使用C＃查找并替换字符串中的多个Instagram urls

Question

I want to find all the instagram urls within a string, and replace them with the embed url.

But I'm keen on performance, as this could be 5 to 20 posts each anything up to 6000 characters with an unknown amount of instagram urls in which need converting.

Url examples ( Could be any of these in each string, so would need to match all )

http://instagram.com/p/xPnQ1ZIY2W/?modal=true
http://instagram.com/p/xPnQ1ZIY2W/
http://instagr.am/p/xPnQ1ZIY2W/

And this is what I need to replace them with (An embedded version)

<img src="http://instagram.com/p/xPnQ1ZIY2W/media/?size=l" class="instagramimage" />

I was thinking about going for regex? But is this the quickest and most performant way of doing this?

Any examples greatly appreciated.

Answer 1

Something like:

Regex reg = new Regex(@"http://instagr\.?am(?:\.com)?/\S*");

Edited regex. However i would combine this with a stringreader and do it line by line. Then put the string (modified or not) into a stringbuilder:

string original = @"someotherText http://instagram.com/p/xPnQ1ZIY2W/?modal=true some other text
some other text http://instagram.com/p/xPnQ1ZIY2W/ some other text
some other text http://instagr.am/p/xPnQ1ZIY2W/ some other text";

StringBuilder result = new StringBuilder();

using (StringReader reader = new StringReader(original))
{
    while (reader.Peek() > 0)
    {
        string line = reader.ReadLine();
        if (reg.IsMatch(line))
        {
            string url = reg.Match(line).ToString();
            result.AppendLine(reg.Replace(line,string.Format("<img src=\"{0}\" class=\"instagramimage\" />",url)));
        }
        else
        {
            result.AppendLine(line);
        }
   }
}

Console.WriteLine(result.ToString());

You mean like this?

class Program
{
    private static Regex reg = new Regex(@"http://instagr\.?am(?:\.com)?/\S*", RegexOptions.Compiled);
    private static Regex idRegex = new Regex(@"(?<=p/).*?(?=/)",RegexOptions.Compiled);

    static void Main(string[] args)
    {
        string original = @"someotherText  http://instagram.com/p/xPnQ1ZIY2W/?modal=true some other text
some other text http://instagram.com/p/xPnQ1ZIY2W/ some other text
some other text http://instagr.am/p/xPnQ1ZIY2W/ some other text";

        StringBuilder result = new StringBuilder();

        using (StringReader reader = new StringReader(original))
        {
            while (reader.Peek() > 0)
            {
                string line = reader.ReadLine();
                if (reg.IsMatch(line))
                {
                    string url = reg.Match(line).ToString();
                    result.AppendLine(reg.Replace(line, string.Format("<img src=\"http://instagram.com/p/{0}/media/?size=1\" class=\"instagramimage\" />", idRegex.Match(url).ToString())));
                }
                else
                {
                    result.AppendLine(line);
                }

            }
        }

        Console.WriteLine(result.ToString());



    }
}

Answer 2

A well-crafted and compiled regular expression is hard to beat, especially since you're doing replacements, not just searching, but you should test to be sure.

If the Instagram URLs are only within HTML attributes, here's my first stab at a pattern to look for:

(?<=")(https?://instagr[^">]+)

(I added a check for https as well, which you didn't mention but I believe is supported by Instagram.)

Some false positives are theoretically possible, but it will perform better than pedantically matching every legal variation of an Instagram URL. (The ">" check is just in case the HTML is missing the end quote for some reason.)