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Fail gracefully always

chef/chef
Based on 9 comments
Ruby

Ensure code handles errors robustly by using protective patterns that prevent resource leaks, provide clear diagnostics, and degrade gracefully when possible:

Error Handling Ruby

Reviewer Prompt

Ensure code handles errors robustly by using protective patterns that prevent resource leaks, provide clear diagnostics, and degrade gracefully when possible:

  1. Use resource cleanup patterns - Prefer block forms for resource management to ensure cleanup happens even during exceptions:
# Good: Resources automatically closed after block
TargetIO::File.open(tempname, "w") do |tempfile|
  tempfile.write(crontab)
end

# Bad: Manual cleanup may be missed on exception paths
tempfile = TargetIO::File.open(tempname, "w") 
tempfile.write(crontab)
tempfile.close # Might never execute if an exception occurs
  1. Validate related parameters together - Check parameter dependencies upfront:
# Good: Clear validation of dependent parameters
def define_resource_requirements
  requirements.assert(:install, :upgrade) do |a|
    a.assertion { new_resource.proxy_user.nil? == new_resource.proxy_password.nil? }
    a.failure_message("Both proxy_user and proxy_password must be specified together")
  end
end
  1. Handle expected failures gracefully - Catch specific exceptions to provide fallbacks:
# Good: Handle missing command gracefully
def loop_mount_points
  @loop_mount_points ||= shell_out!("losetup -a").stdout
rescue Errno::ENOENT
  "" # Return empty string if command doesn't exist
end
  1. Use appropriate exception types - Choose domain-specific exceptions to accurately represent errors:
# Good: Domain-specific exception
raise Chef::Exceptions::Service, "systemctl show not reporting status for #{service_name}!"

# Bad: Using generic or misleading exception type
raise Mixlib::ShellOut::ShellCommandFailed, "Error message" # Implies shell command failed
  1. Provide clear, actionable error messages - Check specific conditions and give targeted feedback:
# Good: Check existence before permissions
if !File.directory?(File.dirname(file))
  ui.fatal "Directory #{File.dirname(file)} does not exist"
  exit 1
elsif !File.writable?(File.dirname(file))
  ui.fatal "Directory #{File.dirname(file)} is not writable. Check permissions."
  exit 1
end

Following these patterns will create more resilient code that fails predictably, provides clear diagnostics, and properly manages resources even during failures.

9
Comments Analyzed
Ruby
Primary Language
Error Handling
Category

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