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.

Pang · Accepted Answer · 2020-11-23 02:43:25Z

183

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, 2020 at 2:43

Pang

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answered Jan 26, 2009 at 13:36

Ishmael

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3 Comments

Jonathan C Dickinson Over a year ago

I would have recommended the Uri class, but I would have been wrong. Good answer.

Dave Over a year ago

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.

Subjective Reality Over a year ago

You'll have to handle ports, if they are specified in either original or new.

Drew Noakes · Accepted Answer · 2013-06-14 13:38:58Z

45

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, 2013 at 13:38

answered Aug 18, 2012 at 10:42

Drew Noakes

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3 Comments

Sam Over a year ago

I suspect it might be better to obtain the Uri instance by calling newUriBuilder.Uri rather than formatting and parsing it.

Drew Noakes Over a year ago

@Sam you're right, the Uri property is a much better option. Thanks. Updated.

CubanX Over a year ago

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.

MaRaNtZ · Accepted Answer · 2025-02-06 11:21:20Z

The answer using UriBuilder is fine, except it may trigger an exception if the host to be replaced is in the form "machinename:port".

This is the refined code i have used to handle also this common situation:

public static Uri ReplaceHost(Uri original, string newHostName) { var builder = new UriBuilder(original); var newhost = new Uri(newHostName.Contains("://") ? newHostName : "http://" + newHostName); builder.Host = newhost.Host; builder.Port = newhost.Port == 80 ? builder.Port : newhost.Port; return builder.Uri; }

Note that if you do not specify a new port, the old port is retained

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