Blogument querystring appending with Ruby

Closes #1130.

content/posts/2021-12-03-ruby-append-querystring.md

+---
+title: "Appending Values to a Querystring with Ruby"
+description: "How to append a query parameter to a URL's querystring in Ruby."
+tags:
+- blogumentation
+- ruby
+license_code: Apache-2.0
+license_prose: CC-BY-NC-SA-4.0
+date: 2021-12-03T14:15:44+0000
+slug: "ruby-append-querystring"
+---
+Let's say that you have a URL and you want to append on query parameters, for instance to add tracking data to a URL.
+
+For example, let's say we want to add on `utm_medium=example&utm_source=my_blog` to a given URL.
+
+You _could_ do this by simply appending `?utm_medium=example&utm_source=my_blog` to a URL we've been given, but that doesn't work in the case that a URL already has a querystring, because a number of URL parsers will reject that as a invalid URL, or it will not parse as you're expecting to.
+
+The solution I've found that works best is to parse the URI, then use `URI.encode_www_form` on the parsed querystring once we've appended our parameters:
+
+```ruby
+def add_tracking(url)
+  parsed = URI.parse(url)
+  query = if parsed.query
+           CGI.parse(parsed.query)
+         else
+           {}
+         end
+
+  query['utm_medium'] = %w(example)
+  query['utm_source'] = %w(my_blog)
+
+  parsed.query = URI.encode_www_form(query)
+  parsed.to_s
+end
+```
+
+This works for the following cases:
+
+```
+add_tracking 'https://foo.com'
+=> "https://foo.com?utm_medium=example&utm_source=my_blog"
+add_tracking 'https://foo.com/'
+=> "https://foo.com/?utm_medium=example&utm_source=my_blog"
+add_tracking 'https://foo.com/?page=1'
+=> "https://foo.com/?page=1&utm_medium=example&utm_source=my_blog"
+add_tracking 'https://foo.com/?page=1&page=2'
+=> "https://foo.com/?page=1&page=2&utm_medium=example&utm_source=my_blog"
+```