Unvalidated redirects and forwards are #10 on the OWASP Top Ten.

Redirects which rely on user-supplied values can be used to "spoof" websites or hide malicious links in otherwise harmless-looking URLs. They can also allow access to restricted areas of a site if the destination is not validated.

Brakeman will raise warnings whenever redirect_to appears to be used with a user-supplied value that may allow them to change the :host option.

For example,

redirect_to params.merge(:action => :home)

will create a warning like

Possible unprotected redirect near line 46: redirect_to(params)

This is because params could contain :host => 'evilsite.com' which would redirect away from your site and to a malicious site.

If the first argument to redirect_to is a hash, then adding :only_path => true will limit the redirect to the current host. Another option is to specify the host explicitly.

redirect_to params.merge(:only_path => true)

redirect_to params.merge(:host => 'myhost.com')

If the first argument is a string, then it is possible to parse the string and extract the path:

redirect_to URI.parse(some_url).path

If the URL does not contain a protocol (e.g., http://), then you will probably get unexpected results, as redirect_to will prepend the current host name and a protocol.

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

A method with Too Many Statements is any method that has a large number of lines.

Too Many Statements warns about any method that has more than 5 statements. Reek's smell detector for Too Many Statements counts +1 for every simple statement in a method and +1 for every statement within a control structure (if, else, case, when, for, while, until, begin, rescue) but it doesn't count the control structure itself.

So the following method would score +6 in Reek's statement-counting algorithm:

def parse(arg, argv, &error)
  if !(val = arg) and (argv.empty? or /\A-/ =~ (val = argv[0]))
    return nil, block, nil                                         # +1
  end
  opt = (val = parse_arg(val, &error))[1]                          # +2
  val = conv_arg(*val)                                             # +3
  if opt and !arg
    argv.shift                                                     # +4
  else
    val[0] = nil                                                   # +5
  end
  val                                                              # +6
end

(You might argue that the two assigments within the first @if@ should count as statements, and that perhaps the nested assignment should count as +2.)

Duplication occurs when two fragments of code look nearly identical, or when two fragments of code have nearly identical effects at some conceptual level.

Reek implements a check for Duplicate Method Call.

Example

Here's a very much simplified and contrived example. The following method will report a warning:

def double_thing()
  @other.thing + @other.thing
end

One quick approach to silence Reek would be to refactor the code thus:

def double_thing()
  thing = @other.thing
  thing + thing
end

A slightly different approach would be to replace all calls of double_thing by calls to @other.double_thing:

class Other
  def double_thing()
    thing + thing
  end
end

The approach you take will depend on balancing other factors in your code.