Using user input when accessing files (local or remote) will raise a warning in Brakeman.

For example

File.open("/tmp/#{cookie[:file]}")

will raise an error like

Cookie value used in file name near line 4: File.open("/tmp/#{cookie[:file]}")

This type of vulnerability can be used to access arbitrary files on a server (including /etc/passwd.

Using user input when accessing files (local or remote) will raise a warning in Brakeman.

For example

File.open("/tmp/#{cookie[:file]}")

will raise an error like

Cookie value used in file name near line 4: File.open("/tmp/#{cookie[:file]}")

This type of vulnerability can be used to access arbitrary files on a server (including /etc/passwd.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

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

This cop checks for uses of the deprecated class method usages.

Example:

# bad

File.exists?(some_path)

Example:

# good

File.exist?(some_path)

This cop checks for uses of the deprecated class method usages.

Example:

# bad

File.exists?(some_path)

Example:

# good

File.exist?(some_path)

This cop checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ruby -cw:

assigned but unused variable - foo

Currently this cop has advanced logic that detects unreferenced reassignments and properly handles varied cases such as branch, loop, rescue, ensure, etc.

Example:

# bad

def some_method
  some_var = 1
  do_something
end

Example:

# good

def some_method
  some_var = 1
  do_something(some_var)
end