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copied!<p><code>&block</code> is the way to define a method in Ruby that accepts a method and to explicitly assign the block to the variable referenced by the <code>&</code>.</p> <p>Specifically, what that code does, it to accept a block, call the block passing a string as argument, then passing the block to the inner response.</p> <p>At first glance, I would say that the specific middleware you saw is basically injecting the string</p> <pre><code>"\n" </code></pre> <p>into the HTTP response body if the request content type is <code>"text/html"</code>, which means an HTTP page.</p> <p>If the request is for an HTTP page, than the response is served and that string is injected. Otherwise, if the request is for another kind of file (for instance a binary file, a text file, a javascript, etc), then the response is served without any modification.</p> <p>The following example will help you to understand a little bit more the scope of <code>&block</code></p> <pre><code>def foo(&block) puts "foo" bar(&block) end def bar(&block) puts "bar" block.call end foo do puts "block" end # => foo # => bar # => block </code></pre> <p>Also note that the variable holding the block can be named anything, not necessary <code>block</code></p> <pre><code>def foo(&my_block) puts "foo" bar(&my_block) end def bar(&another_block) puts "bar" another_block.call end foo do puts "block" end # => foo # => bar # => block </code></pre>

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