be better to obtain the `Uri` instance by calling `newUriBuilder.Uri` rather than formatting and parsing it. – Sam Jun 13 '13 at 02:35
@Sam you're right, the [`Uri`](http://msdn.microsoft.com/en-us/library/system.uribuilder.uri.aspx) property is a much better option. Thanks. Updated. – Drew Noakes Jun 14 '13 at 13:38
Careful of the `.Uri` call. If you have something in that `UriBuilder` that does not translate to a valid Uri, it will throw. So for example if you need a wildcard host `*` you can set `.Host` to that, but if you call `.Uri` it will throw. If you call `UriBuilder.ToString()` it will return the Uri with the wildcard in place. – CubanX Jul 18 '19 at 17:25

Replace host in Uri

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