Browsers have not been limited to two connections per host for quite
some time now. With more connections allowed, the trade-off involved in
asset host distribution isn't so clear and it becomes more important
that developers measure actual performance before and after.

I wrote a utility that helps find areas where you could optimize your program using a frozen string instead of a string literal, it's called [let_it_go](https://github.com/schneems/let_it_go). After going through the output and adding `.freeze` I was able to eliminate the creation of 1,114 string objects on EVERY request to [codetriage](codetriage.com). How does this impact execution?

To look at memory:

```ruby
require 'get_process_mem'

mem = GetProcessMem.new
GC.start
GC.disable
1_114.times { " " }
before = mem.mb

after = mem.mb
GC.enable
puts "Diff: #{after - before} mb"

```

Creating 1,114 string objects results in `Diff: 0.03125 mb` of RAM allocated on every request. Or 1mb every 32 requests.

To look at raw speed:

```ruby
require 'benchmark/ips'

number_of_objects_reduced = 1_114

Benchmark.ips do |x|
  x.report("freeze")    { number_of_objects_reduced.times { " ".freeze } }
  x.report("no-freeze") { number_of_objects_reduced.times { " " } }
end
```

We get the results

```
Calculating -------------------------------------
              freeze     1.428k i/100ms
           no-freeze   609.000  i/100ms
-------------------------------------------------
              freeze     14.363k (± 8.5%) i/s -     71.400k
           no-freeze      6.084k (± 8.1%) i/s -     30.450k
```

Now we can do some maths:

```ruby
ips = 6_226k # iterations / 1 second
call_time_before = 1.0 / ips # seconds per iteration 

ips = 15_254 # iterations / 1 second
call_time_after = 1.0 / ips # seconds per iteration 

diff = call_time_before - call_time_after

number_of_objects_reduced * diff * 100

# => 0.4530373333993266 miliseconds saved per request
```

So we're shaving off 1 second of execution time for every 220 requests. 

Is this going to be an insane speed boost to any Rails app: nope. Should we merge it: yep. 

p.s. If you know of a method call that doesn't modify a string input such as [String#gsub](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37) please [give me a pull request to the appropriate file](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37), or open an issue in LetItGo so we can track and freeze more strings. 

Keep those strings Frozen

![](https://www.dropbox.com/s/z4dj9fdsv213r4v/let-it-go.gif?dl=1)

Added informations about :host options for each url helper
(#javascript_url, #video_url, #stylesheet_url, etc) based on #asser_url
method.

This reverts commit 21ec7fef.

Per #16911, there's actually a good reason for a "blank" value to have a
useful `to_s` here. So let's also add some tests to prove that.

Return an absolute instead of relative path from an asset url in the case of the `asset_host` proc returning nil

    see cc255d34

Update documentation for setting asset_host to a Proc, mention that the request parameter might not be supplied [ci skip]

Updated CHANGELOG.md with entry about :host in asset_url

Context: https://gist.github.com/radar/5793814

The `URI_REGEXP` that various AssetUrl helpers use is currently case
sensitive when checking for a URI scheme. This means if you try to pass
a URL like `HTTP://www.example.com/path/to/image.jpg`, you end up with
a bogus asset path: `/assets/HTTP://www.example.com/path/to/image.jpg`.

URLs are case insensitive, so this regexp should be as well.
Signed-off-by: NDavid Celis <me@davidcel.is>

Historically serving assets from a mountable engine could be achieved by
running ActionDispatch::Static as a part of engine middleware stack or
to copy assets prefixed with an engine name. After introduction of
assets pipeline this is not needed as all of the assets are served or
compiled into main application's assets.

This commit removes the obsolete line making asset_path always generate
paths relative to the root or config.relative_url_root if it's set.

(closes #8119)

Add asset_path/url helper for a consolidated entry point
Expose compute_asset_path as a public API
Expose compute_asset_host as a public API
Move RAILS_ASSET_ID to its own module, AssetIdHelper
Removed AV::AssetPaths

[ci-skip]

http://guides.rubyonrails.org/security.html#regular-expressions

This will set image's both width and height attributes to
value passed in size option.

Automatically handling mime types for things other than :rss and :atom
is not functionality that justifies dependency on Mime::Type from
actionpack.