Replace query parameter with another value/token

Question

I am trying to replace a URL query pattern wID=xxx, where xxx can be a digit, number or white space, with the query wID=[[WID]] (note that the query is case sensitive). I would like to know how can I achieve this. Currently, I am using regex to find the pattern in the URL and replace it using Regex.Replace() as follows:

private const string Pattern = @"wID=^[0-9A-Za-z ]+$";
private const string Replace = @"wID=[[WID]]";
/// <summary>
/// Extension method to evaluate the url token for wid
/// </summary>
/// <param name="rawUrl">Incoming URL</param>
/// <returns>Expected URL</returns>
public string GetUrl(string rawUrl)
{
    if (string.IsNullOrWhiteSpace(rawUrl))
    {
        return string.Empty;
    }

    string result = Regex.Replace(rawUrl, Pattern, Replace);
    return result;
}

But this isn't giving me the desired output, as the regex pattern is incorrect, I suppose. Any better way to do this?
My question was related to the implementation of regex pattern to find and replace the URL query parameter value, I found the URI builder is more helpful in these cases and can be used rather so it's different question.

You shouldnt use Regex for this, there are already built in libraries that help you parse URIs. If you include a sample URL I can provide a regex-less answer — maccettura
– maccettura, Commented Jun 21, 2018 at 14:40
A sample URL is "fod.infobase.com/PortalPlaylists.aspx?xtid=10112&wID=123" The position of wID can be anywhere in the URL — Darshak
– Darshak, Commented Jun 21, 2018 at 14:56
input = "fod.infobase.com/PortalPlaylists.aspx?xtid=10112&wID=123" output = "fod.infobase.com/…" — Darshak
– Darshak, Commented Jun 21, 2018 at 15:01
I've seen the URL, I am asking if you want the resulting url to have the [ and ] characters escaped? — maccettura
– maccettura, Commented Jun 21, 2018 at 15:02

aloisdg · Accepted Answer · 2018-06-22 07:54:43Z

3

As @maccettura said, you can use a built in. Here we will use HttpUtility.ParseQueryString to parse the parameters then we set the value and finally we replace the query.

Try it online!

public static void Main()
{
    Console.WriteLine(GetUrl("http://example.org?wID=xxx"));
}

/// <summary>
/// Extension method to evaluate the url token for wid
/// </summary>
/// <param name="rawUrl">Incoming URL</param>
/// <returns>Expected URL</returns>
public static string GetUrl(string rawUrl)
{
    if (string.IsNullOrWhiteSpace(rawUrl))
    {
        return string.Empty;
    }
    var uriBuilder = new UriBuilder(rawUrl);
    var queryString = HttpUtility.ParseQueryString(uriBuilder.Query);
    queryString.Set("wID", "[[WID]]");
    uriBuilder.Query = queryString.ToString();
    return uriBuilder.Uri.ToString();
}

output

http://example.org/?wID=[[WID]]

edited Jun 22, 2018 at 7:54

answered Jun 21, 2018 at 14:47

aloisdg

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2 Comments

Freggar Over a year ago

What if you got another query parameter name similiar to 'wID' (e.g. 'qwID')?

Alex K. Over a year ago

Probably better to .Remove("wID") then manually prepend wID=[[WID]]&, unfortunately you cannot assign [[WID]] directly as it will get escaped.

Reinder Wit · Accepted Answer · 2018-06-21 14:58:26Z

2

There are better ways of doing this. Have a look at parsing the query string using a NameValueCollection:

 var queryStringCollection = HttpUtility.ParseQueryString(Request.QueryString.ToString());
 queryStringCollection.Remove("wID");
 string newQuery = $"{queryStringCollection.ToString()}&wID=[[WID]]";

edited Jun 21, 2018 at 14:58

answered Jun 21, 2018 at 14:46

Reinder Wit

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2 Comments

Alex K. Over a year ago

ParseQueryString actually uses a specialized Http collection that will escape [ and ] when you .Set.

Reinder Wit Over a year ago

good point @AlexK. I didn't even notice that. I've updated my answer

maccettura · Accepted Answer · 2018-06-21 15:05:30Z

I will toss my own answer in since its a bit more re-usable and it does not escape the brackets ([]):

public static string ModifyUrlParameters(string rawUrl, string key, string val)
{
    if (string.IsNullOrWhiteSpace(rawUrl))
    {
        return string.Empty;
    }

    //Builds a URI from your string
    var uriBuilder = new UriBuilder(rawUrl);        

    //Gets the query string as a NameValueCollection
    var queryItems = HttpUtility.ParseQueryString(uriBuilder.Uri.Query);

    //Sets the key with the new val
    queryItems.Set(key, val);

    //Sets the query to the new updated query
    uriBuilder.Query = queryItems.ToString();

    //returns the uri as a string
    return uriBuilder.Uri.ToString();
}

An input of: http://example.org?wID=xxx

Results in: http://example.org/?wID=[[WID]]

Fiddle here

Mhd · Accepted Answer · 2018-06-21 14:51:46Z

0

You don't need a Regex for that.

var index = rawUrl.IndexOf("wID=");
if (index > -1)
{
   rawUrl = rawUrl.Substring(0, index + 4) + "[[WID]]";
}

edited Jun 21, 2018 at 14:51

answered Jun 21, 2018 at 14:48

Mhd

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1 Comment

maccettura Over a year ago

This does not seem right. Why are you starting at the beginning of rawUrl for your substring? Why is it hardcoded to a 4 length?

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